The permeability structure and stress state found within and near fault zones often determines rates and patterns of fluid flow in high-temperature geothermal systems. Unfortunately, insufficient subsurface information is available to adequately characterize the fluid flow properties of fault zones. In particular, we are unable to measure the in-situ variations in permeability, porosity, and storativity needed to assess their impact on geothermal production. We can, however, use outcrop analogs to aid in interpolating between wells and to provide a basis for extrapolating fluid flow properties from sparse wellbore data. A two-component fault zone model comprising damage zone and fault core provides a valuable framework for fault mapping. Detailed mapping of the geometry and distribution of each component, combined with measured fracture characteristics, yields the quantitative information needed to improve numerical models of fluid flow in fault-controlled geothermal systems. Integrated surface and subsurface data obtained at the Dixie Valley Geothermal Field is used to estimate input parameters for simulating fluid flow, heat transfer, and solute transport in this fault-controlled geothermal system.

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