Inductive interaction between closely spaced steeply dipping tabular conductors located in a resistive host

Abstract

Physical scale‐model studies of the responses provided by horizontal coplanar and vertical coincident coil moving‐source electromagnetic systems when operated over closely spaced, steeply dipping, tabular conductors located in a resistive host are presented. For separations of the conductors that permit separate anomalies to be identified, the detected effect of inductive interaction between the conductors depends on the configuration of the exploration device. As conductors are moved closer together, the horizontal coplanar coil system produces responses for each conductor that become progressively weaker than the individual responses when each conductor is isolated. By comparison, vertical coincident coils detect an initial increase of the anomalies from the individual conductors as the conductor separation is reduced until just before the separate anomalies merge. As the anomalies merge, the vertical coincident coil responses decline in magnitude. After the anomalies merge and present the appearance of the response of a single conductor, both coil systems record an expected strong increase of response which exceeds the response when the conductors are in contact. These mutual inductive interactions cause significant variations in the depth estimates provided by horizontal coplanar coils. Depth estimates provided by vertical coincident coils are always smaller than the true target depths. The vertical coincident coil configuration displays an ability to identify separate conductors at significantly smaller conductor separations than can the horizontal coplanar coils.