Thoughts on Stress around The Geysers Geothermal Field

Abstract

This paper approaches the structural geology of the Geysers geothermal field from the perspective of stress relationships. The least principal stress is horizontal and oriented approximately N80W while ?1 = ?2. . A number of published reports on production trends are reviewed and show that pressure sinks are developing along the conjugate shear directions while injected fluids preferentially utilize structures perpendicular to ?3. Stress in the vicinity of the reservoir is approximated by a simple two dimensional model for stress in the vicinity of a subsurface excavation. This model demonstrates areas of high and low stress surrounding the reservoir. It also demonstrates or concept that a structural arch ahs resulted in the decoupling of the reservoir form the vertical stress. These relationships may be important in planning and managing successful reinjection into the reservoir.