利用V8多功能电法仪开展磁电法勘探方法技术研究

在浅覆盖区开展电法勘探时,由于存在供电电流易被低阻覆盖层吸收和深部电磁信号又被屏蔽减弱,薄层金属矿体难以识别的难题。基于突破高阻或低阻覆盖层屏蔽,获得有效矿致信号的思路,我们开展了磁电勘探法实验研究。采用V8系统与其他仪器设备组合,完成发射与接收工作。分别测量不同频率的交变电磁场对矿体激励所产生的磁场和电位,并计算磁频散率和电频散率。提取局部异常信息,对比研究识别矿体。在安徽省某金矿区薄层矿体识别取得了一定的效果,拓展了V8系统地质找矿中应用范围。

基于数字功放的任意波形电(磁)法信号发送技术研究

针对桥式逆变发送机系统只能发送跳变的矩形波信号且接收回路易受电磁耦合尖峰干扰以及谐波污染等问题,设计了基于数字功放的任意波形电(磁)法信号发送方案,通过对低通滤波后的矩形波放大输出,显著降低发送机输出矩形波边沿变化率,压制人工源信号中高次谐波电流在接收机输入回路中引起的电磁耦合干扰,或直接对正弦波或组合正弦波信号放大输出以压制电磁耦合干扰、消除谐波污染.本文分析了电磁耦合产生机理,模拟计算了发送低通滤波处理后的矩形波对接收回路耦合尖峰的压制效果,搭建了基于数字功放的人工源电(磁)法信号发送装置,对包括低通滤波后的组合矩形波信号在内的任意波形信号进行放大输出测试,并以双频信号为例进行了感应耦合压制实验,取得了良好的实验效果,具有较重要的理论和实际应用价值.

Electrical structure identification of deep shale gas reservoir in complex structural area using wide field electromagnetic method

To fully exploit the technical advantages of the large-depth and high-precision artificial source electromagnetic method in the complex structure area of southern Sichuan and compensate for the shortcomings of the conventional electromagnetic method in exploration depth,precision,and accuracy,the large-depth and high-precision wide field electromagnetic method is applied to the complex structure test area of the Luochang syncline and Yuhe nose anticline in the southern Sichuan.The advantages of the wide field electromagnetic method in detecting deep,low-resistivity thin layers are demonstrated.First,on the basis of the analysis of physical property data,a geological–geoelectric model is established in the test area,and the wide field electromagnetic method is numerically simulated to analyze and evaluate the response characteristics of deep thin shale gas layers on wide field electromagnetic curves.Second,a wide field electromagnetic test is conducted in the complex structure area of southern Sichuan.After data processing and inversion imaging,apparent resistivity logging data are used for calibration to develop an apparent resistivity interpretation model suitable for the test area.On the basis of the results,the characteristics of the electrical structure change in the shallow longitudinal formation of 6 km are implemented,and the transverse electrical distribution characteristics of the deep shale gas layer are delineated.In the prediction area near the well,the subsequent data verification shows that the apparent resistivity obtained using the inversion of the wide field electromagnetic method is consistent with the trend of apparent resistivity revealed by logging,which proves that this method can effectively identify the weak response characteristics of deep shale gas formations in complex structural areas.This experiment,it is shown shows that the wide field electromagnetic method with a large depth and high precision can effectively characterize the electrical characteristics of deep,low-resistivity thin layers in complex structural areas,and a new set of low-cost evaluation technologies for shale gas target layers based on the wide field electromagnetic method is explored.

Singularity-free Green's function for EM sources embedded in a stratified medium

We present a method to unify the calculation of Green＇s functions for an electromagnetic（EM） transmitting source embedded in a homogeneous stratified medium.A virtual interface parallel to layer interfaces is introduced through the source location.The potentials for Green＇s function are derived by decomposing the partial wave solutions to Helmholtz＇s equations into upward and downward within boundaries.The amplitudes of the potentials in each stratum are obtained recursively from the initial amplitudes at the source level.The initial amplitudes are derived by coupling with the transmitting sources and following the discontinuity of the tangential electric and magnetic fields at the source interface.Only the initial terms are related to the transmitting sources and thus need to be modified for different transmitters,whereas the kernel connected with the stratified media stays unchanged.Hence,the present method can be easily applied to EM transmitting sources with little modification.The application of the proposed method to the marine controlled-source electromagnetic method（MCSEM） demonstrates its simplicity and flexibility.

Field testing of the surface electromagnetic prospecting system

To test the performance of the Chinese whole-surface electromagnetic prospecting （SEP） system, system integrations, instrument performances, and large-scale production viabilities in Liaoning province and Inner Mongolia were measured via extensive field tests. Resultant electric fields, magnetic fields, apparent resistivities, impedance phases, and inversion profiles compared favorably with results of commercial equipment from other countries. The inversion results agreed well with the geologic information from boreholes. Field tests showed that the SEP system is stable, reliable, lightweight, and easy to operate, making it suitable and ready for real-field exploration.

Application of the Adaptive Shrinkage Genetic Algorithm in the Feasible Region to TEM Conductive Thin Layer Inversion

Combining the adaptive shrinkage genetic algorithm in the feasible region with the imaging of apparent vertical conductance differential, we have inverted the TEM conductive thin layer. The result of the inversion demonstrates that by adaptive shrinkage in the feasible region, the calculation speed accelerates and the calculation precision improves. To a certain extent, in this method we surmount the transient electromagnetic sounding equivalence and reduced equivalence scope. Comparison of the inverted result with the forward curve clearly shows that we can image the conductive thin layer.