Dispersion in Tracer Flow in Fractured Geothermal Systems

Abstract

Recent field experiments in Japan have emphasized the importance of performing tracer tests in any geothermal utilization in which reinjection is in use or is planned. This is because rapid short- circuiting between reinjection and production wells may occur due to the fractured nature of the system. In cases where fracturing is such that preferred pathways exist in the reservoir, the result may be a rapid thermal drawdown of the field production. Tracer test in g provides a method of evaluating the magnitude of such problems. Previous methods used to analyze the Onuma, Hatchobaru, and Otake tracer tests have used early and long t i m e data, this paper discusses the use of the field concentration/time profile in fractured systems, and the likely forms of dispersion likely to dominate in the process.