The feasibility of making spectral IP measurements in the time domain

Abstract

The time-domain response of a published theoretical IP model has been explored, for single current pulses of infinite and finite duration and for a conventional repetitive pulse train. Because of the very slow increase of charging voltage on many natural outcrops it is impossible to produce a pulse of such a length that it behaves as an infinite input. A repetitive pulse train results in decay curves on which electromagnetic coupling, but not information on the nature of mineralisation, can be recognised. The response to a single finite pulse can be analysed by a rather inelegant curve-matching procedure. Field measurements using very simple equipment showed that black shales have a distinctive IP response but gave no other useful discriminatory information.