MODELING FAULT-RELATED FRACTURING ASSOCIATED WITH A SEGMENTED NORMAL FAULT: IMPLICATIONS FOR GEOTHERMAL ENERGY POTENTIAL

Productive geothermal systems often occur in regions of extensional or transtensional strain where long-term stress creates high-density fractures that permit fluid flow. These fracture zones largely form adjacent to segmented normal faults where multiple fault segments affect stress and strain. In southern Utah, the segmented Sevier normal fault has accommodated strain since the Miocene due to its location between the extending Basin and Range Province and the stable Colorado Plateau. Researchers link high-density fracturing to strain accommodation near fault tips and within transfer zones, so modeling patterns of stress and strain along the Sevier fault can help create a framework of fracture evolution that better predicts geothermal capacity, using field-based fracture intensity and orientation data from damage zones across the Sevier fault zone for validation.

To analyze stress, strain, and fracture evolution in a segmented normal fault system, we used the Fault Response Modeling module of Move 2020 (by Petex) to create 3D models of a 2-fault system, consistent with segments of the steeply-dipping Sevier system, at increasing levels of overlap. Models included a single layer defined by the mechanical properties of Navajo Sandstone, which is present in the study area. We modeled throw, stress, strain, and fracture orientation and intensity at varying fault slip displacements, ranging from 25 to 400 m.

All models showed the highest strain at fault tips, with strain also transferred between tips. Of our models, the less overlapped systems had the most intense strain fields between tips. Throw gradually changed from highly negative to slightly positive in this zone, indicating the initial development of a relay ramp, which has high geothermal potential. In all models, fracturing is most intense in such high stress and strain fields, with fractures curving to connect tips, a feature shown most intensely in less overlapped systems. Fracture intensity is high in the hanging wall, with vertical fractures roughly parallel to the fault. Due to predicted high strain and fracture density, we confirmed that fault tips in segmented normal faults are promising for geothermal energy. Furthermore, slightly underlapped or overlapped faults represent the most likely setting for fracturing that allows geothermal production.