Strength Measurements of The Geysers Reservoir Rock

Abstract

Rock samples taken from two outcrops and cores from well bores at the Geysers geothermal field were tested at temperatures and pressures similar to those found in the field. Both intact cylinders and cylinders containing 30° saw cuts were deformed at confining pressure of 200 to 1000 bars, pore pressure of 30 bars, and temperatures of 150 and 250°C. Constant strain rate tests gave a coefficient of friction of 0.68. Friction was independent of rock type, temperature and strain rate. Most cores taken from the producing zone were highly fractures. For this reasons, intact samples were rarely 50% stronger than the frictional strength. At 500 bars confining pressure, P wave velocity of 6.2 km/sec was measured for a sample taken from an outcrop. Porosities and permabilities were also measured.