On sensitivity of surface‐to‐borehole resistivity measurements to the attitude and the depth to center of a three‐dimensional spheroid

Abstract

Borehole‐to‐surface and surface‐to‐borehole resistivity measurements are versatile but not totally tested methods for detecting anomalies in the vicinity of a borehole. The former method has been discussed by several authors (Alfano, 1962; Merkel, 1971; Merkel and Alexander, 1971; Barnett, 1972; Snyder and Merkel, 1973; Snyder, 1976; Daniels, 1977, 1978, and 1983), but the latter has not received much attention. Morrison (1971) and Daniels (1977) are among the few who have addressed the problem. Each method has its own advantages. Surface‐to‐borehole resistivity measurements are made by placing a current source on the surface and measuring the apparent resistivity in a borehole in which the measuring electrodes are closer to the body than in the borehole‐to‐surface case. Pilot studies presented here suggest that the surface‐to‐borehole method can provide indicators of the attitude and the depth to the center of a body. This paper illustrates a simple method for qualitatively determining the attitude and the depth to the center of a body for a thin three‐dimensional (3-D) conductive oblate body with the surface‐to‐borehole technique. Attitude conveys the orientation of the body— horizontal, vertical dipping toward a borehole, or dipping away from a borehole.