Proposed Geothermal Index and its Application to Geothermal Exploration

Abstract

In order to evaluate the temperature conditions of geothermal wells and surface manifestations, geothermal index (GI) is proposed here. GI is given by the equation of GI = kRAI, where RAI is the revised activity index and k is a coefficient calculated by the highest temperature found in a well. Japanese steam production wells have GI values higher than 35, whereas non-productive ones in the Mizuwake-toge geothermal area, Kyushu, have those smaller than 40. Types of the depth-temperature curves of the Mizuwake-toge wells are also discussed in relation to GI: the upflow types are higher than 20, the heat conduction types are smaller than 20, and the down flow types are smaller than 5. Accordingly. this GI makes it possible to compare the comprehensive thermal conditions for shallow to deep wells as well as for surface manifestations.