Geomechanical analysis of the geothermal reservoir at San Emidio, Nevada

Abstract

The WHOLESCALE (Water and Hole Observations Leverage Effective Stress Calculations and Lessen Expenses) project is aiming to simulate the spatial distribution and temporal evolution of stress throughout the geothermal system at San Emidio, Nevada, United States, via a thermo-hydro-mechanical reservoir model. Focal mechanisms for microseismic events during a temporary shutdown of the geothermal power plant in 2016 were analyzed through linear stress-inversion methods to infer the in-situ reservoir stress state. This analysis was supplemented by other geophysical and geological data, including focal mechanisms from regional earthquakes, slickenlines on exposed fracture surfaces, wellbore stress indicators observed in the surrounding region, and secular strain rate measurements. From the inferences of in-situ reservoir stress, 78 different realizations of stress models were generated over reasonable ranges for the values of maximum compressive horizontal stress (SHmax) azimuth and ratios of principal stress magnitudes. Evaluation of slip tendencies on fault planes determined for the microseismic events for each realization of the initial stress model suggests the reservoir stress state as transtensional with an SHmax azimuth between N and N30∘E.