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  • Table of Content
      20 February 2024, Volume 48 Issue 1 Previous Issue   
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    Chronology and geochemical characteristics of trachytes in the Tiaojishan Formation, Xuanhua Basin, northwestern Hebei Province, and their geological implications
    YANG Ji-Yuan, HU Xin-Zhuo, ZHOU Jing, QI Peng-Chao, LI Ze-Yang, MENG Jia-Bao, XU Fan, ZHANG Hui-Bin, QI Hui-Yun
    Geophysical and Geochemical Exploration. 2024, 48 (1): 1-14.   DOI: 10.11720/wtyht.2024.2503
    Abstract   HTML ( 2 )   PDF (8237KB) ( 13 )

    The Tiaojishan Formation in northwestern Hebei Province is home to volcanic-sedimentary strata. Due to the lack of fossil organisms, insufficient isotopic dating data, and outdated dating methods, the formation epochs of these strata have been controversial. To accurately determine their formation epochs and examine their regional geotectonic setting, this study conducted a detailed field investigation of the lithologic assemblage of the Tiaojishan Formation in the Xuanhua Basin. Petrological, petrogeochemical, and high-precision isotopic dating studies were conducted on the trachytic volcanic rocks in the upper segment of the formation, obtaining the LA-ICP-MS-based zircon U-Pb isotopic ages, which were 161.1±1.2 Ma and 162.5±1.3Ma. As indicated by the petrological and petrogeochemical characteristics, these trachytic volcanic rocks belong to the shoshonite series, exhibiting enriched light rare earth elements, relatively enriched elements including Rb, K, Th, Ce, Zr, and Hf, and relatively depleted Ba, Nb, Sr, P, and Ti. According to the comparison of principal parameters and graphical discrimination, the magma originated primarily from the melting of continental crustal materials and formed in the tectonic setting of compressional continental margin volcanic arcs. The comprehensive research reveals that the Tiaojishan Formation formed primarily during the Middle Jurassic and continued to the Late Jurassic, and the trachytic volcanic rocks in its upper segment formed in the intraplate compressional tectonic setting. The results of this study provide new data for the division and correlation of Mesozoic volcanic-sedimentary strata and the analysis of their formation environment.

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    Geological characteristics and origin of the Mogou fluorite deposit in Fangcheng County, Henan Province
    ZHANG Qing-Song, XIA Ming-Zhe, WANG Chun-Lian, LI Ke-Kun, LIU Zeng-Zheng, JIANG Ji-Yong, JIANG Jian-Lang
    Geophysical and Geochemical Exploration. 2024, 48 (1): 15-23.   DOI: 10.11720/wtyht.2024.2588
    Abstract   HTML ( 0 )   PDF (6964KB) ( 13 )

    The Mogou fluorite deposit of Fangcheng County, residing in the Neoproterozoic Meiyaogou Formation, is a crucial part of the fluorite metallogenic belt in southern Henan Province. Based on the analysis of the geological characteristics of the Mogou fluorite deposit, this study conducted petrographic and petrogeochemical studies to define the source of ore-forming materials and probe into the genetic mechanism of the fluorite deposit. The results show that the fluorite ore body is veined or lenticular, with mineralization-related alterations composed of silicification, fluorite and sericite alterations. Its ore structures are primarily massive, followed by banded, striped, and brecciated types. The chondrite-normalized rare earth element distribution pattern of the fluorite ore body is similar to that of the Meiyaogou Formation marbles and the Yanshanian porphyritic plagiogranites, suggesting a genetic relationship. The possible genetic mechanism is that the F-enriched ore-bearing hydrothermal liquids intruded along the interbedded fault and reacted with the surrounding rocks to form the fluorite ore /mineralized body. The deposit belongs to the epithermal filling type along the interbedded structure.

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    Application of natural thermoluminescence measurement technique in natural gas hydrate exploration in permafrost areas
    WANG Hui-Yan, TANG Rui-Ling, BI Jing
    Geophysical and Geochemical Exploration. 2024, 48 (1): 24-30.   DOI: 10.11720/wtyht.2024.1037
    Abstract   HTML ( 0 )   PDF (2704KB) ( 9 )

    Since natural gas hydrates (NGHs) in permafrost areas feature complex formation mechanisms and multiple sources, there is an urgent need to develop multiple techniques for micro-leakage information capture in order to increase the exploration success rate. This study applied the natural thermoluminescence measurement technique to NGH exploration in a permafrost area for the first time. Specifically, it tested the thermoluminescence intensity in soil samples from the Muli permafrost area of the Qilian Mountains using an RGD-6 thermoluminescent dosimeter. Then, it summarized the heating procedure for NGH exploration in the area, as well as size fractions for sampling. The results show that the soil samples from the Muli permafrost area demonstrated optimal size fractions for sampling ranging from -60~100 meshes, an optimal heating rate of 5 ℃/s, and an optimal heating range of 50~400 ℃. Based on the anomaly characteristics of the natural thermoluminescence intensity in soil samples, this study determined the anomaly boundary of NGHs on the surface of the permafrost area. It revealed that the natural thermoluminescence intensity displayed anomalies on the top, which correspond well to the hydrocarbon anomaly mode. The natural thermoluminescence measurements of soil, unaffected by microorganisms and boasting high sensitivity, can be popularized as a promising method for NGH explorations in permafrost areas.

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    Prospecting for concealed skarn iron deposits using the high-precision gravity-magnetic survey method
    DONG Jian, LI Xiao-Peng, FU Chao, DANG Zhi-Cai, ZHAO Xiao-Bo, ZENG Qing-Bin, HU Xue-Ping, WANG Jin-Hui
    Geophysical and Geochemical Exploration. 2024, 48 (1): 31-39.   DOI: 10.11720/wtyht.2024.1047
    Abstract   HTML ( 0 )   PDF (7885KB) ( 30 )

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

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    Geophysical characteristics and deep prospecting prediction of the Dachaigou gold deposit in the eastern Kunlun area
    YU Zhong-Hong, YAN Ling-Qin, ZHANG Zhan-Xiong, LI Peng, LI Feng-Ting, FU Jia
    Geophysical and Geochemical Exploration. 2024, 48 (1): 40-47.   DOI: 10.11720/wtyht.2024.1126
    Abstract   HTML ( 0 )   PDF (7232KB) ( 19 )

    The eastern Kunlun metallogenic belt, as a significant metal metallogenic belt in China, hosts extensive orogenic gold deposits and large-scale Kunlunhe, Gouli, and Wulonggou gold concentration areas. The Dachaigou gold deposit is a large-scale gold deposit newly discovered in the Wulonggou gold field in recent years. Despite its high metallogenic potential, the western extension of its ore belt has not been defined. Hence, this study conducted induced polarization (IP) sounding and wide-field electromagnetic sounding in the deposit. The results show that the known ore belt is situated in the regional gravity anomaly gradient zone, the transition zone of positive and negative weak magnetic anomalies, the edge of IP anomalies, or the electrical gradient zone. The development zone of the regional tectonic belt resides in the large-scale IP anomaly section. The regional tectonic belt is characterized by a wide range of low-resistivity anomaly zones. The IV and III alteration zones of the known ore belt are located in the opening position of the low-resistivity anomaly zone and the shallow electrical anomaly gradient zone, respectively. Based on the above understanding and the electromagnetic anomaly change patterns of several parallel profiles in the western extension segment, it was inferred that the regional ore-controlling structure extends steadily in the W-NWW direction, forming a favorable prospecting space in the western extension segment of the deposit. The results of deep geophysical exploration in the Dachaigou deposit indicate that geophysical methods manifest significant advantages in deep geological prospecting research, providing successful experience for deep prospecting in the eastern Kunlun gold deposit area.

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    Airborne gravity-magnetic anomalies in the Baiyunhu sag,Qiangtang Basin:Characteristics and implications for oil and gas exploration
    LIU Zhong-Rong, HU Yue, FAN Zhi-Wei, HE Hong-Bing, ZHOU Dao-Qing, GUO Zhi-Hong, CAO Bao-Bao, WEI Yan-Yan
    Geophysical and Geochemical Exploration. 2024, 48 (1): 48-57.   DOI: 10.11720/wtyht.2024.1339
    Abstract   HTML ( 0 )   PDF (10307KB) ( 4 )

    Airborne gravity-magnetic data are effective in revealing the deep structures of a basin.Based on the latest airborne gravity-magnetic data,combined with field-measured physical property data,this study expounded the characteristics and geological origin of airborne gravity-magnetic anomalies present in the Baiyunhu sag.Using the airborne gravity-magnetic data,this study identified the distribution of faults and magmatic rocks in the Baiyunhu sag.Furthermore,it calculated the burial depth of the magnetic basement and the structural morphologies of the Mesozoic basement in the sag using the artificial tangent method, power spectrum analysis method,and Parker-Oldenburg iterative inversion algorithm.Additionally,this study verified the structural stratification results through the integrated interpretations of gravity and magnetism in target sections.The findings suggest that the undulations of the Mesozoic and Paleozoic sediments in the Baiyunhu sag are the primary cause of gravity anomalies,while the regional airborne magnetic anomaly primarily reflects the distribution features of the Precambrian basement.The deeply buried basement of the Baiyunhu sag,featuring continuously distributed,thick Mesozoic strata and the lack of regional faulting and magmatic activity,is scarcely affected by tectonic movements and possesses great potential for oil and gas exploration.

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    Application of integrated geophysical exploration technology in the geothermal exploration of northern Jinan
    ZHANG Yi, LIU Peng-Lei, WANG Yu-Min, ZHANG Peng-Peng, ZHANG Chao, ZHANG Ning
    Geophysical and Geochemical Exploration. 2024, 48 (1): 58-66.   DOI: 10.11720/wtyht.2024.1141
    Abstract   HTML ( 1 )   PDF (8896KB) ( 30 )

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

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    Two-dimensional joint inversion based on the marine controlled-source electromagnetic method and seismic full-waveform
    KONG Fan-Xiang, TAN Han-Dong, LIU Jian-Xun
    Geophysical and Geochemical Exploration. 2024, 48 (1): 67-76.   DOI: 10.11720/wtyht.2024.2583
    Abstract   HTML ( 0 )   PDF (5740KB) ( 6 )

    To reduce the limitations and the multiplicity of solutions of a single geophysical inversion method, this study investigated the two-dimensional joint inversion based on the marine controlled-source electromagnetic (MCSEM) method and seismic full-waveform inversion. The MCSEM method employs the data-space Occam’s algorithm, while the seismic full-waveform inversion utilizes the gradient algorithm. By incorporating a cross-gradient function for the mutual coupling of the two types of physical property parameters, this study developed a two-dimensional joint inversion method, whose accuracy was verified using three different models. As indicated by the results, compared to a single inversion method, the MCSEM-based joint inversion yielded significantly improved inversion results, predominantly in terms of the morphology characterization of anomalous bodies, as well as the reconstruction of their structure and textures and their physical property values. Therefore, the full-waveform inversion can enhance the reliability of the MCSEM inversion results.

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    Bayesian prestack seismic stochastic inversion based on the exact Zoeppritz equation
    NIU Li-Ping, HU Hua-Feng, ZHOU Dan, ZHENG Xiao-Dong, GENG Jian-Hua
    Geophysical and Geochemical Exploration. 2024, 48 (1): 77-87.   DOI: 10.11720/wtyht.2024.2572
    Abstract   HTML ( 0 )   PDF (8080KB) ( 8 )

    The prestack seismic inversion method based on the exact Zoeppritz equation is challenged by seismic data with low signal-to-noise ratios(SNRs).The Markov chain Monte Carlo(MCMC) simulation is a heuristic global optimization algorithm that can achieve effective prestack nonlinear inversion of elastic parameters.The conventional MCMC-based prestack inversion method,which characterizes the statistical properties of elastic parameters via the Gaussian distribution,has significant limitations when applied to complex lithologic reservoirs.Besides,due to the influence of the huge parameter space of subsurface models and the noise in seismic data,the MCMC search process for the posterior probability distribution of elastic parameters is very sensitive to local extrema,making it difficult to obtain stable and accurate results from MCMC-based prestack inversion.This study proposed an improved MCMC-based elastic parameter inversion method to address the challenges faced by the prestack inversion based on the exact Zoeppritz equation under the conditions of actual complex reservoirs and seismic data with low SNRs.First,the method reduced the complexity of the posterior probability distribution by transforming the parameters to be inverted into the perturbations of the model parameters using a low-frequency model (LFM) constraint.Then,the seismic forward modeling process was constrained by taking the logarithm of the likelihood function and utilizing an LFM.Finally,a multi-chain algorithm based on random subspace sampling was employed to perform global optimization for the prestack nonlinear inversion problems,thus avoiding premature convergence of the sampling process to local extrema.As indicated by the tests on the simulated data with low SNRs and the actual data,the method proposed in this study can yield more accurate and stable inversion results while providing credible and quantitative uncertainty estimates for the inversion results.

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    A key seismic processing technique for deep geothermal exploration in igneous province in southern China
    ZHENG Hao, CUI Yue, XU Lu, QI Peng
    Geophysical and Geochemical Exploration. 2024, 48 (1): 88-97.   DOI: 10.11720/wtyht.2024.1084
    Abstract   HTML ( 0 )   PDF (15267KB) ( 9 )

    Southern China's igneous province,as a significant geothermal resource area in China,possesses abundant geothermal resources owing to its favorable accumulation conditions for medium-to-high temperature geothermal resources.However,gravity-magnetic-magnetotelluric exploration methods fail to sufficiently characterize the formation structures,geothermal reservoir boundaries,and the spatial distribution of geothermal reservoirs within the concealed fault zones,posing challenges in exploring deep geothermal resources.Hence,this study delved into the key seismic processing techniques for deep geothermal exploration based on 3D seismic exploration data,establishing a targeted processing flow.First,the problem of low signal-to-noise ratios in deep layers was solved through fine-scale preprocessing for deep geothermal reservoirs,laying a solid data foundation.Then,a high-precision velocity model was built via fault-guided tomography velocity modeling.Finally,the high-precision imaging of deep geothermal reservoirs was achieved using the amplitude-preserving low-frequency reverse-time migration technology,thus improving the imaging quality and the characterization accuracy of geothermal reservoir spaces and high-steep boundaries.Field data-based testing verified the validity and practicability of the processing flow.

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    A petrophysical model of shales considering soft-mineral aspect ratios and its application
    YANG Qi-Yu, LI Jing-Ye, WU Fan, LI Wen-Jin, CUI Jin-Ming
    Geophysical and Geochemical Exploration. 2024, 48 (1): 98-104.   DOI: 10.11720/wtyht.2024.2567
    Abstract   HTML ( 0 )   PDF (3776KB) ( 4 )

    Previous petrophysical modeling of shale reservoirs often ignored the influence of pore types and soft-mineral aspect ratios on the elastic modulus.This study built a petrophysical model for transversely isotropic shales considering pore types and shapes,and soft-mineral aspect ratios.In this study,solid minerals were divided into hard and soft minerals,and soft minerals'anisotropic characteristics and shape changes were considered.According to the actual conditions of reservoirs, pores were categorized into intragranular,organic,and intergranular pores,and they were classified into stiff and soft pores based on their shapes.Finally,the input parameters were inverted using the particle swarm optimization algorithm to further calculate compressional and shear wave velocities,anisotropy parameters,and rock mechanical parameters.Combined with the actual data application,the results of this study were compared with the known results of shear wave velocity and isotropic rock mechanical calculation,suggesting that the model in this study is effective.

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    Prestack seismic inversion of fluid factors in fractured reservoirs based on the global adaptive MCMC algorithm
    ZHANG Jing, WANG Yong, ZHAO Hui-Yan, HENG De, HUANG Jun, ZHANG Xiao-Dan, WANG Wen-Wen, HE Yan-Bing
    Geophysical and Geochemical Exploration. 2024, 48 (1): 105-112.   DOI: 10.11720/wtyht.2024.2608
    Abstract   HTML ( 0 )   PDF (3624KB) ( 5 )

    Fractured reservoirs typically exhibit anisotropic characteristics,and their fractures show different seismic responses when filled with fluids.Accurate identification of fluids in fractured reservoirs plays a significant role in indicating the hydraulic fracturing process in the late hydrocarbon exploration and production stage.This study adopted the concepts of normal and tangential fracture quasi-weaknesses and constructed a new indicative factor for fluids in fractures.Combining the linear slip theory, this study derived the elastic stiffness matrix expression of the fracture-induced HTI medium.Based on the scattering theory and the Born approximation equation,this study derived the linearized P-wave incident anisotropic reflection coefficient equation for the weakly contrasted interface.Moreover,this study proposed an improved global adaptive MCMC algorithm by introducing the adaptation strategy into the MCMC algorithm.The results show that:(1)In the absence of noise,the model testing results were highly consistent with the log data,with a consistency degree of above 90%;(2)The inversion results of the actual data aligned closely with the log interpretation results,and hydrocarbons were discovered through drilling in the target interval.As indicated by the results of model testing and actual data application in a study area in Southwest China,the prestack seismic inversion of fluid factors in fractured reservoirs,yielding highly consistent results with log interpretation data,demonstrates certain reliability and applicability and thus can achieve accurate fluid identification and hydraulic fracturing indication.

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    3D correlation tomography inversion of gravity anomalies constrained by edge features and depth weighting
    AN Guo-Qiang, LU Bao-Liang, GAO Xin-Yu, ZHU Wu, LI Bo-Sen
    Geophysical and Geochemical Exploration. 2024, 48 (1): 113-124.   DOI: 10.11720/wtyht.2024.1053
    Abstract   HTML ( 0 )   PDF (8443KB) ( 3 )

    Correlation tomography is a fast tomography method using correlation coefficients to qualitatively interpret the spatial positions of geobodies. This method, featuring simple, stable, and fast calculations, can quickly and efficiently obtain the distribution of subsurface anomalies without solving large equations. However, the results of direct correlation tomography of gravity anomalies display deep divergence, excessive depth weighting function parameters, and low lateral and vertical resolution between anomalies. According to the fundamental principle of 3D correlation tomography inversion of gravity anomalies, this study introduced the balanced vertical derivative and balanced analytic signal amplitude of gravity anomalies as the edge features to horizontally weight the gravity anomaly correlation tomography, and proposed a more concise depth weighting function. As demonstrated by model tests, the lateral resolution of correlation tomography was improved under the constraint of gravity anomaly edge features, and the vertical resolution of correlation tomography was enhanced using the new depth weighting function. Finally, the method in this study was applied to the actual data of the Australian Olympic Dam polymetallic deposit, yielding consistent weighted tomography results with the actual geological data, thus proving the correctness and effectiveness of the method.

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    Forward modeling of the seismic wave field of pure qP waves in TTI media based on the pseudo-analytical method
    ZHANG Kui-Tao, LIAO Jia-Rong, GU Han-Ming, SUN Ying-Ying, CHEN Yi-Yang, WANG Kai
    Geophysical and Geochemical Exploration. 2024, 48 (1): 125-133.   DOI: 10.11720/wtyht.2024.1090
    Abstract   HTML ( 0 )   PDF (5024KB) ( 8 )

    Forward modeling and reverse-time migration imaging techniques for pure quasi-P (qP) waves in anisotropic media have aroused extensive concern in recent years.However,conventional quasi-acoustic equations are subjected to the interference from quasi-shear waves,the limitation of model parameters (εδ),propagation instability,and low calculation accuracy,thus significantly restricting their application.Hence,this study shifted the quasi-differential equation of qP waves to the space-wavenumber domain and derived the second-order pure qP wave equation of TTI media in the time domain through coordinate transformation.To improve the calculation accuracy,this study conducted the forward modeling of the seismic wave field of pure qP waves in TTI media based on the pseudo-analytical method (PAM).The numerical simulation results show that:(1)The method proposed in this study was free from the limitations of quasi-acoustic equations,the interference from quasi-shear waves,and model parameters,enabling stable propagation of the seismic wave field;(2)Compared to other methods,the PAM can effectively improve the numerical simulation accuracy;(3)The testing of simple and complex models verified the correctness and applicability of the proposed method.

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    Classification of carbonate reservoirs based on pore throat radius distributions
    ZHAO Bing
    Geophysical and Geochemical Exploration. 2024, 48 (1): 134-141.   DOI: 10.11720/wtyht.2024.2576
    Abstract   HTML ( 0 )   PDF (5937KB) ( 9 )

    Since carbonate reservoirs characterized by diverse reservoir spaces and high heterogeneity exhibit intricate internal pore structures,conventional petrophysical classification methods fail to accurately classify these reservoirs,especially the reservoirs with complex porous systems whose pore throat radii manifest a multimodal(e.g.,bimodal,and trimodal) distribution.By investigating the M Formation's carbonate reservoirs in an oil field in the Middle East,this study clarified that the internal pore structures of rocks determine the pore throat radius distribution,which in turn affects the classification of rocks.Hence,starting with the pore throat size distribution,and considering the contribution of pore components corresponding to each peak in the multimodal samples to the rock reservoir space and seepage capacity,this study proposed a pore throat radius parameter Rmax* combining pore throat sizes and their proportions to characterize the pore structures of rocks based on the cumulative permeability curve.Then,this study classified the selected 114 bimodal and 43 trimodal rock samples.Moreover,the characteristics of each type of reservoir were examined in depth by combining with physical properties,mercury injection data,thin-section observational data,and logs.The results of this study show that Rmax* can better characterize the pore structures of reservoirs and improve the reservoir classification effectiveness compared with the classification based on a single pore throat radius(R35,corresponding to mercury saturation of 35%).

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    Log-based evaluation of intralayer heterogeneity of glutenite reservoirs in the Niudong area
    ZHOU Jun, BIAN Hui-Yuan, CHEN Wen-An, ZHANG Di, LIU Guo-Liang, WANG Fei
    Geophysical and Geochemical Exploration. 2024, 48 (1): 142-150.   DOI: 10.11720/wtyht.2024.1146
    Abstract   HTML ( 0 )   PDF (8129KB) ( 3 )

    Glutenite reservoirs in the Niudong area exhibit low porosity and permeability, intricate reservoir structures, and pronounced heterogeneity, making it difficult to classify the reservoirs using conventional logs and further impairing reservoir evaluation accuracy. As indicated by the data from core porosity and permeability tests, thin-section analysis, and X-ray diffraction tests, the glutenite reservoirs in the Niudong area feature high heterogeneity and can be classified into three types based on capillary pressure morphologies. This study evaluated the intralayer heterogeneity of the reservoirs using electrical imaging logs. First, reservoir porosity spectra were derived from the electrical imaging logs. Then, the averages, variances, Lorenz coefficients, and concentration functions of the porosity spectra of different depths were calculated by analyzing these depth-varying porosity spectra. Based on the integrated probability model, the weights of evaluation indices were determined through hierarchical analysis, obtaining the composite index of reservoir heterogeneity. Accordingly, the reservoirs were classified, and the evaluation criteria for reservoir heterogeneity were established. The results of this study were consistent with the results of mercury injection experiments. The method used in this study proves effective in reservoir heterogeneity evaluation, enriching current methods for reservoir heterogeneity evaluation and providing theoretical support for fine-scale reservoir evaluation.

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    Numerical simulation of the field source for the CSAMT folded line source in a homogeneous half-space
    DUAN Yue-Quan, LIU Yun, WANG Zi-Jun, LI Yu-Shan
    Geophysical and Geochemical Exploration. 2024, 48 (1): 151-161.   DOI: 10.11720/wtyht.2024.1103
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    For field surveys using the controlled source audio magnetotelluric (CSAMT) method, it is generally believed that the CSAMT line source is a simplified electric dipole source with a minimal length. However, CSAMT line sources are all arranged in a folded line pattern in field surveys. Based on the previous research results, this study derived the numerical calculation method for the electromagnetic field excited by the folded line source according to the linear superposition principle of electromagnetic fields. Through the calculation of different folded line source models, this study analyzed the influences of the folded line source on the apparent resistivity and impedance phase curves in the homogeneous half-space. Model calculations demonstrate that the folded line source significantly influenced the near and transition zones of the apparent resistivity and impedance phase curves but had no influence on their far zones. The influences on the near and transition zones were primarily caused by the azimuths of folded line segments, and higher azimuths were associated with more significant influences on the apparent resistivity and impedance phase of survey points. In the case of very low azimuth angles, the folded line source can be approximated as a straight line source for processing, improving the work efficiency while fully considering the morphology of the emission source. This study provides theoretical support for the near-field correction of subsequent CSAMT data processing and the CSAMT numerical simulation.

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    Exploring electromagnetic noise suppression technologies for magnetotelluric sounding in high-interference ore districts
    HAO She-Feng, TIAN Shao-Bing, MEI Rong, PENG Rong-Hua, LI Zhao-Ling
    Geophysical and Geochemical Exploration. 2024, 48 (1): 162-174.   DOI: 10.11720/wtyht.2024.1140
    Abstract   HTML ( 0 )   PDF (9636KB) ( 16 )

    Magnetotelluric sounding (MT) has been extensively applied in mineral resource exploration. However, strong anthropogenic electromagnetic interference severely constrains the acquisition of high-quality original MT data. This study provided a detailed summary of the common types of electromagnetic noise sources in China and analyzed the characteristics of electromagnetic noise they produced. By comparing the methods for MT electromagnetic noise reduction at home and abroad, this study developed a rapid and effective construction and processing technology for MT data denoising in high-interference ore districts based on actual production demands. The results indicate that Robust processing, remote reference technique, and manual selection are effective and necessary in enhancing MT data quality. Besides, theoretical calculations suggest that the distance between the remote reference stations should be set at 3.56-fold skin depth or above, as verified by the MT experiments in the ore district of the Hongze salt basin, Jiangsu Province.

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    Application of supervised descent method for 2D magnetotelluric inversion and its application
    FU Xing, TAN Han-Dong, DONG Yan, WANG Mao
    Geophysical and Geochemical Exploration. 2024, 48 (1): 175-184.   DOI: 10.11720/wtyht.2024.1417
    Abstract   HTML ( 0 )   PDF (5394KB) ( 6 )

    Traditional two-dimensional inversion methods of magnetotelluric are mature, but there are still some problems, such as reliance on the initial model, reliance on regularization parameter selection, and easy to fall into local minimum. In order to solve the above problems, this paper adopts the supervised descent method to improve the effect of two-dimensional inversion of magnetotelluric. The supervised descent method is a machine learning algorithm that learns the average descending direction to predict the residual of data. Based on the theory of supervised descent method, this paper develops the two-dimensional inversion algorithm of magnetotelluric, designs the theoretical model synthesis example to verify the correctness of the algorithm, and inverts the measured data on the Tibet Plateau to test the practicability of the supervised descent method. The inversion results of the theoretical model synthesis data and the measured data show that, compared with the traditional nonlinear conjugate gradient inversion, the inversion based on the supervised descent method has the characteristics of fast convergence speed, good inversion effect, and strong anti-noise ability.

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    A prediction model of the industrial components and calorific values of coal seams based on multi-source log data
    YU Yong-Peng, ZHANG Guang-Bing, HUANG Zi-Jun, YAN Jian-Bo, WANG Jia-Wen, YANG Yan-Cheng, MAO Xing-Jun
    Geophysical and Geochemical Exploration. 2024, 48 (1): 185-193.   DOI: 10.11720/wtyht.2024.2553
    Abstract   HTML ( 0 )   PDF (4262KB) ( 7 )

    The industrial components and calorific values of coal seams serve as an important basis for the evaluation of coal quality, and the prediction of them based on log data allows for overcoming the deficiency in the experimental analysis of coal core samples. This study collected data from digital logs and coal quality analysis at different stages (e.g., detailed survey and exploration) of a coal field in Ningxia. Based on the investigation of the coal quality and log responses, as well as statistical analysis, this study developed the methods for extracting log response characteristics, establishing sample sets, and processing data and established a deep neural network-based prediction model. Then, it confirmed the validity of the prediction model by comparing the predicted results of testing data with the results from the experimental analysis.

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    Design and implementation of key technologies for real-time three-dimensional ground-penetrating radar
    YIN Da, XIN Guo-Liang, SUN Xue-Chao, ZHANG You-Yuan, ZHANG Qi-Dao
    Geophysical and Geochemical Exploration. 2024, 48 (1): 194-200.   DOI: 10.11720/wtyht.2024.1030
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    To improve the detection level of municipal roads for rapid and effective municipal road collapse warning and rapid search for municipal pipe network distribution, the 22nd Research Institute of China Electronics Technology Group Corporation designed and developed real-time three-dimensional ground-penetrating radar (3D GPR). With the real-time 3D GPR, which is based on the architecture of field programmable gate array and digital signal processor (FPGA&DSP), the institute achieved the design and implementation of several key technologies for the multi-channel high-speed acquisition system, enriching the road detection techniques and methods. The real-time 3D GPR enables high-speed acquisition of ten-channel radar data using the horizontally polarized antennae equipped with five transmitters and six receivers. The channels can be switched using high-speed switches, which operate in an interactive interpolation manner. The 3D GPR allows for up to 32 channels and detection speeds of above 60 km/h (channel interval: 2 cm). This is attributed to the switching of the antenna array using switches. The optimum antenna polarization design was verified by the comparison of experimental data from cavity- and metal-plate-based experimental sites. As a result, the optimal antenna scheme was determined. The measured results show that, compared to general LTD-2600 radar, the real-time 3D GPR boasts a higher acquisition speed and higher performance in terms of amplitude and phase, conducive to the improvement of road disaster detection technologies. Therefore, there is high market demand for the real-time 3D GPR.

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    Design and implementation of a geochemical field sampling system based on mobile GIS
    ZHOU Yi-Ning, GAO Yan-Fang, CHANG Chan, ZHANG Bi-Min
    Geophysical and Geochemical Exploration. 2024, 48 (1): 201-209.   DOI: 10.11720/wtyht.2024.2410
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    Cumbersome acquisition tools and laborious indoor data processing are bound to impair the quality and accuracy of conventional field geochemical surveys, especially in study areas with many samples and a harsh natural environment. The informatization and intelligence of field geochemical surveys are the requirements of the times and an inevitable trend for the advancement of methods and technologies. Based on the ArcGIS and Android platforms, this study developed a geochemical field sampling system, which comprises task planning, field data collecting, quality control, and other functions, to match the field geochemical survey process using mobile GIS and database technologies. This system enables the informatization and intelligence of the entire field geochemical survey process, simplifying the data collection procedure, reducing the time needed for fieldwork, and enhancing the data collection efficiency. Therefore, this system improves the quality and accuracy of field survey information, advancing the digitization of field geochemical surveys.

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    Development of a digital γ spectral logging probe
    CHEN Yuan-Qing, HUANG Qing-Bo, LIU Jin-Yao, WANG Xian-He, HUANG Liang, WU Wei-Jun
    Geophysical and Geochemical Exploration. 2024, 48 (1): 210-215.   DOI: 10.11720/wtyht.2024.2455
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    Given that it is difficult to accurately determine the uranium and thorium contents in the strata of uranium-thorium mixed deposits,this study developed a digital γ spectrum logging probe based on cerium tribromide (CeBr3) crystals.Using CeBr3 crystals with a diameter of 38 mm×38 mm,the logging probe improved the sensitivity to uranium and the detection efficiency of ore beds with low uranium and thorium contents.The logging probe operated as follows.First,the original signals from the CeBr3 detector were filtered and shaped using the C8051 single-chip microcomputer as the core processor.Then,the γ spectrum data were obtained using the energy spectrum collector.After the spectrum unfolding based on the inverse matrix is performed for the γ spectrum data,precise uranium and thorium contents in the ore beds were obtained.Finally,the γ spectrum data were transmitted to the host computer for logging through the RS-485 bus.The results show that the logging probe had high measurement accuracy in the standard uranium-thorium mixed model,with indication errors of less than 6%,stability of less than 1.5%,and repeatability of less than 1%.Moreover,the 2.62 MeV energy peak drift of thorium 208Tl did not exceed ±0.3 channels,and the relative errors of log anomalies were less than 4%.Therefore,the digital γ spectrum logging probe proposed in this study is applicable to the exploration and logging of uranium deposits.

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    Delineation of areas with high geological background values of heavy metals in soils in Yunnan Province, China based on geological big data technology
    XIAO Gao-Qiang, ZHAO Juan, CHEN Zi-Wan, SONG Xu-Feng, ZHU Neng-Gang
    Geophysical and Geochemical Exploration. 2024, 48 (1): 216-227.   DOI: 10.11720/wtyht.2024.1129
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    This study aims to systematically investigate the distribution and over-limit elements of areas with high geological background values of heavy metals in soils in Yunnan Province. GIS spatial analysis was conducted based on the heavy metal content data from a province-wide 1∶200,000 stream sediment survey and the regional geological map. The analysis results were validated using the data of heavy metals in soils in Kunming, Yuxi, Zhaotong, and other regions. A total of 61 geological units were identified, with heavy metal content in soils exceeding the screening values of agricultural land, accounting for 21.09% of the total land area of Yunnan. The cultivated land in high geological background areas covers an area of approximately 2.844 1 million hectares, accounting for 7.22% of the total land area of Yunnan. The lithologies that cause over-limit heavy metals in soils primarily comprise carbonate rocks, mafic-ultramafic volcanic rocks, intermediate mafic intrusive rocks, coal-bearing clastic rocks, and clastic rocks with mafic components. The over-limit heavy metal elements in high geological background areas are dominated by Cu, Cr, Ni, and Cd. In contrast, As manifests an over-limit risk mainly in carbonate rock formations, Pb and Zn only exhibit an over-limit risk in individual strata, and Hg almost shows no over-limit risk.

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    Cumulative effects of atmospheric dust fall on major environmental elements in soils and their evaluation: A case study of Gaomi City, Shandong Province, China
    JIANG Bing, ZHANG De-Ming, LIU Yang
    Geophysical and Geochemical Exploration. 2024, 48 (1): 228-236.   DOI: 10.11720/wtyht.2024.1136
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    This study aims to investigate the pollution distribution of major environmental elements of atmospheric dust fall in Gaomi City, Shandong Province, as well as its effects on soils in a supergene environment. Hence, this study systematically collected and tested the atmospheric dust fall from Gaomi City, obtaining the testing data of nine environmental elements, including Cu, Pb, Zn, Ni, Cr, Cd, As, Hg, and Se. Furthermore, this study calculated the annual sediment fluxes and annual increments of these elements, simulated the minimum annual sediment fluxes for them to reach limit values, and evaluated their pollution levels. The results show that the average contents of various elements in atmospheric dust fall all exceeded their soil background values, exhibiting different degrees of enrichment. In terms of annual sediment fluxes, Cu was significantly positively correlated with Pb, while Zn, Ni, Cr, Cd, As, and Hg were mostly positively correlated in pairs, and Se showed a non-significant correlation with other elements. A higher correlation suggests a higher homology. Atmospheric dust fall, serving as an input end member of major environmental elements in soils, resulted in annual growth rates of various elements in topsoils ranging from 0.03%~0.52%. Cd would be the closest to its soil limit value over a few years. As revealed by geoaccumulation index-based evaluation, Ni, As, and Cr exhibited non-pollution to slight pollution, Se primarily manifested heavy pollution, Cd and Zn displayed moderate to heavy pollution, and Hg, Cu, and Pb mainly showed slight to moderate pollution, corresponding to a pollution order of Se>Cd>Zn>Hg>Cu>Pb>Ni>As>Cr.

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    Distribution characteristics and source analysis of heavy metals from dry and wet atmospheric deposition in northern Xiushan County, Chongqing
    CAI Ke-Ke, ZHAO Zhi-Qiang, MENG Li, WANG Xiao-Meng, LIU Jian, LUO Ren-Feng
    Geophysical and Geochemical Exploration. 2024, 48 (1): 237-244.   DOI: 10.11720/wtyht.2024.2432
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    This study aims to determine the contents of heavy metals from dry and wet atmospheric deposition in northern Xiushan County for targeted environmental pollution prevention and control and safe farmland soil utilization. Based on the dry and wet atmospheric deposition samples continuously received from 18 sampling sites in northern Xiushan County from November 2019 to November 2020, this study tested the contents of seven heavy metal elements, including Cd, Cr, Cu, Ni, Pb, Zn, and Hg. Considering the topographic features, this study analyzed the distribution patterns and sources of heavy metals from dry and wet atmospheric deposition in northern Xiushan County. Moreover, this study assessed the soil pollution caused by heavy metals from dry and wet atmospheric deposition using the geoaccumulation index method. The results show that except Hg, the other six heavy metal elements exhibited significant zoning, with their high-value deposition areas distributed primarily in the flanks and eastern segment of Chuanhegai, where their contents were much higher than the national and Chongqing's averages. In contrast, their depositional fluxes in other general deposition areas were less than the national averages by 25%. The high dry and wet atmospheric deposition in the flanks of Chuanhegai was subjected to both the mining of the lead-zinc deposit in Huayuan County in the east and the special topography. The abrupt topography increased the fluxes of the seven heavy metals in the dry and wet atmospheric deposition by 49 times. Therefore, the monitoring and assessment of environmental safety in this type of landform area should be strengthened. According to the assessment results of the geoaccumulation index method, the flanks of Chuanhegai were moderately-severely to extremely polluted by Cd, slightly-moderately polluted by Pb, and slightly-moderately to severely polluted by Zn.

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    Speciation of selenium in typical meadow soils in Tumed Left Banner, Inner Mongolia, China
    LIU Jin-Bao, XU Hong-Guo, YUAN Hong-Wei, ZHANG Xiao-Feng
    Geophysical and Geochemical Exploration. 2024, 48 (1): 245-254.   DOI: 10.11720/wtyht.2024.2403
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    This study determined the speciation, available content, and physicochemical properties of selenium in soils using samples of topsoil and soil column profiles from Tabusai Township, Tumed Left Banner, Inner Mongolia, China. Accordingly, this study investigated the compositions of the speciation and available content of soil selenium, as well as their influencing factors. The results indicate that: (1) the major forms of selenium in topsoil include humic acid bound, strong organic bound, and residue forms; (2) the concentration of in the humic acid bound selenium correlates positively with the cation exchange capacity (CEC) and the concentrations of organic matter, phosphorus, and potassium; the total selenium concentration correlates positively with the concentrations of humic acid bound selenium, Fe-Mn oxide bound selenium, strong organic bound selenium, and residue selenium, all of which exhibit promotion effects; (3) the sulfur concentration correlates negatively with the concentration of water-soluble selenium, demonstrating an inhibitory effect; (4) the concentrations of selenium in various forms tend to decrease from the surface layer to the deep layer; (5) the concentration of bioavailable selenium correlates positively with the total selenium concentration, organic-bound selenium, and water-soluble selenium and correlates negatively with the sulfur concentration. The soils in the study area, featuring a high concentration of water-soluble selenium and fairly high bioavailability, are suitable for planting selenium-rich agricultural products.

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    Enrichment characteristics, source identification, and health risk assessment of soil heavy metals in typical cultivated land in the mountainous area of southern Anhui Province
    YANG Yan, LIU Bin, XIA Fei-Qiang, CHEN Ping-Feng, ZHANG Xiang
    Geophysical and Geochemical Exploration. 2024, 48 (1): 255-263.   DOI: 10.11720/wtyht.2024.2595
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    This study aims to explore the enrichment characteristics and origin of soil heavy metals in typical cultivated land in the mountainous area of southern Anhui province. With Ningguo City in southeastern Anhui Province as the research object, this study collected 1399 topsoil samples in the cultivated land for determining the concentrations of As, Cd, Hg, Pb, Cr, Ni, Cu, and Zn. Furthermore, this study conducted a health risk assessment and source identification of heavy metals using the correlation analysis, the soil environmental quality - risk control standard for soil contamination of agricultural land, the geoaccumulation index, the health risk index, and the positive matrix factorization (PMF) model. The results are as follows: (1) The average concentrations of As, Cr, Hg, Pb, Cr, Ni, Cu, and Zn were 15.8×10-6, 0.41×10-6, 0.106×10-6, 31×10-6, 67×10-6, 29×10-6, 29×10-6, and 94×10-6, respectively, which were all higher than their background values in Anhui Province, except Ni. (2) The soil heavy metals generally exhibited low pollution risks, with the heavy metal concentrations of 866 soil samples lower than their risk screening values. (3) The cultivated soil was primarily polluted by Hg, Cd, and As, as indicated by the geoaccumulation index results. (4) Both non-carcinogenic and carcinogenic risk levels in adults in the study area were within the acceptable ranges, as revealed by the health risk assessment results. (5) Four sources of heavy metals in the study area were identified based on the PMF model: industrial and agricultural emissions associated with human activities, atmospheric deposition, soil parent materials related to soil types, and the geological background source.

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    Improvement in active-source surface wave acquisition device and its application in subway construction exploration
    QIN Chang-Chun, WANG Guo-Shun, LI Jing
    Geophysical and Geochemical Exploration. 2024, 48 (1): 264-271.   DOI: 10.11720/wtyht.2024.1132
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    With the rapid development of cities and the accelerated construction of subway tunnels,there is an urgent demand for the detection of unfavorable geological bodies ahead of tunnel excavation.It is difficult for traditional electromagnetic methods to yield excellent detection results in an urban environment with high electromagnetic interference.Active-source surface wave exploration has gained increasing popularity in shallow superficial exploration and engineering geophysical prospecting in cities due to its strong anti-interference,convenient acquisition devices,and low construction cost.However,the traditional active-source reflection seismic method uses only a heavy hammer with limited excitation energy as a seismic source,and the collected signals are prone to be disturbed by urban activities.Meanwhile,the asphalt or cement pavement in urban areas is unfavorable for the placement of geophones and the excitation of seismic signals from a hammer.Given these,this study improved the geophones and seismic source devices at low costs,obtaining a more efficient and user-friendly surface wave acquisition device.As confirmed by practical engineering exploration,the improved device can collect surface-wave signals with strong energy and high signal-to-noise ratios,resulting in high-quality data,desirable inversion and imaging results,and high consistency between the geological defects and actual geological conditions.The improved acquisition device can be extensively promoted and referenced in active-source surface wave exploration in cities.

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    Application of logging-resistivity joint exploration to 3D geological modeling for environmental investigation of a certain landfill site
    SONG Tao, BAO Yi, ZHAO Song, WU Jian-Feng, XU Yuan-Shun, TU Hai-Feng
    Geophysical and Geochemical Exploration. 2024, 48 (1): 272-280.   DOI: 10.11720/wtyht.2024.1100
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    Geological exploration accuracy is a significant factor in the reliability of the comprehensive environmental survey outcomes of informal landfill sites.This study conducted drilling-high-density resistivity joint exploration of an informal landfill site using 754 high-density resistivity measurement points,12 parameter wells,and aerial surveys.Based on the binary analysis method of landfill layers and base,as well as the fuzzy mathematics theory,this study analyzed and interpreted the distribution characteristics of four layers of landfills,base,and leachate.Furthermore,this study established a 3D geological model of the landfill site and analyzed the spatial distribution of environmental geological elements.The drilling-derived verification results and the applicability evaluation demonstrate that the drilling-high-density resistivity joint exploration can be used to investigate informal landfill sites to obtain reliable geological results consistent with site characteristics.

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    Exploring geological conditions for tunnel construction in hydropower engineering using a 3D resistivity method
    HUANG Yao
    Geophysical and Geochemical Exploration. 2024, 48 (1): 281-286.   DOI: 10.11720/wtyht.2024.2602
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    To explore the geological conditions for the tunnel construction in hydropower engineering, this study built a calculation model for tunnel geological conditions using a 3D resistivity method. Through numerical simulations, this study determined the 3D resistivity distribution of the tunnel model. Then, the model was applied to the field exploration of a water resource allocation project in Yunnan, yielding satisfactory exploration results, as verified through drilling. The findings suggest that the 3D resistivity method can be effectively applied to the exploration of geological conditions for tunnel construction in hydropower engineering by accurately determining formation thicknesses, as well as the sizes, locations, and filling characteristics of karst cavities. The quantitative and qualitative data obtained from exploration in this study lay a reliable foundation for the management, informatization, and disaster prevention of tunnel construction.

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