In Situ Stress, Fracture, and Fluid Flow Analysis in Well 38c-9: an Enhanced Geothermal System in the Coso Geothermal Field

Geoscientists from the Coso Operating Company, EGI-Utah, GeoMechanics International, and the U.S. Geological Survey are cooperating in a multi-year study to develop an Enhanced Geothermal System (EGS) in the Coso Geothermal Field. Key to the creation of an EGS is an understanding of the relationship among natural fracture distribution, fluid flow, and the ambient tectonic stresses that exist within the resource in order to design a hydraulic and thermal stimulation of an east-flank injection well, the first step in the creation of a heat exchanger at depth. Well datasets from the east flank of the Coso Geothermal Field are being analyzed to develop an understanding of the relationships between natural fracture distribution, fluid flow, and the ambient tectonic stresses that exist within the resource. During the second year of this project, wellbore logs and stress data were acquired in a new production well drilled in the Coso Geothermal Field, 38C-9. The image analysis results include the discrimination of natural from drilling induced fractures in wellbore image data, natural fracture characterization, and wellbore failure analysis. A hydraulic fracturing stress test at 3,703 feet TVD was used to constrain a normal faulting and strike-slip faulting stress tensor for this reservoir. The shear and normal stresses resolved on the fracture and fault planes were calculated and used to identify the subset of critically stressed planes that act to maintain permeability within the Coso Geothermal Field.