Inversion of surface and downhole electromagnetic data for a 3D earth

Abstract

A program described by Sugeng [1998] which calculates the full domain 3D EM response of an earth modelled by hexahedral finite elements was extended to invert ground survey data using the damped eigenparameter method described by Jupp and Vozoff [1975]. The program is demonstrated using a small numerical model of a SIROTEM-like fixed-loop survey consisting of three surface traverses and a downhole line. Results suggest that provided data are not too noisy, a reasonable model can be recovered if the starting model is quite close to the true model. This suggests that the program might best be used to inverse-model particular features of interest rather than as a starting point for interpretation.