WHOLESCALE - Calibration and Simulation of hydro-mechanical Behavior at San Emidio, Nevada During Operational Changes

Abstract

Changes to geothermal pumping operations produce changes in reservoir fluid pressure that propagate according to the arrangement of fluid sources / sinks (injection / extraction wells, respectively) and reservoir permeability. These changes in fluid pressure induce changes to effective stresses acting on potential fault planes, and thus alter fault stability. For example, Cardiff et al. (2017) used a semi-analytical model, calibrated on existing pressure data, to simulate pressure changes during temporary cessations of pumping when a geothermal plant was shut down for maintenance. They demonstrated that microseismic events observed post-shutdown occurred where predicted fluid pressure increases (and effective stress decreases) between 0.05 MPa - 0.15 MPa were simulated. This work investigates pressure changes associated with similar site shutdowns at the San Emidio Geothermal Field, Nevada. Using existing pumping and pressure change data, we have calibrated finite element numerical models based in the COMSOL and GEOSX platforms. Following calibration, we simulate expected pressure changes and stress field changes within the San Emidio reservoir during site shutdowns. A catalog of microseismic event times and locations measured before, during, and after shutdown can be compared against the spatiotemporal changes in fluid pressures and effective stress simulated by our models. In theory, once properly calibrated these models allow the prediction of future seismicity as site operational changes are implemented, such as new pumping wells or flow rate adjustments. In this paper, we provide a snapshot of work in progress. The work presented herein has been funded in part by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Number DE-EE0009032.