The formation age and petrogenesis of the Yangkang granites in the Qilian block remain controversial. In this study, LA-ICP-MS zircon U-Pb dating and whole-rock geochemical analysis were conducted to constrain the petrogenetic and tectonic processes during the formation of the granites. The results show that U-Pb age of granodiorite in Yangkang pluton is 444±1.2Ma, (MSWD=1.14), indicating that it was formed in the early Late Ordovician and that the rocks belong to weak peraluminous-strong peraluminous I-type granite.The rocks are enriched with large ion lithophile elements (K,Ba, Rb) and Light Rare Earth Elements (LREEs) and Th, but depleted in the high field strength elements (e.g., Ta-Nb). The above results show that Yangkang granites were derived from partial melting of continental crust. Combined with the regional data, the authors suggest that the Yangkang granites were probably formed in an active continental margin during Late Ordovician.

The Leikoupo Formation in northwest Sichuan Basin has great potential in exploration,quite a few wells demonstrate active oil and gas showings during drilling,and good gas-bearing property and reservoir development are interpreted from well logging.Aiming at tackling the unclear distribution of favorable gas-bearing zones of Leikoupo Formation and based on the combination of seismic geological conditions and well logging data,the authors conducted Empirical Mode Decomposition processing to compensate high-frequency energy while preserving the low-frequency energy,which laid the data basis for subsequent bi-media hydrocarbon detection technique.Then amplitude spectrums at different well locations were compared and analyzed,the low-frequency energy enhancement and high-frequency energy attenuation were found where reservoir contained gas.With the optimized frequency range,hydrocarbon detection based on two-phase media theory was implemented on the seismic data of the study area.The results of hydrocarbon detection are well consistent with the data from drilling wells and the geological law,which confirms the validity of proposed techniques and provides the directions for expanding oil and gas exploration range and area of Leikoupo Formation in northwest Sichuan Basin.

Restricted by the low resolution of seismic data,the identification of the top and bottom of a single sand body is difficult in the composite superposed sand bodies of the Guantao Formation in the Bohai S oil field.Moreover,in the time-space domain, sandstones with similar seismic reflection characteristics have very different fluid types,and the oil-water relationship is very complicated. In view of such a situation,based on the two-phase medium theory and the theory of viscous dispersion wave equation,the authors first carried out the time-frequency analysis of the generalized S transform,and selected the low-frequency and high-frequency attribute bodies with reference to the seismic reflection characteristics of the drilling well.Secondly,the top and bottom of the reservoir were accurately identified.Then the analysis of the difference of the spectrum characteristics of oil and water was conducted.The result shows that the seismic responses of the oil and water layers in the frequency domain have obvious characteristics,and the frequency-type attributes are more sensitive to the high-frequency attenuation of seismic waves.By optimizing the low-frequency and high-frequency attribute volume data of the main oil layer of the oil field and the plane data of the spectral attenuation difference between the top and bottom of the reservoir,a new fluid identification factor was jointly constructed to identify oil and water and achieved better results to help the remaining deployment and implementation of more than 10 development wells.

The deep-water turbidite sandstone reservoirs in Niger Delta basin have great oil-gas exploration potential.Drilling results in S Block area indicate that high-porosity water sandstones show "bright spot" and class II-III AVO anomaly,which are similar to features of oil sandstones. It is critical to remove the effect of porosity while fluid detection is conducted.However,conventional analysis method seldom considers the effect of porosity,and the selected fluid factor is sensitive to both hydrocarbon and porosity,which leads to inaccurate detection result.Therefore,in this study,a new quantitative evaluation method based on fluid and porosity substitution is proposed to choose the most sensitive fluid factor,which can highlight hydrocarbon and suppress the effect of porosity.The analysis result shows that λ/μ is the most suitable elastic parameter in this area and can be used to detect hydrocarbon.The real data application result shows that λ/μ can effectively distinguish "bright spot" water sandstones from oil sandstones, and the predicted results are well consistent with the drilling data, which proves the feasibility of this method.

Surface nuclear magnetic resonance (SNMR) can be used to directly find groundwater (brine), and the high-density resistivity method is suitable to distinguish brine from fresh water. This study introduces the joint exploration using the above two geophysical methods in two major salt lake study areas in Tibet-Chagcam Caka and Chalico salt lakes, in order to make full use of the advantages of the two methods while avoiding the limitations and one sidedness of a single method. As a result, the distribution of underground brine in the two salt lakes was identified, thus providing a basis for the overall layout of the exploration and development of potassium ore in brine in the two salt lakes. Furthermore, the joint exploration results of the two geophysical methods were highly consistent with the geological survey results of shallow wells. It can be concluded that the joint application of the above two geophysical methods in Tibet serves as an efficient and accurate exploration mode for the exploration of underground brine.

More than 20 uranium deposits and polymetallic mineralization have been discovered in the Xiangshan ore field at present. However, breakthroughs in polymetallic prospecting are yet to be made in the ore field.This paper compared the Xiangshan ore field with the Lengshuikeng lead-zircon-silver polymetallic ore field at a high exploration level in terms of regional geological setting, strata, magmatic rocks, ore body characteristics, and wall-rock alteration. Based on this, it is found that the Xiangshan and Lengshuikeng ore fields are similar in geological conditions, the geochemical characteristics of rare earth elements (REEs) and trace elements, and the characteristics of ore bodies and alternation. Regarding lithology, both are mainly composed of volcanic rock series of the Cretaceous Ehuling and Daguding formations, which are present as high high-K calc-alkaline basalts and possess quasi-aluminous-weakly peraluminous characteristics. The REE-distribution patterns and trace element spider diagrams of the two ore fields are notably rightward, indicating the enrichment of light REEs, low content of Ba and Sr, and obvious Eu depletion. Therefore, the sediments in the two ore fields mainly originate from the crust. Meanwhile, the magmatic rocks feature a high crystallization differentiation degree, and the wall-rock alteration is dominated by chloritization, sericitization, silicification, and carbonation.By referring to the metallogenic model of the Lengshuikeng ore field, it is considered that the future polymetallic prospecting in the Xiangshan ore field should focus on the porphyry-type polymetallic ore in small rock masses and strata-bound, superimposed polymetallic ore at the K₁d¹ horizon. In this manner, breakthroughs are expected to be made in polymetallic prospecting in the Xiangshan ore field.

In order to make a breakthrough in prospecting in the Youfang area of the Xiangshan ore field, the authors carried out geoelectric extraction and surveying in this area for deep prospecting prediction. It is found that the anomalies are obviously controlled by the faults, and are mainly distributed along the ore-controlling faults and the intersection of the faults. Cluster analysis and factor analysis reveal that there is a significant correlation between the trace elements, thus forming the corresponding element combinations: F1 factor (Ti、V、Mo、Th、U), F2 factor (As、Pb、Sb), and F3 factor (Co、Ni). The spatial distribution of uranium-thorium ratios shows a significant positive correlation with the estimated base depth of AMT, controlled by volcanic rock thickness. The authors synthesized the abnormal features of geoelectrically extracted elements and the mineralization regularity of the Xiangshan ore field, established a comprehensive geological-geoelectrochemical prospecting model, and delineated two corresponding targets in the study area, of which No.1 target area has good prospecting prospect.

Time-lapse seismic survey is an effective technique for reservoir dynamic description,but it has not been widely used since its success in the last century due to the high cost and the limitation of its application range.Since 2007,Shengli Oilfield has put forward the idea of non-uniform time-lapse seismic survey in view of the current situation of the secondary acquisition seismic survey in high mature exploration area.Aiming at tackling a series of technical problems,such as how to evaluate and eliminate the influence of non-uniform acquisition system, how to detect the small difference of monitor changes and how to comprehensively use the time-lapse results,researchers have spent more than ten years to innovate the key technologies,i.e.,the matching technology of non-uniform time-lapse seismic acquisition system,the pre-stack cross equalization technology based on well data,the joint optimization technology of pre-stack and post-stack sensitive attributes,and the comprehensive interpretation technology of time-lapse seismic based on reservoir value.The time-lapse seismic technology of water-drive complex fault block reservoir,small-scale gas reservoir boundary monitoring and steam huff and puff heavy oil reservoir has been formed.The application demonstration of six blocks with an area of 300 square kilometers has been carried out,which shows the broad prospect of the achievements and broadens the ability of reservoir geophysical technology to solve the development problems.

On the basis of summing up the advantages and disadvantages of the existing high-density resistivity instruments and combining with the requirements of urban underground space exploration, a set of multi-parameter parallel measuring high-density electrical system is developed. It has the characteristics of transmitting signal at one time, receiving signal by multiple electrodes at the same time, and measuring multiple parameters at the same time. Compared with the traditional high-density electrical instrument, it can effectively improve the working efficiency. the field test shows that the performance of the new electrical system achieves the desired effect. At the end of the article, the paper summarizes the advantages of the new electrical system and showed the suggestions on the development of high-density electrical instrument.

After analyzing the power supply system design of airborne gravity measurement, aiming at the instability of full load power on or repeated start, a new circuit connection mode based on VICOR power module is proposed to solve the above problems. In the design of aviation gravity power supply, the general circuit structure design and parameter selection refer to the technical manual of the power chip module manufacturer, and the EN port of the rectifier filter module is selected to drive the DC-DC module. However, similar faults such as full load power on difficulty or repeated startup are often encountered, which affect the stable operation of the power supply. In this paper, the BOK output of VICOR module combined with triode is used to control the PC enable port of DC-DC power supply module, which does not affect the power on of front-end rectifier filter circuit. The circuit analysis results show that compared with the EN port drive enable, when using the BOK drive, the threshold voltage lower than 2.3 V can be guaranteed at the output low level, the PC enable port can be fully blocked, and there will be no phenomena such as full load power on difficulty or repeated startup, so that the aviation gravity power supply system can work more safely and stably.

Near-field effects are liable to rise in magnetotelluric signals due to noise, which seriously affects the quality of the collected signals. The widely used remote reference method-Robust-still has some shortcomings in suppressing near-field interference. In this paper, after being verified using numerical simulation in terms of denoising effects, the Hilbert-Huang transform (HHT) was applied to a magnetotelluric signal with serious near-field interference, achieving remarkable effects. Meanwhile, the polarization distribution of the electric and magnetic fields was calculated using the distribution function of polarization directions. It was found that the distribution function was closer to a Gaussian distribution function, also verifying the effectiveness of the HHT in suppressing near-field interference.

In the past seismic exploration in Qaidam Basin,large combination receiving has been often used in order to achieve the purpose of suppressing noise.However,as the exploration goes deeper,the disadvantages of the big combination gradually emerge.The single detector receiver can combine the channels in the post-processing of the data,which can not only suppress the interference but also eliminate the influence of statics in the large combinations,which is beneficial to the resolution, fidelity and imaging accuracy of the data.Based on the data of a survey line in the area of the peak mountain in the basin,this paper deals with and analyzes the trace combination,discusses the method,process and problems that should be paid attention to in the process of the trace combination,completes the function of the field detector combination,and shows the effect of the trace combination treatment.

The measurement of the electrochemical polarization effect of rock (ore) in an AC electric field (i.e., the phase between receiving potential different and transmitting current) using spectral induced polarization (SIP) can provide important information for distinguishing ore from non-ore. Based on the deep research on the key technologies of SIP instruments, this study designs a new synchronous correlation detection technology of weak signals, and accordingly improves the prototype for practical purposes, simplifies the circuit structure, and improves the stability of phase measurement of the SIP instruments. The tests in mining areas show that the improved SIP instrument has lower cost, stronger anti-interference ability, higher practicability, and is suitable for large-scale promotion and application.

Shear wave velocity plays an important role in seismic forward modeling,fluid prediction and AVO analysis.However,due to the high cost of shear wave logging,there are no shear wave velocity logging data in some work areas.The prediction method of shear wave based on rock physics modeling is specific and accurate.In this paper,the method of calculating effective elastic modulus proposed by Sabrina is adopted,and the assumption conditions of CAO for shear wave prediction by this method are extended,rock physics modeling is performed,and the measured porosity is used to calculate the pore compliance so as to further predict the shear wave.Finally,combined with the actual data,the cross velocity data are used to conduct verification,and the results show that the effect is fairly good.

Based on the theories and methods of 3D geological visualization models and the geological data of the Tianhu preselected site, a geological model of the site was established in this study using the Deep Insight TM geoscience modeling software. It describes the 3D tectonic morphology of the preselected site, carries out 3D visual analysis of the geological conditions of the study area from 2D to 3D, from overall to local, and from macroscopic to microscopic aspects,and intuitively expresses the distribution regularity of geological information in the main rockmass used for the disposal of high-level radioactive wastes. The granite rock massatthe Tianhu site occurs in equiaxed rock stocks, with simple lithology and large volume.There is only an NW-tending fault with a length of 2 km developing in the southeastern part of the rock mass. Besides, veins and alteration zones are relatively developed in the rock mass, which affects the integrity of the rock mass to a certain degree. The model can be used to query and update geological data at any time, analyze the distribution characteristics and laws of various geological information in the whole model, and improve the understanding of geological laws. All these willassist in better guiding the site selection, assessment, and construction of disposal repositories.

This study aims to investigate the distribution characteristics of the total selenium content in soil in karst areas in Mashan County, Guangxi and to explore the effects of different soil parent materials, land uses, and soil types on the selenium content in soil. To this end, 492 samples of surface soil (0~20 cm) were collected from the northern part of Mashan County and the distribution of the total selenium content in the samples were studied by statistical methods. The results are as follows. The total selenium content in the soil varies from 0.20×10^-6 to 3.54×10^-6, with an average value of 0.76×10^-6. Meanwhile, the selenium-rich area accounts for 98.29% and the coefficient of variation is 34.49%. The soil in the Permian Heshan formation bearing black shales and coal-measure strata has the highest selenium content, with an average of 1.17×10^-6, while the Carboniferous Maping formation has the lowest selenium content, with an average of 0.64×10^-6. In terms of different soil types, the lateritic red soil has the highest selenium content, with an average value of 1.04×10^-6, while the fluvo-aquic soilhas the lowest selenium content, with an average value of 0.56×10^-6. In terms of land use types,the forestland and orchard have a high selenium content in soil, while the paddy field, grassland, and arid land have a low selenium content. Therefore, the selenium content in soil in the study area is mainly affected by soil parent materials, with the selenium enrichmentin soil being affected by the organic matter content to a certain extent.

Urban land subsidence is liable to induce ground fractures or even collapse,thus causing safety accidents.However,traditional geophysical methods cannot be applied in cities due to the strong human interference and high requirements for safety and environmental protection in the urban environment.The microtremor survey method is a passive,efficient,and environment-friendly geophysical method and it can be used to detect the underground geological conditions in the urban environment with strong interference.Taking Xiegang Primary School in Hefei City as the research site,this paper focuses on the applicability and effectiveness of the microtremor survey method in detecting the causes of land subsidence.Based on the microtremor survey data collected,the dispersion curve was extracted using the F-K method and then the underground shear wave velocity structure was obtained through inversion,thus revealing the underground geological conditions.Finally,verification was conducted through drilling.The results show that the microtremor survey is an effective geophysical method for detecting the information such as the position and scale of underground unconsolidated soil,and thus the secondary accidents in subsidence areas can be eliminated.

In the current gravity survey work, the accuracy of digital elevation model (DEM) used in terrain correction is basically avoided when evaluating the accuracy of terrain correction in gravity intermediate area. Therefore, the mean square error of terrain correction calculated by this data in gravity intermediate area is not comprehensive. Based on the analysis of DEM data error and the comparison of actual data, this paper puts forward a method to evaluate the accuracy of DEM data used for terrain correction in the intermediate area of gravity by using the measured elevation values of gravity measuring points, and discusses how to evaluate the error of terrain correction in the intermediate area of gravity caused by DEM error, so as to obtain the accuracy of terrain correction in the intermediate area of gravity closer to the real situation.

Bouguer gravity anomaly is constantly correlated with terrain in mountainous areas, which is unserviceable to geological interpretation of gravity data. This phenomenon is mainly caused by inaccurate terrain correction density. We ascertain the terrain correction density in mountainous areas based on regression analysis. We obtain the terrain correction density by analyzing the relationship between the free-air gravity anomaly and the elevation, and modify the density according to the relationship between the calculated Bouguer gravity anomaly in each step and the elevation. Based on this, we adjust the terrain correction density of topographic correction successively until we obtain the optimum terrain correction density and the corresponding Bouguer gravity anomaly. We have adopted the proposed method for the terrain correction of the gravity data in the Jiuzongshan mountain and obtained the optimum terrain correction density after 5 iterations, and thus the Bouguer gravity anomaly was calculated. The results of Jiuzhongshan mountain confirmed the correctness of our proposed method.

In order to select the optimized interpolation parameters of 1∶50 000 regular distribution gravity data to provide quantitative interpolation basis for data gridding. We take the gravity data of the theoretical model as an example, use the radial basis function method to optimize the interpolation parameters, such as the interpolation kernel function and the search neighborhood, and using the standard deviationindex to evaluate the interpolation results corresponding to different parameters. The results indicate that the natural cubic spline kernel function corresponds to the highest interpolation accuracy, when the R² parameter is in the first interval (0~1), the interpolation is stable and accurate. The interpolation accuracy is highest when the search neighborhood is elliptical, and the preferred interpolation parameters are as follows: the search radius R₁=3 km, R₂=4.5 km, the number of sectors to search is 4, the search angle is 32°, the anisotropy ratio is 0.667, the anisotropy angle is 32°, the maximum number of data to use from all sectors is 80, the maximum number of data to use from each sector is 20, the minimum number of data in all sectors (node is blanked if fewer) is 8, the node is blanked if more than 3 sectors are empty.

Regularization downward continuation imaging by successive layer optimization (DCSLO) can be used to study the geometrical configuration and physical distribution of geological body(geobody). Due to possible similar features of potential fields for some bodies of different geometrical configurations, the downward continuation imaging is of no-uniqueness. From spectral study of 4 basic configurations of geological bodies and parameter selection for optimum downward continuation for the 35 gravity models of different configurations, a regressive formulas between configuration parameter and shape correction coefficient is obtained and consequently a configuration filter operator is proposed. With the configuration filter operator the DCSLO will enhance the imaging accuracy of geometrical center of complex geobody. A field example of DCSLO for gravity and magnetic data in FengSunChang area in Western Sichuan is given. With the configuration filter operator determined by the seismic structures and the regressive formulas, the DCSLO imaging is consistent with the main geometrical characteristics of the seismic deep structures and overall density logging data. This verified the applicability and effectiveness of the configuration filtering in DCSLO imaging.

Data filling or interpolation is a fundamental and vital problem of potential-field data processing. Some data cannot be measured when some places are unable to reach, such as rivers, or cliffs. If we want to acquire the missing data for better subsequent processing, we need to interpolate or fill in the missing data. Hence, this article introduces the Discrete Cosine Transform (DCT) method into the Projection Onto Convex Sets (POCS) algorithm to tackle this problem, and a generalized exponential threshold attenuation method is also given. Finally, model tests and practical applications show that the POCS algorithm with generalized exponential threshold and based on DCT has the advantages of high accuracy, small filling or interpolating traces and the noise standard of the filled data are closer to real situation.

The measured gravity anomaly is a superimposed field composed of a regional field and a local field, whose characteristics is complex shape and various amplitude changes. In order to complete the geological task better, it is necessary to separate the regional field and the local field. Based on the the measured gravity anomalies, this paper studies the relationship separately between the elevation and free-air gravity anomaly, simple bouguer gravity anomaly, bouguer gravity anomaly. By the way of mathematical statistics to perform regression analysis, the regional field (background field) and the local field (remaining field) are separated which improves the credibility of the interpretation results of gravity data and provides basic services for analyzing and solving geological tasks.

In order to improve the convergence and stability of Euler inverted results, the iTilt-Euler method, which do not depend on the structure index, is used for the calculation. Furthermore, the data points are constrained by the peak values of tilt angle of the total horizontal derivative (TAHG) to optimize the solutions. The method has been demonstrated with synthetic and real data. For synthetic data, the convergence of iTilt-Euler inversion results constrained by the TAHG method is improved effectively to detect the fault structures with deeper depth. Application to gravity data for the ANZA basin in Kenya shows that the iTilt-Euler inversion results constrained by peak values of TAHG have good continuity. The results distribute generally along NW direction, followed by NE direction, and these characteristics are consistent with the identifying features of fault in the second-order vertical derivative and total horizontal derivative anomaly maps. Furthermore, the inversion depth results show that the solutions along NW direction are extend to large scale and with higher values, which is reflected as a basement fault that controls the boundary of the main tectonic units in the study area and usually cut by the superficial faults with NE extension. It is worth noting that a large deep fault with NNE extension is developed in the southeast of the study area, which cuts the north-west direction and the north-east direction fault. It is speculated that it may control the southeast boundary of the regional tectonic unit. We can conclude that the iTilt-Euler deconvolution combined with the peak constraint method can provide a reliable method for fault system interpretation, and has good practicability.

Fast automatic inversion is a primary tool for magnetic data interpretation. The normalized source strength (NSS) is one main method for three-dimensional magnetic data interpretation as it is independent of magnetization direction. In this paper, the vertical difference of the normalized source of strength is introduced, and a fast estimation method of magnetic-source parameters based on the vertical difference of normalized source strength is derived in the light of the vertical difference of NSS at different height. In addition, upward continuation of suitable height can be used to improve the stability of the method. Model tests shows that the vertical difference of NSS has higher resolution ability and can recognize the horizontal locations of magnetic sources, and the proposed automatic inversion method can obtain the depths and structural indices of the sources. In this paper, the proposed method is applied to magnetic anomaly of M area over Inner Mongolia, and obtain the horizontal locations, depths and structural indices of magnetic sources. The results could provide useful information for forecasting the distribution of concealed rock mass.

The forward modeling of a 3D mesh model is the basis of gravity data inversion. High precision and high efficiency forward modeling is helpful to the improvement of the quality of inversion interpretation. In order to solve the problem of high precision and high efficiency gravity forward modeling based on a large-scale surface observation area, this paper presents the gravity anomaly forward modeling method and parallel algorithm of a 3D Tesseroid mesh model in the spherical coordinate system. The forward modeling uses the improved Gauss-Legendre Quadrature integration method to realize the high-precision gravity anomaly calculation based on a large-scale surface observation area, and also uses the MATLAB task parallel algorithm based on OpenMP to realize the high-efficiency forward modeling. The test on the 3D theoretical model and the Eastern China lithospheric model has verified the validity of the proposed method. This method can provide technical support for efficient large-scale gravity field simulation and 3D inversion.

Trinidad Basin, which is located in the northern part of Venezuela in South America and the southern margin of the Caribbean Sea has a good prospect for oil and gas resources. The formers have studied the tectonic evolution, sedimentary characteristics of the basin, the work was mainly focused on the southeastern basin, there is lack of research on the characteristics of the structure of the entire basin. In order to study systematically the distribution of faults and basement characteristics of the basin, predict the prospective areas of hydrocarbon, and provide a basis for further hydrocarbon exploration and development in the basin. This paper uses ship log gravity data and satellite gravity data provided by GETECH to analyze and study the characteristics of the gravity field of the basin, infer the fault structure system of the basin. With the constraints of the three existing seismic profiles, the three gravity profiles with the same position as the above seismic profiles were fitted, the basement depth of the basin is calculated combined with correlation analysis and Parker, the structural units and favorable hydrocarbon exploration areas of the basin are predicted. The results show that the structure of Trinidad basin is complex, there are mainly two groups of faults in NE direction and NW direction, the NE-oriented main faults control the scope of the basin and the development of stratum in the basin. The basement of the basin is undulating and can be divided into six structural units: the eastern subbasin, the northern subbasin, the central uplift belt, the central nappe belt, the western subbasin and the western uplift. The eastern sub-basin, the north sub-basin and the western sub-basin are favorable areas for hydrocarbon exploration.

Tomb of Wei Concubine is the nearest to Zhao mausoleum and the highest level in all the Tomb in Zhao Mausoleum,as also, it is the only construction tomb in Mountain of the Tang Dynasty that has been compouded,so,it is improtant to research and protect Tang-dynasty mausoleum.We survey the tomb of the Wei concubine with uav lidar survey, ground high-precision gravity and magnetic survey, high-density electrical survey, GPR and soil radon gas survey for evaluating the results. Ground high precision gravity and magnetic survey combined with soil radon measurement can effectively delineate the plane position of underground place. The high density electric method accurately delineates the space position under ground. The GPR has clearly detected the fine structure of the tomb with a resolution of up to sub-meter level, These resoults provide valuable information for exploration of Zhao Mausoleum’s underground palace in the future.