The FORGE geothermal reservoir is sited in deep granitic bedrock near the town of Milford, Utah. A Discrete Fracture Network (DFN) model has been created to explicitly represent the natural fracture population using both outcrop fracture trace length data and a Fullbore Formation MicroImager (FMI) resistivity log from a vertical pilot well. Natural fractures identified in the log intersect between 1-8 of the FMI pads. The percentage which fully penetrate the pilot well borehole (8 pads) and the percentage which only penetrate 1-4 pads are tabulated. These statistics are compared with the results of forward modeling many stochastic realizations of the DFN using different size distributions. Forward modeling is possible since the fracture orientations are well specified from both log and outcrop data and the well radius and trajectory are known. While the outcrop trace data for fractures having a radius between 20 – 50 m match both lognormal and power law distributions, the FMI log data appear to sample fractures having a median radius of 1.4 m and are consistent only with the power law distribution found from the outcrop data.
The FORGE geothermal reservoir is sited in deep granitic bedrock near the town of Milford, Utah. A Discrete Fracture Network (DFN) model has been created to explicitly represent the natural fracture population in the reservoir (Finnila et al., 2019). In the DFN, fractures are modeled as planar and roughly circular, having a range of orientations, local intensity, and sizes consistent with what has been observed from both image log data from a vertical pilot well, Well 58-32, and measurements from outcrops in the nearby mountains. Previous to this work, fracture sizes were estimated from the Salt Cove outcrop trace data shown in Fig. 1.