INTERPRETATION OF DIPOLE‐DIPOLE RESISTIVITY SURVEYS USING A HEMISPHEROIDAL MODEL

Abstract

The solutions for the potential due to a current source near a hemispheroidal body of finite resistivity, which have been given by Cook and Van Nostrand, are adapted for use with dipole‐dipole resistivity arrays. In the limiting case where the current dipole is at a large distance from the hemispheroid a simple expression is obtained for the apparent resistivity measured at the center of the hemispheroid. For an arbitrary placement of current electrodes, apparent resistivities are obtained by summing a double series involving the associated Legendre functions. Theoretical results using differently shaped hemispheroids are compared with field data obtained from several dipole‐dipole resistivity surveys of the hot water reservoir of the Broadlands Geothermal Field, New Zealand. The comparison enables an estimate to be made of the depth of the geothermal reservoir.