Interpretation of dipole-dipole resistivity surveys using a hemispheroidal model

Abstract

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.