Frontier Observatory for Research in Geothermal Energy (FORGE) is a US government program supporting research into geothermal energy. ^[1] The FORGE site is near Milford, Utah, funded for up to $140 million. As of 2023, numerous test wells had been drilled, and flux measurements had been conducted, but energy production had not commenced. ^[2]

History

In February 2014, the Department of Energy (DOE) announced the intent to establish "a dedicated subsurface laboratory" ^[1] to investigate and develop enhanced geothermal systems. ^[3] In June 2018 DOE funded a location outside of Milford, Utah for up to $140 million. ^[4]

Site

The site is located along the Colorado Plateau and Basin and Range Province transition zone. It is primarily composed of intrusive Oligocene through Miocene batholith emplaced into Precambrian metamorphic ( Gneiss) and Paleozoic sedimentary rocks. ^{[5] [6]} The site is west of the Mineral Mountains and about two km east of the north–south trending Opal Mond Fault (OMF), perpendicular to the east–west trending Negro Mag Fault (NMF). ^{[5] [7]} FORGE is dominated by a fault-fracture mesh system with OMF as one of its most active features. ^{[6] [8]} Fault structures vary from steeply dipping faults west of the Mineral Mountains to more gently steeping faults to the east. ^{[6] [5]}

The reservoir is located approximately between 1,525 and 2,896 meters (~5,000-10,000 ft) depth in which temperature ranges from 175 to 225 °C. ^[9] The rock is aged from 8 Ma to 25.4 Ma. ^{[10] [11] [12]} Roosevelt Hot Springs (RHS) to the east is a hydrothermal area with temperatures ranging from about 100°C at the surface to over 250 °C at a depth of roughly 4000 meters (13,123.4 ft). ^[8] These temperatures indicate the presence of cooling magma in the shallow crust. ^[8]

Research

More than 80 shallow gradient wells (<500 m depth) and 20 deeps wells (>500 m depth) were drilled. ^{[13] [14]} Analyses from the shallow well data reported that the encountered granitic rocks were not producing fluids, but were hot. ^[13] A lack of fluid production indicated these rocks are impermeable and that the site is a classic example of a hot dry rock energy system. ^[9] The thermal grounds cover most of the northern Milford valley. ^{[13] [14]} The highest temperature wells (greater than 80 °C) are located east of the OMF above the RHS hydrothermal system. ^[14] Near-surface profiles (less than 80 m depth) of temperature gradient are similar in central, southern and western sectors at roughly 70 °C per km and do not exceed 270 °C, even at higher temperature wells to the west. ^[14]

The primary well descends vertically 6,000 feet (1.8 km), then continues 5,000 feet (1.5 kilometers) at a 65 degree angle. The well employed a diamond-tipped bit, cutting drilling costs by 20 percent. ^[2]

References