Surface-borehole transient electromagnetic responses in 3D anisotropic media
The surface-borehole transient electromagnetic method(TEM)has been widely used because of its advantages such as high resistance to interference and strong response signals.In deep ore-prospecting and geo-logical structure exploration,most oil and gas resources are stored in sedimentary rocks with obvious lamina-tions,and the subsurface media exhibit anisotropic electrical conductivity.However,conventional inversion ima-ging techniques based on isotropic models are no longer applicable to the processing and interpretation of aniso-tropic data.To analyze the impact of conductivity anisotropy on the surface-borehole TEM,this paper studies electromagnetic responses in anisotropic media.According to the conductivity tensor of anisotropic media,this paper proposes a three-dimensional(3D)analysis model based on the finite element method(FEM),using the PARDISO solver to solve problems.The transient electromagnetic responses in anisotropic media with different angles are simulated to analyze the influence of anisotropic media on the propagation and reception of electro-magnetic waves.The characteristics of the transient electromagnetic responses in anisotropic media are also dis-cussed.The results show that in vertical anisotropic media when the propagation direction of the electromag-netic wave is perpendicular to the direction of maximum conductivity,the electromagnetic response is the strongest;when the propagation direction of the electromagnetic wave is parallel to the direction of maximum conductivi-ty,the electromagnetic response is the weakest.In horizontal anisotropic media,the response of electromag-netic wave is the strongest when the electromagnetic wave is perpendicular to the direction of the minimum con-ductivity,and the weakest when the electromagnetic wave is parallel to the direction of the minimum conductivi-ty.In addition,this paper analyzes the electromagnetic responses of anisotropic strata and anomalies with differ-ent emission source directions during transient electromagnetic logging.The results show that the transient elec-tromagnetic responses of anisotropic strata and anomalies are related to the direction of the emission sources.Specifically,for the principal axis anisotropic anomalies,the choice of emission source directions directly af-fects the determination of the anisotropic direction of anomalies.The conclusions of this paper provide valuable insights for the research on geophysical methods in oil and gas development.
conductivity anisotropyfinite elementforward modeling of 3D electromagnetic fieldssecond-order backward Eulerian difference method
万方数据
维普
