Calculation of borehole transient electromagnetic apparent resistivity and dip in anisotropic medium

ZHAO Ning; ZHANG Zhaoaoji; JIANG Liming; XIAO Zhanshan; HU Haitao

doi:10.16186/j.cnki.1673-9787.2023020013

Abstract：In the fields of resource exploration and development,as well as geological disaster prevention and control,the electromagnetic method of borehole is an effective tool for monitoring subsurface fluid dis-tribution,particularly in evaluating the effectiveness of hydraulic fracturing and grouting for water control.Transient electromagnetic remote detection fills the gap in geological assessment scale of conventional log-ging and seismic exploration in terms of detection depth and resolution.However,the current theoretical models based on isotropic media do not fully correspond to the actual development environment of most oil and gas fields in China,which is the fact of heterogeneous and anisotropic formations.Objectives Consider-ing the complexity and heterogeneity of subsurface media,it is of great significance to study borehole tran-sient electromagnetic method in anisotropic formations.Methods Based on borehole transient electromag-netic theory,the relationship between apparent resistivity and apparent dip angle of anisotropic formation borehole is derived through analytical calculation by studying the three component induction data.Results The results indicate that for isotropic media models,the apparent resistivity and apparent dip angle effec-tively can better reflect the formation resistivity and dip angle within the model.For anisotropic models with transversely isotropic media with a vertical symmetry axis(VTI),the apparent resistivity and apparent dip angle similarly can better reflect the horizontal and vertical resistivity and dip angle of the anisotropic for-mations.Conclusions The results enable rapid calculation of apparent resistivity and apparent dip angle in anisotropic formations,facilitating quick analysis of the electrical structure near the observation device and significantly contributing to the rapid development of borehole transient electromagnetics in anisotropic media.