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  20 April 2024, Volume 48 Issue 2 Previous Issue   
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A review of thirty years of airborne geophysical surveys in the Qiangtang Basin and future prospect
ZHOU Dao-Qing, XIONG Sheng-Qing, WANG Bao-Di, CAO Bao-Bao, GUO Zhi-Hong, HU Yue, ZHENG Yu-Zhou, ZHAO Rui, WEI Yan-Yan, XIAO Meng-Chu, HU Xia-Wei, YAN Qiao-Juan
Geophysical and Geochemical Exploration. 2024, 48 (2): 287-295.   DOI: 10.11720/wtyht.2024.1413
Abstract   HTML ( 11 )   PDF (7354KB)

Airborne geophysical surveys, characteristic of being green, economical, efficient, and subjected to less influence by surface factors, serve as the one of most effective means of basic surveys and scientific research on the Qinghai-Tibet Plateau. This study reviewed the progress in the airborne geophysical surveys in the Qiangtang Basin of the Qinghai-Tibet Plateau in the past thirty years, systematically summarizing the progress and geological interpretation results of comprehensive airborne geophysical surveys in the basin. Furthermore, this study presented research progress and understanding of major basic geological issues of the basin, such as the basin's boundaries, central uplift zone, basement properties, deep structures, and cover characteristics, as well as the identification of favorable structural areas for oil and gas exploration. Finally, based on an analysis of the developmental trends of airborne geophysical surveys in the Qiangtang Basin, this study proposed opinions and suggestions for key research directions in the future.

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Sulfur isotopic composition and related issues of typical gold ore districts in China
LAN Rui-Xuan, ZHAO Hong-Kun, TANG Shi-Xin, DUAN Zhuang, MA Sheng-Ming
Geophysical and Geochemical Exploration. 2024, 48 (2): 296-313.   DOI: 10.11720/wtyht.2024.1177
Abstract   HTML ( 7 )   PDF (5941KB)

In the Prospecting Breakthrough Strategy (2011~2020), China has made significant progress in the exploration of gold deposits, demonstrating considerable prospecting potential. Element sulfur, a mineralizer, is closely associated with the formation of gold deposits, proved to be the most significant element in gold deposit formation by scholars at home and abroad. Sulfur isotopes have been extensively used to trace the sources of minerals in gold deposits. Different gold deposits reside in distinct geological settings. Since sulfur isotopic compositions are governed by various sulfur sources, sulfur isotopes in gold deposits can reflect the geological settings of mineralization. The ore-district-scale spatio-temporal distribution of sulfur isotopes has theoretical implications, playing a significant role in guiding ore prospecting. The gold resources in China are distributed in 42 gold ore districts, typified by Jiaodong, Xiaoqinling, and Yunnan-Guizhou-Guangxi. This study comparatively analyzed and summarized the characteristics of sulfur isotopes in the three typical gold ore districts, providing theoretical and methodological support for future gold prospecting.

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Practices and future research directions of geophysical exploration for normal-pressure shale gas in complex structural areas,southeastern Chongqing
HE Xi-Peng, LIU Ming, XUE Ye, LI Yan-Jing, HE Gui-Song, MENG Qing-Li, ZHANG Yong, LIU Hao-Juan, LAN Jia-Da, YANG Fan
Geophysical and Geochemical Exploration. 2024, 48 (2): 314-326.   DOI: 10.11720/wtyht.2024.1202
Abstract   HTML ( 7 )   PDF (7986KB)

Southern China boasts great potential for normal-pressure shale gas resources,with distribution areas primarily including the peripheral complex structural areas and the extrabasinal fold belts of the Sichuan Basin.These areas exhibit intricate surface and subsurface geological conditions,leading to poor seismic acquisition quality,low imaging accuracy,and unclear varying patterns of sweet spot parameters.This study systematically summarized the research achievements and technical advances in the seismic acquisition,image processing,and reservoir prediction for normal-pressure shale gas in southeastern Chongqing,including:①The development of variable-density 3D observation system design technique and the seismic excitation and reception technique for complex mountains with limestone surfaces,ensuring sufficient sampling of the reflected wave field in complex subsurface structures and improving data quality and construction efficiency;②The optimization of prestack seismic preprocessing technique for complex mountains,imaging techniques for complex structures in basin-margin transition zones, and imaging techniques for synclinal structures in extrabasinal fold belts,achieving resulting profiles with high signal-to-noise ratios,wide effective frequency bands,and high structural imaging accuracy;③The quantitative prediction of the thickness,formation pressure coefficient,and brittleness of high-quality shales based on research on petrophysical characteristics;the quantitative prediction of the organic carbon content,gas content,and porosity of shales based on statistical petrophysics;the quantitative prediction of fractures formed due to the superimposed effect of multi-stage structural modifications based on the paleo-stress field evolution revealed using the finite element simulation technique;and the ascertainment of the distribution patterns of the current in-situ stress field using the current stress field prediction technique developed using the combined spring model.The above breakthroughs have effectively guided the sweet spot prediction,exploration,and production of normal-pressure shale gas,providing a basis for the discovery of the Nanchuan normal-pressure shale gas field.Subsequent research should focus on more scientific and reasonable seismic acquisition techniques based on seismic reception using 5G wireless nodes,high-precision automatic image processing technologies for high-steep structures in complex mountains,and integrated geology-engineering-economy seismic evaluation methods for sweet spots.

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Fine-scale prospecting targets of skarn iron deposits in the Pandian gravity-magnetic anomaly zone of northwestern Shandong Province: Insights from deep prospecting using the wide-field electromagnetic method
GUO Guo-Qiang, LI Ya-Dong, WANG Yang, YU Jia-Bin, WANG Run-Sheng, GAO Xiao-Feng, ZHANG Da-Ming, HU Dong-Ning, FANG Lei, GUO Wei-Fang
Geophysical and Geochemical Exploration. 2024, 48 (2): 327-333.   DOI: 10.11720/wtyht.2024.1157
Abstract   HTML ( 3 )   PDF (4258KB)

Significant aeromagnetic and gravity anomalies were found in the ultra-deep coverage zone of the Pandian area in the northwestern Shandong Province. Through systematic verification of gravity and magnetic anomalies, a breakthrough in prospecting for deep skarn iron deposits has been achieved through several boreholes around the Pandian gravity-magnetic anomaly zone. However, the gravity-magnetic anomaly zone spreads extensively and its characteristics cannot directly indicate the prospecting target, thus some boreholes failed to find ores or revealed poor ore-finding conditions. Hence, to accurately delineate the ore-forming location in the gravity-magnetic anomaly zone and achieve a further breakthrough in ore prospecting, this study conducted the wide-field electromagnetic (WFEM) sounding in the verified Pandian gravity-magnetic anomaly zone. Combining the drilling verification, this study delineated the deep ore-forming interval of skarn iron deposits in the deep coverage zone and the favorable structural plane for ore-forming, suggesting the deep fine-scale prospecting targets.

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Geophysical identification of Cretaceous reservoirs in the Shinan area, Junggar Basin
LI Lu-Lu, JIANG Guo-Yu, LIU Tao, HE Yan, ZHANG Yong-Bo
Geophysical and Geochemical Exploration. 2024, 48 (2): 334-341.   DOI: 10.11720/wtyht.2024.1077
Abstract   HTML ( 2 )   PDF (7477KB)

Industrial oil flows have been successively obtained from the basal conglomerates of the Cretaceous Qingshuihe Formation in the Shinan area, Junggar Basin. However, this set of reservoirs exhibits multi-layer three-dimensional oil-bearing properties and significant vertical and horizontal variations. Therefore, there is an urgent need to overcome the challenge of the identification and fine-scale characterization of reservoirs. Based on the accurate calibration of seismic and geological horizons, this study reconstructed the paleogeomorphology of the first member of the Cretaceous Qingshuihe Formation using based on the seismic flattening and residual thickness methods in three steps. By combining the reservoir prediction through natural gamma-ray pseudo-acoustic wave inversion, this study roughly identified the predominant factors controlling sedimentation and the spatial distributions of sand bodies. The results of this study provide an effective method combination for predicting Cretaceous reservoirs in the Shinan area. Furthermore, these results offer a sufficient scientific basis for oil and gas exploration in the glutenite reservoirs of the Cretaceous Qingshuihe Formation, thus effectively reducing the exploration risk.

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Application of airborne time-domain electromagnetic method in investigation of permafrost
YU Xue-Zhong, XIE Ru-Kuan, SHAN Xi-Peng, HE Yi-Yuan, SUN Si-Yuan, LI Shi-Jun
Geophysical and Geochemical Exploration. 2024, 48 (2): 342-347.   DOI: 10.11720/wtyht.2024.1246
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Investigating the spatial distribution of permafrost is critical for cryosphere research. At present, China's investigation concerning the spatial distribution of permafrost generally employs the detection method of ground geophysical exploration combined with logs to obtain local point or line data. Alternatively, different remote sensing models can be used to simulate and estimate the thickness of regional permafrost. This study inferred the spatial distribution of permafrost based on airborne time-domain electromagnetic (TDAEM) data and resistivity calculation results. The comparative analysis of the inference results and the known drilling data reveals an average error of 18.5% between the permafrost thickness inferred from the inversion results of TDAEM data and the result determined by borehole temperature measurements. This suggests that the TDAEM method exhibits high effectiveness and accuracy in permafrost thickness investigation. With technical advantages like high efficiency and minor topographic influence, the TDAEM method can be applied to the large-scale, rapid, and quantitative permafrost investigation in the Qinghai-Tibet Plateau and the Greater Khingan Range in northeast China. Therefore, this study provides a new and effective technical solution for a comprehensive investigation of the spatial distribution of permafrost and its influence on ecological environment changes.

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Application of multi-component carbon isotope logging in natural gas exploration: A case study of the BD21 area, Qiongdongnan Basin
HU Yi-Tao, ZHANG Huan-Xu, NI Peng-Bo, HAO Wei, QU Yu-Yang, XIAO Han-Li
Geophysical and Geochemical Exploration. 2024, 48 (2): 348-355.   DOI: 10.11720/wtyht.2024.2158
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This study aims to ascertain the accumulation characteristics of natural gas in the deep-water oil and gas fields in the Qiongdongnan Basin. To this end, it performed continuous multi-component carbon isotope measurements for natural gas wells in the basin. Based on the comparative analysis of a continuous carbon isotope profile from a key well in the basin and the carbon isotope values from key intervals in surrounding wells, this study delved into the genetic types and sources of natural gas in the key well. The results show that dry gas occurs above the first member of the Sanya Formation, dominated by biogenic and secondary biogenic gases. In contrast, wet thermogenic gas exists below the second member of the formation, primarily including associated gas. Besides, natural gas in the BD21-1 block originates from two sources: Eocene high-maturity oil-formed gas and low-maturity gas with a special genesis from the Yacheng Formation. Overall, multi-component carbon isotope logging is effective in investigating the genetic types, sources, and maturity of natural gas.

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Log-based in situ stress prediction of deep coalbed methane reservoirs in the Daji block
XIE Zheng-Long, LIU Zhi-Di, HAN Hong-Lai, WANG Duo, WANG Cheng-Wang, WANG Wei, JI Liang
Geophysical and Geochemical Exploration. 2024, 48 (2): 356-365.   DOI: 10.11720/wtyht.2024.2600
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For deep coalbed methane (CBM) exploration and production, accurate in situ stress prediction holds critical significance for safe and efficient drilling and completion of wells. Deep CBM reservoirs, once considered restricted areas for exploration and exploitation, have been highly anticipated owing to their high yields in recent years. However, their in situ stress prediction model has not been investigated effectively. Hence, this study systematically analyzed six in situ stress prediction models commonly used for conventional oil and gas reservoirs and unconventional gas (like CBM) reservoirs. Based on these prediction models, this study calculated the in situ stress, and found that the combined spring model and the Newberry model yielded relatively high accuracy through comparative analysis of closure pressures. To improve the accuracy of in-situ stress prediction models, the effective stress coefficient of coal rocks was employed to optimize the two models. The optimized in-situ stress models yielded prediction accuracy errors reduced by 4%, roughly meeting the requirements of in-situ stress prediction accuracy for deep CBM exploration and production in the Daji block.

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Prospecting potential of medium-fine-grained rock-type lithium resources in the Xianghualing orefield, Hunan Province, China
SONG Zhi-Fang, YANG Qi-Zhi, ZHU Zhen-Zhen, CAO Neng-Wen
Geophysical and Geochemical Exploration. 2024, 48 (2): 366-374.   DOI: 10.11720/wtyht.2024.1040
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This study aims to explore the distribution characteristics and occurrence patterns of lithium in medium-fine-grained rocks and its paragenetic or associated relationship with minerals such as tungsten, tin, niobium, tantalum, beryllium, and rubidium. Hence, it analyzed the distribution characteristics and diagenetic and metallogenic processes of nonferrous-rare metals in the Xianghualing orefield. With the exposed granitic rock masses as the center, this study divided three ore-forming sections of rare metal lithium, i.e., the Laiziling-Nanjichong, Jianfengling-Xianghuapu, and Tongtianmiao-Yaoshanli ore-forming sections. Moreover, lithium-rich mineralized bodies were discovered in the medium-fine-grained rocks of the former two ore-forming sections. Lithium converges and accumulates in the interior and top of medium-fine-grained granitic rock masses, at the automorphism and alteration positions of high-emplacement apophyses and vein fronts and edges, or in the areas enclosed by silicon-rich quartz veins at the contact zone with silicon-rich surrounding rocks. Dividing these mineralization and alteration sections serves as a crucial approach for exploring medium-fine-grained rock type lithium ore bodies in the Xianghualing orefield.

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Application of comprehensive geophysical prospecting in exploration of the Duhu copper deposit in Xinxing County
HE Jun-Fei
Geophysical and Geochemical Exploration. 2024, 48 (2): 375-381.   DOI: 10.11720/wtyht.2024.1101
Abstract   HTML ( 7 )   PDF (5778KB)

Since individual geophysical exploration methods suffer the multiplicity of solutions, comprehensive geophysical prospecting has been extensively applied in deep ore prospecting presently. This study conducted the geological exploration of the Duhu porphyry copper deposit in Xinxing County using multiple geophysical methods such as high-precision magnetic survey and controlled source audio-frequency magnetotellurics (CSAMT). It was inferred that the CSAMT-derived medium-low resistivity anomalies and the low-gentle anomalies derived from the high-precision magnetic survey serve as significant prospecting indicators. Satisfactory results were achieved in follow-up verification of the anomalies. Specifically, copper, molybdenum, silver, and gold mineralized bodies with a cumulative thickness of 178.2 m were identified in a 1 000 m deep borehole, with the highest copper grade of 1.45%. The application of comprehensive geophysical prospecting holds great significance in guiding the exploration of porphyry copper deposits in western Guangdong.

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Stream sediment geochemistry and prospecting targets in Harper, Liberia
BAI Yang, CHEN Kai-Xu, CHEN Chong, LI Fu-Lin, ZHANG Ji-Chun, WEI Ling-Xiao, SI Ke-Fu, ZHENG Xiong-Wei, HU Yun-Fei, WU Ying, ZHANG Yuan-Pei
Geophysical and Geochemical Exploration. 2024, 48 (2): 382-392.   DOI: 10.11720/wtyht.2024.1128
Abstract   HTML ( 1 )   PDF (8370KB)

Birimian rocks, the most significant Au ore-forming rocks in western Africa, are widespread in Harper, southeastern Liberia. As indicated by the geochemical parameters from the 1∶250 000 stream sediment survey of this region, elements Au and Hg exhibit high enrichment and high differentiation while element As manifests enrichment and high differentiation. These findings suggest considerable potential for Au prospecting. Based on the correlation analysis of elements, this study selected factors F1 (for the Au-Hg-Pb-Sn association) and F2 (for the As-Sb-W association) to effectively guide the exploration of gold deposits. Thirteen composite anomalies were delineated by extracting the anomaly information of Au, Hg, As, and Sb from the two principal factors, effectively reflecting the anomaly distributions of different gold deposits or ore occurrences. The geological and mineral surveys in anomaly areas reveal that areas HS1-HS3 and HS12-HS13 with composite anomalies characterized by directional distribution and high intensities show distinct Au mineralization information. Based on this, two major Au prospects, i.e., Seethum New and Behwan, have been identified for further detailed exploration.

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Application of PNN logging in residual oil evaluation: A case study of the Gaotaizi oil layer in mature oilfields
SU Ke-Jia, QIN Zhen, FENG Min, AI Han-Bing, WANG Gang, GUAN Hua-Ling, FU Yu
Geophysical and Geochemical Exploration. 2024, 48 (2): 393-402.   DOI: 10.11720/wtyht.2024.1075
Abstract   HTML ( 1 )   PDF (7513KB)

As mature oilfields are in their middle to late exploitation stage, the Gaotaizi oil layer exhibits significantly increased water saturation, elusive longitudinal stratification, and unknown distribution patterns of regional residual oil. These complicate the potential exploitation, energy conservation, and emission reduction. To ascertain the distribution of residual oil in the Gaotaizi oil layer in order to guide production operations and clarify potential targets, this study identified the longitudinal distribution of residual oil in the study area using the pulsed neutron-neutron (PNN) logging technique. The comparison between the monitoring results and production data of 10 wells revealed a coincidence rate of measures of 80%. The results of this study show that the PNN logging technique can be used to effectively identify the longitudinal distribution of residual oil in reservoirs and yields encouraging application performance in guiding the hole filling and water plugging for single wells in high-water-cut layers, thus increasing oil production. This technique has increased the evaluation accuracy of residual oil saturation in the Gaotaizi oil layer in the mature oilfield. It can provide technical support for formulating and adjusting subsequent oilfield exploitation schemes and offer a scientific basis for further guiding efficient reservoir exploitation, energy conservation, and emission reduction.

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Log-based identification of gas-bearing shales in the Longmaxi Formation of the Laifeng area: A case study of well WY1
PEI Sheng-Liang, QU Jian-Xin, ZHANG Peng
Geophysical and Geochemical Exploration. 2024, 48 (2): 403-410.   DOI: 10.11720/wtyht.2024.1054
Abstract   HTML ( 0 )   PDF (5106KB)

Except for the Sichuan Basin, the marine shales in the Longmaxi Formation in Hubei show great potential for shale gas exploration. Logging technology is highly mature in the exploration and development of hydrocarbons. This study systematically analyzed the log response characteristics of gas-bearing shales in the Longmaxi Formation based on logs obtained from well WY1 in the Laifeng area. As indicated by the analysis results, the gas-bearing shales of the Longmaxi Formation in well WY1 are characterized by high natural-gamma-ray values, high contents of uranium, thorium, and compensated neutrons, high interval transit time, and low density. Their deep and shallow lateral resistivity is lower than that of the underlying Baota Formation carbonate rocks but is higher than that of the sandy shales. Moreover, the positive differences indicate that high-angle fractures occur in the shales. The superimposition of log curves and the analysis of cross plots for gas-bearing shales reveal that ① the superimposed log curves of both natural gamma ray-lithologic density and interval transit time-lithologic density show significant positive differences, while those of both natural gamma ray-compensated neutrons and interval transit time-compensated neutrons show significant negative differences; ② the superimposed log curves of interval transit time-lithologic density indicate the gas-bearing intervals the most accurately; ③ the organic-rich gas-bearing shales can be identified the most effectively using the log cross plots of interval transit time-compensated neutrons, compensated neutrons-natural gamma ray, and deep lateral resistivity-compensated neutrons.

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Advances in research on the distributed optical fiber acoustic sensing system in the field of geophysical exploration
ZHOU Shao-Yu, BAO Qian-Zong, SHI Wei
Geophysical and Geochemical Exploration. 2024, 48 (2): 411-427.   DOI: 10.11720/wtyht.2024.1304
Abstract   HTML ( 2 )   PDF (7793KB)

Distributed acoustic sensing (DAS) technology, one of the most advanced sound field detection technologies, can achieve distributed, long-distance, and high-precision real-time detection of the ambient vibration and sound field information interacting with optical fiber. The optical fiber exploration system of the DAS technology solves the problems of high cost and deployment difficulty of conventional geophones in complex geological environments. In recent years, the DAS technology has experienced rapid development, especially in monitoring application scenarios that require long-term and large-scale deployment. However, its systematic understanding is insufficient due to divergent research results. To further understand the research advances of the DAS technology in geophysical exploration for more effective subsequent research, this study systematically classified and summarized the development history of the DAS technology and its recent research results in geophysical exploration based on the oil and gas, marine, and environmental engineering application scenarios through literature research. This study focused on the development process of the DAS technology in different directions, the research advances in data processing, and relevant literature with specific results. Finally, this study generalized the development trend and urgent problems of the DAS acquisition system, analyzing the DAS development prospect.

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A method for identifying lithology based on a feature-weighted KNN model
GUO Yu-Shan, WANG Wan-Yin
Geophysical and Geochemical Exploration. 2024, 48 (2): 428-436.   DOI: 10.11720/wtyht.2024.1260
Abstract   HTML ( 1 )   PDF (4553KB)

Lithology identification, as a major geological task, strongly underpins the exploration of solid minerals, oil, and gas. Since the physical properties of rocks bridge lithologies and geophysical fields, their differences can be used for lithology identification. However, the physical property data of different rocks frequently overlap to some extent, posing challenges to accurate lithology identification using cross plots alone. The K-nearest neighbor (KNN) model is suitable for multi-class classification since it is a simple and direct machine learning method with high accuracy and sensitivity. This study introduced a feature-weighted KNN model for lithology identification. In this model, different weights were assigned to different features by combining the conventional KNN model with the information gain of attribute features. This allowed for intuitive reflection of the importance of attribute features to classification. Experiments show that compared to the conventional KNN model, the feature-weighted KNN model can more significantly identify lithologic boundaries, thus improving the overall accuracy and stability of lithology identification.

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A fast imaging technology for screening ambient noise in high-altitude areas based on power spectral density
LIU Di, YANG Tao, SONG Hua-Dong, LI Guang-Chao, WU Guang-Rong, GUO Liang-Chun, ZHANG Jin-Xiang
Geophysical and Geochemical Exploration. 2024, 48 (2): 437-442.   DOI: 10.11720/wtyht.2024.1110
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Acquiring empirical Green's functions with a real and high signal-to-noise ratio serves as a prerequisite for deriving surface wave dispersion and inverting underground structures.However,the distribution of actual noise sources differs from the theory,and the energy and quantity of noise sources are limited in the high-altitude areas.Acquiring empirical Green’s functions with a high signal-to-noise ratio is challenging,apart from a prolonged data acquisition period required.Given these,this study presented a method for screening ambient noise data based on power spectral density.Using this method,this study screened 92-hour ambient noise data from a high-altitude area.Consequently,this method significantly reduced the calculation time of cross-correlation,effectively extracted surface waves with a high signal-to-noise ratio,reduced the interference waves with high apparent velocities,and obtained a high-resolution shallow shear wave velocity structure of shallow parts with burial depths ranging from 0~140 m.This study provides a novel method for challenging,short-term exploration of water conservancy and hydropower generation in high-altitude areas.

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Comparison and summary of different azimuthal anisotropy-based inversion techniques
LIANG Zhi-Qiang, LI Hong
Geophysical and Geochemical Exploration. 2024, 48 (2): 443-450.   DOI: 10.11720/wtyht.2024.1251
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The progress in seismic acquisition techniques characterized by wide azimuths,wide frequency bands,and high densities has greatly promoted the application of the prestack P-wave fracture inversion technique based on the azimuthal anisotropy theory.Azimuthal anisotropy-based inversion can yield the azimuths and intensities of fractures.However,different inversion techniques yield different parameters for fracture intensity characterization,resulting in inconsistent inversion results.Consequently,the azimuthal anisotropy-based inversion results of fractures are non-unique,leading to confusion about accurate results.Based on the Thomsen anisotropy theory,as well as the interrelationships between fracture models(the Hudson coin model and the Schoenberg linear sliding model),this study established the connections of anisotropic parameters between different fracture inversion techniques(VVAZ,Ruger's approximation,and Fourier series),presenting the real meanings and mathematical expressions of results from different azimuthal anisotropy-based fracture inversion techniques.Additionally,this study summarized the relationships of parameters between different inversion techniques and fracture models,further deepening the research on azimuthal anisotropy-based fracture inversion.This study lays solid theoretical and technical foundations for large-scale fracture detection based on the seismic data obtained using the seismic acquisition techniques featuring wide azimuths,wide frequency bands, and high densities.

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3D forward and inverse modeling of self-potential data based on the PARDISO direct solver
SU Zhao-Yang, SHEN Jin-Song, LUO Hui
Geophysical and Geochemical Exploration. 2024, 48 (2): 451-460.   DOI: 10.11720/wtyht.2024.1150
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In recent years, the self-potential method has played a significant role in the exploration and evaluation of seafloor massive sulfide resources. This study explored the 3D forward and inverse modeling algorithms for self-potential based on the PARDISO direct solver. First, the finite volume method was employed to discretize the self-potential control equation, and the PARDISO direct solver was utilized to improve the forward modeling efficiency. The reliability of the forward modeling algorithm was verified by comparing the numerical solution with the analytical solution. The 3D inverse modeling algorithm considered the topographic factor and incorporated the minimum support constraint and depth weighting into the objective function. The inversion results of theoretical model data effectively reconstructed the ore body structure. Finally, the self-potential data obtained from indoor sandbox experiments were inverted using the inverse modeling algorithm, obtaining that the current density anomaly was roughly consistent with the position of the metal bar. Therefore, the inverse modeling algorithm proposed in this study holds critical significance for subsequent inversion of large-scale spontaneous potential data.

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Comparative analysis of stereo and planar sources for slope breaks
CHEN Feng-Ying, WANG Xiang-Chun, SUN Jian, LI Can-Ping, REN Xiao-Qing
Geophysical and Geochemical Exploration. 2024, 48 (2): 461-469.   DOI: 10.11720/wtyht.2024.1160
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Deep-water areas have gradually become the exploration targets of offshore oil and gas resources.Due to the intricate geological conditions of these areas,seismic imaging of moderately deep reservoirs suffers low signal-to-noise ratios and resolution,inevitably affecting the exploration and exploitation of oil and gas resources.To improve the quality of seismic data of moderately deep reservoirs in deep-water areas,this study first acquired seismic data at the same location in a slope break using stereo and planar sources under the same acquisition parameters.Then,after being processed using the same workflow,the seismic data were subjected to comparative analysis from the perspective of wavelets,shot gather spectra,near-trace spectra,superimposed profile spectra,and final imaging.The results indicate that the wavelets of a stereo source outperformed those of a planar source in terms of energy intensity and ghost reflection interference.Moreover,for moderately deep reservoirs of the deep-water area,a stereo source exhibited broader frequency bands and especially rich frequencies within 30~80 Hz.These features enhanced the resolution of seismic profiles and the imaging quality of seismic data.Thus,compared to planar sources,stereo sources enjoy more advantages in improving seismic imaging of moderately deep reservoirs in deep-water areas.Therefore,stereo sources can be employed to acquire seismic data of moderately deep reservoirs with complex geological conditions in deep-water areas,and the purpose is to improve the imaging quality of seismic data.

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Key technologies of non-zero offset time-delay VSP data processing
ZHANG Jie, CHENG Lei-Lei, ZENG Zhao-Han, CHEN Lin
Geophysical and Geochemical Exploration. 2024, 48 (2): 470-478.   DOI: 10.11720/wtyht.2024.1161
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Since non-zero-offset time-lapse vertical seismic profiling (VSP) data contain abundant near-well wave field information,the VSP reflection information and seismic attributes can be applied to effectively monitor the migration of injected fluids near wells,boasting a broad application prospect.Due to the limitation of observation methods,non-zero-offset time-lapse VSP data exhibit limited superposition times,thus demanding more stringent processing for two-phase VSP data.By introducing the repeatability analysis and consistency processing method of two-phase data into the conventional processing technology for non-zero-offset VSP data,this study developed a processing technology flow for non-zero offset time-lapse VSP data.Moreover,this study conducted analysis and tests of the methods for processing the intra-shot consistency of time-lapse data and the consistency of two-phase data.As verified by the application in well A,the processing flow and key technology for non-zero-offset time-lapse VSP data proposed in this study enjoy high operability and practicability and,thus,have the potential for wide applications.

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Simultaneous reconstruction and denoising of seismic data based on rank reduction and sparsity constraints
LI Wen-Jie, ZHANG Hua, REN Wang, YE Hai-Long, WU Zhao-Qi, YANG Xi-Xi, PENG Qing
Geophysical and Geochemical Exploration. 2024, 48 (2): 479-488.   DOI: 10.11720/wtyht.2024.1404
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Field seismic data contain various random noise and irregular channel missing. Their simultaneous reconstruction and denoising is necessary for subsequent data processing. Currently, most simultaneous reconstruction and denoising methods only use a single sparsity or rank reduction constraint. The sparsity constraint exhibits high efficiency but lacks adaptability to various data. In contrast, the rank reduction constraint can adapt to various data but shows a high computational cost. To take a full advantage of different constraints, this study proposed a method for simultaneous reconstruction and denoising of seismic data based on combined constraints. This method regards projection onto convex sets (POCS) based on Fourier transform as the sparsity constraint, and damped multichannel singular spectrum analysis (DMSSA) as the rank reduction constraint. It employs the truncated singular value decomposition (TSVD) algorithm and the exponential threshold equation, fully utilizing the high computational efficiency of the sparsity constraint and the strong adaptability of the rank reduction constraint. As indicated by the processing results of theoretical and field data, this method based on combined constraints can consider and utilize the spatio-temporal correlations of seismic data, achieving higher signal-to-noise ratios via fewer iterations compared to methods based on a single constraint.

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Comparative study on lithology classification of oil logging data based on different machine learning models
JIANG Li, ZHANG Zhi-Mo, WANG Qi-Wei, FENG Zhi-Bing, ZHANG Bo-Cheng, REN Teng-Fei
Geophysical and Geochemical Exploration. 2024, 48 (2): 489-497.   DOI: 10.11720/wtyht.2024.1492
Abstract   HTML ( 0 )   PDF (2671KB)

Specific computational tools assist geologists in identifying and classifying the lithology of rocks in oil well exploration,reducing costs,and enhancing operational efficiency. Machine learning methods integrate a vast amount of information,enabling efficient pattern recognition and accurate decision-making. This article categorizes the lithology of five oil wells in the Norwegian Sea,randomly dividing the data into a training set (70%) and a test set (30%). Using multivariate well log parameter data for training and validation,the application effectiveness of models such as Multilayer Perceptron (MLP),Decision Tree,Random Forest,and XGBoost is compared. The research results indicate that the XGBoost model outperforms others in terms of data generalization,achieving an accuracy of 95%. The Random Forest model follows with an accuracy of 94%. Meanwhile,Multilayer Perceptron (MLP) and Decision Tree models exhibit good robustness,with accuracies of 92% and 90%,respectively.

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Research on magnetotelluric time series classification based on artificial neural network
YANG Kai, LIU Cheng, HE Jing-Long, Li Han, YAO Chuan
Geophysical and Geochemical Exploration. 2024, 48 (2): 498-507.   DOI: 10.11720/wtyht.2024.1144
Abstract   HTML ( 0 )   PDF (6330KB)

With the development of society,high-quality magnetotelluric signal acquisition is becoming more and more difficult because of various types of human interference are increasingly intensified. Scholars have proposed many corresponding denoising methods for different types of noise to improve data quality. It is impossible to manually interpret each data before denoising due to the huge amount of data. So an efficient noise recognition and classification method is urgently needed. Based on this, artificial neural network is applied in the classification of magnetotelluric time series in this paper. Four types of time series,namely,simulated square wave, power frequency, impulse noise, and measured noiseless data, were used to conduct noise classification training and measured data classification on LSTM、FCN、ResNet、LSTM-FCN and LSTM-ResNet models. The results show that FCN and LSTM-FCN has a relatively good effect on the classification of magnetotelluric time series. Among them, the highest classification accuracy of FCN measured data can reach 99.84%, and the average time for each epoch is 9.6 s. LSTM-FCN has higher classification accuracy than FCN,the highest classification accuracy of measured data sets is nearly 100%, but the average time for each epoch is 24.6 s, and it is easier to overfit than FCN. Overall, LSTM-FCN can achieve higher classification accuracy when the amount of data is relatively small, if the amount of data is large, it is necessary to consider the time cost,using FCN is more appropriate. Finally,the magnetotelluric data containing different types of noise was successfully processed using the magnetotelluric noise processing system which constructed by the LSTM-FCN classification model and the LSTM denoising model.

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Spatio-temporal combined ground-penetrating radar clutter suppression based on empirical mode decomposition and Karhunen-Loeve transform
SHAO Quan-Jie, SUN Ling-Zhi
Geophysical and Geochemical Exploration. 2024, 48 (2): 508-513.   DOI: 10.11720/wtyht.2024.1170
Abstract   HTML ( 1 )   PDF (2443KB)

Due to factors such as environment,the signals received by ground-penetrating radar (GPR) contain various clutter interference,posing high challenges in subsurface anomaly interpretation and late-stage imaging.Clutter,primarily including noise,antenna-coupled waves,and surface direct waves,cannot be eliminated effectively using single data processing methods.Hence,this study proposed a spatiotemporal combined clutter suppression method. In the temporal dimension,threshold processing based on empirical mode decomposition(EMD) was applied to the data of all survey points in the echo profile,achieving effective noise removal.In the spatial dimension,the Karhunen-Loeve(KL) transform was employed to remove residual interference in the entire radar echo profile by utilizing the correlation of target echoes and the randomness of clutter at all survey points.Both theoretical simulation and measured data processing verify that the method proposed in this study is effective in eliminating clutter and highlighting weak signals.

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A numerical simulation study on array acoustic logging of fractured granite reservoirs in buried hills
DU Wei-Yi, ZHANG Chong, HAN Hua-Yang, ZHAO Teng-Teng, ZHANG Wen-Yi
Geophysical and Geochemical Exploration. 2024, 48 (2): 514-520.   DOI: 10.11720/wtyht.2024.1252
Abstract   HTML ( 0 )   PDF (3722KB)

The buried-hill reservoirs in the Qiongdongnan Basin of the South China Sea exhibit intricate reservoir spaces and numerous fractures, leading to their pronounced heterogeneity. Since granite sediments spread across the study area, it is critical to effectively evaluate the development of fractures in granite reservoirs. Based on the COMSOL Multiphysics software and the finite element method, this study simulated the use of array acoustic logging to detect granite reservoirs with different widths, dip angles, and lengths, summarizing the response characteristics of fractures in different development states. The results are as follows: (1) Shear waves in fractured formations are subjected to non-significant influence of fracture widths, and their attenuation is inversely proportional to fracture dip angles and directly proportional to fracture lengths; (2) Stoneley waves manifest significant response to the changes in fracture widths, dip angles, and lengths, and their attenuation is proportional to both fracture widths and dip angles; (3) The attenuation of Stoneley waves is directly proportional to fracture lengths below 0.1 m but shows subtle response to fracture lengths above 0.1 m. The results of this study provide a basis for determining the development state of fractures in granite reservoirs using the array acoustic log method.

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Evaluating the nutritional and safety quality of camellia oil, oil content of camellia oleifera fruits, and site soils in Youyang
LI Yu, ZHANG Yu-Han, GUAN Kai-Jiang, BAO Li-Ran
Geophysical and Geochemical Exploration. 2024, 48 (2): 521-526.   DOI: 10.11720/wtyht.2024.1089
Abstract   HTML ( 0 )   PDF (1118KB)

To ascertain the nutritional quality, oil content characteristics, and growing environment of camellia oleifera in Youyang, Chongqing, China, this study analyzed the fatty acid composition of camellia oil and the oil content of camellia oleifera fruits produced in different strata. Furthermore, this study evaluated the soil nutrients and environmental quality of the site. The results indicate that the camellia oil from Youyang exhibited a similar fatty acid composition to olive oil, suggesting that camellia oleifera seeds are valuable high-grade oilseeds. The oil content of camellia oleifera fruits is significantly associated with strata. Camellia oleifera fruits produced in the Permian strata exhibit the highest oil content, followed by those in the Silurian and Ordovician strata sequentially. The cause of the differences lies in the varying geochemical composition of soils in different strata. The camellia oleifera site in Youyang manifests average soil nutrients but relatively high soil environmental quality, with only slightly over-limit Cd content. Therefore, camellia oleifera should be cultivated by applying various fertilizers in a scientific manner to ensure its healthy growth.

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Distribution and sources of n-alkanes in sediments in the Fangchenggang sea area
PANG Guo-Tao, YANG Yuan-Zhen, XIE Lei, LI Wei, ZHANG Xiao-Lei, YAN Xing-Guo
Geophysical and Geochemical Exploration. 2024, 48 (2): 527-533.   DOI: 10.11720/wtyht.2024.1088
Abstract   HTML ( 0 )   PDF (2425KB)

n-alkanes, exhibiting stable chemical properties, are ubiquitous in nature. They are favorable indicators of the source of organic matter. Using the gas chromatography-mass spectrometry (GC/MS), this study detected n-alkanes in the surface sediments sampled from the Fangchenggang sea area in September 2021. It analyzed their content and distribution, as well as their source based on characteristic parameters. The results are as follows: ① The n-alkanes of the Fangchenggang sea area manifested a content range of (67.51~850.08)×10-9 (dw), averaging 476.69×10-9 (dw), with high values primarily distributed in the southern sea area of Qisha Peninsula; ② They were principally composed of extensive n-C14~n-C35 n-alkane homologues in a bimodal distribution. The former peak group displayed an even-carbon number advantage, while the latter showed an odd-carbon number advantage; ③ The terrestrial-marine alkane ratio (ΣT/ΣM), carbon predominance index (CPI), and terrestrial-marine alkane predominance ratio (TAR) all indicate a significant terrestrial influence on n-alkanes in the Fangchenggang sea area; ④ The average chain length (ACL), alkane index (AI), and Pmar-aq further suggest that n-alkanes were mainly from terrestrial herbs; ⑤ The T-ALK/C16 ratio implies that the Fangchenggang sea area experienced oil pollution; ⑥ The pristane/phytane ratio (Pr/Ph) reveals that n-alkanes in the sediments of the Fangchenggang sea area formed in an oxidizing environment.

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Ge in soils of cultivated land in Qixingguan District: Geochemical characteristics and absorption by crops
ZHANG Hong-Wei, YANG En-Lin, JIAO Shu-Lin, WANG Gui-Yun, YANG Shan-Jin
Geophysical and Geochemical Exploration. 2024, 48 (2): 534-544.   DOI: 10.11720/wtyht.2024.1046
Abstract   HTML ( 0 )   PDF (4106KB)

Determining the content and absorption by crops of germanium (Ge) in soils of cultivated land holds great significance for the development and utilization of Ge in the land, as well as the scientific seed selection for the land. However, few studies on the Ge element in soils of cultivated land in Qixingguan District have been reported. Based on the data from a project of the geochemical investigation and evaluation of the land quality in the district, this study made statistics of geochemical parameters such as the Ge content and analyzed the geochemical characteristics of Ge in soils and the absorption of Ge by crops. The results show that the soils of cultivated land in Qixingguan District exhibit a Ge content ranging from (0.86~2.48)×10-6 (average: 1.74×10-6), which is equivalent to the background value of Ge in China. Based on the geostatistical analysis, this study determined that Ge-rich cultivated land covers an area of 65 853.54 hm2, accounting for 47.41% of the total cultivated land in the district, and is primarily distributed in the northwestern and southwestern portions. The biological absorption coefficients (Ax) to Ge in soils by crops are all below 1%, suggesting an extremely low absorption level. This study explored the causes of Ge enrichment in the soils and the environmental factors affecting Ge absorption by crops using methods such as correlation analysis, drawing the following conclusions: ① The Ge content in soils is principally governed by soil parent materials, accompanied by the influence of pedogenetic weathering process for soil formation. These factors, coupled with high organic matter content and slightly acidic soil, contribute to the Ge enrichment in the cultivated land of Qixingguan District; ② The correlation between Ax and pH is slightly negative in acidic soils but positive in neutral to alkaline soils, implying that slightly acidic soil reduces the absorption of Ge by crops in the study area.

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Factors influencing the Se content in tea leaves and rhizosphere soils of the Liubao tea in Wuzhou City, Guangxi
PENG Xue-Rui, CHEN Xiang, ZHOU Si-Yu
Geophysical and Geochemical Exploration. 2024, 48 (2): 545-554.   DOI: 10.11720/wtyht.2024.1034
Abstract   HTML ( 2 )   PDF (1585KB)

This study aims to investigate the characteristics and influencing factors of selenium (Se) content in the tea leaf-rhizosphere soil system of the Liubao tea in Wuzhou, Guangxi. With the main tea gardens in Liubao and Shizhai towns, the core production areas of the Liubao tea, as study areas, this study conducted statistical analysis of the Se content in the tea leaves, rhizosphere soils, and tea leachate samples of the Liubao tea. The results show that: ① The Se content in soils of the study areas ranged from (0.40~1.98)×10-6, averaging 1.08×10-6; ② The Se content in Liubao tea leaves was between (0.03~0.25)×10-6, averaging 0.07×10-6, with a Se enrichment rate of 68%; ③ The leaching rates of Se in tea leachate ranged from 0~23.95%; ④ The Se content in the rhizosphere soils of tea gardens principally depended on soil parent materials and silica-sesquioxide ratios; ⑤ The P and N elements in soils can facilitate the absorption of soil Se by tea leaves, while the iron and aluminum oxides in acidified soils hinder the full utilization of soil Se by the Liubao tea. Hence, appropriate biochemical and agronomic measures are recommended for acidified soil amelioration to enhance the Se enrichment ability of the Liubao tea.

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Investigation and evaluation of phytoplankton diversity of the Honghu lake basin in winter
ZHENG Xiong-Wei, HU Ming-Yi, ZHANG Zhi-Yi, XU Yuan-Zhang, BAI Yang, LIU Lei, WANG Jun-Feng
Geophysical and Geochemical Exploration. 2024, 48 (2): 555-564.   DOI: 10.11720/wtyht.2024.1044
Abstract   HTML ( 1 )   PDF (3805KB)

To discern the community structure of phytoplankton in the water of Honghu Lake Basin, this study deployed 10 sampling sites in Honghu Lake in October 2021, and evaluated the phytoplankton community using the diversity indices. The results show that there were 66 species of phytoplankton belonging to 49 genera in six phyla, of which the cyanophyta was the most species, followed by bacillariophyta. The phytoplankton biomass of the Honghu Lake Basin in winter ranged from 7.85~42.45 mg/L, averaging 22.35 mg/L. A comprehensive evaluation of the nutrient status of the lake water was conducted based on Margalef's richness index (M), Shannon-Weiner's diversity index (H), Simpson's diversity index (D), Pielou's evenness index (J), and the species dominance index (Y), suggesting that the Honghu Lake Basin water was moderately to severely polluted. This study holds that the water quality of the Honghu Lake Basin can be improved from the following aspects: ① The water protection of the Honghu Lake Basin should be enhanced by strictly controlling the inflow of various water pollutants from downstream and surrounding areas, implementing timely and efficient prevention and control of rural water pollution in the lake area, and properly organizing the balanced harvesting of aquatic phytoplankton; ② The water environment treatment should be strengthened to gradually restore the self-purification capacity of the lake water; ③ The publicity efforts should be intensified by regularly conducting educational activities on water pollution prevention and control in rural areas, residential communities, and schools.

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An experimental study on the influence of step topographies in strip mines on the exploration performed using the high-density resistivity method
ZHAO Zi-Hao, LI Peng-Hui, LYU Hai-Jian, KANG Sen
Geophysical and Geochemical Exploration. 2024, 48 (2): 565-572.   DOI: 10.11720/wtyht.2024.3503
Abstract   HTML ( 1 )   PDF (4709KB)

The stability assessment of strip mine slopes is a fundamental means to prevent slope accidents. To investigate the influence of step topographies on the exploration using the high-density resistivity method on strip mine steps, this study conducted flume experiments for simulation using similar materials to explore the current field distribution in the profile to be surveyed. The experimental results show that: (1) The shallow positions near the upper and lower slope lines and the breadth line of the cleaning berm exhibited high current densities and even current distributions; (2) The middle positions manifested sharply changed current densities, with their contours akin to the step topography; (3) The deep positions displayed low current densities and tardy current changes; (4) A significant current gathering effect was observed near the slope bottom line on the profile; (5) Compared to flat topographies, step topographies exhibited high current densities and uneven current distributions. This suggests that in the exploration using the high-density resistivity method, step topographies in strip mines can cause abnormal inversion results for the middle positions and positions near the slope bottom line.

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AN ANALYSIS OF THE SPECIAL WAVE IMPACT ON THE INTERPRETATIONOF THE COALFIELD COLLAPSE COLUMN
YANG Xiao-Dong, YANG De-Xi
Geophysical and Geochemical Exploration    2010, 34 (5): 627-631.  
Abstract2635)      PDF (4180KB)(4916)      


In the light of typical coneshaped columns in the Lu'an mine of Shanxi Province, the authors

established a mathematical model for the collapse column, and used the wave equation model for

seismic ray tracing and wavefield simulation of collapse columns. The simulation results show that,

due to the special nature of the collapse columns, such waves as the normal reflected wave, the fault

point diffraction wave, the delay diffraction wave, the delay reflected wave and  the "diffraction

wave" consisting of Pwave field are formed around the collapse columns. On such a basis, the field

shot was simulated, and then a single shot record for routine processing  was generated to produce

stacking sections and migrated sections. The forward section and the actual data analysis reveal that

the fallen columns of the special wave constitute an important feature for recognizing collapse

columns; nevertheless, the resultant scale of the actual seismic data interpretation is often smaller

than the scale of actual collapse column. Some suggestions are also put forward for reference.

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The application of integrated geological, geochemical and geophysical techniques to the exploration of the Bogutu gold deposit
YAO Tie, ZHOU Yong, DU Zhan-Jun, ZHAO Zhen-Ming
Geophysical and Geochemical Exploration    2015, 39 (5): 877-884.   DOI: 10.11720/wtyht.2015.5.01
Abstract1353)   HTML151)    PDF (12833KB)(4310)      

Low density geochemical survey in Yishenjilike mountain area led to the discovery of a huge gold geochemical block, and the verification and evaluation of gold anomalies led to the discovery of the Bogutu gold deposit. In combination with the geological characteristics of the prospecting area, the authors carried out a series of geological-geophysical-geochemical exploration work, delineated quite a few geochemical and IP anomalies, and detected the characteristics of ore-bearing structural belt. Through trenching and drilling verification, the authors found more than 40 gold orebodies, thus achieving good ore-prospecting results.

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The application of integrated geophysical prospecting methods to the exploration of urban buried fault
LIU Wei, HUANG Tao, WANG Ting-Yong, LIU Yi, ZHANG Ji, LIU Wen-Tao, ZHANG Qi-Bin, LI Qiang
Geophysical and Geochemical Exploration    2021, 45 (4): 1077-1087.   DOI: 10.11720/wtyht.2021.1525
Abstract770)   HTML408)    PDF (4078KB)(3837)      

The existing geological data show that there are several buried faults in the main urban area of Chengdu. However, the specific location and distribution of these faults are still unclear, which poses great security risks to the comprehensive and scientific exploitation and utilization of underground space resources and the optimization of urban construction planning and layout in Chengdu. In view of such a situation, four geophysical methods, namely, micromotion survey, high-density electrical method, transient electromagnetic method and soil radon measurement, were used in this paper to comprehensively explore the buried Baojiangqiao fault in the work area. The integrated geophysical prospecting methods not only identified the stratigraphic structure along the survey line, but also obtained the location, property, attitude and scale of the buried Baojiangqiao fault. This work indicates that the integrated geophysical prospecting methods can achieve better results in the exploration of urban buried fault.

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A NEW DEVELOPMENT PERIOD OF THE GRAVITY AND MAGNETIC EXPLORATION
ZHANG Chang-Da, DONG Hao-Bin
Geophysical and Geochemical Exploration    2010, 34 (1): 1-7.  
Abstract3376)      PDF (431KB)(3535)      

A review on the airborne gravity survey and airborne magnetic survey are given in this paper. The

authors hold that these techniques have entered into a new development period, as evidenced by the

emergence of such technologic indicators as airborne vector magnetometry, magnetic fulltensor LTSSQUID

and HTSSQUID gradiometry, airborne gravimetry, gravity gradiometry and geophysical survey by UAV.

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THE ADVANCES IN THE STUDY OF THE AIRBORNE GRAVIMETRY SYSTEM
WANG Jing-Bo, XIONG Sheng-Qing, ZHOU Xi-Hua, GUO Zhi-Hong
Geophysical and Geochemical Exploration    2009, 33 (4): 368-373.  
Abstract2959)      PDF (1014KB)(3408)      

This paper gives a brief review of the history of the airborne gravimetry. Based on the principle of the airborne gravimetry, the paper deals emphatically with the history, the present  research situation and the developments of the airborne scalar gravity survey system. Further development trends are also indicated.

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3D DISPLAY FOR GROUND PENETRATING RADAR BASED ON Matlab
WU Bao-Jie, JI Mei-Xiu, YANG Hua
Geophysical and Geochemical Exploration    2009, 33 (3): 342-344.  
Abstract6761)      PDF (532KB)(3147)      

 With powerful Matlab image processing functions, this paper has realized the 3D display of ground penetrating radar data, whose procedures are simple to prepare and easy to learn. A detailed description of the code is given, and the three-dimensional test data show that, by setting transparency, the target can be displayed in an intuitive and visual way.

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CALCULATION OF THE ANOMALY AREA
Zhao Rongjun
Geophysical and Geochemical Exploration    2000, 24 (2): 154-156.  
Abstract1578)      PDF (346KB)(2674)      

This paper puts forward a new method for calculating anomaly area—the polygonous approximation method,and gives corresponding algorithm and precision controlling technique.With this method,one can calculate anomaly area rapidly and precisely,thus yielding relatively satisfactory results.

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THE UTILIZATION OF EXCEL TO THE PERFORMANCE OF R-MODE CLUSTER ANALYSIS
CHUN Nei-ya
Geophysical and Geochemical Exploration    2007, 31 (4): 374-376.  
Abstract4616)      PDF (659KB)(2656)      

The R-mode cluster analysis is a mathematic statistical method for obtaining the quantitative similarity of several elements. Its procedure includes: the conversion of the original data; the solution of the relevant coefficient ; the clustering of the result. The above operation can be realized by using the data analysis tool of Excel. This method is quite suitable for field utilization.

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THE CHOICE OF GRIDDING METHODS FOR GEOPHYSICAL DATA
LIU Zhao-Ping, YANG Jin, WU Wei
Geophysical and Geochemical Exploration    2010, 34 (1): 93-97.  
Abstract3165)      PDF (1939KB)(2630)      

In drawing the contour map of geophysical data, suitable gridding methods should be chosen according to objective

environment characteristics and characteristics of data themselves. With practical examples, this paper deals with some common

gridding methods such as inverse distance to a power, Kriging, Minimum Curvatrue, Nearest Neighbor, Polynomial Regression, Radial

Basis Function, and Triangulation/Liner Interpolation, probing into their choosing means, applicable fields and parameter

installment.

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THE APPLICATION OF THE GRADIENT SOUNDING PROFILE METHOD TO THE GOLD PROSPECTING IN THE YINAN GOLD MINE
DU Li-ming, WU Jun-jie, YANG Jin-duo, WANG Peng, YU Bao-xian
Geophysical and Geochemical Exploration    2013, 37 (2): 225-228.   DOI: 10.11720/j.issn.1000-8918.2013.2.07
Abstract2348)      PDF (964KB)(2543)      
IP is an important method for mineral resources exploration, but it can only be applied in a few pivotal places because its difficult performance, and hence the information obtained from the survey area is very limited. The aim of this study is to find a simple and effective IP method with which we can get much valuable information form the survey area so as to improve the exploration effect. In the Yinan gold ore district, the authors applied the gradient sounding profile method, calculated 2D resistivity and obtained the IP model. The results show that the gradient sounding profile method is simple and effective.
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THE APPLICATION OF ATOM INTERFEROMETER TO THE MEASUREMENT OF GRAVITATIONAL ACCELERATION
ZHANG Chang-da
Geophysical and Geochemical Exploration    2000, 24 (5): 321-326.  
Abstract1743)      PDF (673KB)(2537)      

This paper has described and reviewed the pinciples,expermental set up and observational results of applying atom interferometer to measuring the earth's gravitational acceleration.This method was developed by Nobelist Steven Chu,M.Kaservich,A.Peters et al.,who demonstrated a resolution of 10-10.The application of this technique to geophysics and the related problems are also discussed.

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CHEMICAL COMPOSITIONS OF CONTINENTAL CRUST AND ROCKS IN EASTERN CHINA
Yan Mingcai, Chi Qinghua, Gu Tiexin, Wang Chunshu
Geophysical and Geochemical Exploration    1997, 21 (6): 451-459.  
Abstract3030)      PDF (2969KB)(2408)      

Element abundances of the continental crust and rocks cited in the past and recent literature have been based on compilations of data from various studies. This leads to uncertainties in sample representativeness and data quality. The present study is based on systematic collection of 28 253 individual rock samples over an area of 3.3 million km2 in eastern China, east of eastern longitude of 105°.The sampling involves more than 800 igneous intrusive bodies and metamorphic complexes as well as more than 500 type stratigraphic sections. From the individual rock samples, 2 718 composite samples were made and analyzed for 77 elements by 15 specific methods, dominantly XRF and INAA. Analytical quality was controlled by international and national preliminary geochemical reference materials of GSR, GAu and GPt series. Synthetic results from geological, geochemical and geophysical studies were used to construct crustal constitution model, from which element abundances of the continental crust in the North China platform, the upper crust and exposed crust in eastern China, chemical composition of igneous rock in China and of sedimentary rock and metamorphic rock in eastern China were derived.

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THE APPLICATION OF NEW GEOCHEMICAL EXPLORATION METHODSTO MINERAL EXPLORATION AND ITS GEOLOGICAL EFFECT
JIANG Yong-Jian, WEI Jun-Hao, ZHOU Jing-Ren, WANG Zhong-Ming, JI Zhao-Jia, WANG Fa-Yan
Geophysical and Geochemical Exploration    2010, 34 (2): 134-138.  
Abstract4304)      PDF (403KB)(2381)      

As an important prospecting technique and an effective means for obtaining mineralization data,

geochemical exploration has been proved to be very successful in mineral exploration. This paper focuses on

commenting the present research situation and application effect of some new methods such as structural

superimposed halos method, heat released mercury method, separatory electrogeochemistry method, enzyme leach, and

geogas and selective leaching of mobile metals method. It is emphasized that any one of these methods has its

unique applicability and that, in the practical application, we should pay attention to the cooperation of

geochemical exploration, geologicalgeophysical exploration and remote sensing and depend on the study of

geological background so as to demonstrate the usefulness and effectiveness of geochemical exploration.

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RECENT ADVANCES IN THE RESEARCH AND DEVELOPMENT OF QUANTUM MAGNETOMETERS
ZHANG Chang-da
Geophysical and Geochemical Exploration    2005, 29 (4): 283-287.  
Abstract1731)      PDF (376KB)(2366)      

In this paper, recent advances in the research and development of quantum magnetometers have been described together with some suggestions on further research work.

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THE EXTRACTION METHOD AND PROGRAM DESIGN FOR DISPERSION CURVE IN F-K DOMAIN
LI Jie, CHEN Xuan-hua, ZHANG Jiao-dong, ZHOU Qi, LIU Gang, LIU Zhi-qiang, XU Yan, LI Bing, YANG Jing
Geophysical and Geochemical Exploration    2011, 35 (5): 684-688.  
Abstract3738)      PDF (534KB)(2296)      

Based on two-dimensional Fourier transform and half-wave theory, this paper has studied the seismic Rayleigh wave dispersion curve extraction in f-k domain and made this theory fit in with a program by means of Delphi7.0. It is concluded that the f-k method overcomes the shortcomings of the one-dimensional digital processing technology and makes full use of multi-channel Rayleigh wave data record.

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THE PRESENT SITUATION AND RESEARCH ADVANCES OF EXPLORATION GEOCHEMISTRY FOR PORPHYRY COPPER DEPOSITS
HU Shu-qi, MA Sheng-ming, LIU Chong-min
Geophysical and Geochemical Exploration    2011, 35 (4): 431-437.  
Abstract3739)      PDF (643KB)(2266)      

Porphyry copper deposit is the most important copper deposit type in China. With the deepening of mineral exploitation, exploration geochemistry in mineral exploration has become increasingly important. Based on related literature, this paper sums up the exploration geochemical research results of porphyry copper deposits, which include such aspects as geochemical characteristics, exploration methods, anomaly evaluation and prospecting indicators. Exemplified by the Fujiawu copper deposit, this paper reports the latest advances in the study of porphyry copper deposits.

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FEATURES OF GEOPHYSICAL COMPOSITE ANOMALIES AND ORE RESOURCES IN YIHUANG AREA, JIANGXI PROVINCE
WANG Wei-Beng, FANG Ying-Yao, TUN Cheng-Beng
Geophysical and Geochemical Exploration    2010, 34 (5): 573-578.  
Abstract3069)      PDF (2717KB)(2237)      

According to the data obtained from air-borne electromagnetic and magnetic survey and

ground two-frequency IP and magnetic survey, this paper discusses the relationship between the

features of air-borne and ground geophysical composite anomalies and the ore resource distribution.

On the basis of an integrated analysis, geophysical composite anomaly criteria in search for iron, zinc

and lead deposits were established, and 12 important ore-prospecting targets were delineated, which

provides very important clues for finding iron, zinc, lead and some other ore resources.

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Characteristics of gravity and magnetic fields in Ordos Basin and their geological significance
Bing LI, Yan-Bing SONG, Lei SHI, Qi WANG, Jiu-Ming JIANG, Jiu-Qiang JIN, De-Wen ZHOU, Ming XU, Gang-Yi XIAO, Min-Ying XIE
Geophysical and Geochemical Exploration    2019, 43 (4): 767-777.   DOI: 10.11720/wtyht.2019.1391
Abstract621)   HTML3)    PDF (3147KB)(2227)      

According to aeromagnetic and gravitational data, the boundary and range of Ordos basin were determined based on an analysis of the characteristics of gravity and magnetic fields. And on the basis of compiling depth map of the metamorphic basement and structuring zoning map, research was conducted on the basin’s basement structure, characteristics and features of depth change, structure framework, and caprock thickness. The research indicates that the metamorphic basement is composed of Proterozoic metamorphic series, and the buried depth of crystalline basement can reach 5 000 to 20 000 meters. The caprock is the layers of Ediacaran, Paleozoic, and Mesozoic. The occurrence and development of the basin are restricted by nearly NE-and NWW-trending structures, forming a pattern of four depressions and three uplifts. All the new understanding and conclusions provide a reference for further oil and gas exploration in the basin.

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RESEARCH AND APPLICATION ON NUMERICAL INTEGRATIONOF HANKEL TRANSFORMS BY DIGITAL FILTERING
ZHANG Wei, WANG Xu-Ben, QIN Qing-Yan
Geophysical and Geochemical Exploration    2010, 34 (6): 753-755.  
Abstract3726)      PDF (363KB)(2211)      

 Numerical integration of Hankel transforms is effective tools for EM Sounding 's forward numerical simulation, this paper made out formula derivation of numerical integration of Hankel transforms by digital filtering, and use digital coefficients to do numerical compute which was put forward by Guptasama and Singh,finally contrasted to theoretical resolve expression and analyzed this algorithm's error distribution. The results show that the calculation of this algorithm continuously approximate its theoretical solution, it has no oscillation, high precision and great practical value in the numerical simulation study.

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PARAMETER SELECTION IN VIBROSEIS SEISMIC EXPLORATION
XUE Hai-Fei, DONG Shou-Hua, TAO Wen-Peng
Geophysical and Geochemical Exploration    2010, 34 (2): 185-190.  
Abstract3498)      PDF (3477KB)(2197)      

 Vibroseis exploration, as an important method of seismic exploration, has become increasingly valued by geologists. During the field work, different geological conditions need different parameters, and the choice of suitable excitation parameters has become a very important problem. This paper mainly introduces six kinds of parameters, namely numbers of controlled seismic source, scanning bandwidth, vibration period, scanning length, scanning slopes, and vibration rate. The influence of these parameters on the quality of seismic records was studied in detail, and the simulation of the proper parameters was performed in Jiulishan area to enhance the resolution of vibroseis exploration and improve the signaltonoise ratio of seismic records.

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THE UTILIZATION OF SURFER TO CONDUCT THE DRAWING OF PROFILE-PLAN
SUN Zhong-ren, ZHAO Dong-liang
Geophysical and Geochemical Exploration    2006, 30 (2): 172-174.  
Abstract3557)      PDF (572KB)(2160)      

This paper has put forward the idea of utilizing Surfer to draw the initial data profile-plan. The programme compiled can realize the construction of Bln file. The profile-plans for regular net and irregular net have been constructed, and the results are satisfactory.

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ABUNDANCE OF CHEMICAL ELEMENTS OF SOILS IN CHINA AND SUPERGENESIS GEOCHEMISTRY CHARACTERISTICS
Yan Mingcai, Gu Tiexin, Chi Qinghua, Wang Chunshu
Geophysical and Geochemical Exploration    1997, 21 (3): 161-167.  
Abstract2618)      PDF (2180KB)(2155)      

On the basis of accurate analysis of 154 composite soil samples collected from various landscape in China and other reference information, abundance of 79 elements and composition of soils in China have been given, chemical composition of soils under the influence of matrix rock and supergenesis geochemistry condition have been studied preliminarily.

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MIGRATION VELOCITY ANALYSIS AND MIGRATION IMAGING RESEARCH
YE Jing-Yan, YAO YA-Lin, WANG Yan-Qun, LI Qing
Geophysical and Geochemical Exploration    2009, 33 (6): 674-677.  
Abstract2817)      PDF (1927KB)(2144)      

Migration velocity analysis and migration imaging constitute two important parts in seismic data processing. At

present, time migration has become mature, and depth migration is getting more and more perfect. The common method for time

domain migration imaging is pre-stack time migration. By adopting stacking velocity analysis along the layer, exact layer

stacking velocity can be obtained. Through dip correction, pre-stack time migration and CRP de-migration velocity analysis, the

velocity is optimized step by step, and then a desired RMS velocity field that is up to the geological rule is acquired. In

addition, the method for building the accurate migration velocity field is summed up through the study of the depth migration

method. A new seismic data processing flow in combination of Kirchhoff arithmetic based on ray tracing and wave equation

arithmetic based on wave field extrapolation is presented. As a result, migration velocity analysis and migration imaging are

considerably improved.

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THE AUTOMATIC FORMATION OF THE SUFFER SOFTWARECONTOUR LEVEL FILE BASED ON AREA STATISTICS
REN Lei, CHEN Hua-Gen
Geophysical and Geochemical Exploration    2009, 33 (5): 595-598.  
Abstract3649)      PDF (830KB)(2127)      

The implied contour level and color scheme in Surfer software fail to express the subtle difference of DEM and the effect

of color solid. In addition, the artificial setting of the levels and color values are timeconsuming and laborious, and the

results are sometimes not perfect. With the consideration of contour level and color scheme and on the basis of Surfer platform

automation technology, this paper presents a program that can automatically generate a level file with different intervals and

different colors, thus resulting in satisfactory effect and efficiency.

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THE INVERSED PROBLEM IN GRAVITY AND MAGNETICEXPLORATION: A REVIEW
Zeng Hualin
Geophysical and Geochemical Exploration    1990, 14 (3): 182-190.  
Abstract2041)      PDF (737KB)(2093)      

On the basis of mote than230 English and Russian papers or monographsissued in the last 30 years as well as nearly 50 Chinese articles published overthe past 10 years on the inversed problem in g avity and magnetic explora-tion, combined with his practice in the study of the inversed problem, the all-thor expounds the inversed methods in gravity and magnetic exploration cur-rently used both at home and abroad, briefs the readers about the researchsituation in China and foreign countries, and makes a detailed review on achi-evements gained in China in comparison with the research levels abroad.Final-ly, suggestions are put forward concerning some subjects which are worthnoticing in future research work.

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WAVE FIELD SEPARATION NUMERICAL MODELING OF SECOND ORDER ELASTIC WAVE EQUATION BY HIGH-PRECISIONSTAGGEREDGRID FINITE DIFFERENCE SCHEME
CHEN Ke-Yang, YANG Wei, LIU Hong-Lin, WU Qing-Ling
Geophysical and Geochemical Exploration    2009, 33 (6): 700-703.  
Abstract3172)      PDF (1060KB)(2073)      

This paper proposes an equivalent second order elastic wave equation to solve the problem of being unable to completely

separate the coupled P and S wave by full elastic wave equation. Through solving this equivalent wave equation by high-order

staggeredgrid finite difference scheme together with Flux Correction Technology (FCT) and separating wave fields of the

isotropic model and layered model, the authors accurately obtained the hybrid wave field and completely separated fields of pure

P wave and pure S wave fields. An analysis of the numerical results shows that the method is effective and reliable in isotropic

media, and there exists abundant energy transform information in separated pure P and pure S wave field. The result of the study

is of significance in understanding the propagating law and the elastic wave theory in the complex wave field.

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THE PROGRESS AND PROSPECT OF THE ELECTRICAL RESISTIVITY IMAGING SURVEY
YAN Jia-yong, MENG Gui-xiang, LV Qing-tian, ZHANG Kun, CHEN Xiang-bin
Geophysical and Geochemical Exploration    2012, 36 (4): 576-584.   DOI: 10.11720/wtyht.2012.4.13
Abstract4948)      PDF (1427KB)(2032)      
This paper has summed up the progress of the ERI method over the past decade of years as well as its future development trend in the following aspects: ① A comparison of the performances of the main ERI instruments used at present shows that the ERI instruments tend to develop in the multi-channel, multi-parameter, multi-functional, high-power direction; ② ERI measurement environment has changed from surface measurement to water surface, underwater and cross-hole measurements, with the last three kinds of measurements analyzed in this paper; ③ On the basis of analyzing ERI data processing method and inverse development status, this paper describes three-dimensional and four-dimensional inversion theory of ERI with practical examples; ④ ERT applications are summed up, and several new applications are introduced. It is concluded that, with the improvement of the probing depth and observation precision as well as the diversification of the observation models, the application field of ERI will become broader and broader, and this technique will surely have wide development prospect.
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Geophysical and Geochemical Exploration    1982, 6 (3): 154-156.  
Abstract1167)      PDF (190KB)(2008)      
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PML ABSORBING BOUNDARY CONDITION FORNUMERICAL MODELING OF RAYLEIGH WAVE
XIONG Zhang-Qiang, TANG Sheng-Song, ZHANG Da-Zhou
Geophysical and Geochemical Exploration    2009, 33 (4): 453-457.  
Abstract3442)      PDF (2025KB)(2005)      

The algorithm of the finite difference oforder velocitystress staggered grids has been built, which is

suitable for the perfectly matched layer (PML) absorbing boundary for elastic media. Meanwhile, the construction of the

PML absorbing boundary condition and the realization of the finitedifference algorithm are discussed in detail. Wave

field modeling calculations show that, compared with the conventional decaying exponential absorbing boundary and non

absorbing boundary, the PML absorbing boundary can perform absorption much more clearly and absorb the boundary

reflection from various angles, whose absorptivity (the ratio of absorption energy to unabsorbable energy) can reach

99.99%. The PML absorbing boundary can well eliminate the periodic folding effects, which makes the calculation of the

wave field characteristics very distinct, and the Rayleigh wave can be clearly shown in the waveform record.

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PRESENT RESEARCH SITUTATION AND DEVELOPMENT TREND OF AIRBORNE GRAVITY GRADIOMETER
SHU Qing, ZHOU Jian-xin, YIN Hang
Geophysical and Geochemical Exploration    2007, 31 (6): 485-488.  
Abstract2204)      PDF (690KB)(2005)      

The development of the gravity gradiometer is described simply in this paper, and the measuring principle and development experience of the rotating accelerometer gravity gradiometer are emphatically discussed. On the basis of researches on the existing airborne gravity gradiometer, the prospects of the airborne gravity gradiometer are also presented.

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SOME PROBLEMS CONCERNING THE CONVERSIONOF MAPS BETWEEN SURFER AND MAPGIS
QIN Lin-Jiang
Geophysical and Geochemical Exploration    2010, 34 (5): 677-680.  
Abstract5478)      PDF (865KB)(2003)      

With the extensive adoption of computer technology in geology and geophysics, computer graphics becomes more and more important. For the purpose of improving quality and efficiency, several software should be combined in practical work. In this paper, some basic characteristics of Surfer and MapGIS are discussed, and their application in geological field is described from the angle of geological mapping, thus drawing forth the necessity of the conversion between Surfer and MapGIS. The general method and steps for the conversion of maps between Surfer and MapGIS are presented in detail, and several problems concerning the conversion and corresponding solutions are emphatically discussed.

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YANG Li-De
Geophysical and Geochemical Exploration    2009, 33 (6): 741-742.  
Abstract2203)      PDF (240KB)(1990)      
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THE APPLICATION OF SEISMIC REFRACTION WAVE METHOD ANDHIGHDENSITY RESISTIVITY METHOD TO TUNNEL INVESTIGATION
ZENG Guo, CUI De-Hai, LIU Jie, LI Kai
Geophysical and Geochemical Exploration    2009, 33 (5): 608-612.  
Abstract3225)      PDF (1351KB)(1965)      

 Basic principles and techniques for the shallow seismic refraction wave method and the highdensity resistivity method

are described in this paper in combination with engineering practice to explain the results of the refraction wave method and the

high-density resistivity method in railroad and highway tunnel exploration. The application effects of the combination of these two

methods in detecting positions, sizes, natures and characteristics of such harmful geological bodies as concealed faults and shatter

zones are also discussed. Some measures for improving the investigation accuracy of these two methods are put forward.

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THE COMPARATIVE STUDY AND APPLICATION OF SEVERALTIMEFREQUENCY ANALYSIS METHODS IN THE COAL FIELD
HU Ming-Shun, PAN Dong-Ming, XU Hong-Li, ZHAO Li-Gui
Geophysical and Geochemical Exploration    2009, 33 (6): 691-695.  
Abstract2502)      PDF (2110KB)(1960)      

In the light of the characteristic time-frequency properties of different time-frequency analysis methods, it is

important to select an optimal time-frequency analysis method for high precision seismic exploration in the coal field on the

basis of comparing and studying these methods. Aimed at probing into STFT, Wavelet Transform, S-Transform, Choi-Williams

Distribution, Wigner-Ville Distribution and its improved methods, this paper studied advantages and disadvantages of every method

through numerical simulation in time resolution, frequency resolution and interference. The First Break Picking and Separate

Frequency Display for Collapse Column interpretation were realized by SPWVD and S-Transform, with a good result obtained.

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The application of the integrated geophysical-geochemical method to the Yiliu polymetallic ore district in northern Guangdong Province
WU Wei-Guo
Geophysical and Geochemical Exploration    2015, 39 (6): 1097-1103.   DOI: 10.11720/wtyht.2015.6.01
Abstract1137)   HTML152)    PDF (11771KB)(1942)      

The main minerals in the Yiliu polymetallic ore district are mainly As, Sb, Pb, Zn, Ag, W, Sn, Nb and Ta, the deposit types and the ore-controlling factors are complex and diverse. Recently, by using 1:50000 geochemical stream sediment survey, geochemical soil survey and CSAMT method in this ore district, supergene distribution of elements were found, and many integrated anomalies were delineated. A comprehensive evaluation of all kinds of anomalies shows that the F3 fault has features of ore-passage structure and ore-storage structure, and the area sandwiched between F2 and F3 fault are favorable ore-forming place, whereas the depression parts of biotite granite which have high resistance and multiple sets of fracture intersections are most favorable places for mineralization.

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A TENTATIVE DISCUSSION ON THE RESOLUTION OF THE GROUND-PENETRATING RADAR
YUAN Ming-de
Geophysical and Geochemical Exploration    2003, 27 (1): 28-32.  
Abstract2522)      PDF (512KB)(1906)      

In the light of the pulse width of the radar wave, this paper deals with the difference and the relationship between the vertical resolution and the transverse resolution of the ground-penetrating radar, indicates the influence of the noise upon the resolution and, with practical examples, points out that the digital handling of the signal can greatly improve the resolution of the radar.

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THE EXPLORATION EFFICIENCY OF THE TERRATEM ELECTROMAGNETIC SYSTEM,IN THE CONCEAL IRON DEPOSIT,HENAN PROVINCE
LI Shui-Peng, ZHANG Tong-Zhong, JING Jin-Ming
Geophysical and Geochemical Exploration    2009, 33 (4): 424-426.  
Abstract2776)      PDF (608KB)(1899)      

This thesis supply a profile about performance of TerraTEM system and the  distinguishing feature of TEM. By exploring

work on two conceal iron deposit in HeNan province and analyzing. the abnormal value of the TEM system.combining with drill

drawing,The writer prove that the TEM can take a obvious effect on exploring iron mineral.

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THE APPLICATION OF THE RAYLEIGH SURFACE WAVE TECHNIQUE TO RAILWAYS
LI Hai
Geophysical and Geochemical Exploration    2002, 26 (2): 160-162.  
Abstract1910)      PDF (480KB)(1891)      

With practical examples, this paper deals with the basic principle and technique of the Rayleigh surface wave exploration, the technology for its application to railways, the data acquisition, processing and interpretation, and the calculation method for converting the velocity of the Rayleigh surface wave to the bearing capacity. The reliability of applying this technique to railways is also pointed out.

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CHAMP, GRACE AND GOCE: THREE SATELLITES FOR SENSING AND/OR MEASURING THE EARTH'S GRAVITY FIELD
ZHANG Chang-da
Geophysical and Geochemical Exploration    2005, 29 (5): 377-382.  
Abstract2115)      PDF (749KB)(1880)      

In this paper, the working principle of three satellites (CHAMP, GRACE and GOCE) has been described, and the important geopotential models and the newest geopotential models (EIGEN-CG01C, GGM02) have been introduced.

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A COMPARISON OF SEVERAL THRESHOLD DETERMINATION METHODS IN GEOCHEMICAL DATA PROCESSING: A CASE STUDY OF STREAM SEDIMENTS IN CHABAQI AREA OF INNER MONGOLIA
DAI Hui-Min, GONG Chuan-Dong, BAO Qing-Zhong, SUN Zhong-Ren, YOU Hong-Liang, JIN Xin, GAO Fei
Geophysical and Geochemical Exploration    2010, 34 (6): 782-786.  
Abstract3888)      PDF (1006KB)(1868)      

The authors made statistic calculation of stream sediment data using such means as traditional statistics, robust estimation,cumulative percentage of 85% and multifractal statistical method in Chabaqi area and compared the thresholds obtained by the four methods. The thresholds of the same elements obtained by the four methods are obviously different from each other. The thresholds calculated by the cumulative percentage statistics are lowest except for lead, and the thresholds calculated by the other three methods fail to show obvious regularity.The results are closely related to the distribution characteristics of the geochemical data and the statistical methods used. Comparing the anomaly characteristics with the geological characteristics, the authors have found that, although weak and gentle geochemical anomalies will be mostly detected by cumulative percentage of 85%, the larger anomaly areas will bring difficulties to anomaly inspection in the field. It is therefore thought that the thresholds obtained by multifractal statistical method are suitable for the study area. A comparative study of the thresholds has led the authors to believe that the reasonable method must be combined with the actual geological conditions and based on a thorough study of the geological background of the study area.

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Progress and prospect of gravity and magnetic techniques for hydrocarbon exploration in China
LIU Yun-Xiang, SI Hua-Lu, QIAO Hai-Yan, LIU Bai-Chuan
Geophysical and Geochemical Exploration    2023, 47 (3): 563-574.   DOI: 10.11720/wtyht.2023.1484
Abstract555)   HTML344)    PDF (3583KB)(442)      

This study summarized the progress and major application performance of gravity and magnetic techniques for onshore hydrocarbon exploration in China in recent years.By combining the research results of the authors,this study elucidated the new progress made in the gravity and magnetic techniques for hydrocarbon exploration from the prospect of acquisition,processing,interpretation,and application and sorted the application performance of these techniques in key fields including deep targets,complex areas,and volcanic rocks.Moreover,this study future analyzed the demand for the gravity and magnetic techniques for hydrocarbon exploration.By combining the new trends of gravity and magnetic exploration techniques at home and abroad,this study proposed the development direction and application prospect of gravity and magnetic techniques for oil and gas in deep strata and igneous rocks in complex areas.The results of this study show that significant progress has been made in gravity and magnetic exploration techniques,which play an important role in supporting the current hydrocarbon exploration.It is expected to develop high-precision and high-density gravity and magnetic exploration techniques and gravity-gravity-electricity-seismic collaborative innovation techniques.

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Research on edge depth inversion of 2D geological body based on gravity and magnetic field
WANG Wan-Yin, LUO Xin-Gang
Geophysical and Geochemical Exploration    2023, 47 (3): 547-562.   DOI: 10.11720/wtyht.2023.1464
Abstract319)   HTML383)    PDF (8058KB)(493)      

The edge depth of geological body plays a crucial role in the semi-quantitative interpretation of gravity and magnetic potential field exploration. At present, the main inversion methods of geological body edge depth mainly include Werner deconvolution method, analytical signal amplitude method, local wave number method, Tilt-depth method, Euler deconvolution method and curvature attribute inversion method. These methods all have problems of solution selection, stability and adaptability. This paper mainly studies the adaptability of different types of data and models. Through basic principle analysis and model test, the results show that Werner deconvolution method and Euler deconvolution method are applicable to the most types of data sources, followed by curvature attribute, and Tilt-depth is the least; Werner deconvolution method, Euler deconvolution method and curvature attribute methods can adapt to many models, the Tilt-depth is least. For gravity data, the analytical signal amplitude of the first vertical derivative as the data source is applicable to all methods. For magnetic data, the analytical signal amplitude as data source is applicable to all methods. At the same time, it is suggested that other scholars should follow the following principles when using these methods to invert the edge depth of the two-dimensional body: It is recommended that Werner deconvolution is preferred, followed by curvature attribute and Euler deconvolution. The gravity data source of Werner deconvolution method and Euler deconvolution method is recommended to use the horizontal derivative of the first vertical derivative, and the magnetic data source is recommended to use the horizontal derivative. The gravity data source of curvature attribute method is recommended to use the analytical signal amplitude of the first vertical derivative, and the magnetic data source is recommended to use the analytical signal amplitude. In addition, based on the above research conclusions, some suggestions on the future research directions of the solution screening, stability and adaptability of the edge depth inversion are given.

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A review of the research progress and application status of seismic full waveform inversion
CHEN Zi-Long, WANG Hai-Yan, GUO Hua, WANG Guang-Wen, ZHAO Yu-Lian
Geophysical and Geochemical Exploration    2023, 47 (3): 628-637.   DOI: 10.11720/wtyht.2023.1469
Abstract297)   HTML14)    PDF (3181KB)(348)      

As resource exploration deepens and becomes increasingly difficult,improving the imaging precision and the reservoir prediction accuracy under a complex tectonic setting has become a top priority of research.The full waveform inversion (FWI) method developed in recent years can be applied to complex geological structures.This method can reveal structural details in a complex geological setting using the dynamic and kinematic information in the pre-stack seismic wave field.However,this method involves many research elements such as model parameterization,building of inverse error function,data preprocessing,numerical simulation of wavelengths,and wavelet estimation.Thus,its development is bound to be a long-term gradual improvement process.The FWI method has been applied to actual observation data with the development of theory and computer technology.This study introduced the principle and processing flow of the FWI method and summarized its development history and its application status in marine and onshore seismic data,and deep seismic reflection data.Accordingly, this study presented the current application bottlenecks,data processing difficulties, and challenges of deep-crustal inversion imaging for subsequent research and application of the FWI method.

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Application of integrated geophysical methods in deep ore prospecting of Laochang polymetallic mining area in Lancang, Yunnan
YOU Yue-Xin, DENG Ju-Zhi, CHEN Hui, YU Hui, GAO Ke-Ning
Geophysical and Geochemical Exploration    2023, 47 (3): 638-647.   DOI: 10.11720/wtyht.2023.1578
Abstract271)   HTML20)    PDF (6931KB)(420)      

Laochang, Lancang, Yunnan is one of the most important polymetallic mining areas in the southern part of Sanjiang Tethys metallogenic belt. After years of mining, the shallow resources are nearly exhausted. In recent years, granite porphyry and porphyry polymetallic mineralization have been newly discovered in the deep part of the mining area, highlighting the prospecting potential of deep polymetallic deposits. In order to trace the occurrence of deep ore-controlling strata and structures in the study area and help to make a breakthrough in deep ore prospecting, high-power induced polarization method and audio magnetotelluric method were implemented to image the deep structure situated. Results obtained from the inversion of the measured induced polarization and electromagnetic data recuperated the distribution of induced polarization anomalies and the characteristics of deep electrical structure within the study area. Combined with the available regional geological settings, the main conclusions are as follows: The low resistance and high polarization anomalies in the northwest of the survey area are deeply related to the surface ferromanganese, silver manganese, and deep polymetallic mineralization, and the high resistance and high polarization anomalies in the middle and east of the survey area are in good agreement with the deep polymetallic mineralization. The upper Carboniferous limestone and dolomite strata are thick in the west and thin in the east, with the west strata dipping to SW and the east strata overlying the Yiliu Formation of the lower Carboniferous. The concealed granite porphyry dips in NE direction, and the coupling part between its deep 2 300~2 800 m horizontal section and deep fault is a favorable area for deep polymetallic mineralization. Notably, joint interpretation yielded from the high-power induced polarization method and the audio magnetotelluric method applied improved the reliability of deep polymetallic ore detection and provided more information of positioning the subsequent drilling layout.

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Distribution of microorganisms in the typical geothermal field environment and its significance for geothermal exploration
ZHENG Xu-Ying, XU Ke-Wei, GU Lei, WANG Guo-Jian, LI Guang-Zhi, GUO Jia-Qi, ZOU Yu, BORJIGIN Tenger
Geophysical and Geochemical Exploration    2023, 47 (5): 1127-1136.   DOI: 10.11720/wtyht.2023.1151
Abstract265)   HTML17)    PDF (4903KB)(225)      

As a kind of clean energy, geothermal energy has attracted the attention of scholars all over the world in recent years. Previous geochemical exploration methods for geothermal resources are limited to the analysis of individual geochemical indices. Moreover, previous studies of microorganisms in geothermal fields mostly focus on hot spring outcrops, lacking ecological studies of geothermal resources in complex terrains. This study investigated the soil geochemistry and microbial diversity of the Bantang Hot Spring geothermal field in Chaohu, Anhui Province. Geochemical indices such as head-space gas, soil gas, acid-hydrolyzed hydrocarbons, and altered carbonate were detected in this study. Combined with the microbial high-throughput sequencing technology, this study analyzed the composition and spatial-temporal distribution of the microbial population above the geothermal fields in uplifted mountains and the relationship between these bioinformatics characteristics and the geochemical indices. The results indicate that the acid-hydrolyzed hydrocarbons on the surface of the geothermal field showed a maximum methane concentration of 43.7 μL/kg in the area between faults F2 and F3, adequately reflecting the fault location of the geothermal field.Bacillaceae, Hydrogenophilaceae, and Thermodesulfovibrionaceae in the geothermal field and the background area showed large relative abundance differences, which were 0.178%, 0.108%, and 0.060%, respectively. This result indicates that they are sensitive to geothermal resources and correspond well to geochemical indices above the known geothermal field. This study preliminarily investigated the diversity of geothermal microorganisms in the geothermal field and analyzed the corresponding relationships between microbial distribution characteristics and geochemical indexes, providing technical support for the microbiological exploration of geothermal resources.

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Aerogeophysical anomalies and prospecting direction in the Fengtai ore concentration area
XU Xue-Yi, XIONG Sheng-Qing, YANG Xue, GAO Wei-Hong, FAN Zheng-Guo, JIA Zhi-Ye
Geophysical and Geochemical Exploration    2023, 47 (5): 1157-1168.   DOI: 10.11720/wtyht.2023.0068
Abstract214)   HTML9)    PDF (14675KB)(243)      

The Fengtai ore concentration area is an important producing area of plumbum-zinc and gold ores in the middle of the Qinling orogenic belt. It hosts many large to super-large deposits, such as Qiandongshan-Dongtangzi, Bafangshan-Erlihe, Baguamiao, and Shuangwang deposits. With the exploitation proceeding, the reserves of these deposits have decreased significantly, and the ore prospecting in these deposits has shifted from the surface to the deep part. However, the geophysical fields in the deposits are yet to be ascertained, severely restricting research on the metallogenic regularity of the deposits and the ore prospecting and exploration in the peripheral zones. Based on the latest 1∶50,000 aeromagnetic and airborne radioactivity survey data, as well as gravity data, this study investigated the multi-source geophysical fields on the scales of the region, the ore concentration area, and deposits, aiming to summarize the distribution patterns of geophysical anomalies of different scales and provide evidence for research on metallogenic regularity and prospecting prediction. The results show that the Fengtai and the Xicheng ore concentration areas, with similar magnetic structures, are separated by the zone with strong magnetic anomalies caused by the crystalline basement of the Huicheng Basin. The first vertical derivative of gravity reveals that the Fengtai and Xicheng ore concentration areas have density structures similar to the Huicheng Basin. It can be inferred that the shallow part is a unified basin and that a large prospecting space exists between the two ore concentration areas. Many NW-trending linear magnetic anomaly zones occur in the Fengtai ore concentration area. Their locations are highly consistent with those of fault structures, and they were offset by NE-trending structures due to late transformation. The second vertical derivative of gravity reveals that many intermediate-acid intrusive stocks or veins have developed in the deep part of the Fengtai ore concentration area. Structural boundaries can be effectively identified based on the first vertical derivative, X-directional derivative, and wavelet transform of aeromagnetic data. Furthermore, ore bodies are mostly distributed in the NW direction along the tectonic belt. All these will play an important role in guiding ore prospecting and exploration in the Fengtai ore concentration area.

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An application study of the comprehensive geophysical prospecting method in the exploration of mineral water: A case study of the Langqiao area, Jing County
ZHANG Zhi, XU Hong-Miao, QIAN Jia-Zhong, XIE Jie, CHEN Hao-Long, ZHU Zi-Xang
Geophysical and Geochemical Exploration    2023, 47 (3): 690-699.   DOI: 10.11720/wtyht.2023.1443
Abstract199)   HTML15)    PDF (7344KB)(329)      

The area around Maduqiao Village, Langqiao Town, Jing County has great potential for the development of high-quality mineral water. However, due to the geological conditions and the inhomogeneity of water-bearing media, the investigation of the distribution range of the mineral water in the area and the quantitative evaluation of the water quantity and quality have always been challenges to the development and utilization of mineral water in the area. With the Langqiao area of Jing County as the target area, an application study on the comprehensive geophysical prospecting method that comprehensive ground geophysical prospecting with hydrogeological logs was conducted, achieving important progress. The major results are as follows: (1) The fault structures in granodiorites were precisely located through comprehensive ground geophysical prospecting, and the horizon of tectonic fissure water was precisely identified based on hydrogeological logs; (2) The metasilicate natural mineral water for drinking with a single well water yield of 50~80 m3/d was identified; (3) The water-rich fault structures in the study area have a medium to shallow burial depths of about 75~140 m and primarily have a NW strike. These results reveal the spatial distribution characteristics of the mineral water-bearing structures in the study area and are of great significance to the subsequent investigation of the mineral water range. Moreover, the systematic research philosophy and technical methods used for the Langqiao area of Jing County in this study can guide the mineral water exploration in similar areas.

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Gravity survey and audio magnetotellurics-based insights into the deep structures and geothermal resource potential of the Rucheng Basin
ZHAO Bao-Feng, WANG Qi-Nian, GUO Xin, GUAN Da-Wei, CHEN Tong-Gang, FANG Wen
Geophysical and Geochemical Exploration    2023, 47 (5): 1147-1156.   DOI: 10.11720/wtyht.2023.1449
Abstract193)   HTML8)    PDF (8018KB)(308)      

Geothermal resources are significant clean energy and tourism mineral resources. The Rucheng Basin, a carbonate basin in the southeastern mountainous area of Hunan Province, possesses favorable conditions for the formation of convective geothermal energy. However, the basin is enclosed on three sides by the giant Zhuguangshan rock mass, and its basement is subjected to the intrusion and destruction by the rock mass, resulting in severely deformed formations, crisscrossing faults, and significantly different eastern and western structures. The understanding of the basin's water- and heat-conducting pathways and deep reservoir structures remains elusive, thus restricting the investigation of the basin's geothermal potential. Hence, this study probed the basin's deep structures through gravity survey and audio magnetotellurics (AMT), obtaining the following insights: (1) The Rucheng Basin has developed into a bidirectional ramp structure due to east-west differentiation. The synclinorium in the east experienced compression and clockwise rotation due to the emplacement of the Yanshanian rock mass, rocks were fragmented in the core zone, and strike-slip fracture zones were found at the boundary. The faults have vertical cutting depths exceeding 4 km, widths ranging from 300~600 m, and dip angles between 80°~90°. (2) The basin's basement anticlinal axis hosts several NWW-directed concealed rock masses, with diameters from 3~4 km and buried depths from 0.5~1.5 km. Hot springs reside in the fracture zones crossing the boundaries of the concealed rock masses. (3) The basin boasts favorable conditions for the formation of convective geothermal energy. Folds, fault zones, and concealed rock masses match each other to form a unified spatial combination of heat-controlling elements, manifesting heat accumulation characterized by east-west recharge and intermediate discharge. With more thriving deep geothermal reservoirs in the east, the basin has high potential for geothermal resources.

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Advancements in research on geochemical exploration methods and technologies for mineral resources in overburden areas
SUN Yue, ZHANG Zhen-Yu, FENG Bin, YANG Shao-Ping, WANG Zhi-Feng
Geophysical and Geochemical Exploration    2023, 47 (6): 1387-1399.   DOI: 10.11720/wtyht.2023.0109
Abstract188)   HTML13)    PDF (2899KB)(243)      

Following China's planning for ore prospecting in overburden areas, China's geochemical exploration researchers have conducted extensive research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas in the past decade. They achieved significant advances mainly in two aspects: (1) the research on the migration mechanism, occurrence state, and anomaly formation mechanism of elements in overburden areas; (2) advances in methods and technologies, including geoelectrochemistry, active state of elements, geogas, separation of micro-fine-sized soil particles, soil thermomagnetic composition, and integrated gas survey, as well as numerous experimental demonstrations. These advances represent continuous progress in the research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas, providing new geochemical methods and technologies for ore prospecting breakthroughs in overburden areas.

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An experimental investigation of the CO2 and SO2 gas geochemical survey method for mineral exploration in forested areas
WAN Wei, WANG Ming-Qi, CHENG Zhi-Zhong, FAN Hui-Hu, ZUO Li-Bo, LI Jun-Hui
Geophysical and Geochemical Exploration    2023, 47 (5): 1137-1146.   DOI: 10.11720/wtyht.2023.1615
Abstract184)   HTML7)    PDF (4627KB)(153)      

This study aims to explore the feasibility of the carbon dioxide (CO2) and sulfur dioxide (SO2) gas geochemical survey method for mineral exploration in forested areas. Based on the newly designed gas rapid analysis instrument, this study conducted an experimental investigation of the method in the forested Jiapigou gold concentration area, Jilin Province. The results show that significant CO2 and SO2 anomalies were observed above the concealed ore bodies and structures. In the forested area, the CO2 and SO2 gas geochemical survey method reflected the fault structures and effectively indicated the deep concealed gold deposit. This method holds critical significance for the breakthrough of prospecting technology in China's covered areas.

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Spatial distribution patterns of concealed plutons in the western Zhen’an area based on gravity anomalies
ZHANG Jin-Ai, YANG Yuan, ZHANG Lin
Geophysical and Geochemical Exploration    2023, 47 (3): 618-627.   DOI: 10.11720/wtyht.2023.1465
Abstract178)   HTML11)    PDF (8220KB)(299)      

The western Zhen'an area enjoys superior ore-forming conditions of tungsten-molybdenum polymetallic deposits. A batch of large and medium-scale tungsten-molybdenum deposits such as Dongyang, Qipangou, Guilingou, Yueheping, and Hetaoping, have been discovered in this area, and they are related to intrusions. To explore tungsten-molybdenum ore bodies, it is necessary to carry out studies on intrusions related to mineralization, especially concealed intrusions. Based on high-precision gravity anomalies, this study extracted the gravity anomaly data of concealed plutons using the minimum curvature potential field separation method. Moreover, it investigated the plane positions of the concealed plutons in the western Zhen'an area by combining the geophysical characteristics of the exposed plutons, identifying five concealed plutons, namely Lanbandeng, Shapingcun, Yuehetai, Dongchuanjie, and Huangjinmei, through investigation. Moreover, this study conducted the 3D gravity anomaly inversion for typical concealed plutons, determining the spatial distribution characteristics of the concealed plutons. The Yuehetai and eastern Lanbandeng concealed plutons have been verified through boreholes, with high-grade wolframite being discovered. The method proposed in this study can provide technical support for the study of concealed plutons in the Zhen'an area and other areas, as well as important data for the study of the tectonic-magmatic-metallogenic evolution of the southern Qinling metallogenic belt.

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Application of the opposing-coils transient electromagnetic method in urban geological surveys
HE Sheng, WANG Wan-Ping, DONG Gao-Feng, NAN Xiu-Jia, WEI Feng-Feng, BAI Yong-Yong
Geophysical and Geochemical Exploration    2023, 47 (5): 1379-1386.   DOI: 10.11720/wtyht.2023.1554
Abstract174)   HTML4)    PDF (5856KB)(298)      

With the rapid development of urban infrastructure,the demand for urban geological work is increasing,and urban geological surveys become particularly important.Urban geophysical exploration has different exploration purposes and working environments from conventional geophysical exploration.Accordingly,compared with conventional geophysical exploration methods,the geophysical exploration methods for urban geological surveys face the challenges of many interference factors,limited construction sites and time,and high requirements for exploration accuracy.The opposing-coils transient electromagnetic(OCTEM) method enjoys a strong anti-interference ability,convenient and efficient construction,and high resolution.Therefore,this study employed the OCTEM method to investigate the test profile in the urban geological survey and evaluation of Haidong City.This test profile was subjected to numerous interference sources since it crossed 11 highways and railways and passed through factories,schools,logistics parks,villages,living quarters,and rivers.Consequently,the OCTEM results agree well with the results of single-point resistivity sounding and drilling results.Therefore,the OCTEM method proposed in this study is effective for urban geological surveys.

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Predicting the geothermal resources of the Tangyu geothermal field in Meixian County, Shaanxi Province, based on soil radon measurement and the controlled source audio magnetotelluric method
XUE Dong-Xu, LIU Cheng, GUO Fa, WANG Jun, XU Duo-Xun, YANG Sheng-Fei, ZHANG Pei
Geophysical and Geochemical Exploration    2023, 47 (5): 1169-1178.   DOI: 10.11720/wtyht.2023.0010
Abstract171)   HTML10)    PDF (4345KB)(284)      

Despite abundant geothermal reserves of the Tangyu geothermal field in Meixian County, Shaanxi Province, long-term exploitation has decreased the water temperatures and yields of its existing geothermal wells year by year. Hence, there is an urgent need to explore new potential geothermal resources in the geothermal field. Since the known geothermal wells in the geothermal field are significantly controlled by faults, investigating the deep fault propagation holds critical significance for exploring the geothermal field’s potential geothermal resources. Due to the method limitations and the topographic influence, identifying thermal control faults through conventional geological route investigation or large-scale engineering is not applicable to the geothermal field. Therefore, a new technical method combining the penetrating soil radon measurement and the controlled source audio magnetotelluric (CSAMT) method was employed in this study to find concealed faults and delineate potential geothermal areas. Based on the measured surface soil radon concentration anomaly data and the subsurface electrical structure model derived from the CSAMT data inversion, this study inferred six new concealed faults on the basis of corroborating the known faults, predicted two potential geothermal areas, and built a conceptual model for the Tangyu geothermal field. As revealed by the results, the soil radon concentrations at concealed faults are much higher than the regional background value, and the concealed faults are located in the low-resistivity fracture zones as indicated by the apparent resistivity results based on CSAMT data inversion. Besides, the two potential geothermal areas spread from 450~750 m and 850~1 150 m on the profile, respectively, at depths of approximately 250~300 m. This study concludes that the geothermal field resides in a low-resistivity region with soil radon anomalies three times the regional background value. The results of this study provide a reference for the subsequent sustainable production and utilization of potential geothermal resources in the region.

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Geochemical characteristics and prospecting potential of Jianchi Town, Shaanxi Province, China based on 1∶25,000 stream sediment survey
ZHANG Jia-Sheng, ZHOU Wei, LI Wei-Liang, QI Xiao-Peng, YANG Jie, WANG Lu
Geophysical and Geochemical Exploration    2023, 47 (3): 659-669.   DOI: 10.11720/wtyht.2023.1122
Abstract167)   HTML217)    PDF (6805KB)(270)      

Jianchi Town of Shaanxi Province is located in the Nanjiang foreland-superimposed basin on the northern margin of the Yangtze Plate. To determine the prospecting potential, this study conducted a 1∶25,000 stream sediment survey in the study area. Based on the testing results of 12 elements and compounds closely related to mineralization, namely K2O, Na2O, CaO, MgO, Cl, S, B, Rb, Cs, Li, Br, and I, this study analyzed the geochemical characteristics of these elements and compounds and determined that Li is the major metallogenic element, Li-B-Rb-Cs-K2O is the indicator element association for the prospecting of lithium deposits, and the spatial morphology of Li agrees with that of various geological bodies. By combining the metallogenic geological setting, this study delineated 18 integrated anomalies. Through the follow-up examination of the anomalies, multiple lithium ore bodies (mineralized points) were discovered, indicating that the study area has favorable metallogenic geological and geochemical conditions and great prospecting potential.

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Regional geochemical characteristics and metallogenic prospect area prediction of strategic mineral antimony in the Eerguna block, Heilongjiang Province, China
WAN Tai-Ping, ZHANG Li, LIU Han-Liang
Geophysical and Geochemical Exploration    2023, 47 (5): 1179-1188.   DOI: 10.11720/wtyht.2023.1439
Abstract164)   HTML3)    PDF (4012KB)(153)      

The Eerguna block with metallogenic geological conditions is an important metallogenic area in Heilongjiang Province. Globally, China boasts the richest resource of antimony. However, the high mining intensity in recent years imposes huge challenges to this resource advantage of China. In this context, it is necessary to ascertain the geochemical characteristics of antimony in the Eerguna block. Based on the data of the 1∶250 000 stream sediment survey in the Eerguna block, this study explored the geochemical parameters of antimony in different tectonic units and the regional geochemical anomalies of this block. The results show that the study area has median and average concentrations of antimony of 0.33×10-6 and 0.55×10-6, respectively. The Mohe foreland basin is rich in antimony, with median and average concentrations of antimony higher than those of the study area. Furthermore, zones with high and extremely high antimony concentrations in the study area are distributed primarily in the Mohe foreland basin. Based on the 85% cumulative percentage, this study determined 66 geochemical anomalies of antimony, among which two reach the scale of geochemical provinces. Furthermore, this study identified significant geochemical anomalies of antimony in the discovered gold, antimony, and plumbum deposits or ore occurrences (mineralization points). Based on the spatial distributions of geochemical anomalies and metallogenic geological conditions of antimony, arsenic, and gold, this study delineated three metallogenic prospect areas of antimony: the Beijicun-Sanlianshan metallogenic prospect area, the Wangsushan-Daling metallogenic prospect area, and the Baikalushan-Huzhong metallogenic prospect area. In addition, the geochemical anomalies and metallogenic prospect areas for antimony, arsenic, and gold provide important areas for searching for sulfide deposits such as gold, antimony, and plumbum ones in the study area.

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Application of integrated geophysical exploration technology in the geothermal exploration of northern Jinan
ZHANG Yi, LIU Peng-Lei, WANG Yu-Min, ZHANG Peng-Peng, ZHANG Chao, ZHANG Ning
Geophysical and Geochemical Exploration    2024, 48 (1): 58-66.   DOI: 10.11720/wtyht.2024.1141
Abstract159)   HTML8)    PDF (8896KB)(244)      

Ji'nan possesses highly abundant geothermal resources, which are hosted by Ordovician-Cambrian karst-fissured geothermal reservoirs and Neogene-Paleogene clastic pore-fissure geothermal reservoirs. The geothermal exploration in this study focuses on the Ordovician-Cambrian karst fissured geothermal reservoirs in Daqiao Town in northern Ji'nan. Through geophysical profile measurements, this study aims to identify the distributions of strata and fault structures and the burial depths of geothermal reservoirs, infer the attitudes and spatial morphologies of fault structures associated with heat control and conduction, delineate the target area for geothermal well construction, and conduct drilling verification in the favorable underground water-rich position. Building on the collected data, this study interpreted and inferred the fault structures in the study area and comparatively analyzed the water-bearing properties by employing direct-current sounding, controlled source audio magnetotellurics, and magnetotelluric survey. A geothermal exploration and production combined well was constructed in a favorable position of the geothermal target area, manifesting a completion depth of 1 532.06 m, a static-water burial depth of 13.03 m, a wellhead water temperature of 50.1 ℃, a water yield of 132.998 m3/h, and a dropdown depth of 18.27 m.

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Geological and geochemical characteristics and prospecting potential of rare element and rare earth element deposits in Saima alkaline complex
NAN Zhe, WANG Lin-Shi, HOU Xu, ZHAI Zheng-Bo, WANG Yang, LIU Yang
Geophysical and Geochemical Exploration    2023, 47 (3): 670-680.   DOI: 10.11720/wtyht.2023.2185
Abstract157)   HTML10)    PDF (5011KB)(234)      

The Saima alkaline complex is a unique and complex geologic body. It is well known for its diverse rock types and mineral types and high contents of uranium, thorium, and rare and rare earth elements. This study analyzed and summarized the geological exploration results of the Saima alkaline complex area in recent years, discovering that the rocks in the second intrusive stage of the Saima alkaline complex show the wide mineralization of rare and rare earth elements, with a moderate- to low- mineralization temperature. There are mainly two types of deposits in Saima alkaline complex area, namely the residual magmatic metasomatism type and the skarn type. Furthermore, the prospecting potential of the whole alkaline complex was analyzed by combining the 1∶200,000 stream sediment survey data and the 1∶10,000 primary halo survey data. Three predicted metallogenic zones of rare earth and radioactive elements were delineated in the Saima alkaline complex and its surrounding area, namely Saima-Gujia, Aiyang, and Shuangshanzi. This study is of great significance for the prospecting of rare and rare earth polymetals in the Saima alkaline complex area.

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Simulated detection experiments of underground water supply pipeline leakage based on ground penetrating radar
WANG Yu-Cheng, WANG Hong-Hua, SU Peng-Jin, GONG Jun-Bo, XI Yu-He
Geophysical and Geochemical Exploration    2023, 47 (3): 794-803.   DOI: 10.11720/wtyht.2023.1199
Abstract153)   HTML10)    PDF (7153KB)(277)      

As an important part of urban infrastructure, underground water supply pipelines frequently leak or break due to disrepair,corrosion,and poor construction quality.It is of great significance to identify the leakage locations and affected areas of underground water supply pipelines using a non-destructive testing method for the purpose of early warning and follow-up treatment.This study conducted simulated detection experiments and analysis of underground water supply pipeline leakage using the ground penetrating radar (GPR) method.Firstly,this study established the leakage model of water supply pipelines in sandy soil using the SEEP/W module in the GeoStudio software and calculated the volumetric water content of different leakage locations and leakage times.Then,it established the relative dielectric constant and conductivity model for water supply pipeline leakage using the Topp equation and the empirical equations of electrical conductivity and water content.On this basis,this study conducted the GPR simulated detection of the water supply pipeline leakage model with different leakage locations and different leakage times using the finite difference time domain (FDTD) method and analyzed the simulation results.Finally,this study conducted the GPR-based physical simulated detection tests of water supply pipeline leakage and compared the test results with the numerical simulation results.The study results are as follows.Compared with the hyperbolic diffracted wave of the water supply pipelines without leakage,that of the water supply pipelines with leakage at different locations are stated as follows.For the leakage on the upper side,a longer leakage area and a larger leakage area were associated with an earlier present hyperbolic diffracted wave with weaker energy,while the horizontal position of the hyperbolic diffracted wave's vertex remained unchanged.For the leakage on the lower side,two hyperbolic diffracted waves appeared,which moved up and down individually.Moreover,a longer leakage time corresponded to two weaker and more separated hyperbolic diffracted waves.The horizontal positions of the hyperbolic diffracted waves' vertexes remained unchanged.For the leakage on the left (right) side,a longer leakage time was associated with a weaker hyperbolic diffracted wave,whose vertex deviated farther toward the upper left (right).The simulated detection results of this study can provide a reliable basis for early warning and follow-up treatment of water supply pipeline leakage.

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Comparison and summary of different azimuthal anisotropy-based inversion techniques
LIANG Zhi-Qiang, LI Hong
Geophysical and Geochemical Exploration    2024, 48 (2): 443-450.   DOI: 10.11720/wtyht.2024.1251
Abstract153)   HTML0)    PDF (3440KB)(71)      

The progress in seismic acquisition techniques characterized by wide azimuths,wide frequency bands,and high densities has greatly promoted the application of the prestack P-wave fracture inversion technique based on the azimuthal anisotropy theory.Azimuthal anisotropy-based inversion can yield the azimuths and intensities of fractures.However,different inversion techniques yield different parameters for fracture intensity characterization,resulting in inconsistent inversion results.Consequently,the azimuthal anisotropy-based inversion results of fractures are non-unique,leading to confusion about accurate results.Based on the Thomsen anisotropy theory,as well as the interrelationships between fracture models(the Hudson coin model and the Schoenberg linear sliding model),this study established the connections of anisotropic parameters between different fracture inversion techniques(VVAZ,Ruger's approximation,and Fourier series),presenting the real meanings and mathematical expressions of results from different azimuthal anisotropy-based fracture inversion techniques.Additionally,this study summarized the relationships of parameters between different inversion techniques and fracture models,further deepening the research on azimuthal anisotropy-based fracture inversion.This study lays solid theoretical and technical foundations for large-scale fracture detection based on the seismic data obtained using the seismic acquisition techniques featuring wide azimuths,wide frequency bands, and high densities.

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Application of the geochemical block method to the assessment of copper resources in Ethiopia
XIANG Wen-Shuai, BAI Yang, JIANG Jun-Sheng, LEI Yi-Jun, HUNDIE Melka, SISAY Degu, ZHANG Yuan-Pei, WU Ying, ZHENG Xiong-Wei
Geophysical and Geochemical Exploration    2023, 47 (4): 845-855.   DOI: 10.11720/wtyht.2023.1198
Abstract149)   HTML5)    PDF (6040KB)(154)      

Low-density geochemical mapping is characterized by high order streams to be sampled and a large coverage area and can be used to effectively trace geochemical blocks with high metal contents. Based on the 1:1,000,000 low-density geochemical mapping data of Ethiopia and the processing of the testing data of Cu in the original stream sediments, this study calculated the anomaly threshold of Cu at 37×10-6 through iterative deletion. Then, this study delineated three geochemical blocks and two regional anomalies with 37×10-6, 42×10-6, 47×10-6, 52×10-6, 59×10-6, and 66×10-6 as grading intervals. It calculated the mineralization coefficient of Cu ore bodies in the study area at 0.055% by referencing the known reserves of Cu deposits in geochemical blocks with a high level of copper exploration in the same metallogenic belt. Moreover, this study estimated the Cu resources in the study area at 2,600,000 t based on a rock mass thickness of 1,000 m. By combining the analysis of metallogenic geological conditions, this study determined that the zones where geochemical blocks nos. 2, 3, and 4 are located can be considered key metallogenic prospect areas for further detailed exploration.

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Artificial neural network-based transient electromagnetic imaging
YOU Xi-Ran, ZHANG Ji-Feng, SHI Yu
Geophysical and Geochemical Exploration    2023, 47 (5): 1206-1214.   DOI: 10.11720/wtyht.2023.1547
Abstract147)   HTML3)    PDF (4517KB)(193)      

The transient electromagnetic method (TEM) commonly uses the all-time apparent resistivity parameter for interpretation, which involves complex formulas and time-consuming iterative processes. Based on the characteristics of TEM data, this study employed the artificial neural network (ANN) for TEM pseudo-resistivity imaging. First, this study designed a multi-hidden-layer BP neural network and calculated a response amplitude through TEM analysis. The response amplitude, as the mapping parameter of pseudo resistivity, was used for network training. Then new data outside the training set were used to test the trained network. A homogeneous half-space and one-dimensional layered model was built to verify the correctness and adaptability of the neural network. The imaging of the three-dimensional geoelectric model was performed. As revealed by the results, the pseudo resistivity calculated based on the neural network can reflect the target anomalies of the geoelectric model, with highly accurate network imaging results. Finally, the measured data were processed using the neural network algorithm, further indicating that the neural network-based imaging can serve as a basis for data interpretation. This study verified the feasibility of the ANN in TEM imaging, thus providing a new approach for TEM imaging.

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Research on structural characteristics and mineral prediction of the Luoning area based on the characteristics of gravitational and magnetic fields
ZHANG Lei, WANG Wan-Yin, WANG Xiao-Bo, LI Wen, ZHANG Xue-Li, SONG Hao, YANG Min, AN Li-ming
Geophysical and Geochemical Exploration    2023, 47 (3): 608-617.   DOI: 10.11720/wtyht.2023.1462
Abstract146)   HTML178)    PDF (10842KB)(359)      

The Luoning area is located at the junction of the Xiaoshan Uplift and the Luoning Basin and falls into the Quaternary shallow overburden area. Large-scale silver-lead-zinc deposits such as Laoliwan and Zhonghe have been discovered in this area, and their formation is closely related to the acidic plutons controlled by fault structures. This study investigated the distribution of fault structures and acidic plutons based on the processing of 1:50000 gravity and magnetic data using the minimum curvature potential field separation technique, the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique, the correlation analysis method, and the three-dimensional physical property inversion. The study results are as follows: (1) The Luoning area is affected by the NW-, NE-, and EW-trending structures; (2) Centering on the Laoliwan area, multiple sets of faults present a ring-shaped distribution with a radius of 6.5 km; (3) Multiple concealed plutons were discovered, and the boundaries of Laoliwan and Zhonghe plutons were re-determined; (4) The distribution of granites is controlled by ring-shaped structures and have a burial depth of about 3 km; (4) The ring-shaped structures are well correlated with magnetic anomaly gradient zones, where ores were found in many boreholes. Therefore, it is of great significance to carry out prospecting studies in these zones.

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Prospecting for concealed skarn iron deposits using the high-precision gravity-magnetic survey method
DONG Jian, LI Xiao-Peng, FU Chao, DANG Zhi-Cai, ZHAO Xiao-Bo, ZENG Qing-Bin, HU Xue-Ping, WANG Jin-Hui
Geophysical and Geochemical Exploration    2024, 48 (1): 31-39.   DOI: 10.11720/wtyht.2024.1047
Abstract145)   HTML7)    PDF (7885KB)(223)      

The Laiwu area in central Shandong Province, situated in the eastern North China Craton, is a significant production area of skarn iron-rich ores. Its ore deposits occur primarily in the contact zone between the mining rock mass and the Middle Ordovician carbonate formation. Based on the latest areal gravity and magnetic survey results, this study thoroughly investigated the characteristics of gravity and magnetic anomalies along the Shijiaquan-Liujiamiao area in the western periphery of the mine rock mass. Then, this study delineated the deep prospecting target combining the characteristics of gravity and magnetic fields of the known iron deposits in the Laiwu area. Large-scale gravity and magnetic profiles were arranged in the favorable mineralization area. With the known boreholes as constraints, the gravity and magnetic anomalies were qualitatively and quantitatively interpreted using the 2.5D gravity-magnetic joint inversion technique. The interpretation results provide a basis for the location and depth of the borehole to be placed, which revealed a 15.8 m-thick iron-rich ore deposit, suggesting remarkable prospecting effects. This study holds critical indicative significance for further exploration of skarn iron ore deposits in this area.

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A study of tectonic framework of the Qinnan sag in Bohai Basin and its adjacent areas based on satellite gravity anomalies
YANG Rong-Xiang, WANG Wan-Yin, CAI Meng-Ke, WANG Ding-Ding, LUO Xin-Gang
Geophysical and Geochemical Exploration    2023, 47 (3): 584-596.   DOI: 10.11720/wtyht.2023.1463
Abstract144)   HTML174)    PDF (15824KB)(248)      

The Bohai Basin has the most offshore oil and gas fields discovered in China. As a potential hydrocarbon-rich sag in the Bohai Basin, the Qinnan Sag is of high value in exploration. Therefore, the study of the tectonic framework of the sag and its adjacent areas is of great significance and application value. Based on satellite gravity anomalies, this study determined the Bouguer gravity anomalies by correcting the influences of land topography and seawater and obtained the planar distribution and apparent depths of faults, the thickness of Cenozoic strata, and the boundaries of tectonic units using methods such as the normalized vertical derivative of the total horizontal derivative (NVDR-THDR), the Euler deconvolution, the minimum curvature potential field separation, and the fast for the gravity field based in a dual interface model. Based on the geological and geophysical data, this study analyzed the distribution and geophysical characteristics of major faults and tectonic units in the study area. The results of this study are as follows: The faults in the Qinnan Sag and its adjacent areas mainly have NE, NEE, and NW strikes and an apparent depth of primarily 1~10 km, which is up to 15~25 km at some positions of the sag-controlling faults and the intersections of the faults; The Cenozoic strata have a thickness of 0~11 km. The Cenozoic tectonic units are distributed in alternating NE and NEE directions, and their boundaries are mostly controlled by faults; Through further investigation, this study classified the sub-sag on the west side of the Qinnan sag as the Laoting sag and adjusted the boundaries of other tectonic units. The results of this study on the distribution of the faults and tectonic units can provide geophysical data for hydrocarbon exploration in the Qinnan Sag.

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Application of wide field electromagnetic method in the fracturing monitoring of well Anye-2
HU Zhi-Fang, LUO Wei-Feng, WANG Sheng-Jian, KANG Hai-Xia, ZHOU Hui, ZHANG Yun-Xiao, ZHAN Shao-Quan
Geophysical and Geochemical Exploration    2023, 47 (3): 718-725.   DOI: 10.11720/wtyht.2023.1089
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To evaluate the fracturing performance of two horizontal wells of well Anye-2,this study explored the layout of the fracturing monitoring network and data acquisition and processing using the fracturing monitoring technique combined with the wide field electromagnetic method.Through the qualitative and semi-quantitative difference analysis of the pre-,in-,and post-fracturing monitoring data,this study preliminarily determined the propagation direction of induced fractures and semi-quantitatively calculated the parameters such as fracture length and height.For each fracturing interval,the parameters such as fracture height and length were quantitatively determined through fine-scale inversion with depth as constraints and difference calculation.The fracturing monitoring results show that the fractures at two horizontal wells had lengths of 100~125 m and heights of 20~25 m.The fracturing production was guided by evaluating the fracturing performance of each fracturing interval.The fracturing results of the previous interval were used to guide the fracturing of the subsequent interval.Finally,the fracturing performance of all fracturing intervals was evaluated.The application results show that the wide field electromagnetic method can effectively predict the spread direction and range(e.g.,fracture length) of fracturing fluids,achieving encouraging performance.

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Application of the wide-field electromagnetic method in hydrogeological exploration under the extremely-thick low-resistivity layer: A case study of a coal mine in the Huainan area, Anhui Province
Qi Zhao-Hua
Geophysical and Geochemical Exploration    2023, 47 (3): 700-706.   DOI: 10.11720/wtyht.2023.1178
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To investigate the water yield properties of the aquifers in the hanging and foot walls of coal seams under the extremely-thick low-resistivity layer, this study conducted the hydrogeological exploration using the wide-field electromagnetic method (WFEM) targeting a coal mine in the Huainan area, Anhui Province. The geological results obtained through multiple means, such as test analysis and data acquisition and interpretation, agree well with the downhole conditions. As indicated by the successful WFEM application in the hydrogeological exploration of the coal mine, the WFEM features strong penetrability, large investigation depth, and high accuracy. Therefore, the WFEM can be used as a new geophysical exploration method for the hydrological survey of large-depth coal fields.

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Influence of DEM grid spacing and correction radius on terrain correction in gravity exploration
ZHANG Fei-Fei, WANG Wan-Yin, LI Qian, WANG Lin, MA Jing
Geophysical and Geochemical Exploration    2023, 47 (3): 597-607.   DOI: 10.11720/wtyht.2023.1472
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To remove the effect of terrain mass on observed gravity values, it is necessary to conduct terrain correction in gravity exploration. Terrains have the greatest impact on gravity values because they are the closest to observation points. However, the complex topographic relief makes it difficult to precisely determine the variation of topographic relief. Therefore, terrain correction is the most critical factor in the improvement of the precision of gravity exploration. The grid size of terrain data and the terrain correction radius are the key factors affecting the calculation precision of terrain correction. This study collected the DEM data with resolutions of 5 m, 10 m, 25 m, 50 m, and 100 m for plains, hills, and mountains. Based on these data, this study calculated conventional and generalized terrain correction values under different grid spacings and correction ranges and analyzed the influence of different grid spacings and correction radii on terrain correction in gravity exploration. The results are as follows: the gravity effect of the terrain mass above the geoid on the observation points was mainly concentrated in the range of 0~5 000 m and accounted for about 90% of the influence value of the total terrain mass. Attention should be paid to the correction of the middle and far areas during the terrain correction of hills and mountains, and it is necessary to appropriately increase the correction range of the middle areas; Different types of terrains had different requirements for grid spacings, and greater variations in topographic relief imposed higher requirements for the resolution DEM data. Based on the results of the comparative analysis, this study proposed some suggestions on the selection of DEM grid spacings and correction radii for different types of terrains. This study provides an important reference for the theoretical study and specification refinement of gravity terrain correction and has a great prospect for applications.

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Regularized joint inversion of magnetotelluric and gravity data based on inequality and Gramian constraints
CHEN Xiao, ZENG Zhi-Wen, DENG Ju-Zhi, ZHANG Zhi-Yong, CHEN Hui, YU Hui, WANG Yan-Guo
Geophysical and Geochemical Exploration    2023, 47 (3): 575-583.   DOI: 10.11720/wtyht.2023.1474
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Regularized joint inversion based on Gramian constraints is a hot research topic in the field of geophysical joint inversion. Given the difficulty in selecting weighted factors of the regularization and constraint items, it is necessary to introduce inequality constraints into the regularized joint inversion. To investigate the regularized joint inversion of magnetotelluric (MT) and gravity data based on Gramian constraints, this study compared the application effects of the penalty function method and the transform function method in the joint inversion and processed the measured data of a survey line in Xiangshan, Jiangxi Province. According to the results from model experiments, both methods can effectively constrain petrophysical parameters, and the penalty function method has higher flexibility but requires the artificial setting of the weighted factors. Moreover, the processing of the measured data shows that the joint inversion based on inequality and Gramian constraints is highly practical and can improve the precision of geophysical interpretation.

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Environmental quality characteristics of soil and health risk assessment of crops of farmlands in the southern suburb of Baotou
Bao Feng-Qin, Cheng Hang-Xin, Yong Sheng, Zhou Li-Jun, Yang Yu-Liang
Geophysical and Geochemical Exploration    2023, 47 (3): 816-825.   DOI: 10.11720/wtyht.2023.1159
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To investigate and assess the characteristics of cadmium, lead, and zinc in the soil and crops in the farmland around the old industrial area in the south of Baotou City, this study analyzed and tested the heavy metal content in soil, crop root soil, and seeds, assess the pollution according to relevant standards, and conducted the risk assessment and source analysis of heavy metals using the pollution index, the bioconcentration factor, and human health risk index. The results are as follows:Regarding the soil environmental quality, the soils in the study area are dominated by clean soils, with the polluted soils distributed primarily on both sides of the old sewage canals.The sites of over-limit root soils are also primarily distributed around the old sewage canals.Among the heavy metal morphologies, carbonate-bound, Fe-Mn-bound, and residue heavy metals account for relatively high proportions, while exchangeable heavy metals (water-soluble and ion-exchange) account for relatively low proportions. Most of the seed samples exhibited normal and low enrichment of heavy metals. Compared with other crops, sunflower seeds showed super adsorptivity of cadmium, lead, and zinc, posing significant non-carcinogenic and carcinogenic health risks to children and adults.

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First-arrival wave travel time-based tomography inversion with surface wave information as constraints
ZHANG Li-Zhen, SUN Cheng-Yu, WANG Zhi-Nong, LI Shi-Zhong, JIAO Jun-Feng, YAN Ting-Rong
Geophysical and Geochemical Exploration    2023, 47 (5): 1198-1205.   DOI: 10.11720/wtyht.2023.1536
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The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.

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Migration and enrichment patterns of vanadium in the soil and plant system of farmland
ZHAO Yu-Yan, JIANG Tao, YANG Bing-Han, ZHANG Ze-Yu, LI Zheng-He, LI Bing, TANG Xiao-Dan
Geophysical and Geochemical Exploration    2023, 47 (3): 835-844.   DOI: 10.11720/wtyht.2023.1206
Abstract139)   HTML10)    PDF (1991KB)(378)      

Vanadium (V) is an essential trace element required by organisms for maintaining their normal life activities. It is also a harmful element listed as a priority environmental pollutant by the United Nations Environment Programme (UNEP). The study of the migration and enrichment patterns of V in the soil and plant system is of great practical significance for further understanding the ecological geochemical behavior of V and ensuring the safety of agricultural products and human health. This study systematically sampled the soil and plants in some ordinary farmland in Linyi City, Shandong Province and analyzed and tested the contents of V and its associated elements in the soil and plant samples. Moreover, this study conducted the source analysis and pollution assessment of V and investigated the migration and transformation patterns of V in the soil-plant system using statistical methods such as descriptive statistics, correlation analysis, and cluster analysis, as well as the single factor pollution index method, the potential ecological risk index method, and the biological enrichment coefficient method. The results are as follows: V is relatively concentrated in the study area, and its content increases with an increase in the Fe and Ti contents and decreases with an increase in the SiO2, Na2O, Sr, and CaO contents; The V in the study area mainly originates from the weathering of parent rocks, and the parts with a high V content is related to magnetite; As shown by the results of the single factor index method and the potential ecological risk index method, V is relatively clean in the soils of the study area, but attention should be paid to the pollution of the associated Cd; V is enriched primarily in the roots of plants, and plants' absorption capacity of V is generally negatively correlated with the contents of Cu, Pb, Zn, Ni, Co, Cd, and especially Cr in soils and is positively correlated with the As content in soils. This study enriches the ecological geochemical theory of V and provides a scientific basis for regional agricultural production, environmental quality assessment, and ecological pollution control.

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Chronology and geochemical characteristics of trachytes in the Tiaojishan Formation, Xuanhua Basin, northwestern Hebei Province, and their geological implications
YANG Ji-Yuan, HU Xin-Zhuo, ZHOU Jing, QI Peng-Chao, LI Ze-Yang, MENG Jia-Bao, XU Fan, ZHANG Hui-Bin, QI Hui-Yun
Geophysical and Geochemical Exploration    2024, 48 (1): 1-14.   DOI: 10.11720/wtyht.2024.2503
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The Tiaojishan Formation in northwestern Hebei Province is home to volcanic-sedimentary strata. Due to the lack of fossil organisms, insufficient isotopic dating data, and outdated dating methods, the formation epochs of these strata have been controversial. To accurately determine their formation epochs and examine their regional geotectonic setting, this study conducted a detailed field investigation of the lithologic assemblage of the Tiaojishan Formation in the Xuanhua Basin. Petrological, petrogeochemical, and high-precision isotopic dating studies were conducted on the trachytic volcanic rocks in the upper segment of the formation, obtaining the LA-ICP-MS-based zircon U-Pb isotopic ages, which were 161.1±1.2 Ma and 162.5±1.3Ma. As indicated by the petrological and petrogeochemical characteristics, these trachytic volcanic rocks belong to the shoshonite series, exhibiting enriched light rare earth elements, relatively enriched elements including Rb, K, Th, Ce, Zr, and Hf, and relatively depleted Ba, Nb, Sr, P, and Ti. According to the comparison of principal parameters and graphical discrimination, the magma originated primarily from the melting of continental crustal materials and formed in the tectonic setting of compressional continental margin volcanic arcs. The comprehensive research reveals that the Tiaojishan Formation formed primarily during the Middle Jurassic and continued to the Late Jurassic, and the trachytic volcanic rocks in its upper segment formed in the intraplate compressional tectonic setting. The results of this study provide new data for the division and correlation of Mesozoic volcanic-sedimentary strata and the analysis of their formation environment.

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Migration of heavy metals in the soil-tea plant system and health risks of drinking tea: A case study of Qiongzhong County, Hainan Province
GONG Qiu-Li, YANG Jian-Zhou, WANG Zhen-Liang, YAN Hui
Geophysical and Geochemical Exploration    2023, 47 (3): 826-834.   DOI: 10.11720/wtyht.2023.1321
Abstract129)   HTML13)    PDF (2497KB)(198)      

This study sampled the soil and the corresponding roots, stems, and leaves (including large leaves, new leaves, and sprouts) of tea plants from three ecological tea plantations in Qiongzhong County, Hainan Province. Based on these samples, this study investigated the migration of heavy metals in the soil-tea plant system and analyzed the migration patterns of heavy metals and the health risks caused by heavy metals in tea. As indicated by the results, the Pb, Cr, Cd, As, and Hg concentrations in the soil are slightly higher than the background values of corresponding soil elements in Hainan, showing non-significant accumulation. The enrichment of heavy metals varies significantly in different organs of tea plants. Specifically, Cr, Zn, Pb, Hg, and Cd are enriched in roots, while Cu and Ni are enriched in leaves; Pb, Cd, and Hg have higher concentrations in large leaves than in new leaves and sprouts, indicating that these elements are enriched with the growth of leaves; Cu, Ni, and Zn have higher concentrations in sprouts than in leaves, showing that these elements are enriched in the growing parts of leaves. Bio-concentration factors (BCF) indicate that soil physicochemical composition, heavy metal species, and leaf age have effects on the absorption of heavy metals by tea leaves. The results of the risk assessment show that the target hazard quotients (HQ) and hazard indices (HI) of all samples are less than 1, indicating acceptable health risks caused by heavy metals in tea. This study can provide a scientific basis for the prevention and control of heavy metals in tea plantations and has a positive guiding significance for managing tea plantations and ensuring the health of tea consumers.

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Grain-scale experimental study of samples using the large-scale micro-channel system survey technique for the cold, semi-arid grassland landscape: A case study of the rare Li-Be ores in the Qiemoge Mountain
BAO Shan-Dong, XIE Xiang-Lei, WANG Ya-Dong, XU Yun-Fu, ZHANG Xin-Yuan, ZENG Biao
Geophysical and Geochemical Exploration    2023, 47 (3): 648-658.   DOI: 10.11720/wtyht.2023.2700
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The Qiemoge Mountain area in Tianjun County, Qinghai Province has a cold, semi-arid grassland landscape. A pegmatite belt with a width of 300~500 m and an intermittent extended length of 7 km has developed on the surface of this area. The rare Li-Be ores have been discovered during the current exploration in this area. To provide a reliable geochemical basis for the prospecting of rare metals and rare earth elements (REE) in areas with similar landscapes, this study conducted the grain-scale experiment and validity investigation in this study area using the large-scale micro-channel system geochemical survey technique. Based on the 1∶25,000 geochemical survey, grain sizes of -4~+ 20 meshes, -4~+ 40 meshes, -10~+ 40 meshes, and -10~+ 60 meshes were adopted in sampling for the experimental study in the zones bearing pegmatite veins. The contents of Cu, W, Sn, Be, Li, Nb, Rb, Zr, La, and Y were analyzed. The results show that relevant elements exhibited significant enrichment and dispersion characteristics and the geochemical distribution of these elements agreed well with the geological and mineral characteristics when grain sizes of -4~+ 40 meshes and -10~+ 40 meshes were adopted for the sampling of Be, Li, Nb, Rb, and Zr, grain sizes of -10~+ 40 meshes were adopted for the sampling of rare earth elements such as La and Y, and grain sizes of -10~+ 60 meshes were adopted for the sampling of nonferrous metal elements such as Cu, W, and Sn. The results of this study prove that the large-scale micro-channel system survey technique can obtain significant results in the geochemical prospecting of rare metals and REEs in areas with similar landscapes.

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Machine learning-based calculation and characteristic analysis of terrestrial heat flow in the Songliao Basin
GONG Ming-Xu, BAI Li-Ge, ZENG Zhao-Fa, WU Feng-Shou
Geophysical and Geochemical Exploration    2023, 47 (3): 766-774.   DOI: 10.11720/wtyht.2023.1241
Abstract128)   HTML13)    PDF (6079KB)(254)      

Terrestrial heat flow has a high reference value for the evaluation of geothermal resources since it can directly indicate the Earth's internal heat on the surface.However,no high-quality and high-resolution terrestrial heat flow measurements have been conducted in the Songliao Basin due to costly and difficult conventional heat flow measurements based on the drilling technology.Machine learning,as a technology for data analysis,can identify patterns in data and utilize these patterns to automatically calculate unknown data.This study calculated the regional terrestrial heat flow using the machine learning method.Based on the measured data of global terrestrial heat flow and the geological structure data,both the Kriging regression algorithm and the machine learning algorithm were used to calculate the terrestrial heat flow in a known heat flow distribution area,as well as the root mean square error and the correlation coefficient.The machine learning algorithm yielded results with a smaller error and a higher correlation.Then,the terrestrial heat flow in the Songliao Basin was calculated using the machine learning method.As revealed by the calculation results,the terrestrial heat flow is the highest (more than 80 mWm-2) in the Songliao basin and gradually decreases outward in a circular pattern centered on the area between Daqing and Songyuan.The results are highly consistent with the measured results of the regional geothermal gradient,providing a reference for further analysis of the distribution patterns of geothermal resources in the Songliao Basin.Finally,the sensitivity of geological characteristics was analyzed using the Sobol method to quantify the effects of various parameters.This study verifies that the machine learning method has a high research and application value in the calculation of terrestrial heat flow.

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Feasibility of the transient electromagnetic method in the exploration of double-layer waterlogged goafs with different layer spacings in coal mines
ZHANG Fan, FENG Guo-Rui, QI Ting-Ye, YU Chuan-Tao, ZHANG Xin-Jun, WANG Chao-Yu, DU Sun-Wen, ZHAO De-Kang
Geophysical and Geochemical Exploration    2023, 47 (5): 1215-1225.   DOI: 10.11720/wtyht.2023.1525
Abstract128)   HTML5)    PDF (5416KB)(229)      

It is difficult to explore the overlapping double-layer waterlogged goafs using the transient electromagnetic method. The reason is that upper waterlogged goafs will hinder the propagation of the electromagnetic field, thus prolonging the observation of the lower waterlogged goafs and reducing the signal-to-noise ratio. Besides, the burial depths and layer spacings of double-layer waterlogged goafs affect the signal-to-noise ratio and the observation time of transient electromagnetic signals. By building a double-layer waterlogged goaf model based on the Majiayan coal mine in Shanxi, this study analyzed the electromagnetic field propagation under layer spacings of 25 m, 50 m, 75 m, and 100 m,and calculated the observation time of waterlogged goafs with different layer spacings. Furthermore, it quantitatively characterized the differences between induced voltages in the double-layer waterlogged goafs with different layer spacings using root mean square errors. Additionally, this study proposed the identification criteria for explorable lower waterlogged goafs based on the record errors and noise levels during the observation. The results of physical simulation experiments are as follows: The differences between the induced voltages of double-layered waterlogged goafs with different layer spacings occur mainly in the late stage; the differences between induced voltages gradually decrease as the layer spacing and the burial depth of upper waterlogged goafs increases; the difference between induced voltages is close to the noise level when the layer spacing is greater than 75 m. The actual detection of the double layer waterlogged goaf with a spacing of 75 meters was conducted in Majiayan Coal Mine, and the results showed that the lower waterlogged goaf was not effectively identified.Therefore, It is difficult to effectively explore the lower waterlogged goafs when the layer spacing is greater than 75 m.

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Calculation and analysis of zero drift rates of gravimeters in two-way reciprocal observations based on different specifications
CHANG Xiao-Peng, CHEN Liang, ZHANG Xiang, ZHANG Ling-Xiao, ZHU Zhang-Liu, QIAO Yan-Yi
Geophysical and Geochemical Exploration    2023, 47 (5): 1307-1315.   DOI: 10.11720/wtyht.2023.1526
Abstract122)   HTML0)    PDF (928KB)(124)      

Gravity survey is an important part of geodetic mapping and geophysical exploration. Different gravity specifications adopt different methods to calculate the zero drift rates in two-way reciprocal observations (i,j,j',i'). The repeated measurements of point j are subjected to static drift in the geological survey specification. By contrast, the zero drift rate is calculated through regression analysis in the petroleum specification. Different processing methods for the repeated measurement interval of point j yield significantly different zero drift rates based on the two specifications. Through theoretical formula analysis and comparison of measured data, this study analyzed the influence of g'j- g j and t'j-tj in the repeated measurements of point j on the calculation of the zero drift rate. By comparing with the regression analysis, this study illustrated the importance of static drift in reducing the uncertainties caused by instrument performance and measurement environment. Moreover, this study proposed the applicable conditions of the two specifications.

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Effects of seawater layer on seismic reflection characteristics
DU Yi-Jing, SUN Cheng-Yu, WANG Zhi-Nong, CAI Rui-Qian, WANG Sheng-Rong, JIAO Jun-Feng
Geophysical and Geochemical Exploration    2023, 47 (3): 757-765.   DOI: 10.11720/wtyht.2023.1366
Abstract114)   HTML735)    PDF (4212KB)(227)      

In marine seismic exploration,seismic reflection characteristics play an important role in AVO analysis,inversion for seabed parameters,and structural analysis.When seismic waves propagate in the ocean,their seismic reflection characteristics are affected by the seawater layer and the sediments beneath the seabed.However,previous studies mainly focus on the influence of the sediments beneath the seabed,while there is a lack of studies on the effects of the seawater layer on the seismic reflection characteristics.This study analyzed the changes in the seismic wave field during the seismic wave propagation in the seawater layer.Based on the boundary conditions of fluid-solid and free interfaces,this study derived the P-P amplitude ratio between the incident and reflected waves on an elastic interface and obtained the mathematical expression of the seawater layer effect accordingly.Then,this study analyzed the influencing factors,such as the frequency of incident waves,the depth of the seawater layer,the impedance contrast of the seabed,and the incident angle,on the filtering effect of the seawater layer.The analysis results are as follows:The seawater layer had a periodic frequency selective filtering effect on seismic P-waves;The period of the frequency selective filtering effect was inversely proportional to the frequency of incident waves and the depth of the seawater layer and was directly proportional to the incident angle;A higher incident angle corresponded to severer attenuation of seismic P-waves;The effects of impedance contrast on amplitude was related to the frequency of incident waves and the depth of the seawater layer.Finally,the study verified the effects of the seawater layer on seismic reflection characteristics through numerical simulations.

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New geophysical evidence for karst water-bearing seepage pathways in the Xiaohewei reservoir,Wenshan City
ZHOU Jian-Bing, LUO Rui-Heng, HE Chang-Kun, PAN Xiao-Dong, ZHANG Shao-Min, PENG Cong
Geophysical and Geochemical Exploration    2023, 47 (3): 707-717.   DOI: 10.11720/wtyht.2023.1244
Abstract114)   HTML13)    PDF (7271KB)(349)      

As a karst reservoir with the highest altitude in Wenshan City,the Xiaohewei reservoir has been suffering from severe water seepage since its completion.Despite several seepage control treatments,the seepage of the reservoir is still not effectively controlled.To determine the locations of underground karst seepage pathways of the reservoir and guide the later seepage control project,this study detected the seepage pathways in the project area combining the high-density resistivity method and the audio magnetotelluric method.The 2D inversion trial calculation of geophysical testing data indicates the feasibility of combining the two methods.The methods show highly consistent geophysical anomaly positions and can accurately reflect the geological conditions at different burial depths.Thus,their detection results can be referenced for later design and construction.Based on the inversion of measured data,the surface geological data,and the drilling verification means,it is speculated that the reservoir mainly has two NNE-directed karst water-bearing seepage pathways with an elevation of more than 1 800 m.These two karst seepage pathways (No.1 and No.2) are located near the contact zone between limestones and siliceous rocks,and in the karst fissures inside limestones,respectively.Based on the geophysical exploration results,this study also puts forward some suggestions on the deployment of the curtain grouting project for later seepage control of the Xiaohewei reservoir.

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Common problems and solutions in the use of instrument calibration points in high-precision ground magnetic surveys in the field
GENG Tao
Geophysical and Geochemical Exploration    2023, 47 (4): 1078-1082.   DOI: 10.11720/wtyht.2023.1358
Abstract114)   HTML0)    PDF (1837KB)(166)      

To ensure the high quality of data acquisition in high-precision ground magnetic surveys in the field, it is an important link to ascertain the instrument performance in a period using instrument calibration points. However, some workers fail to properly use instrument calibration points and thus fail to monitor the operation state of instruments on a day through the early and late calibration measurement of the instruments, affecting the acquisition of high-precision magnetic survey data. Based on the analysis of specific examples, this study proposed that the checking of early and late calibration measurement results of instruments should consider both the differences between these results, as well as the differences between these results and the actual magnetic field values of instrument correction points. The purpose is to ensure the high-quality field acquisition of high-precision magnetic survey data.

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A method for strong noise suppression based on DC-UNet
ZHOU Hui, SUN Cheng-Yu, LIU Ying-Chang, CAI Rui-Qian
Geophysical and Geochemical Exploration    2023, 47 (5): 1288-1297.   DOI: 10.11720/wtyht.2023.1386
Abstract114)   HTML0)    PDF (6456KB)(129)      

Seismic data acquired from mature industrial areas frequently contain a large amount of local strong noise with high amplitude due to the continuous operation of production equipment.However,such local strong noise can be hardly suppressed using conventional denoising methods.This study integrated dilated convolution(DC) and U-Net into a DC-UNet network for suppressing local strong noise.For the circular DC blocks at the front end of the DC-Unet network,a circularly expanded DC kernel was used to extract the features of strong noise at different scales,with the receptive field being expanded.Meanwhile,an encoder was used at the back end of the network to extract the features of strong noise and restore the details of strong noise.Subsequently,the DC-UNet network was employed to perform a nonlinear mapping from noisy data to noise.On this basis,strong noise was suppressed by subtracting the learned strong noise from the noisy data.As indicated by the experimental results of synthetic and real data obtained from the training using the PyTorch framework in the GPU environment,the DC-UNet network can effectively suppress the local strong noise and improve the signal-to-noise ratio compared with DnCNN,U-Net,and PCA-UNet networks.

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Characterization of multi-attitude fractures in tight sandstones in the Yuanba area, northeastern Sichuan Basin
HUANG Yan-Qing
Geophysical and Geochemical Exploration    2023, 47 (5): 1189-1197.   DOI: 10.11720/wtyht.2023.1352
Abstract113)   HTML3)    PDF (9055KB)(113)      

This study proposed a fracture prediction method based on unsupervised clustering of fracture sensitivity attributes to accurately characterize the distribution of fractures with different attitudes in tight sandstones of the Upper Triassic Xujiahe formation in the Yuanba area, northeastern Sichuan. First, the sensitivity of fractures was extracted and selected based on the optimized post-stack seismic data. Then, the convolutional neural network, a deep learning algorithm, was used to learn global massive fault and fracture databases of various types, obtaining the intensities, dip angles, and azimuths of fractures. In combination with high-precision-guided curvature attributes, an unsupervised clustering algorithm based on the Bayesian probability model was used to predict the intensities of fractures with different dip angles through dimensionality reduction using principal component analysis (PCA). The prediction results are highly consistent with both the fracture interpretation results from imaging logs and the geological results. The results of this study show that the third member of the Xujiahe Formation has more developed fractures than the second member. Fractures in the third member include both the fault-induced fractures distributed near the faults in the southeast flank of the Jiulongshan anticline and the fold-induced fractures in the areas with large formation flexures. By contrast, only fault-induced fractures near the faults occur in the second member.

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Application of the integrated geophysical exploration technology in the exploration of deep carbonate geothermal reservoirs: A case study of the Xiong'an New Area
ZHANG Zhao, YIN Quan-Zeng, ZHANG Long-Fei, ZHANG Da-Ming, ZHANG Shi-Hui, HUANG Guo-Shu, ZHAO Shi-Feng, YANG Biao, TAI Li-Xun, ZHANG Deng-Liang, WANG Jin-Chao, DUAN Gang
Geophysical and Geochemical Exploration    2023, 47 (4): 926-935.   DOI: 10.11720/wtyht.2023.1354
Abstract110)   HTML1)    PDF (7787KB)(199)      

Xiong'an New Area has great potential for geothermal resources. Carbonate rocks are favorable reservoirs for deep geothermal resources in this area. The integrated geophysical exploration technology is an effective way to ascertain the deep structures and the characteristic stratigraphic structure of carbonate geothermal reservoirs. Aiming at the exploration target of deep carbonate geothermal reservoirs, this study put forward a surface-line-point hierarchical and progressive geophysical exploration model. Using the high-precision gravity and aeromagnetic data, this model first investigated the distribution range of carbonate rocks, the thickness of carbonate strata, the distribution of deep-seated faults, and the fluctuation of bedrocks. Then, it analyzed the low-resistivity anomalies of geothermal reservoir strata using the magnetotelluric method. Finally, this model finely characterized the geothermal reservoir strata using two-dimensional seismic profiles and analyzed the velocity structure and regional structural characteristics of anomaly zones in the geothermal field. Based on the exploration precision and reliability of gravity, aeromagnetic, magnetotelluric, and seismic geophysical methods in the geothermal resource exploration of different stages, as well as other factors such as construction cost and efficiency, this study analyzed the economic applicability of geophysical methods in the exploration of deep karst geothermal reservoirs and suggested that the carbonate geothermal resources should be explored using the geophysical exploration technology combination of gravity, magnetic, and magnetotelluric methods.

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Quantitative prediction technology for the hydrocarbon production capacity of fractures and vugs in fault-controlled carbonate reservoirs in the Shunbei area
LIU Jun, HUANG Chao, YANG Lin, ZHANG Yong-Sheng, ZHA Ming
Geophysical and Geochemical Exploration    2023, 47 (3): 747-756.   DOI: 10.11720/wtyht.2023.2579
Abstract110)   HTML14)    PDF (6046KB)(192)      

The strike-slip fault system and the fractures and vugs in fault-controlled reservoirs have become new Ordovician exploration targets in the Shunbei area.This study explored a multi-attribute quantitative prediction technique for the single-well production of fault-controlled reservoirs,aiming to provide a scientific basis and technical support for well deployment and well trajectory optimization in the fault zones of the Shunbei area.Faults serve as pathways for hydrocarbon migration in fault-controlled reservoirs.Their connectivity to provenance areas can be characterized by their longitudinal extension and the width of the fault zone,and their convergence can be characterized by their lateral extension and the planar intersection structure between major and secondary faults.Both characteristics of faults were used to indicate the fault characteristics in the oil source conditions for oil accumulation.The space for hydrocarbon accumulation in fault-controlled reservoirs is dominated by dissolution fractures and vugs,such as caves.The fracture-vug characteristics,which represent the space for hydrocarbon accumulation and its connectivity,were characterized by the scale of fault-controlled reservoirs,the volume of the fractures and vugs,and the density of fractures in faults.The single-well production of fault-controlled reservoirs is related to both the fault characteristics and the fracture-vug characteristics.Therefore,the quantification of fault characteristics and the fracture-vug characteristics is the basis for the quantitative prediction of single-well production.The fault characteristic values were determined through the fine-scale interpretation of faults based on seismic data and their multiple attributes.Moreover,the range of fault-controlled reservoirs was delineated based on structure tensors;the distribution and volume of caves,fractures,and vugs were characterized using the amplitude of anomalous bodies;and the density of fractures in faults can be characterized using the maximum likelihood probability.Then,the three attributes were fused to determine the fracture-vug characteristic values.Finally,the quantified fault characteristic values and fractured-vug characteristic values were fused into the characteristic value of fault-controlled reservoirs.Through the statistical analysis of the characteristic value and annual liquid production of drilled wells,the statistical relationship between the annual fluid production and the characteristic value of fault-controlled reservoirs was determined,thus achieving the quantitative prediction of the single-well production of fault-controlled reservoirs.

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A technique for automatically extracting regions of interest from ground penetrating radar data of roads based on the row-column variance method
XU Li, FENG Wen-Ya, JIANG Yan-Nan, WANG Jiao, ZHU Si-Xin, QIN Zi-Xin, LI Qin-Lin, ZHANG Shi-Tian
Geophysical and Geochemical Exploration    2023, 47 (3): 804-809.   DOI: 10.11720/wtyht.2023.1161
Abstract109)   HTML12)    PDF (4363KB)(187)      

With the rapid development of the economy and society,traffic loads have increased sharply,gradually causing a series of pavement diseases.Ground penetrating radar (GPR),which is a non-destructive testing technique,can present the echo information of subsurface targets on the GPR profile.The echo information of diseases,such as voids,cavities underneath the pavement,and loosely infilled voids,constitutes a region of interest(ROI) on the GPR profile.The traditional manual ROI extraction method features high technical requirements and high laborious intensity due to massive data.Therefore,this study proposed an automatic ROI extraction method that combines the threshold segmentation data and the row-column variance.The experimental results show that the method proposed in this study can effectively extract the location information of multi-type and multi-target ROIs.This method has great potential for improving road detection efficiency based on GPR.

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Research on time-frequency electromagnetic method detection of Wumishan Formation thermal reservoir in deep Xiong’an New Area
Cheng Zheng-Pu, Lian Sheng, Wei Qiang, Hu Wen-Guang, Lei Ming, Li Shu
Geophysical and Geochemical Exploration    2023, 47 (6): 1400-1409.   DOI: 10.11720/wtyht.2023.1611
Abstract109)   HTML5)    PDF (2331KB)(191)      

Xiong’an New Area is one of the areas with the best conditions for the development and utilization of geothermal resources in sedimentary basins of eastern China. Wumishan Formation of Jixian System is the main thermal reservoir, with buried depth of the top boundary varies greatly, which istypical carbonate type thermal reservoir. In order to find out the stratigraphic structure and concealed faults within 6 km of the starting area of Xiong’an New Area, focus on finding out the spatial distribution and structural characteristics of the main deep thermal reservoirs, and predict the favorable geothermal areas, the time-frequency electromagnetic method is applied to the geothermal resources exploration of Xiong’an New Area. Through high-standard data acquisition, refined data processing and resistivity-constrained inversion, the pseudo-seismic imaging technology and borehole data are used to calibrate the resistivity horizon, which effectively improves the reliability of interpretation results. In this work, 8concealed faults were identified, mainly NNE strike normal faults, which controlled the salient-depression pattern and stratigraphic distribution of the study area. The study area is divided into Rongcheng salient, middle sub-depression, Niutuozhen salient and Baxian depression from west to east. The thermal reservoirs of Wumishan Formation is mainly distributed in Niutuozhen salient, Rongcheng salient and middle sub-depression, with buried depth of top interface is about 600~2600m. Vsing the inversion results of the time-frequency electromagnetic method, the three-dimensional geological model of the study area is constructed, and the Niutuozhen salient area is considered to be the optimal geothermal favorable area from the aspects of heat source, channel, reservoir, caprock and fluid, especially near the footwall of F4.

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Application of frequency division AVO in the gas-bearing analysis of reservoir in the Xu-2 Member of the Anyue gas field
SONG Chen, JIN Ji-Neng, PAN Ren-Fang, ZHU Bo-Yuan, YU Zhi-Hua, TANG Xiao-Ling
Geophysical and Geochemical Exploration    2023, 47 (3): 681-689.   DOI: 10.11720/wtyht.2023.1273
Abstract108)   HTML13)    PDF (6171KB)(225)      

The second member of the Xujiahe Formation (the Xu-2 Member) in the Anyue area of the Sichuan Basin enjoys abundant tight gas reserves.However,this member has complex geological characteristics,and conventional amplitude versus offset (AVO) analysis has relatively low precision in predicting the gas-bearing property of the reservoir in this member.Therefore,it is necessary to develop a more fine-scale seismic prediction method. Based on the analysis of single-well petrophysical characteristics and forward models,the AVO attributes of the dominant frequency range were selected through the frequency division AVO inversion based on wavelet transform.Then,these AVO attributes were fused to form the gas-bearing indicator,using which the distribution of favorable gas-enrichment zones in the Xu-2 Member of the Anyue area was predicted.The results are as follows:The gas zones in the Xu-2 Member primarily present class IV AVO anomalies;For the gas and water zones,their AVO responses in the dominant frequency range (35~45 Hz) differed significantly from those in the full frequency band,and their gas-bearing response characteristics were more pronounced in the dominant frequency range;The AVO attributes sensitive to the gas-bearing property included the difference in the S-wave velocity,the difference in Poisson's ratio, and the fluid factor.The gas-bearing indicator was obtained through the fusion of these AVO attributes,and the negative anomalies of the gas-bearing indicator were indicative of favorable gas-bearing zones;The seismic-log correlation shows that the AVO attributes in the dominant frequency range yielded positive gas-bearing prediction effects.The method proposed in this study is expected to provide technical support for unconventional oil and gas exploration.

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Determination of fluorine content in chemical fertilizer samples using the ultrasonic extraction-ion selective electrode method
LIU Bin, XU Jin-Li, DU Xue-Miao, TANG Rui-Ling, ZHANG Peng-Peng, BAI Jin-Feng, YU Lin-Song, WAN Fang
Geophysical and Geochemical Exploration    2023, 47 (3): 775-781.   DOI: 10.11720/wtyht.2023.1150
Abstract107)   HTML11)    PDF (624KB)(161)      

As shown by the geochemical survey of national land quality, the land with excess fluorine in China covers an area of about 315 000 km2. As an element closely related to human health, fluorine has received wide attention and has been studied. Especially in recent years, the high-fluorine fertilizers used in agricultural activities have become a potential source of fluorine in soils. Moreover, the circulation and migration patterns of fluorine in soils, animals, and plants are yet to be further investigated. To prepare for a new round of national soil survey and modern health-related geological survey, it is necessary to develop a method to accurately determine the fluorine content in chemical fertilizers. Through experiments, this study compared four methods for sample decomposition, namely the extraction methods based on HCl boiling, NaOH molten water, and the Na2O2 molten water and the HCl ultrasonic extraction method at room temperature. The results show that the optimal method for sample pretreatment is to extract and decompose samples using ultrasound and HCl at room temperature, adjust the acidity using NaOH-H2SO4, and take sodium citrate as the ion buffering agent. Through investigation, the ultrasonic extraction time and temperature were determined to be 20 min and 20 ℃, respectively. The main quality parameters of the method were determined under the optimal sample pretreatment conditions, including the limit of detection of 1.63×10-6, the precision of 0.98%, and the recovery rate of 91%~108%. The results of this study show that the pretreatment of this method is simple, fast, and easy to operate. With the mode of establishing standard curves in sections, the quality parameters determined can fully meet the requirements for the analysis of chemical fertilizers.

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Correction of the influence of mountains on grounded-source transient electromagnetic responses
ZHOU Zhong-Hang, ZHANG Ying-Ying
Geophysical and Geochemical Exploration    2023, 47 (5): 1236-1249.   DOI: 10.11720/wtyht.2023.1489
Abstract105)   HTML1)    PDF (5591KB)(185)      

The grounded-source transient electromagnetic (TEM) method, which enjoys the advantages of high topographic adaptability and large exploration depths, is suitable for deep resource exploration in mountainous areas. However, the TEM responses can be distorted due to topographic effects, causing great difficulties in data interpretation. This study investigated the influence patterns and correction method of topographic effects based on the three-dimensional unstructured time-domain finite element method. First, this study conducted the fine-scale description of mountains using unstructured tetrahedral grids, calculated the response of various topographic models, and analyzed the influence patterns of topographic effects. Then, it proposed a correction method for topographic effects based on the principle of the linear superposition principle of electromagnetic fields, established a geoelectric model of mountains according to the actual elevation data, and calculated the model responses through three-dimensional forward modeling. Subsequently, this study determined the topographic responses by subtracting the flat Earth model responses from the mountain model responses and then obtained the corrected TEM responses by removing the topographic responses from the total responses. The results are as follows: (1) The influence of mountains on the TEM responses is concentrated in the early stage and weakens gradually with time; (2) The topographic effects are concentrated near mountains, and their intensity depends on the distance of survey points from mountain peaks; (3) The influencing range and response amplitude of mountains are proportional to the mountain scale. In other words, a larger mountain scale corresponds to a larger influencing range and higher response amplitude; (4) Mountains with relatively high resistivity show more intense topographic influence. As shown by multiple models with simple and regular topographic anomalies, the corrected TEM responses, which match well with the responses from direct forward modeling, can effectively eliminate topographic effects to a certain extent. The research on the influence and correction method of topographic effects can be used as a reference for the processing and interpretation of TEM data of areas with complex terrain.

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Resistivity characteristics of natural gas hydrate-bearing sediments and the application progress of the Archie equation
WANG Ying-Mei, JIAO Wen-Ze, LIU Sheng-Hao, WANG Qian, SONG Han-Yu
Geophysical and Geochemical Exploration    2023, 47 (3): 782-793.   DOI: 10.11720/wtyht.2023.1147
Abstract104)   HTML12)    PDF (2996KB)(186)      

Studying the occurrence of natural gas hydrates (NGHs) is of profound significance for NGH exploration. The evaluation of the NGH saturation mainly relies on the Archie equation using the electrical parameters of rocks. The key to accurately calculating the NGH saturation is to select corresponding values of rock electrical parameters for different geological environments, especially the porosity index (m) and the saturation index (n). However, it is still a challenge to select the optimal m and n values for NGH evaluation in resistivity logging. To ascertain the relevant resistivity regularity of NGHs and the determination method of rock electrical parameter values in the Archie equation, this study systematically reviewed relevant references and summarized the resistivity influencing factors of NGHs. Moreover, this study analyzed the influencing factors for the accurate evaluation of the NGH saturation based on the Archie equation. Accordingly, this study generalized the resistivity characteristics of NGH-bearing sediments and proposed the application research direction of the Archie equation.

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