Two hot dry rock (HDR) geothermal energy reservoirs were created by hydraulic fracturing of granite at 2.7 to 3.0 km (5000 to 10000 ft ) at the Fenton Hillsite, near the Valles Caldera in northern New Mexico. Both reservoirs are research reservoirs, in the sense that both are fairly small, generally yielding 5 MWt or less, and are intended to serve as the basic building blocks of commercial-sized reservoirs, consisting of 10 to 15 similar fractures that would yield approximately 35 MWt over a 10 to 20 yr period. Both research reservoirs were created in the same well-pair, with energy extraction well number 1 (EE-1) serving as the injection well, and geothermal test well number 2 (GT-2) serving as the extraction, or production, well. The first reservoir was created in the low permeability host rock by fracturing EE-1 at a depth of 2.75 km (9020 ft ) where the indigenous temperature was 185?C (364?F). Reservoir performance was evaluated by a 75-day long period of closed-loop operation from January 28 to April 13, 1978. Hot water from the production well was directed to a water-to-air heat exchanger where the water was cooled to 25?C before reinjection. The relatively low power produced did not economically justify the conversion of the geoheat to beneficial usage, so it was simply dissipated to the atmosphere by this heat exchanger. cooled water, in addition to the makeup water that was required to replace downhole losses to the rock surrounding the fracture, was then pumped down the injection well and then through the fracture system. Heat was transferred to the water by means of conduction with in the nearly impervious rock contiguous to the fracture surfaces and the heated water was withdrawn by means of the production well. Results of the 75-day assessment of the first reservoir were presented by Murphy et al. (1978), Tester and Albright (1979), and Murphy and Tester (1979) but are summarized for comparison with the second reservoir below.

A second, larger reservor was formed by extending a small existing fracture at 2.93 km (9620 ft ) in the injection well about 100 m deeper and 10?C hotter than the first reservoir. Large fracture propagated upward to about 2.6 km (8600 ft ) peared to have an inlet -to- outlet spacing of 300 m (1000ft), more than three times that of the first fracture. Comparisons are made with the first reservoir in Table 1. Evaluation of the new reservoir was accomplished in two steps: (1) with a 23-day heat extraction experiment that began October 23, 1979, the results of which are described by Murphy (1980), and (2) a-second, longer-term heat extraction experiment still in progress, which as of November 25, 1980 has been in effect for 260.days. The results of this current experiment are compared with earlier experiments below.

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