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Characterization of geothermal reservoirs with electrical surveys: Beowawe geothermal field
Authors:Sabodh K. Garg  John W. Pritchett  Philip E. Wannamaker  Jim Combs
Affiliation:1. Science Applications International Corporation, 10260 Campus Point Drive, San Diego, CA 92121, USA;2. Energy and Geoscience Institute, University of Utah, 423 Wakara Way, Salt Lake City, UT 84108, USA;3. Geo Hills Associates, 1710 Winter Moon Court, Reno, NV 89523, USA
Abstract:
The work reported here was undertaken to test the utility of electrical surveys for geothermal reservoir characterization using existing exploration and well data sets from the operating Beowawe geothermal field located in the Basin and Range Province of western USA. The STAR geothermal reservoir simulator was used to model the natural state of the system, and to compute the subsurface distributions of temperature and salinity, which were in turn utilized to calculate pore-fluid resistivity. Archie's law, which relates formation resistivity to porosity and pore-fluid resistivity, was adopted to infer the formation resistivity distribution. Subsequently, direct current (DC) resistivity, magnetotelluric (MT) and self-potential (SP) postprocessors were used to compute the expected response corresponding to available survey data. The measured apparent resistivity distribution from a dipole–dipole DC resistivity survey is in good agreement with the computed values. The calculated self-potential distribution agrees with the main features of an available SP survey. Although the computed MT apparent resistivity sounding curves reproduce the shapes of the measured MT sounding curves, an overall scale factor exists between the measured and calculated MT responses, and similarly with the computed dipole–dipole resistivity model. Possible reasons are static shifts in the coarsely sampled MT stations, and resistivity anisotropy due to the stratigraphy. Taken as a whole, the results of this study support the view that a suite of carefully designed electrical surveys (DC, MT, and SP) may be employed to infer favorable subsurface geothermal reservoir characteristics.
Keywords:Hidden geothermal systems   Electrical surveys   Dipole&ndash  dipole DC resistivity   Magnetotellurics   Self-potential   Natural state   Numerical simulation   Basin and Range   Beowawe   Nevada   USA
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