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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

To investigate and assess the characteristics of cadmium, lead, and zinc in the soil and crops in the farmland around the old industrial area in the south of Baotou City, this study analyzed and tested the heavy metal content in soil, crop root soil, and seeds, assess the pollution according to relevant standards, and conducted the risk assessment and source analysis of heavy metals using the pollution index, the bioconcentration factor, and human health risk index. The results are as follows:Regarding the soil environmental quality, the soils in the study area are dominated by clean soils, with the polluted soils distributed primarily on both sides of the old sewage canals.The sites of over-limit root soils are also primarily distributed around the old sewage canals.Among the heavy metal morphologies, carbonate-bound, Fe-Mn-bound, and residue heavy metals account for relatively high proportions, while exchangeable heavy metals (water-soluble and ion-exchange) account for relatively low proportions. Most of the seed samples exhibited normal and low enrichment of heavy metals. Compared with other crops, sunflower seeds showed super adsorptivity of cadmium, lead, and zinc, posing significant non-carcinogenic and carcinogenic health risks to children and adults.

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

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.

Regularized joint inversion based on Gramian constraints is a hot research topic in the field of geophysical joint inversion. Given the difficulty in selecting weighted factors of the regularization and constraint items, it is necessary to introduce inequality constraints into the regularized joint inversion. To investigate the regularized joint inversion of magnetotelluric (MT) and gravity data based on Gramian constraints, this study compared the application effects of the penalty function method and the transform function method in the joint inversion and processed the measured data of a survey line in Xiangshan, Jiangxi Province. According to the results from model experiments, both methods can effectively constrain petrophysical parameters, and the penalty function method has higher flexibility but requires the artificial setting of the weighted factors. Moreover, the processing of the measured data shows that the joint inversion based on inequality and Gramian constraints is highly practical and can improve the precision of geophysical interpretation.

To evaluate the fracturing performance of two horizontal wells of well Anye-2,this study explored the layout of the fracturing monitoring network and data acquisition and processing using the fracturing monitoring technique combined with the wide field electromagnetic method.Through the qualitative and semi-quantitative difference analysis of the pre-,in-,and post-fracturing monitoring data,this study preliminarily determined the propagation direction of induced fractures and semi-quantitatively calculated the parameters such as fracture length and height.For each fracturing interval,the parameters such as fracture height and length were quantitatively determined through fine-scale inversion with depth as constraints and difference calculation.The fracturing monitoring results show that the fractures at two horizontal wells had lengths of 100~125 m and heights of 20~25 m.The fracturing production was guided by evaluating the fracturing performance of each fracturing interval.The fracturing results of the previous interval were used to guide the fracturing of the subsequent interval.Finally,the fracturing performance of all fracturing intervals was evaluated.The application results show that the wide field electromagnetic method can effectively predict the spread direction and range(e.g.,fracture length) of fracturing fluids,achieving encouraging performance.

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.

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

The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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