Fracture Detection and Characterization for Geothermal Reservoir Definition

Abstract

As more data from geothermal systems have been gathered and analyzed, there has been growing documentat ion and verification that fractures have a major effect on the performance of most geothermal reservoirs. In contrast to oil and gas reservoirs, geothermal resources are often encountered in rocks with low matrix permeability, such as volcanic formations and plutonic assemblages. Experience at several geothermal fields has shown that reservoir fluids are produced in important volumes only from narrow and infrequent zones containing fractures that are both open and well-connected hydraulically. In addition to their importance for well targeting, the locat i o n and characterization of open fractures within specific geothermal wells is also vitally important to engineers for interpreting pressure and flow test data, and for designing a proper reinjection scheme that avoids premature thermal breakthrough of injected fluids into production wells. This paper is a shortened version of an LBL technical report (Goldstein, 1984) in which the present state of technology in fracture detection and mapping is reviewed. present the author's opinion of present research needs.