Geophysical Signatures of the Utah FORGE Site, Northern Milford Basin, Utah

Abstract

Geophysical data collected in the 2017 field season were combined with legacy data and used in a preliminary characterization of the Utah FORGE site located in the northern Milford basin of southeastern Utah. The site is situated over buried Tertiary-Quaternary granitic intrusions and Precambrian gneiss that crop out in the Mineral Mountains to the east and are at 3.1 km depth in the Acord-1 well near the center of Milford Valley 10 km to the west. A recently compiled suite of geophysical data consists of downhole geophysical logs, thermal data, and gravity and Transient Electromagnetic Method (TEM) measurements. A total of 342 new gravity and 23 TEM stations have been added to the existing area for the FORGE project. Modeling of the 20 mGal gravity low, the result of basin fill overlying the granitic basement, was accomplished using a decreasing density contrast with increasing depth based primarily on geophysical downhole logs and local geologic information. Preliminary 2D models show the granite gently dips to the west beneath surficial alluvial fan deposits on the western edge of the Mineral Mountains. At the FORGE site, the initial gravity models indicated basin-fill thickness over the geophysical basement to be 650 m and drilling confirmed the thickness to be 653 m. As this project moves forward, future 3D models created from gravity, TEM, and well logs will enhance our understanding of the subsurface properties and structures within the study area. These findings will provide insight into how these characteristics affect the thermal regime.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018