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Gravity field characteristics and boundaries of geotectonic units on the northeastern margin of the Linyi uplift, Shandong Province WANG Run-Sheng, WU Bin, ZHANG Hai-Rui, YU Jia-Bin, DONG Yan-Long, GUO Guo-Qiang, KANG Yi-Ming Geophysical and Geochemical Exploration    2023, 47 (2): 279-289.   DOI: 10.11720/wtyht.2023.1144 Abstract （894）   HTML （25）    PDF （9602KB）（588）       Knowledge map    The northeastern margin of the Linyi uplift is located at the eastern end of the Luxi Block and immediately adjacent to the Yishu fault in the east. The main structural framework of the study area is controlled by the NE-trending Tangwu-Gegou fault and the NW-trending Mengshan fault. Covered by the Cenozoic sediments, the boundaries of main tectonic units in the study area are almost all concealed, and it is necessary to further investigate the change in the strike of the eastern end of the Mengshan fault as well as the distribution of the angular unconformity along the northern boundary of the Linyi uplift. Using the latest 1:50,000 high-precision gravity data, this study mainly investigated the positions and intersection relationships of the boundaries of tectonic units based on the qualitative analysis of gravity field, the interpretation of multiple gravity potential field conversion, and the division scheme of geotectonic units in Shandong Province. The analysis results are as follows. The Mengshan fault at the junction of the Mengshan uplift and the Pingyi sag transitions from the NW trending to nearly-EW trending in the east of Bancheng Town, significantly cuts the NE-trending Tangwu-Gegou fault, and shows a NW-trending turn to the east again. The angular unconformity at the junction of the Linyi uplift and the Pingyi sag neither ends in the Mengshan fault in the north nor turns southward but extends to the Tangwu-Gegou fault in the east. This unconformity also controls the southern boundary of the Pingyi sag, making the NW-trending banded gravity anomalies of the sag turn eastward. Consequently, the boot-shaped low-value gravity anomalies were formed in the study area. Based on the high-precision gravity boundary identification, this study determined the fault system and tectonic division of the northeastern margin of the Linyi uplift, providing high-precision gravity data for the basic geological study in the study area and laying a good foundation for further mineral geological survey. Table and Figures | Reference | Related Articles | Metrics

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Seismic characteristics of the paleo-underground river system in Ordovician carbonate paleo-buried hills in the western Lungu area DAN Guang-Jian, ZHOU Cheng-Gang, LIU Yun-Hong, LI Xiang-Wen, ZHANG Liang-Liang, ZHANG Ming, WANG Chun-Yang Geophysical and Geochemical Exploration    2023, 47 (2): 290-299.   DOI: 10.11720/wtyht.2023.1052 Abstract （333）   HTML （16）    PDF （8684KB）（290）       Knowledge map    Many karst fracture-vug reservoirs have been found in the Ordovician carbonate paleo-buried hills in the Lungu area,Tarim Basin.Hydrocarbons are mainly enriched in these fracture-vug reservoirs,which are mainly related to the paleo-underground river system in carbonate paleo-buried hills.The paleo-underground river system is well developed,especially in the western Lungu area.The fracture-vug reservoirs related to the paleo-underground river system have strong longitudinal and lateral heterogeneity,and ascertaining the seismic and geological characteristics of the paleo-underground river system in this area is the key to the efficient development of fracture-vug reservoirs in this area.Based on the characteristics of modern karst underground rivers and the log and drilling data of this area,this study established a geological model of underground rivers for forward modeling.The study results are as follows.The underground river system developing under the tight limestone setting showed continuously linear strong reflections on the seismic profile.The seismic amplitude decreased as the height and width of underground rivers decreased,and higher seismic amplitude corresponded to larger underground river caves and lower filling velocity.The amplitude can accurately characterize the horizontal range of the underground river on the seismic profile.Meanwhile,the frequency and phase can describe the outline of the underground river on the seismic profile,but the outline described was larger than that of the real underground river.The main channels of the underground river system were prone to be filled with mud.By contrast,the branch channels had a low filling probability and thus serve as the main areas for both the occurrence of underground river reservoirs and the hydrocarbon accumulation. Table and Figures | Reference | Related Articles | Metrics

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Identification of footwalls and roofs of coal seams in underground coal mines using borehole radar LIU Si-Xin, SHI Wei, SONG Zi-Hao, CHEN Chun-Lin, DAI Zheng Geophysical and Geochemical Exploration    2023, 47 (2): 365-371.   DOI: 10.11720/wtyht.2023.1392 Abstract （173）   HTML （16）    PDF （3287KB）（189）       Knowledge map    In coal mining, the accurate determination of the locations of the footwalls and roofs of coal seams and the identification of the geological structures that threaten the safety of excavation are important measures to ensure safe coal mining. This study proposed a technique for detecting the footwalls and roofs of coal seams, which consisted of a mining face-based borehole radar detection method for underground coal mines and a data processing process. Then, this study applied this technique to the Xinyuan coal mine. Specifically, radar profiles were denoised and enhanced through the correction of zero-moment point, DC elimination, band-pass filtering, direct wave removal, and gain processing of measured borehole radar data of boreholes along a mining face of the Xinyuan coal mine. Then, the locations of the roofs and footwalls of coal seams in the underground coal mines were identified and presented through a series of processing and interpretation, including velocity pickup, reflective surface extraction, and diffraction stack migration, as well as time-depth conversion, flipping, splicing, and the correction of borehole trajectories. The technique proposed in this study serves as an effective means for the safe operation of coal mines and thus is of value for promotion. Table and Figures | Reference | Related Articles | Metrics

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Prediction of the soil element accumulation trends based on 1∶250 000 and 1∶50 000 geochemical surveys and assessments of land quality:A case study of Xixiangtang District, Nanning City, Guangxi zhuang Autonomous Region WANG Lei, ZHUO Xiao-Xiong, WU Tian-Sheng, LING Sheng-Hua, ZHONG Xiao-Yu, ZHAO Xiao-Meng Geophysical and Geochemical Exploration    2023, 47 (1): 1-13.   DOI: 10.11720/wtyht.2023.2613 Abstract （394）   HTML （44）    PDF （3192KB）（309）       Knowledge map    The heavy metal element contents in soil affect the quality of soil environment. Their prediction using different models based on survey data is an important means to study the changing trends of soil element contents and soil environmental quality. Based on the data from 1∶250 000 multi-purpose regional geochemical surveys and 1∶50 000 land quality geochemical assessments, this study predicted the contents of five heavy metal elements in the soil of the study area in 2027 using the single-period incremental model and the input-output flux model individually. The results are as follows. The two models yielded different prediction results but consistent trends that the contents of five heavy metal elements increased to different degrees. Moreover, the single-period incremental model yielded larger increments than the input-output flux model. Among the various input channels of the flux model, Cd and Pb entered the soil mainly through dry and wet atmospheric subsidence, As and Cr entered the soil mainly through fertilization, and Hg entered the soil mainly through irrigation water. Based on the survey and prediction data of soil monitoring sites, the soil environmental quality grade was classified for these sites. The proportion of the sites for priority protection showed a downward trend, indicating that the soil environmental quality decreased year by year. Table and Figures | Reference | Related Articles | Metrics

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Iterative inversion method for ultradeep fault-controlled fracture-vug reservoirs:A case study of the Fuman oilfield,Tarim Basin ZHANG Ming, LI Xiang-Wen, JIN Meng, ZHENG Wei, ZHANG Lei, MA Wen-Gao Geophysical and Geochemical Exploration    2023, 47 (1): 22-30.   DOI: 10.11720/wtyht.2023.1049 Abstract （250）   HTML （21）    PDF （6873KB）（246）       Knowledge map    The ultradeep Ordovician limestone fracture-vug reservoirs in the Fuman oilfield on the south bank of the Tahe River in the Tarim Basin is the core target area for the production capacity construction of the oilfield.These reservoirs in the study area contain massive dissolution vugs formed by the formation fracturing due to the strike-slip faulting and thus are highly heterogeneous.The low-frequency models based on conventional wave impedance inversion are built using data on horizons,faults,and logs,and thus they cannot characterize the fault-controlled heterogeneity of the reservoirs.For this reason,this study proposed an iterative inversion method constrained by fault fractured zone facies to predict reservoirs.The technical process of this method is as follows.First,the original seismic data were interpreted to obtain the attribute volumes that can reflect the characteristics of the fault fractured zones of the reservoirs.Then,the attribute volumes were proportionally fused with the initial low-frequency model and the spatial profile data of high-quality reservoirs obtained from the conventional inversion based on wave impedance.As a result,a new heterogeneous low-frequency model was formed.Using this model,multiple rounds of iterative inversions were conducted.The inversion results can truly describe the characteristics of the fault fractured zones in the heterogeneous reservoirs.The prediction results of 10 wells had coincidence rates of up to 92.86%.As indicated by the application,the method proposed in this study can improve the reservoir prediction performance and the prediction precision of fault-controlled reservoirs,thus effectively supporting the work in the study area. Table and Figures | Reference | Related Articles | Metrics

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Research progress in the geological characteristics and material sources of fluorite deposits in the Heyu-Checun area, western Henan Province ZHANG Kai-Tao, BAI De-Sheng, Li Jun-Sheng, LIU Ji-Feng, XU Dong, SU Yang-Yan, FAN Kang Geophysical and Geochemical Exploration    2022, 46 (4): 787-797.   DOI: 10.11720/wtyht.2022.1438 Abstract （715）   HTML （72）    PDF （4836KB）（693）       Knowledge map    Based on the data on the geology, minerals, exploration, and geochemistry of more than 30 fluorite deposits in the Heyu-Checun area, western Henan Province, this study summarized the types, spatial distribution, and geochemical characteristics of fluorite deposits in the area and explored the genesis and material sources of the deposits. The fluorite deposits in this area have simple types and are distributed in Yanshanian granites and along the fault zone of the external contact zone of the granites. The formation ages of the Heyu and Taishanmiao plutons are 124.7~148.2 Ma and 115~123.1 Ma, respectively. The mineralized age of fluorites is 120~126.8 Ma, indicating that the mineralization occurred in the late stage of the intrusion of the Heyu pluton and the early stage of the intrusion of the Taishanmiao pluton. The ore-forming fluids belong to the NaCl-H2O system with a medium-low temperature, a low salinity, and a low density, indicating that the deposits in the area are medium-low-temperature supergene hydrothermal fluorite deposits. The chondrite-normalized REE patterns of fluorites in the area can be divided into slightly leftward, flat, and rightward types dominated by the rightward type. Moreover, the rightward chondrite-normalized REE patterns of fluorites are similar to those of the Yanshanian granites, both showing strongly negative Eu anomalies and weakly negative Ce anomalies. This finding indicates that the Yanshanian granites provide materials for the formation of fluorites. The metallogenic element F may mainly originate from the Heyu and Taishanmiao plutons, while the metallogenic element Ca partly comes from granites as surrounding rocks. Table and Figures | Reference | Related Articles | Metrics

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Joint application of active and passive surface wave in 3D imaging of loess covered area SHAO Guang-Zhou, LI Yuan-Lin, YUE Liang Geophysical and Geochemical Exploration    2022, 46 (4): 897-903.   DOI: 10.11720/wtyht.2022.1546 Abstract （569）   HTML （64）    PDF （4096KB）（749）       Knowledge map    Due to the strong attenuation effect of loess cover on seismic and electromagnetic waves, the successful application of seismic reflection wave method and electromagnetic wave method in loess covered area is limited.In view of the characteristics of large thickness and fine stratification of loess cover, the active source and passive source surface wave methods are combined in this paper, so that the advantages of the two surface wave methods are complementary and the geological stratification of loess covered area can be accurately detected.The study area is located in the suburb of Fengxiang County,Weihe Basin.It is a typical loess covered area, and the thickness of loess cover is 80~120 m.By processing the measured data of active and passive surface waves in the study area, the positions of the main strata on the 2D shear wave velocity profile are basically consistent with the actual borehole test results, and the 3D stratum structure in the study area is also obtained.The results of joint imaging show that it is feasible and effective to use passive and active surface wave joint exploration for stratification of loess covered area, which provides technical support and beneficial idea for geological mapping of loess covered area. Table and Figures | Reference | Related Articles | Metrics

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Epigenetic anomaly in soil or regolith and deep-penetrating geochemistry ZHAO Yang, WANG Ming-qi, Zhang He Geophysical and Geochemical Exploration    2021, 45 (2): 257-265.   DOI: 10.11720/wtyht.2021.1573 Abstract （1215）   HTML （475）    PDF （637KB）（746）       Knowledge map    Syngeneic and epigenetic components in soil or regolith were discussed from definition. Epigenetic anomalies were classified as lateral and top anomalies,and top epigenetic anomalies are the base for deep penetration technology design. The principle of deep penetrating geochemical exploration technology is to extract the epigenetic components related to deep mineralization without destroying or less destroying the soil matrix (syngeneic components). The authors use a case study to illustrate what the epigenetic anomalies are and why conventional geochemical exploration (total) cannot be used for mineral exploration in overburden areas. From the perspective of extracting epigenetic anomalies in soil, the history, updates and problems of various deep penetration technologies are analyzed. Table and Figures | Reference | Related Articles | Metrics

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The application of frequency division ant tracking based on synchronous extrusion improvement of short time Fourier transform in crack detection HUANG Wei, ZHOU Jie, GAO Li-Jun, WANG Sheng-Li, YAN Hai-Tao Geophysical and Geochemical Exploration    2021, 45 (2): 432-439.   DOI: 10.11720/wtyht.2021.1022 Abstract （733）   HTML （123）    PDF （4303KB）（544）       Knowledge map    Since the application of the time-frequency analysis method in the field of geophysics,it has been favored by geophysicists and is widely used to detect faults and cracks.Therefore,seeking for time-frequency analysis methods with higher precision has become the goal pursued in the field of seismic signal processing.The improved short-time Fourier transform method has low accuracy of time-frequency analysis due to its own window function limitation.In order to improve the time-frequency resolution to a greater extent,the authors squeezed the time-spectrum values after the improved short-time Fourier transform,and developed synchronous extrusion improved short-time Fourier transform.The synthetic signal analysis results show that synchronous squeeze improved short-time Fourier transform has higher time-frequency convergence,and can more accurately characterize the time-frequency characteristics of the signal.The theory shows that the high-frequency components of seismic data can accurately engrave tiny secondary cracks,and ant tracking technology is an effective means to detect crack and fault information.Therefore,based on the high-resolution time-frequency analysis method and the ant tracking technology,the authors predicted the three-dimensional data volume of the South China Sea by cracks.The results show that the method can describe the micro-cracks and associated folds well,and the recognition accuracy is obviously improved as compared with the algorithm of the traditional ant tracking method,thus proving the effectiveness and practicability of the proposed method. Table and Figures | Reference | Related Articles | Metrics

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Distribution feature of soil selenium in west Sanjiang plain and its influencing factors NIU Xue, HE Jin, PANG Ya-Jie, MING Yuan-Yuan Geophysical and Geochemical Exploration    2021, 45 (1): 223-229.   DOI: 10.11720/wtyht.2021.2596 Abstract （592）   HTML （144）    PDF （2152KB）（549）       Knowledge map    In recent years, precious selenium-rich land has been discovered in Sanjiang plain, Heilongjiang Province; nevertheless, studies of the distribution and the controlling factors of soil selenium content have been rarely reported. Geochemical investigation of land quality in the western part of Sanjiang plain has revealed that the surface soil in this area is mainly sufficient, without selenium poisoning. The selenium-rich soil is mainly distributed in the alluvial lacustrine low plain area between the front of Wanda Mountain and the Naoli River, and secondarily distributed in the lacustrine denudation platform in the north of Luobei County. The selenium-deficient and selenium-potential-deficient areas mainly existalong the Songhua River and the ancient course of Luobei River in Luobei area. Based on the combination of statistical correlation analysis, factor analysis, clustering analysis and the selenium spatial distribution, the authors consider that the selenium content in the surface soil of Sanjiang plain is mainly affected by the adsorption of organic matter and clay minerals in the surface soil. Oxides of iron, manganese and other elements as well as soil pH have a relatively weaker effect on selenium enrichment.The comprehensive evaluation of soil environmental quality shows that Sanjiang plain area is mostly a risk-free area, which is a precious clean land resource. Green selenium-rich agriculture can be developed by relying on selenium-rich land. Table and Figures | Reference | Related Articles | Metrics

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Exploration and analysis of geophysical methods in curtain grouting water control WEI Hai-Min, LI Xing, SUN Bang-Tao, ZHOU Sheng, NIU Jie Geophysical and Geochemical Exploration    2021, 45 (1): 245-251.   DOI: 10.11720/wtyht.2021.1146 Abstract （543）   HTML （143）    PDF （3596KB）（641）       Knowledge map    Taking the Maoping mining area of Yilang in Yunnan Province as an example, the authors used the opposing coils transient electromagnetic method (OCTEM) and the audio-frequency magnetotelluric (AMT) method to detect the development of water-bearing fault zone within 700 m below the axis of curtain grouting project, with the intention to provide guidance for curtain grouting water control project. Through the comprehensive analysis of geophysical exploration, 7 anomalies with water-rich were delineated. The results show that OCTEM method can identify small water-bearing joints or cracks, AMT method is more sensitive to large-depth water-bearing fracture zone, and the combination of the two has obvious effect on the detection of bad water-bearing geological bodies. It can be seen that the application effect of integrated geophysical exploration in curtain grouting water control is good, the deep extension of water-bearing channel is effectively identified, and the target area is provided for curtain grouting water control. Table and Figures | Reference | Related Articles | Metrics

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The prediction of Archean buried hill fracture reservoir in BZ-A structure of the Bohai oilfield LI Yao, ZHANG Xiao-Jie, LIU Gong-Li, GONG Min Geophysical and Geochemical Exploration    2021, 45 (1): 37-45.   DOI: 10.11720/wtyht.2021.2569 Abstract （404）   HTML （128）    PDF （9647KB）（402）       Knowledge map    Drilling has revealed that the Archean buried hill of BZ-A has great potential for natural gas exploration.In the target area,the metamorphic rock fracture reservoir in Archean buried hill has many problems such as great buried depth,strong heterogeneity of the reservoir and rapid lateral changes,which pose challenges to the exploration.Based on the study of the genetic mechanism of fractured reservoirs in buried hill,the authors comprehensively analyzed the features of the weathered fractured zone and the inner fractured zone,and established a targeted technical system for the description of fractured reservoirs in buried hill.For the weathered zone fractured reservoir,the pre-stack fracture reservoir porosity prediction technology based on the double-parameter was innovatively used,and the fracture reservoir porosity was predicted by the 3D elastic parameter analysis,and the distribution of the fractured reservoir in the weathered zone was finely described.For the inner fractured zone,the F-K domain coherence enhancement technique was used to improve the imaging of the buried hill.The method of edge enhanced crack detection based on clustering analysis was used to comprehensively characterize the distribution of reservoir in the inner fracture zone.Through the comprehensive application of targeted geophysical techniques, the exploration evaluation of BZ-A has been strongly promoted,thus providing a strong basis for the further exploration evaluation of the target area. Table and Figures | Reference | Related Articles | Metrics

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Geochemical characteristics and geological significance of uranium-rich granites in Lincang area TIAN Jian-Min, XU Zheng-Qi, YIN Ming-Hui, LI Tao, SUN Kang Geophysical and Geochemical Exploration    2020, 44 (5): 1103-1115.   DOI: 10.11720/wtyht.2020.1554 Abstract （1160）   HTML （131）    PDF （5345KB）（474）       Knowledge map    Petrographic and geochemical study and U-Pb dating of uranium-rich granite bodies in Lincang area were carried out for Shuangjiang 701 and Fengqing 901 uranium mines, with the purpose of exploring the relationship between petrogenesis type, diagenetic tectonic background and uranium mineralization. The results show that Lincang uranium-rich granite body has high Si (up to 90.11%, averaging 71.6%), rich alkali, high potassium and high Ca, thus belonging to high Al and high potassium calcium alkaline series rocks. U-Pb zircon dating yielded 214±12 Ma, and thus Lincang uranium-rich granite body was formed in Late Indochina. Rare earth elements show a slightly rightward "V" shape, with obvious fractionation of light and heavy rare earth elements (w(LREE)/w(HREE) 7.26 on average), obvious negative Eu anomaly (δEu=0.28 ~ 0.49), relative enrichment of Rb, U and Th, and relative loss of Ba, Nb, Sr, Ti and Eu. Comprehensive analysis shows that Lincang uranium-rich granite belongs to S-type granite with obvious differentiation, which must have originated from melting of upper crust material and was formed in a mountain-building and rift environment in late collision, belonging to the simultaneous collision of granite related to the Lancang River collision zone. Its high content of uranium provided part of the uranium source for the uranium mineralization process. Uranium elements were transported to the vicinity of the fault fracture zone and was enriched to form granite-type uranium deposits by leaching. Table and Figures | Reference | Related Articles | Metrics

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Density interface inversion method in spherical coordinates and its application in the South China mainland WANG Xiang, GUO Liang-Hui Geophysical and Geochemical Exploration    2020, 44 (5): 1161-1171.   DOI: 10.11720/wtyht.2020.0067 Abstract （522）   HTML （135）    PDF （4704KB）（389）       Knowledge map    The density interface inversion method has been playing an important role in the oil and gas exploration, regional structure inference studies as well as crustal crystal basement surface and Moho undulations researches. Most of the density interface inversion methods are generally based on the Cartesian coordinate system. When large regional or even global scale data are dealt with, the influence of earth curvature cannot be ignored, and the density interface inversion method based on Tesseroid model of spherical coordinate system needs to be considered. However, due to the limitations of calculation accuracy and efficiency, the existing density interface inversion method based on Tesseroid cannot be well applicable to the surface gravity observation data. In this paper, on the basis of previous studies, a density interface inversion method of spherical coordinate system suitable for surface observation data is proposed. Firstly, the gravity Gauss-Legendre integral formula in the spherical coordinate system is simplified to improve the forward calculation efficiency. Then, an optimized adaptive subdivision algorithm is introduced to enhance the calculation accuracy. According to the previous forward calculation and by using Cordell iterative optimization algorithm, the authors propose a density interface inversion method for the surface observation data in the spherical coordinate system. The proposed inversion method in this paper can be verified through the synthetic data test. The inversion results show that the proposed method can overcome the limitation of calculating precision and efficiency of the surface observation data. In addition, the inversion results based on spherical coordinate system are better than those based on cartesian coordinate system. Finally, tests on real data from South China mainland verify the feasibility of the presented methods. The results show that Moho depth rises gradually from the west to the east, with the western part uplifting dramatically and the eastern part uplifting gently. Between Wuling Mountain and Guizhou-Guangxi border, there is an obvious NNE-Moho step. Table and Figures | Reference | Related Articles | Metrics

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New research progress in theory and application of wide field electromagnetic method HE Ji-Shan Geophysical and Geochemical Exploration    2020, 44 (5): 985-990.   DOI: 10.11720/wtyht.2020.0192 Abstract （818）   HTML （175）    PDF （453KB）（915）       Knowledge map    Mineral resources are the lifeblood of national economic development. Electromagnetic method is one of the most effective methods to search for mineral resources.With the depletion of shallow resources, developing a both large-depth and high-precision electromagnetic method has become big challenge for all countries in the world, which is also the research hotspots. Aiming at the problems of shallow depth and low precision of the original artificial source frequency domain electromagnetic methods,from theory, method, technology to application, the author carried out systematic research and invented WIDE FIELD ELECTROMAGNETIC METHOD. It is a great leap forward for the development of frequency domain electromagnetic method from coarse to fine. As a result, the achievements of "large depth and high precision wide field electromagnetic exploration technology and equipment" have been formed, it won the First Prize of National Technological Invention in 2018.Wide field electromagnetic method provides a new technical means for oil and gas exploration, deep prospecting, coal mine water disaster detection, geological disaster prevention, fracturing monitoring and urban geophysical exploration. It has strongly supported the "deep ground" strategy oriented to the major needs of the country.The papers collected in this column are mainly distributed in the technical research fields of solid mineral, shale gas and geothermal exploration, fracturing monitoring and airborne geophysical application. This paper focuses on these papers and discusses the development of the theory and application of wide field electromagnetic method. Reference | Related Articles | Metrics

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The application of wide field electromagnetic method to shale gas exploration in Wuling Mountain area: A case study of Tongzi area in northern Guizhou LI Di-Quan, WANG Zhen-Xing, HU Yan-Fang, WANG Han, SU Yu-Di Geophysical and Geochemical Exploration    2020, 44 (5): 991-998.   DOI: 10.11720/wtyht.2020.1570 Abstract （520）   HTML （155）    PDF （4513KB）（596）       Knowledge map    After the major breakthrough in oil and gas was obtained from the Well Anye 1, the Ministry of Natural Resources increased the residual shale gas and oil and gas exploration and development of 7,800 square kilometers in the Wuling Mountain. The Wulong Mountain area has complex geological structures, undulating terrain and large areas of carbonate rock, which has led to great challenges to traditional oil and gas exploration methods based on seismic exploration. Wide field electromagnetic method has the characteristics of green, high efficiency and low cost, and hence has become one of the powerful methods for oil and gas exploration and is now being widely used in shale gas exploration in southern China. It is a favorable method for shale gas exploration in southern China. The strata in Tongzi Guizhou are relatively stable, and the organic carbon content in the upper Ordovician Wufeng-Lower Silurian Longmaxi Formation is high. Through surface sample collection and well logging data analysis, the organic shale in this formation shows obvious low resistivity characteristics, which has the physical conditions of electromagnetic exploration. The wide field electromagnetic method was used to carry out shale gas exploration in Tongzi area of northern Guizhou, which overcame the complex influence of topography, carbonate rocks and structure. It is found that the structure pattern of Tongzi area is characterized by "depression and uplift" from northeast to southwest. The spatial distribution characteristics of the Wufeng-Longmaxi Formation in the target layer were detected, and four favorable areas for shale gas exploration were delineated. The prediction of shale gas exploration target area by wide area electromagnetic method is expected to help realize the breakthrough of shale gas exploration and development from point to surface in Wuling Mountain area and promote the development of clean energy industry along the river. Table and Figures | Reference | Related Articles | Metrics

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The application of multiple non-seismic methods to geothermal exploration in Qihe, Shandong Province Hui ZHANG, Shao-Qiang SUI, Luo-Ran QIAN, Xin-Wei WANG Geophysical and Geochemical Exploration    2020, 44 (4): 727-733.   DOI: 10.11720/wtyht.2020.1413 Abstract （707）   HTML （160）    PDF （4897KB）（628）       Knowledge map    Non-seismic methods have been proved to be effective in geothermal exploration.This paper describes a two-step method for investigating the geothermal potential in Fountain Village,Rongsheng,Qihe,Shandong Province.The geological background of the target area is very complicated;for instance,many complex faults are developed and the formations usually have strong horizontal anisotropic property,which enhances the difficulty of exploration.The two-step method put forward by the authors utilizes the electrical and elastic features in different formations to solve these difficulties.The first step is to investigate the location of huge fault structure and the depth of resources by using electromagnetic method,which can locate the water-rich regions.The second step focuses on the more precise features of faults based on microtremors method. This method can help locate the sweet spot area more accurately and bring constructive suggestions to well location determination.Drilling results have testified the feasibility and applicability of this two-step method,which opens up a new path in complex geothermal exploration. Table and Figures | Reference | Related Articles | Metrics

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Geochemical characteristics and influential factors of soil selenium in typical agricultural area, Chongqing YU Fei, ZHANG Feng-Lei, ZHANG Yong-Wen, WANG Rui, WANG Jia-Bin Geophysical and Geochemical Exploration    2020, 44 (4): 830-838.   DOI: 10.11720/wtyht.2020.1471 Abstract （528）   HTML （146）    PDF （1906KB）（544）       Knowledge map    Nanchuan District is a typical agricultural area in Chongqing. The authors investigated the geochemical characteristics and influential factors of soil Se from Nanchuan District of Chongqing City to provide some scientific bases for the survey of environment background and regional production as well as human health. More than 8 496 soil samples from the topsoil layers(0~20 cm)all over the Nanchuan District were collected and analyzed for content and distribution of soil Se and their relationships with parent material, soil properties (pH and Corg), altitude and human factors. The research results show that the content of total selenium ranges from 0.056×10-6 to 10.80×10-6 with a mean value of 0.46×10-6, which indicates that the most of the soils are in the category of Se-sufficiency to Se-abundance, with 42.31% being Se-enrichment. The spatial characteristics of soil Se content in Nanchuan District show "high in the south and low in the north", and the soil Se enrichment areas are mainly distributed in Shuijiang Town, Nanping Town, Nanchuan urban area and Jinfo Mountain. Among the types of soils existing in the Nanchuan District, Se content is the highest in industrial and mining land soil and the lowest in farmland. The spatial characteristics of soil Se content and strata show a similar variation pattern. The soil Se enrichment is mainly distributed in Permian, Triassic (Feixianguan Formation and Jialingjiang Formation), Silurian, Ordovician and Cambrian strata, which indicates that the soil Se content is mainly controlled by parent materials in Nanchuan District. In addition, Se content in soil is significantly positively correlated with soil organic matter and altitudes, but significantly negatively correlated with soil pH. Table and Figures | Reference | Related Articles | Metrics

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The result analysis of the comparison between SAG-2M and KSS31M marine gravimeters Fei-Fei ZHANG, Jian-Wei SUN, Bo HAN, Run-Lin DU, Wan-Yin WANG Geophysical and Geochemical Exploration    2020, 44 (4): 870-877.   DOI: 10.11720/wtyht.2020.0077 Abstract （525）   HTML （152）    PDF （1743KB）（573）       Knowledge map    A comparison for the marine gravimeters on the same vessel was carried out between SAG-2M marine gravimeter developed by China and KSS31M marine gravimeter designed by Germany in order to test the technical performance and data reliability of SAG-2M marine gravimeter. The raw gravity data acquired from these two marine gravimeters were preprocessed according to the standards of marine geologic survey to obtain the free air gravity anomalies, and the comparison and relativity for those two types of gravity data were studied by analyzing the cross-point differences, survey lines and grid data. The result shows that the SAG-2M marine gravimeters have the same level of measurement accuracy with the KSS31M marine gravimeter because there is a highly linear relationship between the data from two marine gravimeters with an approximately similar variation trend. Based on the results of comparison, it is concluded that the self-developed SAG-2M marine gravimeter shares the similar standard of measurement accuracy with the KSS31M marine gravimeter with a stabilized technical performance, which provides an important reference for the future application of SAG-2M marine gravimeter. Table and Figures | Reference | Related Articles | Metrics

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Geochemical survey method of land quality in hilly areas:A case study of the geochemical survey of land quality in Ganzhou Guo-Guang CHEN, Xiao-Hong LIANG, Jie ZHANG, Zhong-Fang YANG Geophysical and Geochemical Exploration    2020, 44 (3): 463-469.   DOI: 10.11720/wtyht.2020.1566 Abstract （721）   HTML （182）    PDF （1742KB）（768）       Knowledge map    In view of the characteristics of obvious changes in topography, geologic background and significant influence on geochemical element content in hilly area, this paper puts forward a method for geochemical investigation of land quality in hilly areas based on geological background analysis, with emphasis on soil geochemical survey of arable land, garden andgentle-slope land.According to the geological and geographical features of Ganzhou, detailed sample method laying in basins, valleys and mountains are,the method of plot-assignment based on geological background, the combination of eco-geological investigation and soil geochemical survey, the method of combining the pollution-free se-enriched concentration and the land quality files as the core. Table and Figures | Reference | Related Articles | Metrics

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The calculation method of full tensor geomagnetic gradient based on IGRF model Yang ZHONG, Yan-Wu GUAN, Jia-Qiang SHI, Feng XIAO Geophysical and Geochemical Exploration    2020, 44 (3): 582-590.   DOI: 10.11720/wtyht.2020.1416 Abstract （804）   HTML （167）    PDF （3448KB）（880）       Knowledge map    The international geomagnetic reference field (IGRF) is a general international model for describing the earth’s main magnetic field. At present,this model can be used to calculate the seven elements of geomagnetic field at any point. However,with the development of aeronautical full tensor magnetic measurement technology,there is an urgent need for full tensor geomagnetic gradient data. In this paper,the calculation principle of the IGRF model is summarized and the expression of the full tensor geomagnetic gradient with spherical harmonic expansion is derived. The calculation of the seven elements of geomagnetic field and the full tensor geomagnetic gradient at any given point is realized. Comparing with the calculated data from the website of the National Oceanic and Atmospheric Administration of the United States (NOAA),the results are accurate and reliable. The contour map of the full tensor geomagnetic field in a region is drawn, and the results were in accordance with the Laplace equation. It provides the theoretical basis for the selection of learning flight working area and flight height in the aeromagnetic survey. Table and Figures | Reference | Related Articles | Metrics

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A review of seismic tomography methods Chang LIU, Zhen-Chun LI, Ying-Ming QU, Yi-Peng XU, Wei-Jie ZHAO Geophysical and Geochemical Exploration    2020, 44 (2): 227-234.   DOI: 10.11720/wtyht.2020.1243 Abstract （1372）   HTML （950）    PDF （550KB）（1357）       Knowledge map    As a method for effectively reducing the velocity model of the subsurface media,seismic tomography provides a reliable initial velocity model for full waveform inversion.The finite frequency characteristics of seismic wave propagation are realized from primitive ray toe to phase shift travel time tomography and instantaneous travel time tomography.From the acoustic wave equation to the elastic wave equation and from the isotropic medium to the VTI,TTI media,the simulation of the real underground medium is realized.The morbidity of mitigating tomographic inversion has also been a research hotspot.The commonly used methods have regularization,and the sensitive nucleus of Gaussian beam tomography has replaced the traditional ray-sensitive nucleus.Furthermore,in order to avoid the dependence of the accuracy of the imaging results on the true depth of the reflection bits on the common imaging gather,the angular domain double differential reflection tomography can converge stably and efficiently to the accurate migration velocity model.At present,tomography is gradually transitional to anisotropic media,data used are transitional from VSP to WVSP,and a single waveform is developed into multiple waveforms combined inversion.However,problems related to resolution and computational efficiency still require attention. Reference | Related Articles | Metrics

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The identification of gravity anomaly body based on the convolutional neural network Yi-Chen WANG, Lin-Tao LIU, Hou-Ze XU Geophysical and Geochemical Exploration    2020, 44 (2): 394-400.   DOI: 10.11720/wtyht.2020.1504 Abstract （935）   HTML （133）    PDF （1573KB）（684）       Knowledge map    This study combines the deep learning with the identification of gravity anomaly body. Based on the CNN (convolutional neural network) which has been gaining its use in the past several years in the field of image identification, the contour image of gravity signal is taken as the unidentified image, while the space parameters of the gravity anomaly body will be identified through CNN. In the training phase, a large number of the 3D anomaly bodies are generated with random variation of parameters, then the network is fed with parametric labels and the computed gravity contour images. The testing is performed with generated testing models to estimate the performance of the trained model. The trained CNN accuracy shows excellent accuracy in the identifications. Then the CNN model is tested with measured main gravity anomaly data of Kauring area in West Australia, and the identified parameters of the 3D anomaly body are compared with known results. It is shown that the generalization of CNN can handle identification of the measured gravity data. Table and Figures | Reference | Related Articles | Metrics

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Inversion of gravity gradient tensor based on unstructured grids Tian-Tong HUANG, Xin-Fa PENG, Zi-Qiang ZHU Geophysical and Geochemical Exploration    2020, 44 (1): 132-140.   DOI: 10.11720/wtyht.2020.2256 Abstract （456）   HTML （128）    PDF （3191KB）（434）       Knowledge map    Gravity gradient tensor is the second derivatives of gravitational field. Compared with the traditional gravitational exploration, gravity gradient tensor can reach a better resolution. Gravity gradient tensor has 5 independent components, so they can contain more geological information. Therefore, gravity gradient tensor can be used to recover the causative bodies in the subsurface with high accuracy. Due to strong adaptability and flexibility of the unstructured grid, it can smoothly approximate the irregular and complex boundaries of anomalous source. Compared with the structured grid, the unstructured grid can provide researchers with more accurate discretization and calculation with less computation time. In order to reduce the ambiguity of the inversion, the authors chose to jointly and simultaneously invert all gravity gradient components based on tetrahedron grids with the help of the so called generalized objective function which is widely used in geophysical inverse problems. The authors applied the algorithm to each gravity tensor component at the beginning to ensure that the depth weighting function makes a difference in the inversion. It turns out that the depth weighting function works well. To explore all components of the gravity gradient tensor as much as possible, the authors described the joint-inversion in detail in this paper. The inversion results show that 3D inversion of gravity gradient tensor based on unstructured grids can obtain the position of causative bodies in the subsurface and the density distribution. Based on a comparison with rectangular grid inversion results, the authors highlighted the advantages of unstructured grid inversion. And the practicability of the method was verified through two synthetic models. Table and Figures | Reference | Related Articles | Metrics

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Ecological risk assessment and source analysis of heavy metals in sediments of Liujiang River Catchment Xiao-Yu ZHONG, Tian-Sheng WU, Jie LI, Guo-Dong ZHEN, Xiao-Xiong ZHUO, Dong-Chao GUAN, Lei WANG, Bing-Ji MO Geophysical and Geochemical Exploration    2020, 44 (1): 191-199.   DOI: 10.11720/wtyht.2020.1210 Abstract （542）   HTML （143）    PDF （1827KB）（599）       Knowledge map    In this study, 91 sediment samples were collected from the middle and lower reaches of Liujiang River. The geochemical characteristics of As, Cd, Cr, Cu, Hg, Ni, Pb, Zn and other elements were analyzed. The current pollution situation and potential risks were predicted and evaluated, and the sources of heavy metals were analyzed. The results show that: The spatial dispersion of elements in the sediments of Liujiang River Catchment is relatively large, and the distribution of heavy metal elements shows strong regional characteristics.Distribution of heavy metal elements in Liujiang River Catchment shows strong regional characteristics.As, Cr, Cu, Hg and Ni are mainly from natural sources, while Cd and Pb are mainly from human sources. The high-value areas of Cd natural source contribution mainly distribute in Longjiang River Catchment, while the high-value areas of industrial and mining sources contribution mainly distribute around Jincheng River and Liuzhou District of Liujiang River. Table and Figures | Reference | Related Articles | Metrics

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The application of full azimuth migration imaging technology to Nanmazhuang buried hill tectonic belt Hong-Wen ZHANG, Xi-Heng LIU, Xing-Hai ZHOU, Liu-Wu LI, Xi-Shan DU, Cheng-Quan WANG Geophysical and Geochemical Exploration    2020, 44 (1): 25-33.   DOI: 10.11720/wtyht.2020.1042 Abstract （423）   HTML （151）    PDF （2155KB）（467）       Knowledge map    With the deepening of the oil and gas exploration and development,geological object is becoming more and more complex.Due to the requirement of increasing the precision of seismic imaging,especially with the development of high-density and wide-azimuth and wide-band seismic exploration technology,the direction of anisotropy is more and more prominent in the seismic data processing.However,the conventional Kirchhoff prestack time and depth migration uses both offset gathers,the angle gathers information fails to be retained and therefore it is unable to meet the demand of the current seismic processing.By way of full wave field and multipath,full azimuth migration imaging applies all seismic data in a continuous manner in underground local angle domain and generates two complementary full azimuth direction angle gathers and full azimuth common refection angle gathers.Fairly good application effect has been achieved in the migration imaging of Nanmazhuang buried hill tectonic belt,as shown by the facts that the imaging accuracy is improved,the geological phenomena is clearer,and the prediction of fracture density and development direction is more reliable. Table and Figures | Reference | Related Articles | Metrics

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The application of seismic meme inversion to thin sand distribution prediction under coal shield Yan-Hu CHEN, Jia CHEN Geophysical and Geochemical Exploration    2019, 43 (6): 1254-1261.   DOI: 10.11720/wtyht.2019.1325 Abstract （504）   HTML （140）    PDF （5020KB）（439）       Knowledge map    It is difficult to predict the thin sand beneath the coal seam because of the influence of the strong shield.It is difficult for conventional wavelet decomposition techniques to decompose stable wavelet sets,and even the decomposed wavelet sets have no definite geological significance.In this paper,a new seismic meme inversion is proposed,which uses the similarity of seismic waveforms as an indicator factor to drive broadband logging curve simulation and realize high resolution inversion.Firstly,the dynamic clustering analysis of seismic waveform is realized by singular value decomposition,and the sample set of seismic waveform and well curve characteristics is established.Then the common structure in the sample is determined as the initial model in the wavelet domain,and the inversion results with high resolution are obtained by modifying the initial model according to the inversion of the actual seismic waveform structure under the constraint of the Bayesian framework.Through forward modeling and Jurassic case study in Junggar Basin,it is concluded that seismic meme inversion overcomes the limitation of seismic vertical resolution and can better predict thin sand affected by strong shield.Seismic meme inversion provides a new way for predicting thin sand affected by coal shield in Jurassic in Junggar Basin,Ordos Basin and Turpan-Hami Basin.It has a wide range of applications and important practical significance. Table and Figures | Reference | Related Articles | Metrics

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Summary of development and key issues of offshore OBC-OBN technology Bin LI, Qi-Kun FENG, Yi-Biao ZHANG, Fu-Qiang HUANG Geophysical and Geochemical Exploration    2019, 43 (6): 1277-1284.   DOI: 10.11720/wtyht.2019.0370 Abstract （1350）   HTML （233）    PDF （5024KB）（1428）       Knowledge map    In recent years,offshore OBC and OBN technology has achieved rapid development.Whether it is OBC acquisition or OBN acquisition,many new equipment and methods were developed.Based on the latest research results and published papers,this paper summarizes the development history and research status of offshore OBC and OBN technology,and summarizes the technology and equipment for offshore four-component seismic exploration and acquisition,as well as processing and interpretation techniques.It is considered that the seabed multi-component seismic is the development trend of marine seismic,because it has the advantages of multi-component data, wide azimuth and wide frequency compared with the marine tow streamer.But the processing of data and conversion wave need to be researched.Now offshore oil and gas exploration is in the stage of complex structures and lithologic reservoirs,as the cost of submarine seismic decreases and the processing technology advances, it will be get more applications. Table and Figures | Reference | Related Articles | Metrics

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A study of structural optimization design of the wide-energy range gamma spectra logging system Zhuo-Dai LI, Huai-Qiang ZHANG, Wei-Huang LU, Jin-Yang LIU, Miao-Miao YAN Geophysical and Geochemical Exploration    2019, 43 (6): 1291-1296.   DOI: 10.11720/wtyht.2019.0225 Abstract （503）   HTML （234）    PDF （2174KB）（485）       Knowledge map    The gamma spectrometry logging is widely used in survey of radioactive, metallic and non-metallic deposits and stratigraphic correlation. In order to obtain a wider energy range of gamma spectra, the authors designed the wide-energy spectra logging system with the combination of LaBr3 and BGO detectors. To determine the optimal selection principle of the wide-energy range gamma spectra logging system, the authors built a model of wide-energy spectra logging system on MCNP to simulate the measured gamma spectrum. The simulation shows that the best effect is achieved when the shield is made of tungsten-iron-nickel alloy. When the shield thickness reaches 14 cm, simulation shows better shielding effect for the distal detector. The effect for the proximal detector is close to the distal one when its relative position is 35 cm or more. The effect of changing the position of the neutron source on the thermal neutron shielding is limited. As a thermal neutron shield, boron could achieve obvious shielding effect with 0.2cm layer. The effect of fast neutron can be reduced by increasing shield thickness and the distance between the proximal detector and the shield. Table and Figures | Reference | Related Articles | Metrics

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Characteristics of selenium in crops and roots in China and recommendations for selenium-enriched soil standards Xiao-Meng CHENG, Rong-Rong MA, Min PENG, Ke YANG, Kuo LI, Hui-Yan WANG, Chao WU, Zheng YANG Geophysical and Geochemical Exploration    2019, 43 (6): 1367-1372.   DOI: 10.11720/wtyht.2019.0187 Abstract （772）   HTML （212）    PDF （1128KB）（742）       Knowledge map    Selenium (Se) in plants is mainly derived from soil, and plants can be used not only to alleviate the problem of selenium deficiency, but also to manage environmental selenium toxicity. On the basic of 6 917 co-samples of soil and rice, 1 489 co-samples of soil and wheat, and 1 816 co-samples of soil and corn seed, the Selenium concentration in selenium-enriched soil was 0.22×10 -6≤w(Se)<3.0×10 -6 for rice producing areas, 0.31×10 -6≤w(Se)<1.0×10 -6 for wheat planting area, and 0.94×10 -6≤w(Se)<4.91×10 -6 for corn planting area. It is of great significance to the scientific utilization of selenium-enriched soil resources and the development of selenium-enriched agricultural products. Table and Figures | Reference | Related Articles | Metrics

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Thermomagnetic component measurement: A geochemical prospecting method for transported overburden region Shi-Xin TANG, Jian-Jun LI, Sheng-Ming MA, Shu-Qi HU Geophysical and Geochemical Exploration    2019, 43 (4): 749-757.   DOI: 10.11720/wtyht.2019.0041 Abstract （453）   HTML （188）    PDF （4942KB）（609）       Knowledge map    Aimed at the technical problem of ore-prospecting in transported overburden region, the authors carried out experimental studies of the method of thermalmagnetic component measurement in the known mining areas, which included the Caijiaying hydrothermal type lead-zinc-silver deposit in Hebei Province, the Shaquanzi magmatic copper-nickel sulfide deposit in east Tianshan, and the skarn type iron-copper polymetallic deposit in Yemaquan area. The experimental results of Caijiaying and Shaquanzi area show that, compared with the small and weak anomalies obtained by conventional soil measurement, the surface anomalies measured by thermal-magnetic components are significant, which can well reflect the spatial location and distribution pattern of deep orebodies and have the advantages of strengthening weak anomalies and discovering new ones. The results of the experiment in Yemaquan area show that there are anomalies delineated by thermomagnetic component measurement at the known mining areas with transported sediments covering more than 100 meters. And well matched abnormal elements in space provide a new target area for prospecting in the unknown area. It has been proved by experiments that the thermomagnetic component measurement technology provides an effective method for solving the problem of ore-prospecting in the transported covered region. Table and Figures | Reference | Related Articles | Metrics

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The application of direct-current sounding method in the coastal plains: A case study of Guanyun area in Lianyungang Shao-Bing TIAN, Xiang-Qian LI, Tong-Xiao SHANG, Jian OU, Da-Lian ZHANG Geophysical and Geochemical Exploration    2019, 43 (4): 783-793.   DOI: 10.11720/wtyht.2019.0054 Abstract （495）   HTML （200）    PDF （14412KB）（769）       Knowledge map    In this study, the authors used direct-current sounding method (DC method) to explore the electrical resistivity property of Guanyun area in northern Jiangsu basin, based on the 1:50000 geological map. In combination with drilling, well-logging, geological combined profile and shallow layer reflection methods, the authors evaluated the economics and effectiveness of the DC method. The authors obtained the geomorphological electric characteristics of the study area based on the DC method,which provided a basis for the desalinization of saline-alkali land in the study area. The authors first obtained the distribution of brackish water in this area based on the salinization characteristics of underground water, and provided a guidance for the use of fresh water resources. Then, the authors described the distribution of fractures and regional bedrock surface, and fixed the location of the Huaiyin-Xiangshui fault in the northeastern part of the study area. In combination with the results of drilling, the authors holds that DC sounding is an effective and simple method of geological mapping in plain area and will be a useful compensation of the low borehole density in the study area. Therefore, it is suggested that the DC method is an effective exploration method and can be widely used in geological mapping in plain areas. Table and Figures | Reference | Related Articles | Metrics

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A study of automatic correction method for the influence of formation water salinity on compensating neutron logging Peng-Ju LI, Yong-Yong LI, Mao-He XU, Yong-Lu FU, Tian TIAN Geophysical and Geochemical Exploration    2019, 43 (4): 815-821.   DOI: 10.11720/wtyht.2019.0012 Abstract （415）   HTML （197）    PDF （2820KB）（580）       Knowledge map    In the previous Monte Carlo numerical simulation of compensated neutron logging, formation water salinity was mostly set at 0, but in fact, the alteration of formation water salinity would affect compensated neutron logging. In this paper, Monte Carlo method was used to simulate the influence of formation water salinity on compensated neutron logging, and its correction method was proposed. The relationship between salinity and counting rate, salinity and counting ratio, and the effect of salinity on the relationship between counting ratio and porosity and porosity sensitivity under different porosity conditions were simulated successively. According to the calculated results, under the same porosity condition, the counting rate decreases with the increase of salinity, and the counting rate of far detector decreases faster than that of near detector; the near-far counting ratio increases linearly with the increase of salinity as a quadratic function; based on a large number of simulation data, a bivariate function relationship between porosity and salinity is established for different formation water salinity conditions, which eliminates the influence of formation water salinity on compensated neutron logging. In addition, the sensitivity of porosity is obviously affected by salinity in medium and low porosity formations. The bivariate function relation between porosity and salinity established in this paper has completed the automatic correction of salinity effect, simplified the subsequent correction work related to formation water salinity effect, avoided complex instrument re-calibration, and provided a theoretical basis for accurate evaluation of reservoir porosity. Table and Figures | Reference | Related Articles | Metrics

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The processing technology of narrow azimuth Quasi three-dimensional seismic data acquisition by single source and single long streamer system in marine seismic exploration Gui-Lin DENG, Long-Xiang DING, Fu-Yuan LI, Bao-Jin ZHANG Geophysical and Geochemical Exploration    2019, 43 (4): 828-834.   DOI: 10.11720/wtyht.2019.1194 Abstract （452）   HTML （206）    PDF （6612KB）（490）       Knowledge map    The structure of Mesozoic in Chaoshan sag in the north of the South China Sea is quite complex,so two-dimensional seismic data imaging can not accurately reveal the inside of the structure,and the environment in this area is complex and not suitable for conventional multi-cable three-dimensional seismic data acquisition system.Based on the characteristics of quasi three dimensional seismic data acquisition by single source and single long streamer system,the authors used air-gun de-bubble technology in combination with multiple suppression method,Compact Fourier Interpolation technology and three-dimensional prestack time migration technology in the seismic data processing project.It is for the first time that three-dimensional prestack time migration data were obtained in this area,and the quality of the imaging profile is greatly improved relative to that of the two-dimensional data.It can accurately reveal the inner curtain of the thrust structure and solve the problem that can not be solved by the former two-dimensional seismic exploration. Table and Figures | Reference | Related Articles | Metrics

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Natural resources period: Big data and systematic science of the earth -More on exploration geochemistry during the overall development period Xiao-Huan XI Geophysical and Geochemical Exploration    2019, 43 (3): 449-460.   DOI: 10.11720/wtyht.2019.0197 Abstract （584）   HTML （420）    PDF （611KB）（963）       Knowledge map    The important marks and essential characteristics of China's exploration geochemistry are big information and systematic science of the earth. The overall development of exploration geochemistry persists in the policy of laying equal stress on resources and environment, truly and actively reflects the historical locus of the development of national economy and society, and has typical significance in the field of science and technology. During the natural resources period, the connotations of geological work related to resources are from mineral resources, land resources to all natural resources, whereas the connotations of geological work related to environment are from geological environment, land environment to all natural environments which include life community of mountains, water, forests, cultivated land, lakes and grass. At the time when the Ministry of Natural Resources is established and geological work is faced with deep transformation, the author, following writing a comment on this problem in 2008, here makes another discussion on this topic in some aspects which are worthy of attention, such as big data information science and geochemical survey of natural resources, establishment of geochemical theoretical system and geochemical evaluation system for natural resources guided by systematic science of the earth, important scientific problems aimed at the field of natural resources, deepening geochemical application research and theoretical research, and establishment of perfect scientific system. The long-term aim of exploration geochemistry lies in revealing the situation of natural resources and natural environment, realizing scientific development, and rational utilization and integrated protection of the earth's resources by means of big data information and systematic science of the earth, thus creating an environment that mankind can harmoniously coexist with the earth. Therefore, the whole process of the development of China's exploration geochemistry will be permeated with transformation and upgrade. Geochemistry will emerge in national professional department and science and technology field with the multi-purpose and all-round appearance characterized by the role of systematic nature, comprehensive nature and integration as well as application practice, thus extremely expanding and deepening its role in economic and social development. With its technological advantages, exploration geochemistry will implement big survey, big data and big application strategy, establish big environment, big ecology and big earth outlook, and transform itself into big geology, big resources and big science, so as to provide a geochemical scheme for solving problems of natural resources and ecological environment and promote exploration geochemistry in the period of overall development from the advantages of big data information application and the height of systematic scientific theory to the realm of 'big geochemistry'. Reference | Related Articles | Metrics

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The application of pre-stack simultaneous inversion to gas hydrates reservoir prediction in the western Pearl River Mouth basin Zhi-Bin SHA, Xiao-Ming WAN, Zhong-Quan ZHAO, Jin-Qiang LIANG, Rui-Zhao YANG, Yu BAI, Yi CHAI Geophysical and Geochemical Exploration    2019, 43 (3): 476-485.   DOI: 10.11720/wtyht.2019.0019 Abstract （595）   HTML （176）    PDF （8770KB）（469）       Knowledge map    Weak BSR or no BSR is developed in western Pearl River Mouth basin.The conventional post-stack inversion obtains only one parameter,and it is difficult to accurately predict the gas hydrates distribution characteristics.Based on seismic gather optimization,fine velocity analysis,petrophysical analysis and accurate establishment of low-frequency models,the authors used pre-stack simultaneous inversion technology to predict gas hydrate reservoirs in western Pearl River Mouth basin,adopted facies and fluid probabilities analysis technology to comprehensively identify the gas hydrate reservoirs in the study area,and achieved a fine characterization of the gas hydrates.The inversion prediction results show that the gas hydrates are developed well in the study area,and the prediction results are consistent with the drilling results,implying that the application effect of pre-stack simultaneous inversion technology is ideal. Table and Figures | Reference | Related Articles | Metrics

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The key technologies for the processing of low-quality deepwater block seismic data in southern South China Sea Zhi-Zhong ZHANG, Lan XIE, Hua CHEN, Dian-Min QIN, Qiu-Han HE, Min ZHAO, Kun CHANG Geophysical and Geochemical Exploration    2019, 43 (3): 576-583.   DOI: 10.11720/wtyht.2019.1007 Abstract （455）   HTML （201）    PDF （10238KB）（476）       Knowledge map    The prospect of exploration in southern South China Sea is widest,but the seismic data are very rare and the quality is low.The deepwater block seismic data in southern South China Sea are constrained by low quality seismic data acquired in the 1970s,characterized by no navigation text,time uncertainty of record about seabed,serious lack of traces and very short cable,which results in unique seismic processing results with serious multiples,low signal-to-noise ratio and illegibility of stratigraphic structure record on paper.To solve these problems,the authors use and develop a set of key technologies that are suitable for seismic data processing in this area,such as using navigation reconstruction technique to solve the problem of lack of navigation text,using self-correlation technique to solve the problem of seabed records uncertainty,using the frequency limited F-K domain interpolation technique to solve the problem of lack of traces,using combination multiples suppression technique to solve the problem of multiples suppression caused by short cable.The final results show that the applications of key technologies make the seismic data achieve expected effect in this area.These technological achievements not only provide reliable seismic data for deepwater oil and gas exploration in southern South China Sea but also provide some ideas and techniques for similar low-quality seismic data processing. Table and Figures | Reference | Related Articles | Metrics

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Deep sea methane electrochemical in-situ long-term monitoring technology and its significance in the ocean environmental investigation and gas hydrate exploration Chun-Yan SUN, Dong-Lin WANG, Shi-Qiang ZHANG, Hui-Ce HE, Hao ZHAO, Fan LING, Wen-Bin YIN Geophysical and Geochemical Exploration    2019, 43 (1): 1-16.   DOI: 10.11720/wtyht.2019.1250 Abstract （739）   HTML （364）    PDF （7218KB）（699）       Knowledge map    The continuous acquisition of dissolved methane concentration data in the deep sea has important scientific significance and practical application value for dynamic monitoring of marine environment and methane diffusion in gas hydrates development. This paper introduces key technologies of electrochemical in-situ long-term monitoring technology for deep sea methane in detail, which include the technical ideas of "seawater degassing, quantitative injection of gas samples, and high-precision electrochemical detection", the technical method of "sea water circulation controlled by supercharged drainage system, decompressed steady flow, gas-liquid separation, and improvement of high precision detection technology for hydrocarbon components". Based on the long-term monitoring experiment data obtained from bottom water in Jiaozhou Bay during 94 days, the authors studied and evaluated the technical performance, data quality and geological effect of the in-situ sensors. Some conclusions have been reached: (1) In-situ sensor has an index range of 0.01~10 000 nmol/L and sensitivity reaches 0.01 nmol/L. It has good stability and selectivity for the detection of hydrocarbon components; (2) The range of dissolved methane in the monitoring area is 19.01~106.87 nmol/L, the normal methane background is 32.41 nmol/L, and the local anomalous methane background is 80.60 nmol/L. These data show that abnormality is related to sewage discharge and seawater pollution; (3) The results of measured methane data are consistent with those obtained from previous investigation and study of seawater environment in Jiaozhou Bay, which proves that the measured data are objective and scientific; (4) The sea trial monitoring results show that the in-situ sensor is reliable in testing, reasonable in structure design and scientific in design ideas, and it basically has the capability for acquiring seawater methane concentration data in marine scientific investigation. It has practical application value and scientific significance in the dynamic monitoring of methane diffusion and long-term monitoring of deep sea methane concentration during the development of marine gas hydrate in the future. Table and Figures | Reference | Related Articles | Metrics

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An improved algorithm for surface reconstruction of 3D orebody based on contour line Zhao-Liang LI, Lin-Fei WANG, Sheng-Qing XIONG, Feng LUO, Hao-Fei YAN, Zi-Qiang ZHU Geophysical and Geochemical Exploration    2019, 43 (1): 118-124.   DOI: 10.11720/wtyht.2019.1342 Abstract （547）   HTML （158）    PDF （2671KB）（357）       Knowledge map    The 3D orebody surface modeling method based on contours is the main method of orebody modeling; nevertheless, in practical application, the traditional modeling method has shortcomings, which have been improved with the method in this paper. In general, contour lines of these methods are used to reconstruct the surface model by artificial selection of two contour lines, but it is difficult to grasp the overall trend of the orebody as a whole, and the shape of the three dimensional orebodies is relatively coarse. When researchers deal with the problem of branch, it is very tedious to add the branch point in that it takes a lot of manpower and time, and it is difficult to guarantee the correct result. The surface model of the orebody exhibits a lot of degenerated triangles, even in the situation that the surfaces of the orebodies are self-intersected or overlapped, hence the geometric quality of the model is so poor that it influences subsequent visualization and model calculation. The trend line for a group of contours is introduced, and it can also be edited. Then the encryption method for refining the intermediate contours so as to achieve the control of the orebody shape is used. Through projection, the shortest distance between closed contours is calculated, and branch points are automatically added. The constrained triangulation with holes is used to achieve the building of branch automatically, which greatly saves human resources and ensures the accuracy of branch of orebody. According to the problem of poor geometric quality of the initial 3D orebody surface model, the quality control to achieve the reconstruction of the surface model is introduced, which ensures the model quality and subsequent calculation. These improvements have achieved good results in practical application. Table and Figures | Reference | Related Articles | Metrics

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Improved particle swarm optimization and its application to full-waveform inversion of GPR Qian-Wei DAI, Wei CHEN, Bin ZHANG Geophysical and Geochemical Exploration    2019, 43 (1): 90-99.   DOI: 10.11720/wtyht.2019.1183 Abstract （822）   HTML （143）    PDF （1524KB）（667）       Knowledge map    Ground penetrating radar (GPR) is a high-precision geophysical exploration method whose main purpose is to invert the physical properties of underground structures.In this paper,an improved particle swarm optimization (PSO) is used to solve GPR inverse problem.The inversion takes the signal mean square error as the objective function and uses the finite-difference time-domain method to do forward modeling.In addition,the inversion accuracy is improved by the amplitude compensation of the forward result.Compared with the results based on classical particle swarm optimization inversion method,the algorithm shows considerable improvement in accuracy and efficiency.An analysis of the one-dimensional inversion results of multi-layer simulation data shows that the inversion method is effective for multi-parameter inversion and has good noise immunity. Table and Figures | Reference | Related Articles | Metrics

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