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.
Thermodynamic calculations of calcium carbonate scaling in geothermal wells, Dixie Valley geothermal field, U. S. A
Abstract Wells in the Dixie Valley geothermal field of central Nevada intercept a fracture-dominated hydrothermal system at depths of 2.5 to 3 km. The reservoir water is a dilute sodium-bicarbonate-chloride type solution thought to be in equilibrium with quartz, calcite, chlorite, and albite. Fluid sampling and chemical analysis of production during an early flow test gave remarkably low calcium concentrations. Thermodynamic calculations of mineral stability in the presence of the reservoir water indicate that five times the amount of calcium measured in fluid reaching the surface is actually in solution in the reservoir fluid. Approximately 80 percent of the calcium is lost as calcium carbonate scale on the well casing before the fluid reaches the surface. The results of thermodynamic calculations compare well with the scale-volume measurements of Benoit (1989).
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.