An Investigation of the Dixie Valley Geothermal Field, Nevada, Using Temporal Moment Analysis of Tracer Tests

The method of analysis of the first temporal moment (mean residence time) of tracer return data was utilized to investigate the swept volume and fluid velocity between pairs of injection and production wells in the Dixie Valley geothermal field. Calculations were made using a spreadsheet program available from the Idaho National Laboratory. Jointly sponsored industry–government research at the Dixie Valley field provided several tracer tests over many years, and a test of six, chemically similar tracers, injected between 1998 and 2001, provided the tracer concentration data used in this study. The calculated parameters of mean residence time, fracture volume in contact with the tracer, fluid velocity, and heterogeneity of the reservoir were compared to published descriptions of the reservoir to evaluate their usefulness in refining the conceptual model of the Dixie Valley geothermal reservoir. Temporal moment analysis provided more information about the fractured fluid path between wells and the volume of the reservoir contacted by the tracers. Tracer injection in the center of the Dixie Valley field and production of that tracer in the northeastern and southwestern production wells clearly demonstrated that no barrier to flow exists between the two areas of producing wells.