Layered earth models using downhole electromagnetic receivers

Abstract

The transient electromagnetic (TEM) responses of several layered earth models are examined for the configuration consisting of a vertical downhole receiver and a large fixed loop source, on or above the earth's surface. It is shown that a conductive overburden will cause the magnetic field at depth to be greatly attenuated at early times, but considerably enhanced at late times. The use of a downhole receiver will improve the resolution of conductive units, but adds nothing to the already low probability of detecting resistive units using TEM methods. Compared with surface receivers, a downhole receiver will have a much improved probability of detecting whether or not a buried layer has an intrinsic IP response. Lastly, it is shown that the combination of an airborne transmitting loop and a downhole receiver would constitute an interesting and feasible exploration method.