Radioactive Tracers Used to Characterize Geothermal Reservoirs

Abstract

The use of radioactive tracers to chart the downhole movement of fluid is a powerful tool in unscrambling the complex flow paths within man made hot dry rock geothermal reservoirs. Tracer profiles are useful to delineate changes in the hydraulic fracture system, particularly in determining the flow patterns, establishing fracture volumes and areas, characterizing fluid dispersion, and identifying injection and production zones. Data obtained from Br2 tracer injections with downhole gamma ray monitoring were used to quantify flow fractions entering and leaving the GT-2B and EE-1 reservoirs at various depths. The Br2 tracer method is also provided data needed to characterize changes in the reservoir volume and flow distribution within fracture system during the recent 281 day sustained heat extraction experiment at the Hot Dry Rock Fenton Hill Site.