| Authors |
Kurt L. FEIGL, Hao GUO, Erin CUNNINGHAM, Jesse HAMPTON, Matthew FOLSOM, John AKERLEY, Matteo CUSINI, Chris SHERMAN, Ian WARREN, CorneÌ KREEMER, Hiroki SONE, Michael A. CARDIFF, Neal E. LORD, Peter E. SOBOL, Clifford H. THURBER, and Herbert F. WANG |
| Abstract |
The WHOLESCALE acronym stands for Water & Hole Observations Leverage Effective Stress Calculations and Lessen Expenses. The goal of the WHOLESCALE project is to simulate the spatial distribution and temporal evolution of stress in the geothermal system at San Emidio in Nevada, United States. To reach this goal, the WHOLESCALE team is developing a methodology that will incorporate and interpret data from four methods of measurement into a multi-physics model that couples thermal, hydrological, and mechanical (T-H-M) processes over spatial scales ranging from the diameter of a borehole (~0.1 m) to the extent of the entire field (~10 km) and temporal scales ranging from the duration of a microseismic event (~1 second) to the typical lifetime of a producing field (3 decades). The study site at San Emidio includes a volume with length of ~6 km, width ~5 km, and depth ~2 km. The WHOLESCALE team is taking advantage of the perturbations created by changes in pumping operations during a planned shutdown in April 2022 to infer temporal changes in the state of stress in the geothermal system. This rheological experiment is based on the key idea that increasing pore-fluid pressure reduces the effective normal stress acting across preexisting faults. The WHOLESCALE team conducted a field experiment in 2022 to collect data from seismology, drilling, geology, geodesy, and hydrology. A seismic array consisting of 450 three-component seismographs recorded for about a month around the time of a planned shutdown in April 2022. The hydrologic data set consists of pressure and temperature measurements in 13 observation wells recorded every 5 minutes from April through May 2022. Routine measurements of pressure, flow rate, and temperature at production and injection wells were also recorded. We are analyzing geodetic data from two continuously operating GPS stations, SEMS and SEMN, installed on monuments attached to idle wellheads within the geothermal field at San Emidio as well as from a third GPS station, named GARL, located outside the geothermal area in the mountain range to the northeast of the power plant, to calculate daily time series of displacement in three dimensions. We are analyzing Interferometric Synthetic Aperture Radar (InSAR) data acquired by the TerraSAR-X and TanDEM-X satellite missions operated by the German Space Agency (DLR) as well as the SENTINEL-1A and SENTINEL-1B satellite missions operated by the European Space Agency (ESA). At San Emidio, Ormat is drilling three new production wells (17A-21, 18A-21, and 25B-21 to the south of the power plant) and two new injection wells (84-20 and 25-28 to the north). Logs describing the lithology of the cuttings and circulation of the drilling mud are especially useful for characterizing the 3-dimensional structure. To capture fractures and breakouts, the drilling team is deploying Schlumberger’s full-bore Formation Micro Imager (FMI) tool in each of the the five new boreholes. In addition, well 17A-21 has been logged using the 3D Far-Field Sonic Service (3DFFS) from Schlumberger. In addition, rock cuttings from well 17A-21 were collected to measure density and porosity. An updated 3-D geologic and structural model of San Emidio has been completed, following an exhaustive review and re-interpretation of well cuttings and logs. The new model includes two separate fault strands that intersect the boreholes where circulation was lost during drilling. The San Emidio Fault and the southern end of the Piedmont Fault account for the loss zones seen in wells 61-21 and OW-9. To interpolate and interpret these rich data sets, the WHOLESCALE team is calculating the stress, strain, pressure, and temperature in the geothermal system using an open-source, numerical simulator named GEOSX. 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. |