Research On Transient Electromagnetic Response Simulation Method Considering Polarization Effec

Transient electromagnetic method,because of its simple principle,portable transmitting and receiving devices,convenient operation and short detection time,has been widely used in surface,underground,marine,aviation and other electromagnetic methods.With the expansion of exploration field,the transient electromagnetic detection method is gradually extended to the detection and application of seabed metal sulfide ore and unconventional shale oil and gas in addition to its application in the field of engineering environment.For these new detection fields,it is urgent to consider the transient electromagnetic response analysis method and processing interpretation technology considering polarization effect.On the basis of previous studies,this paper first derives the transient electromagnetic response equation with polarization effect,uses regular hexahedron subdivision,and deduces the finite difference dispersion equation of three-dimensional staggered grid;Based on the analytical solutions of half space model and layered medium model,the accuracy of staggered grid finite difference is verified.In order to reduce the subdivision area,the discretization relationship of chew’s telescopic transformation PML boundary condition(CPML)is derived,and the calculation characteristics of Dirichlet boundary condition with non-uniform grid and CPML)are compared,so as to realize the efficient calculation of staggered grid finite difference.In order to be suitable for the processing of measured big data,GPU parallel algorithm is used to realize the staggered grid finite difference algorithm of transient electromagnetic response of complex underground targets.The transient electromagnetic response characteristics of different detection targets considering polarization response are analyzed,which provides an effective tool for the processing and interpretation of measured data.Through the simulation results of the response characteristics of high and low resistance abnormal bodies,it is known that when there is a low resistance body in the high resistance background stratum,the transient electromagnetic method can clearly outline the boundary of the low resistance anomaly,and the response information of the abnormal body below the low resistance experience will be shielded,which shows the sensitivity of the transient electromagnetic method to the low resistance body.For the high resistivity anomaly under the background of low resistivity,if the volume of the anomaly is small,under the interference of the surrounding environment,the response information of the high resistivity anomaly is weak and difficult to be well distinguished.In transient electromagnetic detection,the polarity reversal of the electromagnetic field response is related to the polarization effect.