Interpretation of Schlumberger soundings from Mt. Cagua, Philippines, and TEM soundings from Svartsengi-Eldvorp, SW-Iceland

Abstract

An overview is given of the DC-Schlumberger sounding method and different methods of interpretation. The results of an extensive Schlumberger sounding survey from the Mt. Cagua geothermal prospect in the Philippines are presented. Using both one-dimensional and two-dimensional modelling, the interpretation of the Schlumberger soundings delineated a conductive body that covers most of the prospect area. Two geothermal centers are postulated. One is connected to the geothermal system of Cagua Volcano to the west and the other to Baua Volcano in the eastern part of the prospect area. The basic principles of the central-loop transient electromagnetic (TEM) method are presented. A TEM survey was conducted in the Svartsengi-Eldvorp geothermal field, SW-Iceland, for the purpose of locating the best site for a proposed reinjection well. The results are compared to older Schlumberger sounding data, and confirm the better vertical resolution of the TEM soundings than the Schlumberger in a terrain with a highly resistive surface but low resistivities at deeper levels. A site for the planned reinjection well is proposed, based on the results of the TEM soundings.