A New Look at the Thermal Regime Around Roosevelt Hot Springs, Utah

摘要

Recent re-evaluation of thermal data from over 100 wells drilled mostly during the 1970s and 1980s in the area of Roosevelt Hot Springs (RHS) has refined earlier interpretations of the thermal regime. These data have been combined with pre-existing gravity and magnetotelluric data to construct a 3-D model of the area as part of the site characterization phase of U.S. Department of Energy's Frontier Observatory for Research in Geothermal Energy (FORGE) initiative. The project goal is to create an enhanced geothermal system (EGS) reservoir in crystalline rock where temperatures of 175 to 225°C are present at depths between 1.5 and 4 km to test development concepts and technology. The 3-D model is amply supported by well data, both in terms of suitable temperatures and depth to crystalline basement (Precambrian gneiss and Tertiary plutons), and shows that FORGE temperature and lithologic requirements can be met over an area of at least 100 km~2. The total volume of crystalline basement rock with temperatures over 175°C above 4 km depth is more than 100 km~3. Temperatures greater than 175°C within plutonic basement rock are expected at depths ranging from about 1.8 to 3.0 km, depending on the specific location, over most of the area best suited for deep FORGE drilling based on land ownership, existing roads, and topographic features. Nearly all of the FORGE area achieves 175°C by 4 km depth. While RHS is an active hydrothermal system, heat transport farther to the west, on the opposite side of the Opal Mound fault, is primarily conductive. The thermal regime based on deep temperatures and reservoir rocks suggests the site is ideal for FORGE development.