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Structural controls on geothermal systems in the Great Basin (Northern Basin and Range Province), Nevada, U.S.A

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. In collaboration with the UNR, we will contribute to the characterization of fractured reservoir rocks in order to understand the structural controls on fluid flow.

The approach will include 3D structural geological modeling, stress field determination based on surface and subsurface data and fault stress modeling of complex fault systems applying the slip tendency analysis. The main goal is to develop successful exploration strategies in extended terranes. To elucidate the controls on fluid flow, we are conducting detailed structural assessments and 3D modeling studies in different systems, e.g., Astor Pass geothermal field within the Pyramide Lake Paiute Reservation; San Emidio geothermal area, Washoe County; NAS Fallon and Hawthorne; Brady’s geothermal area, Churchill County.

Significant work is carried out in 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. Our structural assessment 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 fault pattern will 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 the planned EGS development.

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