Resistivity of Rocks in Geothermal Systems: a Laboratory Study

Abstract

This paper describes a limited series of laboratory resistivity measurements on a selection of core samples taken from geothermal fields in New Zealand and the Philippines. The resistivities of these cores, selected to include a range of clay contents and porosities, were measured using various saturating fluid s (NaCl solutions with resistivities ranging from 0.3 to 3 oh-m) and at temperatures between 2OoC and 90?C. The temperature behaviour of the measured resistivity values implies that ionic conduction is the dominant charge transport mechanism occurring under these conditions. Multiple linear regression analysis of all the data confirms the expected dependence of the resistivity of these hydrothermally a1tered rocks upon temperature, saturating fluid resistivity. porosity and clay content. This dependence can be described by a variant of Archie's relation, modified to allow for the effecto f the clay mineral content and temperature.