Kinetics of fluorescein decay and its application as a geothermal tracer

Abstract

Fluorescein is a dye used to trace the path of injected fluids through geothermal reservoirs. We have measured its thermal stability at temperatures up to 300°C in hydrothermal autoclaves at various fluid compositions, pHs, and oxygen concentrations. The results of these experiments indicate that fluorescein will decay less than 10% during a one month tracer test in geothermal reservoirs with temperatures below 210°C. For tracer tests involving longer times and/or higher temperatures, the activation parameters presented in this study can be used to correct for thermal decay. These parameters were applied to a tracer test conducted at the Dixie Valley, Nevada geothermal system to correct for the thermal decay of fluorescein and to deduce the effective temperature of the injection-production flow path.