The Nature of Steam Bearing Fractures in The South Geysers Reservoir

Abstract

The distribution of steam bearing fractures over 100 wells in the South Geysers reservoir indicates an effectively random fracture network. Low angle productive fractures of limited lateral extent are irregularly dispersed within blocks bounded by high angle fractures of random strike. The upper surface of the reservoir exhibits major vertical offsets at block edges. The lower, and the northeastern and southeastern reservoir margins are gradational in nature and dominated by high angle fractures with diminishing fracture density. Permeability is enhanced in the north to north northeast direction as evidenced by tracer studies. This is compatible with the stress field orientation in the Geysers as determined from seismic studies.