High rock temperatures, a high degree of fracturing, high tectonic stresses, and low permeability are the combination of qualities that define an ideal candidate-Enhanced Geothermal System (EGS) reservoir. The Coso Geothermal Field is an area where fluid temperatures exceeding 300?C have been measured at depths less than 10,000 feet and the reservoir is both highly fractured and tectonically stressed. Some of the wells within this portion of the reservoir are relatively impermeable, particularly on the margins of the field. Geoscientists from the Coso Operating Company, EGI-Utah, and GeoMechanics International Inc. are using well datasets from the east flank of the Coso Geothermal Field to develop an understanding of the relationships between natural fracture distribution, fluid flow, and the ambient tectonic stresses that exist within the resource. Technical results from the first year of analysis are presented.

The results discussed here are from the first year of a five year project and include the discrimination of natural from drilling-induced fractures in wellbore image data in the four study wells, natural fracture characterization, wellbore failure characterization, and the correlation of natural fractures and faults with fluid flow indicators. Cuttings collected during the drilling of each of the four east-flank study wells are used to determine the lithologies of the hydrothermally altered zones, the characteristics of the vein fillings, and the extent of large-scale faulting.

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