Heat Extraction Performance and Modelling


H. D. Murphy

Geo Location:

Fenton Hill, New Mexico; Valles Caldera, New Mexico


Stanford Geothermal Workshop







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On May 28, 1977, as the production well GT-2 at Fenton Hill was being redrilled along a planned trajectory, it intersected a low-impedance hydraulic fracture indirect communication with the injection well, EE-1. Thus, a necessary prerequisite for a full- scale test of the LASL Hot Dry Rock Concept, that of establishing a high flow rate between wells at low wellhead differential pressures, was satisfied. Previously, communication with EE-1 had been through and between high-impedance fractures, and flow was insufficient to evaluate the heat- extraction concept.

In September a preliminary test of the entire system-surface plant and downhole flow paths was conducted. During 96 h of closed-loop circulation, fluid total dissolved solids remained low ( ~ 4 0 0 ppm), water losses continually decreased, and no induced seismic activity occurred. The operating power level was 3.2 MW (thermal) and fluid temperature reached 130?C at the surface. This test demonstrated for the first time that heat could be extracted at a usefully high rate from hot dry rock at depth and transported to the surface by a manmade system.

Full-scale operation of the loop occurred for 75 days from January 27 to April 12, 1978. This test is referred to as Phase 1. Segment 2 and was designed to examine the thermal drawdown, flow characteristics, water losses, and fluid geochemistry of the system in detail. Results of these studies are the major topic of this paper which is divided into three separate parts covering first the heat extraction performance, second the flow characteristic s and geochemistry and third the use of acoustic techniques to describe the geometry of the fracture system. In the third section, dual- well acoustic measurements used to detect fractures are described. These measurements were made using modified Dresser Atlas logging tools. Signals intersecting hydraulic fractures in the reservoir under both hydrostatic and pressurized conditions were simultaneously detected in both wells. Signal attenuation and characteristic waveforms can be used to describe the extent of fractured rock in the reservoir. A detailed account of the field test can be found in ref.[l].

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