The marine controlled source electromagnetic (MCSEM) method is widely used in the exploration of natural gas hydrate, seabed oil and gas resources, and seabed geological structures. In the process of marine operation, the shipborne power supply unit transmits high-voltage and high-power electric power to a marine controlled source electromagnetic transmitter on the seabed through deep towing cables, during which it is necessary to carry out the automatic and real-time measurement and monitoring of the insulation resistance in the high-voltage power supply circuit to ensure the safe transmission of electric energy and timely deal with the abnormal power supply. This study collected the leakage current between the high-pressure end and the ground using high-voltage broadband couplers, insulation detection modules, remote data transmission units, and PC monitoring software. Meanwhile, this study amplified the leakage current using an analog amplifier and then calculated the insulation resistance by measuring voltage, thus achieving the automatic measurement and monitoring of the insulation resistance between the high voltage circuit and the ground. As verified by offshore tests, the automatic online insulation monitoring technology can meet the requirements of the MCSEM system and achieve the ideal online evaluation of the insulation performance of the system, thus providing a useful reference for the research and development of similar functions of marine instruments.

Ocean bottom electromagnetic receivers (OBEMs) are mainly used for high-precision observation and measurement of magnetotelluric signals and controlled-source electromagnetic signals at the sea bottom. To overcome the shortcomings of large volume, high power consumption, and high cost of the existing OBEMs (OBEM-Ⅲ type), this study conducted technical research regarding miniaturization, low power consumption, and low cost. As a result, the overall power consumption of the existing OBEMs (OBEM-Ⅲ type) has been reduced from 1 600 mW to 500 mW or less (by equipment of inductive magnetic sensors) due to the development of a low-power control unit and preamplifier, the installation of low-power fluxgate sensors, and adoption of advanced power management technology. Traditional acoustic releasers are expensive and bulky and require more suitable buoyant materials. By integrating the underwater acoustic communication module and being equipped with the external erosion wearing release device, the MicrOBEMs make release and recovery possible using only a 17-inch glass sphere, thus greatly reducing the volume and hardware cost of the instrument and improving the integration and operation efficiency of devices. Compared to the OBEM-Ⅲ type, the volume, power consumption, and cost of the newly developed MicrOBEMs are reduced by 3/4, 2/3, and 1/2, respectively. A deep-water geomagnetic test was conducted in March 2021 in the southern South China Sea, preliminarily verifying the geomagnetic measurement function of the MicrOBEMs and reflecting that the MicrOBEMs have the advantages of small size, low power consumption, and low cost.

An ocean bottom electromagnetic receiver (OBEM) is primarily designed to measure the submarine electromagnetic signal. In order to verify the function of the instrument and improve the accuracy of result, the instrument is self-checked by a built-in channel calibration before OBEM enters the water. OBME-Ⅲ needs to export the calibration file generated by channel calibration from the instrument, and then use the Matlab program on the PC side to perform calibration calculation, which has shortcomings such as complex offshore operations and low calculation efficiency. In order to solve these problems, the author developed a calibration calculation program based on the ARM-Linux platform. By entering the relevant commands, the channel calibration calculation can be realized locally in OBEM-Ⅲ, reducing the trouble of exporting data for calculation on multiple platforms. The mixed-base fast Fourier transform calculation method adopted reduces the calculation time from 90 s to 11 s while ensuring the calculation accuracy, which greatly improves the calculation speed and improves the efficiency of the instrument's offshore operations. In the magnetotelluric scientific research mission carried out in the southwest of the South China Sea from July to August 2020, the program performed well and successfully obtained high-quality submarine magnetotelluric sounding data.

In the process of hydraulic fracturing for shale gas extraction, the injection, flowback, retention, and absorption of fracturing fluids will cause changes in electric fields in the case of the excitation by the electromagnetic field from an artificial source in a far area or the excitation by the geoelectric field. The time-dependent change in the information on fracturing can be reflected by monitoring the change in weak electric fields above the hydraulic fracturing area. To meet the needs of the real-time monitoring of the fracturing field, this study focuses on the preliminary study of the monitoring technology based on the nodal acquisition devices of distributed weak electric fields. The monitoring system only collects two horizontally orthogonal electric field signals, monitors the real-time information on the electric field within a certain range, and transmits the preliminarily processed data back to the data center in a wireless way. Test results show that the monitoring system has stable performance, a standby time of more than 10 days, and high sealing performance, and is applicable to complex field environments. Therefore, this monitoring system can provide important technical support for obtaining images of fracturing fluid migration in the future.

The transparency of the fully mechanized mining face achieved using advanced exploration equipment and technology can make the information on coal seams more comprehensive and accurate and can lay a solid foundation for the intelligent production of the fully mechanized mining face. DC resistivity method is a common method for geophysical exploration. Owing to the high stability, great anti-interference performance, and sensitive responses to low- and high-resistance bodies, the DC resistivity method is one of the key means of achieving the transparency of the mining face. To explore the application effects of the method in the transparency of the mining face, this study used different working methods to conduct three-dimensional forward and inverse modeling of the response characteristics for solving proven water-bearing structures of the mining face and frontal advanced detection of roadways. The results show that the distribution laws of 3D DC inversion data obtained by corresponding working methods were basically consistent with those of the initial model, and the DC resistivity method can well distinguish between high- and low-resistivity bodies. Therefore, this study can guide the application of the DC resistivity method in the transparency of mining face in practical engineering.

The requirements for the design and manufacturing of nodal devices are relatively low. The most basic modules of a nodal device include controllers, acquisition circuits, GNSS timing circuits, geophones, batteries, interfaces, downloading cabinets, data downloading & compositing servers, optional testing circuits, signal generators, and QC manuals. As mature supply chains are available for all the above modules, manufacturers pay more attention to organically integrating the above modules into products that can stably work and meet the needs for the signal acquisition of seismic exploration. However, the absence or neglect of some details in some products on the market due to design or cost considerations will cause difficulties in the field application of seismic data acquisition. The data acquisition quality of the nodal devices relies entirely on the independent performance and stability of each nodal device, which further rely entirely on the manufacturers’ understanding of signal acquisition for seismic exploration and data acquisition operations and the resultant design. The requirements of oil and gas exploration and development in new situations must be considered in the design of nodal devices. The focus of oil and gas exploration and development is constantly shifting to deep and ultra-deep parts with more complex ground surfaces, and thus high precision and resolution are required for signal pickup. As a result, nodal devices should be more capable of acquiring weak signals and broadband signals, which cannot be compromised in the design. This paper elaborates on the fundamental details of signal acquisition, test functions, circuit design, storage, batteries, profile, auxiliary systems, quality control, and auxiliary devices in order to avoid problems such as signal distortion, coupling, and EMC.

The computational efficiency of the forward modeling for gravity and gravity gradient anomalies determines the feasibility of inverse modeling. It also forms the basis for the efficient building of sufficient and diverse deep learning sample data. Inspired by the application of moving-footprint—a fast forward modeling method in the aerospace electromagnetic field and based on the fast space-domain forward modeling of geometric lattice functions of grid points, the authors proposed a computation method for the forward modeling of gravity and gravity gradient anomalies by applying “moving-footprint”, aiming to further improve the speed of the forward calculation for gravity and gravity gradient anomalies. Specifically, this method selects the subspace in a certain effective range directly below an observation point in the underground half-space. The observation point anomaly approximates the total anomalies of the cuboid units in the corresponding subspace while ignoring the anomalies produced by the cuboid units outside the subspace. When the observation point moves, the corresponding subspace moves accordingly. Therefore, the large-scale underground half-space cuboid model can be decomposed into the subspace corresponding to each calculation point for the forward calculation. As shown by the results of a model test, when 32×32×15 subspace was selected in the underground half-space of a 256×256×15 rectangular parallelepiped model for calculation, the relative average error of gravity anomalies and partial gradient anomalies was less than 10% and the calculation speed was increased by 19 times. Moreover, the calculation time of 1024×1024×15 rectangular parallelepiped model is approximately 32 minutes. Compared with the existing algorithms with a bottleneck in the ultra-conventional calculations, the method proposed in this study has significant advantages regarding computation.

Based on the landscape characteristics of the arid Gobi desert in the Beishan area, Gansu Province, this study carried out a 1:50,000 stream sediment survey in the Sanbaidun area and delineated 10 integrated anomalies. Then, the As-3 anomaly was preferentially selected for detail inspection by taking lithic fragments with grain sizes of 2~20 mm at multiple locations within 1/3 line spacing using a grid density of 100 m × 20 m. As a result, three integrated anomalies of lithic fragments were delineated and their characteristics were investigated. The dominant ore-forming elements were identified as As and Au, and two integrated anomalies were preferentially selected for detailed inspection using methods such as geochemical profile and trenching. Consequently, four Au orebodies, two As orebodies, one Au mineralized body, and one As mineralized body were found. The prospecting results indicate that the geochemical survey of lithic fragments can achieve ideal prospecting effects in the arid Gobi desert landscape area of Beishan and that 1:10,000 surveys of lithic fragments can be used to verify the anomalies of 1:50,000 stream sediment surveys.

In recent years, prospecting in coverage areas has become an important topic in China due to the strong demand for energy and mineral resources, and there is an urgent need for new targeted methods and technologies of prospecting. This study put forward a technology system for the collaborative and rapid prospecting of copper-nickel deposits in coverage areas that combines airborne-ground-borehole prospecting methods and technologies. Meanwhile, this study established the framework and description of the collaborative, rapid, and effective exploration technology system. Taking the terrain and geology of coverage areas, as well as the distribution characteristics of deep mineral resources in the area as preconditions, this technology system mainly uses the methods of aero geophysics combined with ground and borehole geophysical exploration and focuses on big data fusion, weak information extraction, and geophysical-geological modeling methods. Meanwhile, it takes geological structure and metallogenic theory as guidance. This technical system has been verified in the exploration of the concealed magmatic copper-nickel deposit in the Qixin area, Ruoqiang County, Xinjiang, achieving positive results.

The Pengshui area,located in the Wuling fold belt at the southeast margin of Sichuan Basin,has a typical karst mountain landform and very complex near-surface structures.Such a geological setting leads to a poor seismic acquisition effect and a low signal to noise ratio (SNR),which seriously affects the oil and gas exploration in this area.This study carried out the excitation tests and research,such as charge type,excitation mode,excitation well depth,and excitation dose,as well as receiving tests on interference wave investigation and geophone types and their combination means on the ground surface in the mountainous areas with exposed carbonate rocks.Furthermore,this study selected a set of excitation and receiving parameters with a strong economy and maneuverability and established the technology used to determine the optimal excitation point location for complex mountainous terrain.Compared with the previous data,this study achieved significantly improved energy,SNR,and first-grade product rate of the newly acquired single-shot records.Moreover,the new data processing profiles obtained in this study show rich information,clear reflection characteristics,and high SNR and display a distinct seismic tectonic pattern of carbonate rock area.

The "Dongfang No.1" rock mass in the Maping area, Zhenyuan County, Guizhou is the parent rock of a primary diamond-bearing deposit discovered in China for the first time. Studies have shown that the rock mass found in the Maping area is of the shallow facies of the kimberlite magmatic system, and large-scale concealed rock pipes or buckets may exist in the deep part. To reveal the spatial distribution of deep diamond-bearing concealed rock pipes or buckets in the Maping area, this study carried out the audio-magnetotelluric (AMT) data acquisition in the area using a high grid density of 80 m × 40 m. Then it simulated the pure terrain response in the study area using the 3D forward modeling and deducted the pure terrain response from the measured data. The obtained qualitative interpretation results restored the distribution morphology of AMT impedance phase invariants to some extent that was distorted by static effects. Afterward, this study performed the 3D inversion of the data using the AR-QN quasi-Newtonian inversion method. Based on the lithologic statistical results of the study area, the resistivity variation intervals of the underground units were set during the inversion, obtaining a reliable 3D electrical structure. Finally, this study carried out a fine interpretation of the geoelectric model of this area based on geological data such as rock tubes found on the surface and multiple dikes revealed by boreholes, outlining the morphology of concealed rock pipes or buckets. This study will provide a geophysical basis for the future prospecting and prediction of primary diamond deposits in this area.

This study analyses the geochemical characteristics, genesis, and properties of hydrocarbon components using data of surface soil samples collected from the permafrost regions in the Qiangtang Basin, the Qilian Mountains, and the Mohe Basin. The results revealed that the hydrocarbon gases in the superficial soils in the permafrost regions mainly comprise methane, as well as a small amount of ethane, ethylene, propane, butane, and pentane. The hydrocarbon gases in the Qiangtang and Mohe basins are mainly of pyrolytic genesis and their types include soil-formed gas and the mixed gas of soil-formed gas and coalbed methane. In contrast, hydrocarbon gases in the superficial soil in the permafrost zone in the Qilian Mountains are of pyrolytic and biogenic genesis and their types include soil-formed gas, coalbed methane, and biogenetic gas. The study provides a basis for exploring oil and gas resources such as natural gas hydrates in the continental permafrost regions in China.

In recent years, China has been strengthening the exploration of rare earth resources in order to secure the status of China as a large rare earth resource country. Geochemical exploration is an important means of mineral exploration, This paper summarizes the geochemical exploration of rare earth, finds out the existing problems and puts forward solutions. The carbonatite related rare earth anomalies are characterized by low contrast and small scale, the reasons are: ① the industrial grade of rare earth ore is enriched to a low degree relative to the abundance of the earth's crust, which is easily diluted by non-mineral anomalies caused by granite, etc.; ②the size of rare earth ore-forming indicator minerals are small and difficult to sort by traditional method, thus the epigenetic migration and enrichment pattern is not well understood, and it is difficult to develop a targeted sampling method. The automatic mineral analysis system based on scanning electron microscopy and energy spectrum can realize the quantitative statistics of chemical composition and morphological parameters of rare earth minerals at the micron level, which provides the basis for the study of epigenetic migration pattern of rare earth minerals. In recent years, in the field of geochemical exploration, previous research on the variation pattern of micro scale grain mineral content in the ore body-stream sediment system using the automatic mineral analysis system has shown the good application prospect of this method. In the future, the automatic mineral analysis system can be used to carry out:①research on the change of rare earth mineral size during weathering process; ②research on the migration and enrichment of rare earth minerals in the ore body-aqueous sediment system. Thus, the distribution characteristics and migration and enrichment rules of rare earth indicative minerals in ore-body, soil-stream sediment system are clarified, providing theoretical support for geochemical exploration of rare earth.

Owing to the small impedance difference with surrounding rock and complex gas-water relationships,it is difficult to identify high-quality reservoirs in block S in the Sulige gas field through the post-stack P-wave impedance inversion.According to the petrophysical analysis of the study area,the pre-stack parameter v_p/v_s ratio can be used to effectively identify lithology and gas-bearing properties.This study firstly determined the seismic response characteristics of the reservoirs through forward modeling.Secondly,it conducted petrophysical modeling and the prediction of shear-wave velocities using the Xu-White model suitable for sandstone and mudstone and accordingly established a petrophysical model.Thirdly,the CRP gathers were optimized using the processing methods such as linear denoising and residual amplitude compensation.Finally,the thickness and gas-bearing properties of the reservoirs in block S in the Sulige gas field were quantitatively predicted through simultaneous pre-stack inversion.The results are as follows.(1)The top boundary of the reservoirs in the study area shows the seismic reflection characterized by strong trough reflection,while the bottom boundary of the reservoirs shows unapparent seismic reflection;(2)The v_p/v_s ratio of less than 1.68 can be used to effectively determine sandstone.This combined with the P-wave impedance of less than 12200 g·cm^-3 ·m·s^-1 can be used to predict the reservoirs in the study area. Moreover, a v_p/v_s of less than 1.57 can be used to identify the gas-bearing properties;(3)Reservoir distribution and the predicted gas-bearing range have similar trends but differ locally.The development degree of reservoirs is not necessarily positively correlated with the gas content.The method proposed in this paper is expected to provide strong technical support for delineating the favorable gas-bearing reservoir area and deploying well locations in the future.

The Laowan area in Henan Province is an important gold minerogenetic area in the Tongbai-Dabie noble nonferrous metal metallogenic belt. Based on the comprehensive analysis of the metallogenic factors of the area, the authors extracted and established nine predictive variables, i.e., strata, ductile shear zones, brittle fault zones, magmatic rocks, gold-related alteration zones, and single-element anomalies of gold, arsenic, antimony, and sliver in stream sediments. Then, the authors predicted metallogenic prospect areas of gold in this area using the weight of evidence model and the MRAS software. Grid cells with a size of 0.10 km×0.10 km were used for prediction, and they were divided into classes A, B, and C in terms of prospecting prediction through the prior probability calculation, weight statistics, independence tests, and posterior probability calculation of each prediction variable. Based on the distribution characteristics of various classes of prediction grid cells and the geological characteristics of gold deposits in the study area, this study delineated four first- and four second-order prospecting target areas. According to comprehensive analysis, most of the known gold deposits or gold ore occurrences fall into the prediction blocks of classes A and B and the prediction blocks of class C lie around the prediction blocks of classes A or B. This analytical result is consistent with the gradual changes of the metallogenic belt from the center to the edges. Gold deposits or ore occurrences have been discovered in all the delineated first-order prospecting target areas, and the posterior probabilities have a high average. Therefore, first-order prospecting target areas have great gold prospecting potential.

Gold deposits of the quartz-vein-type are the product of post-magmatic hydrothermal and metamorphic hydrothermal processes and are generally controlled by major and secondary faults. Their metallogenic materials originate from the surrounding rocks. The assemblages and contents of metal sulfides in ores of various deposits differ with geological setting and ore-forming and controlling conditions. Moreover, sulfide-gold-quartz ores predominate. The gold deposits of this type have distinct comprehensive geophysical prospecting features, and various physical prospecting methods yield a high degree of regularity. Taking a gold deposit of the quartz-vein-type in northwest China as an example, this study carried out comprehensive physical prospecting of deposits of this type, performed a quantitative prediction based on forward modeling, and conducted interpretation and analysis by combining theories related to geophysical prospecting.

The main part of the Nanling Basin in Anhui Province is a red Mesozoic continental basin, under which the distribution of marine strata is still undetermined and the potential of shale gas resources is unidentified. Based on the physical property characteristics that the Permian organic-rich shale reservoirs around the study area contain pyrite, this study carried out a geological survey of shale gas using the complex resistivity method. Specifically, this study designed an observation system suitable for the different geological characteristics inside and outside the basin, conducted fitting and inversion using Cole-Brown and Cole-Cole models, and plotted maps of near-field parameters electromagnetic resistivity and apparent charging rate. The results show that: (1) The Permian organic-rich shale contains high carbonaceous content and rich pyrite particles and has distinct characteristics of low resistivity and high polarizabi-lity. Therefore, it can be effectively distinguished from its surrounding rocks, which is favorable for the shale gas exploration using the complex resistivity method; (2) Polarizability is an effective parameter that can be used to identify deep organic-rich shale strata and even shale gas reservoirs; (3) Drilling tests were carried out based on the exploration results obtained using the complex resistivity method, successfully discovering the Triassic carbonate strata and predicting that below the red basin in the Nanling Basin is the favorable area of Permian shale gas reservoirs. This study demonstrates that the complex resistivity method can detect pyrite-bearing shale strata with a depth of greater than 2,000 m and a cumulative thickness of about 200 m in the Nanling Basin and is the only method that can directly indicate shale gas reservoirs in electromagnetic exploration. Therefore, the complex resistivity method can be applied to the geophysical prospecting of the marine shale gas in the Nanling Basin with complex geological conditions and even Southern China. The results of this exploration also provide a basis for the further exploration of the marine shale gas in the Nanling Basin.

As an ultra-deep fault-karst reservoir located in the Tarim Basin of Xinjiang,the Shunbei oil and gas field prosses the characteristics of the large burial depth and fault development in the target formations.This oil and gas field is difficult to explore due to the low signal-to-noise ratio and low resolution of seismic signal data since seismic signals are absorbed by the desert surface and thereby suffer severe attenuation.The microbial prospecting developing based on the theory of vertical hydrocarbon microseepage can detect the oil and gas-bearing properties of fault zones.This technology,combined with geophysical exploration,can improve the success rate of the prediction of the oil and gas-bearing properties of fault zones.This experimental study of microbial prospecting in fault zone No.5 in the Shunbei oil and gas field shows that the abundance anomalies of hydrocarbon-consuming microorganisms show good near-surface response to fault-karst reservoirs.Compared to areas with vegetation,hydrocarbon-consuming microorganisms (including methane- and butane-oxidizing bacteria) as indicators of microbial prospecting in desert areas are characterized by low measured values and slight fluctuation.However,hydrocarbon-consuming microorganisms can better reflect the near-surface information induced by the vertical microseepage of deep-buried oil and gas since they are less disturbed by other microbial communities due to the special ecological conditions in desert areas.According to the application results,the high-amplitude anomalies of both methane- and butane-oxidizing bacteria are primarily distributed in the vicinity of fault zone No.5,and favorable anomalies also occur in the vicinity of fault zone No.1 in the Shunbei oil and gas field.Furthermore,the strike of these anomalies roughly coincides with that of fault zones,indicating that the microbial anomaly zones correlate strongly with fault-karst reservoirs.Therefore,the microbial prospecting for hydrocarbons has great application prospects in the exploration of the fault-karst reservoirs.

Owing to geographical factors and historical reasons,the urban underground square cavities show increasing number,density,and chaotic state,leading to unclear interpretation results of the ground penetrating radar(GPR) images of these underground square cavities.This study divided the left side of an image(with the symmetry axis as a boundary) of square cavities obtained from the GPR scanning close to the ground into three stages based on the whole process of ground penetrating radar scanning detection.Then,this study established the relationships between horizontal distance and echo delay of each stage.Furthermore,it systematically analyzed the changes in the GPR images of square cavities with different burial depths and sizes.Finally,this study obtained the scientific explanation of geological radar imaging mechanisms of underground square cavities based on GPR detection examples.It is concluded that the three stages of the left side of a GPR scanning image of the underground square cavities in uniform media include a continuous straight line with a constant slope,a monotonically decreasing continuous concave curve,and a continuous horizontal straight line unrelated to the horizontal distance.With an increase in the burial depth and cavity size,the curve tends to be gentle and its open radian tends to increase.

Plane beam signals form when multiple excitation sources simultaneously emit pulses with the same center frequency (multiple-source concurrency),thus enhancing the quality of data records.This paper compares and analyzes the electromagnetic wave absorption effects of unsplit recursive convolutional perfectly matched layer (PML) as the absorbing boundary condition and Mur second-order absorbing boundary condition under multi-source concurrency through numerical simulation.According to study results,the traditional Mur second-order absorbing boundary condition did not perform well in absorbing electromagnetic waves under the conditions of multi-source concurrency and multi-angle grazing,and it will cause waveform distortion and spurious reflections in the case of large offsets.For the unsplit recursive convolutional perfectly matched layer as the absorbing boundary condition under multi-source concurrency,coordinate scale factors were introduced into the finite-difference time-domain (FDTD) algorithm.Then,the PML equation for coordinate stretching was transformed from frequency domain into time domain through the inverse Fourier transform.Finally,the electric and magnetic field values were solved using the recursive convolution method in the discrete state,thus avoiding the complicated calculation involved in directly determining the numerical solution of convolution.This allows less memory space and high calculation efficiency while ensuring accuracy.Therefore,the unsplit recursive convolutional perfectly matched layer method improves the electromagnetic wave absorption effect at the positions where the grid terminate without inducing wave-field splitting.

Deep seismic reflection is one of the most effective means of studying the deep geological structure of the Earth.However,the energy of seismic waves exponentially decreases due to the filtering by the Earth,resulting in weak energy of effective deep seismic reflection signals.In this case,deep seismic reflection data are liable to be seriously disturbed by background noise,and thus it is difficult to obtain accurate images of deep geological structures.According to the study on the differences in the distribution of effective signals and random noise of deep seismic reflection data on different scales in the Shearlet domain,seismic signals on different scales are affected by random noise to different extents.Furthermore,with the signal-to-noise ratio,the L2 norm of Shearlet coefficients,and the residual errors of random noise in deep seismic reflection data as the parameters for threshold estimation,this study developed a random noise suppression method that is adaptive to different scales to minimize the effects of random noise.Theoretical model data and actual tests of deep seismic reflection data verified that this method can effectively eliminate the disturbance of random noise,improve the overall signal-to-noise ratio of seismic sections,and realize the accurate imaging of weak deep seismic reflection signals.

To overcome the shortcomings of traditional nonpolarizing electrodes, such as the poor stability of potential difference, high low-frequency noise, short life, and requiring regular maintenance, the authors researched and developed maintenance-free ultra-low noise Pb-PbCl₂ nonpolarizing electrodes after over a decade of development and constant tests. Lab test results show that the new nonpolarizing electrodes have a potential difference drift within one month of less than ±0.06 mV and a temperature coefficient of less than 20 μV/℃, which are 5% and less than one-fifth of those of the PMS9000 electrodes exported from France, respectively; under the ideal condition of the distance between two adjacent electrodes of 100 m, the signal-to-noise ratios relative to the natural induced electric field are 40dB@10³s, 20dB@10⁴s, and 10dB@10⁵s. The field comparative tests show that the newly developed solid nonpolarizing electrodes can significantly improve the acquisition accuracy of geoelectric field signals and the data quality of dead and low magnetotelluric frequency bands.

This study aims to eliminate the electromagnetic coupling interference in IP sounding. Based on the theory that frequency-and time-domain data can be mutually converted, this study achieved rapid decoupling while retaining the IP information to the greatest extent by using decoupling methods including static IP inversion, the full waveform IP inversion of Cole-Cole parameters, and delay inversion. This study investigated a gold deposit in Yinan County, Shandong Province and conducted the inversion of time-domain IP sounding data before and after decoupling. The results are as follows. The electromagnetic coupling effect of symmetrical quadrupole devices and unconventional electrode array increases with an increase in the distance between adjacent electrodes, and its influencing depth is mostly less than 150 m in the inversion results of time-domain IP sounding; the electromagnetic coupling interference produced by the unconventional electrode array that adopts a collinear device of dislocation multipoles (tripoles, quadrupoles, and dipoles) is apparently greater than that of symmetrical quadrupole devices and monopole-dipole devices; noncollinear monopole-dipole devices generate slight electromagnetic coupling effect in the process of time-domain IP sounding.

Full waveform inversion (FWI) is one of the most accurate velocity inversion tools.It can be used to obtain high-precision subsurface structures through iterative inversion and provide a more accurate velocity field for prestack imaging technology,thus satisfying the increasingly complex demand for petroleum exploration and development.However,FWI requires accurately estimated source wavelets,which are very difficult to extract from the seismic data collected in the field.Furthermore,in the inversion process,there is a strong nonlinear relationship between model parameters and observed data,which is liable to induce cycle skipping.To overcome the cycle skipping and the difficulty in extracting seismic wavelets in the inversion process of medium-low wavenumber,this paper developed a multi-scale waveform inversion method using combined source encoding.Specifically,the wavelets and seismic data were combined by applying time-shift stacking,and gradients can be determined through only one calculation of reverse time migration.According to the calculation results using a model,the FWI method using combined source encoding can be used to achieve multi-scale inversion and obtain more stable inversion results.Meanwhile,relatively accurate inversion results can be obtained by combining this method with a source-independent method.

The distortion correction of magnetotelluric sounding curves is critical to magnetotelluric exploration. Based on the comparison between the resistivity logging curves of basin D and the basin's inversed sounding curves before and after being corrected through magnetotelluric sounding translation, this study constructed a transformation function and calibrated magnetotelluric sounding curves using logging curves. The magnetotelluric inversion results improved using the calibration technology proposed in this study are highly consistent with the verification boreholes. Finally, this study effectively revealed the structural characteristics of basin D by combining drilling, seismic, gravitational, and magnetic data.

This study developed a workflow of Rayleigh-wave dispersion inversion using the Python programming language, and the detail is as follows.First,carry out the forward modeling of the dispersion curves on a horizontal layered model using the pysurf96 software package.Second,create an objective function used to describe the fitting degree of the dispersion curves.Third,complete the dispersion curve inversion using the heuristic algorithm in the scikit-opt software package.The problems encountered in the function call in the workflow were proposed and solved.The results show that the Python-based dispersion curve inversion of Rayleigh wave in multilayered media is reliable and offers a certain computational efficiency.In this way,this study built a Python-based inversion platform of underground layered structures using the wave dispersion,thus providing a method for other researchers to do inversion using open-source software.Finally,this study carried out the inversion of the crust and upper mantle structures using the dispersion curves extracted from the study of Yi-bo Peng on the noise in the Hailar Basin,achieving ideal results.

This study investigates the geochemical characteristics and genesis of selenium (Se) in the soil in Xuancheng City, Anhui Province using the samples of surface and deep soil collected through a 1:250 000 multi-purpose geochemical survey. The results are as follows. The Se content in the surface soil in Xuancheng City is (0.12~8.80)×10^-6, with an average of 0.44×10^-6. Se-sufficient and Se-rich soils are widely distributed in the study area, accounting for 61.90% and 35.63%, respectively. Se-rich soils are mainly distributed in the Ningdun Town in Ningguo City-Fulingtown in Jixi County, Yangong Town in Jingxian County-Baikeshu area in Xuanzhou District, Chencun Village-Chikeng Mountain in Jingxian County, and Xinhang Town in Guangde County. The Se content in the soil is mainly controlled by parent rocks and soil-forming parent materials. Se content is high in soils in the distribution areas of carbonaceous shale and carbonaceous siliceous mudstones, such as the SinianLantian Formation and Cambrian Hetang and Yangliugang formations, as well as Permian, Triassic, Carboniferous, Cambrian, and Ordovician limestone distribution area. In contrast, Se content is low in Yanshanian intermediate-acid intrusive rocks and Quaternary distribution area. In terms of soil-forming parent materials, Se content is higher in soils with parent materials of carbonate, light clastic rocks, and epimetamorphic rocks than that in soils with parent materials of Late Pleistocene loess, alluvium, and acid rocks. In terms of soil type, Se content is higher in limestone soil, skeleton soil, stonysoil, and red soil than paddy soil, yellow-cinnamon soil, and fluvo-aquic soil. Se content in soil is correlated closely with physicochemical indices, such as V, Cd, Ba, Ag, Zn, Mo, U, Ni, Sb, P, S, and organic matter. Meanwhile, total Se content is correlated closely with bioavailable Se content. Furthermore, all the 47 rice samples collected in the study area are rich in selenium, with a selenium accumulation rate of 100%. However, tea and maize are not rich in Se, and some types of vegetables are rich in Se. Therefore, different types of crops have different absorption capacities of Se in the soil.

Anning City, Yunnan Province, China is an important area of economic development and ecological civilization construction in central Yunnan on the upper reaches of the Yangtze River. This study investigated the contents and enrichment degrees of elements including heavy metals in the surface soil samples that were systematically collected in the Anning area from 2018 to 2020. Then, this study assessed the ecological risks of heavy metals in the soil using the geoaccumulation index and the assessment indices of potential ecological risks and analyzed the sources of heavy metals using the methods of the Pearson correlation and principal component analysis. The results show that heavy metals Cr, Zn, As, Cd, Pb, Hg, and radioactive element U in the soil in the study area have significantly higher contents than corresponding background values of soil in Yunnan Province and show high-degree variation and uneven spatial distribution. Moreover, Cr has the highest accumulation degree of geological anomalies, elements As, Cd, and Hg have high potential ecological risks, and ecological risks are mainly concentrated in the phosphate mining area and the vicinity of steel plants and chemical plants in the Tanglangchuan basin. In terms of sources, Cr, Ni, and Cu may mainly originate from soil parent materials; areas with high Cd, Pb, Zn, and As contents are significantly affected by human activities, and Hg may have a composite pollution source. These results will provide a scientific basis for understanding the sources of heavy metals in soil in Anning City and for the management and protection of local land resources.

The acid-base properties and Se background values of the soil in Qinghai Province were obtained by analyzing the pH and Se content of the soil based on the data derived from the geochemical survey of land quality conducted in Qinghai Province. The Se enrichment models of root soil and crops such as wheat, rapeseed, pea, garlic, and forage were established accordingly. The recommended values of Se-rich soil in Qinghai were calculated by combining the recommended in take of Se in the population with the standard value of Se content in Se-rich agricultural and livestock products in Qinghai Province. It is recommended that the lower limit of Se-rich soil for alkaline soil and neutral and acidic soil in Qinghai Province should be 0.23×10^-6 and 0.25×10^-6, respectively. This study is greatly significant for the formulation of the local standards for Se-rich soil in Qinghai Province and for guiding the development of the selenium industry.

Since a large amount of domestic and industrial wastewater containing heavy metals has been discharged into the Haihe River Basin, many heavy metals enter the water environment and accumulate in the sediments. Traditional ecological risk assessment methods ignore the speciation and distribution of heavy metals, leading to the low reliability of ecological risk assessment. This study investigated the plain section of the Haihe River Basin and researched the speciation and distribution of heavy metals in the sediments in the Haihe River Basin and carried out the ecological risk assessment. Sediment samples were collected at the collection points deployed in the Haihe River Basin. Afterward, the samples were processed using mixed acids at the laboratory. Then, the contents of heavy metals in the samples were determined using atomic absorption spectrometry, and the speciation and distribution of heavy metals in the sediments were analyzed. For the ecological risk assessment, abundance calculation was adopted to improve the ecological risk assessment indices and design the ecological risk assessment standard of heavy metals. The experimental results show that the obtained evaluation of the sampling points and various heavy metals were closer to the actual situation, has higher reliability, and displayed better evaluation performance compared to results obtained using traditional assessment methods.