Thermal Gradient Holes At Fenton Hill HDR Geothermal Area (Purtymun, Et Al., 1974)

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Exploration Activity: Thermal Gradient Holes At Fenton Hill HDR Geothermal Area (Purtymun, Et Al., 1974)

Exploration Activity Details
Location Fenton Hill HDR Geothermal Area
Exploration Technique Thermal Gradient Holes
Activity Date - 1972
Usefulness useful
DOE-funding Unknown

Exploration Basis
Drilling at the Fenton Hill site began around 1972, when thirteen temperature gradient holes were drilled around the periphery of the Valles caldera in order to locate an of high heat flow that would serve as a favorable test site for the HDR concept.
Data from these wells are report in Reiter et al. (1976) and Purtyman (1973). Of these wells, well GT-1 was the first hole drilled at Fenton Hill. Well GT-1 was drilled to a depth of 785 m in Barley Canyon, and was designed to measure the heat flow at the site, acquire samples of basement rocks, and to test hydraulic fracturing techniques in crystalline basement rocks. The well encountered basement rocks consisting of Precambrian amphibolite and granitic gneiss at 642 m depth. Maximum temperatures in excess of 96°C were measured at the bottom of the hole. Temperature gradients in GT-1 decreased with increasing depth, from 137.9 +/- 2.5°C/km (60-140 m depth), to 125 +/- 5.3°C/km (140-480 m depth), to 94.8 +/- 2.2°C/km (490-640 m depth), and final to 46.8 +/- 4.3°C/km (640-720 m depth). These variations in temperature gradient were interpreted to result from channeled groundwater flow in the lower sections of the hole. Despite these results, the overall heat flow was found to be highest on the western margin of the caldera, and the Fenton Hill site was chosen to test the HDR concept. These drilling activities are the closest approximation to exploration work conducted at the site prior to development of the HDR reservoirs.


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