SUBSURFACE RESISTIVITY STRUCTURE BASED ON MAGNETOTELLURIC MODELING IN BLAC ROCK DESERT, UTAH

Abstract

Unconventional geothermal systems such as Enhanced Geothermal Systems (EGS) offer a clean energy solution by utilizing heat from deep, dry hot rocks. The successful implementation of EGS requires a thorough understanding of subsurface geological structures, particularly faults and fractures that can act as fluid pathways and thermal conductors. The Black Rock Desert in Utah is considered a promising region for EGS development due to its favorable geological features, including active faults, thick alluvial sedimentary deposits acting as cap rocks, and high subsurface temperatures based on previous drilling data. All MT data used in this study are publicly available (open source) data obtained from the Geothermal Data Repository (GDR). This study aims to perform two-dimensional subsurface resistivity modeling based on Magnetotellurics (MT) data, identify key geological structures, and assess their relationship with EGS potential in the study area. The data consists of three MT survey lines, which were analyzed using 2D inversion modeling by combining transverse electric (TE) and transverse magnetic (TM) modes. Each profile underwent 30 iterations, producing root mean square (RMS) error values ranging from 2.1 to 3.9. Additional analyses, includ- ing phase tensor, tipper, and polar diagram evaluations, were carried out to interpret subsurface complexity and structural orientation. The inversion results reveal the presence of conductive zones with low resistivity values (<10 ohm.m) interpreted as clay altered cap rocks, and deeper resistive zones (>100 ohm.m) associated with hot dry crystalline rocks. These resistive bodies are considered suitable targets for EGS reservoirs. Furthermore, the presence of fault structures and lateral resistivity contrasts indicates potential pathways for fluid migration an essential element in the functioning of EGS. Overall, the results support the interpretation that the Black Rock Desert possesses a favorable subsurface configuration for high temperature geothermal development through EGS applications.