The northwestern Great Basin (NGB) in the western USA hosts abundant, generally amagmatic geothermal activity. Significant geothermal exploration is ongoing, but controls on fluid flow in the geothermal systems are generally poorly understood. To elucidate the controls on fluid flow, we are conducting a detailed structural assessment and 3D modeling study of the Brady’s geothermal field ~80 km east-northeast of Reno, Nevada. It has an estimated reservoir temperature of 175-205°C at 1- 2 km depth and supports a combined flash and binary geothermal power plant with a total electrical generation capacity of 16-17 MWe. The surface expression of the Brady’s system is a 4-km-long, NNE-trending zone of extensive sinter, warm ground, fumaroles, and mud pots along the Brady’s fault, which is part of a complex en echelon normal fault system locally with Quaternary scarps.

Optimized utilization of this mature geothermal field necessitates a detailed 3D understanding of the complex fault system and its impact on channeling fluids. Over the past decades, abundant wells and detailed geophysical surveys have been generated and provide extensive subsurface data, which can be used for 3D geological modeling. Our structural assessment therefore combines detailed geological field mapping, fault plane analysis, stress inversion, 3D structural geological modeling and stress modeling to contribute to concepts for EGS development. The structural 3D geological model will be validated by well and seismic data. The discrete fracture surfaces will be populated with geomechanical parameters and stress data derived from the surface and subsurface. The fault pattern will also be characterized in terms of slip and dilation tendency. The results are not only important for better understanding permeability anisotropy in the geothermal reservoir but also for estimating the fault reactivation potential, which is crucial for EGS development at Brady’s well 15-12. Our integration of detailed field studies, stress modeling, and 3D structural modeling may be valuable for geothermal development where cost-effective exploration strategies are needed.

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