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

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 distribution， 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 logging 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.ObjectivesConsidering the complexity and heterogeneity of subsurface media， it is of great significance to study borehole transient electromagnetic method in anisotropic formations.MethodsBased on borehole transient electromagnetic 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.ResultsThe results indicate that for isotropic media models， the apparent resistivity and apparent dip angle effectively 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 formations.ConclusionsThe 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.