Determing parameters of a geological environment

Abstract

A method of determining parameters of a geological environment having a known electrical resistivity R.sub.h, with a heterogeneity in the environment having an electrical resistivity R.sub.e, and with a borehole extending into either the environment or the heterogeneity at an unknown distance p from the interface between the environment and the heterogeneity. A measuring assembly is extended into the borehole, including an electrical emitter and two or more electrical detectors. Electrical energy is applied to the emitter and detected by one of the detectors at a distance d from the emitter, and the borehole resistivity R.sub.a at the distance d is determined. This is repeated for others of the detectors at other distances d. A curve is plotted of the resistivity ratio R.sub.a /R.sub.h as a function of the distance d. The plotted curve is compared with previously obtained curves of the resistivity ratio R.sub.a /R.sub.h as a function of d for various combinations of the values of the resistivity ratio R.sub.h /R.sub.e and the borehole-interface distance p, and a resistivity ratio R.sub.h /R.sub.e and a borehole-interface distance p are determined for the plotted curve. The resistivity R.sub.e of the heterogeneity is then calculated. The location of the heterogeneity can be determined from the distance p, and the nature of the heterogeneity is indicated by its resistivity R.sub.e.