EM target response in complex hosts

Abstract

Electromagnetic exploration methods are only useful if they give the user an enhanced likelihood of finding economic targets or at least decrease the probability of drilling false targets. Given reasonably clean data, many schemes exist to identify simple targets in uniform hosts. However, the EM responses of potential economic targets are often obscured by those from heterogeneities in the host as well as a number of structural factors like topography and unconformities. The AEM response is further complicated by system factors such as airframe currents, plus variations in bird position and flight path. This paper examines the changes in response of a simple target as its environment becomes increasingly more complicated. We start with a 1km long conducting dipping dyke and then add overburden, topography, a paleochannel, heterogeneities, faults and then put it at the boundary between two rock units. We also look at system factors such as transmitter angle, airframe currents and non-level flight as well as the effect of different flight paths. Although CDIs do not yield an accurate picture of the subsurface geoelectric structure, they nonetheless represent a useful transform on the data that can be used for pattern recognition studies.