Isotopic and Chemical Constraints on Reservoir Fluids from the Coso Geothermal Field, California

Abstract

Sampling of reservoir fluids from more than 45 geothermal production wells has provided excellent light stable isotopic and chemical constraints on field wide reservoir characteristics. Hydrogen, oxygen, carbon and sulfur isotopic compositions give information on the sources of these components and constrain fluid rock interactions and reservoir processes which have occurred in the system. Studies of reservoir fluid chemical variations indicate a very complex reservoir. Two discrete two phase regions appear to exist, as well as three distinct single phase (liquid) regions of the field. This apparent compartmentalization of Coso reservoir chemistry can be interpreted to reflect one or more of the following: 1) a very young reservoir, 2) one that is poorly interconnected or 3) one strongly affected by local wall rock variations or reservoir processes.