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High-temperature geothermal systemsSystems with temperatures >225 °C. Here, it is denoted that geothermal resources are ones where fluids are present, allowing for power generation using flash and/or binary power plant technology.

Keywords 13 Geothermal exploration, 3D structural-geological modeling, structural permeability, stress 14 field analysis, fault stress modeling, Brady's 15 16 Abstract 17Fluid-bearing fracture zones are typically the focus of geothermal exploration as preferential 18 targets for production wells. The ability of fractures to channel fluids is commonly affected by 19 the current stress field. In this study, a three-dimensional structural-geological model of the 20 Brady's geothermal system (Basin-and-Range Province, USA) was developed. We 21 demonstrate that by incorporating slip-and dilation tendencies as a function of the stress field 22 and fault geometry, our 3D-model can efficiently contribute to the identification of favorable 23 drilling targets. 24 the Brady's geothermal field consists of a Mesozoic metamorphic and plutonic basement 66 covered with Cenozoic volcanic and sedimentary sequences. Geological understanding of 67 Brady's has been gained by detailed 1:24,000 geological mapping (Faulds and Garside, 2003; 68 Faulds et al., 2012; Fig. 2), geophysical surface exploration (i.e., 2D seismic reflection 69 surveys, gravimetry) and drilling (Faulds and Garside, 2003; Hinz, unpublished data, 2011; 70 Queens, unpublished data, 2011). The known geothermal reservoir is located at a depth of 71 600-1,500 m below the surface and lies within the Oligocene ash-flow tuffs and Miocene lava 72 flow formations. 73 74 Figure 2: The simplified geological map (modified after Faulds and Garside, 2003; Faulds et al., 2012) 75 provides a brief overview of the major stratigraphic units in the study area. SBF: Southern Brady's fault; 76 NBF: Northern Brady's fault; BFSO: Brady's fault step over; Coordinate System: NAD 1983 UTM Zone 77 11N. 78 79 A major feature of the Brady's geothermal system is the Brady's major fault zone, a ~10 km 80 long, NNE-striking fault zone, which dips 60°-80° to the NW as determined by surface 81 exposures of faults and 2D seismic reflection surveys (Rudisill, 1978; Faulds et al., 2010a). In 82 the immediate vicinity of the Brady's geothermal power plant is the ~600 m wide Brady's 83 fault step over (or relay ramp, cf., Larsen, 1988), mapped in detail by Faulds and Garside 84 (2003) and Faulds et al. (2012). The Brady's fault step over consists of multiple minor en 85 échelon faults (small left steps) that connect the major overlapping fault segments (Faulds et 86 al., 2006, 2010b), and concentrates active geothermal surface manifestations over a ~200-300 87 m broad area, including fumaroles, seasonally dried out mud pools, warm and steaming 88 grounds, hydrothermal alteration zones, and calcareous sinter deposits (but no hot springs). 89 Production wells target primarily this part of the Brady's fault zone at a depth of 600-1,500 m 90 b.s.l. where highest production rates are obtained (Fig. 6B-D; Davatzes et al., 2013). Elevated 91 permeabilities in the hanging wall of the Brady's fault zone have suggested the possibility of 92 lateral stratigraphic units acting as a potential reservoir (Faulds et ...

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