Research On 3D Forward And Inversion Of Magnetotelluric Sounding Based On COMSOL Simulation Software

Among the many geophysical exploration methods,the magnetotelluric sounding method(MT)has the advantages of large detection depth,no high-resistance shielding,and sensitivity to underground low-resistance anomalies.Based on these advantages,the numerical simulation technology of the magnetotelluric sounding method is also constantly developing,especially with the continuous development of information technology,many commercial softwares are also more extensively studied in the numerical simulation of the magnetotelluric sounding method.Therefore,based on the support of the Open Fund of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Engineering,the three-dimensional forward and backward inversion study of the anisotropic magnetotelluric parameters of oil and gas reservoir parameters(PLC2001802),the paper is based on the finite element numerical simulation software Comsol Multiphysics The 3D forward and backward inversion study of magnetotellurics focused on the analysis of 3D forward response characteristics of apparent resistivity,impedance phase,impedance tensor,phase tensor and tilter of different models.Comsol software was used to analyze the 3D relief terrain model and 3D The effect of static effect on apparent resistivity and impedance phase provides a new research method for the future field construction and data processing of three-dimensional large electromagnetic sounding method.This article first introduces the Comsol software,and summarizes the research work of many scholars at home and abroad using the Comsol software for geophysical numerical simulation.Secondly,it introduces in detail the process of Comsol software for three-dimensional magnetotelluric forward modeling,and focuses on the steps of meshing,setting of the solver and post-processing.In addition,the correctness verification of the Comsol software is the basis of the entire 3D magnetotelluric forward modeling research.The analysis results of the Comsol software for the layered model and the 3D model DTM1 are compared with the analytical solution and mt3 dinv.3D magnetotelluric forward modeling accuracy requirements.Finally,by comparing the computational efficiency of different algorithms in the Comsol software,the stable biconjugate gradient method(BICGSTAB)was finally determined to complete the entire three-dimensional magnetotelluric forward study.The analysis of the three-dimensional forward results of different parameters of the COMMEMI3D-1 standard model shows that the Comsol software is feasible to study the forward parameters of three-dimensional magnetotellurics.In order to get closer to the actual exploration situation,the Comsol software was used to compare and analyze the forward results of the high-low resistance combination model and the vertical fault model with different parameters.In addition,the forward results of the apparent resistivity and impedance phase of the 3D relief terrain model show that the apparent resistivity at the top of the mountain is less than the background resistivity,and the apparent resistivity at the root of the mountain is greater than the background apparent resistivity,and the impedance phase is the largest at the top of the mountain,while The forward result of the valley model is just the opposite of the mountain peak.The apparent resistivity and impedance phase curves of different survey lines prove the above phenomenon.In the forward results of the uniform half-space static model,the apparent resistivity curves at the measuring points of the inhomogeneous body range are small,the impedance phase curve is only small at high frequencies,and the apparent resistivity contours at different measurement lines In the figure,the area where the uneven body exists presents a low-resistance band in the entire frequency band,and the contour of the impedance phase only appears in the high frequency band.In the forward model of the static model containing the abnormal body,due to the ground The existence of the homogenous body shields the information of the low-resistance anomalous body underground.In order to further verify the accuracy of the forward results of the Comsol software,the limited memory quasi-Newton method(LBFGS)was used to perform full impedance tensor inversion and inversion on the impedance tensor of the COMMEMI3D-1 model,the combined high and low resistance model and the vertical fault model.The results are in good agreement with the actual model.Therefore,the overall research work shows that the Comsol software provides a new research idea for the three-dimensional forward modeling of MT.