3-D finite element analysis of induction logging in a dipping formation

Electromagnetic induction (EMI) by a magnetic dipole located above a dippin g interface is of relevance to the petroleum well-logging industry. The pro blem is fully three-dimensional (3-D) when formulated as above, but reduces to an analytically tractable one-dimensional (1-D) problem when cast as a small tilted coil above a horizontal interface. The two problems are relate d by a simple coordinate rotation. An examination of the induced eddy curre nts and the electric charge accumulation at the interface help to explain t he inductive and polarization effects commonly observed in induction logs f rom dipping geological formations. The equivalence between the 1-D and 3-D formulations of the problem enables the validation of a previously publishe d finite element solver for 3-D controlled-source EMI.