LASL Hot Dry Rock Geothermal Project. Progress report, July 1, 1975--June 30, 1976

Abstract

Successful drilling into hard crystalline rock was accomplished to depths of about 3 km. Hydraulic fractures in the crystalline rock with radii as large as 150 m were produced. Values of in situ permeability of the Fenton Hill granite were measured. Directional drilling at depths of up to 3 km was accomplished. At least 90 to 95 percent of water injected into fractured regions was recovered. A connection was established between two deep boreholes through a fractured region of hot granite for the first time. Instruments were developed to operate for several hours under the downhole conditions. The compressional and shear components of seismic signals produced by fracture extension and inflation were detected downholes. Acoustic ranging has generally identified the relative positions of two boreholes at several depths. Self-potential and induced potential techniques have determined vertical fracture lengths at the borehole. Pressure-flow and fluid residence time distribution studies have measured properties of the downhole system. Core sample studies have provided physical and chemical data. Techniques were developed to examine reservoir performance. A geothermal power-production model was formulated. (MHR)

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