Seismic Reflection Profiling at the FORGE Utah EGS Site

摘要

New three-dimensional multichannel and two-dimensional seismic reflection data were acquired across, and extending eastward and westward from, the FORGE Utah site in November 2017 and were processed and interpreted between December 2017 and February 2018. These data supplement two previously existing two-dimensional seismic lines located adjacent to the south and west edges of the site that were licensed in September and October 2017 from Seismic Exchange, Inc. The data image two broad rock types comprising basin fill sediments and crystalline basement rocks; the latter is mostly made of Miocene granitoids that will host the proposed EGS reservoir. The contact between these rock types forms an inclined surface that dips 20° - 30° west and appears as a strong reflection on all seismic lines within and to the south of the site. These data add to numerous independent datasets, including new geological, geophysical, and geochemical surveys, plus drilling and logging of the new deep vertical well 58-32 to 7536 ft (2248 m) depth and help to confirm the suitability of the FORGE Utah site for development of an underground EGS laboratory. This paper briefly describes the data acquisition effort and processing techniques used to create the seismic images, and focuses on the interpretation of the 3D survey. The key finding is a west-dipping valley and ridge structure to the granitoid surface. The simplest interpretation is that the granitoid surface is likely an erosional feature similar in scale to the western flank of the Mineral Mountains, rather than the previously interpreted detachment fault surface. This does not preclude detachment tectonics occurring during basin evolution.