Newmont transient electromagnetic system

Abstract

Field data collected using Newmont's EMP system show good agreement with theoretical models for the halfspace and tabular bodies, given a non-ideal step excitation and the usual effect of horizontal layering. In particular the "smoke ring" or ring current effect predicted by Nabighian is observable for transient systems when the transmitter and receiver coil are not coincident. It is demonstrated that interpretation is best carried out when the response can be represented by the late time assymptotic expressions predicted by theory, for both the halfspace and tabular bodies. It is suggested that a sensitivity of 1/10 microvolt/amp at 50 msecs is necessary to recognise late time behaviour, particularly in the presence of conductive overburden.