Steam Chemistry Monitoring the Navy I Area of the Coso Geothermal Field

Abstract

Steam chemistry is used to monitor the wells that supply steam to the Navy I power plant at the Coso Geothermal Field. Almost all of the wells are dry steam wells, that are part of a steam cap. Analysis of the Non-condensable gas is used to calculate reservoir temperature and steam saturation using the Methane breakdown and pyrite-H2S reaction. Reservoir vapor saturation of Y values are calculated between 5-15 percent. With temperature from 220 to 270 Degrees C calculated. Reservoir Temperature calculations vary more than the Y fraction calculations. Variable Non- condensable gas concentrations monitor the influx of fluids that mix in the reservoir. Specifically changes in H2S to the Navy I area as a whole. Sustained stable steam flowrates have been produced to the Navy I power plants over the last four years. A State of equilibrium between natural recharge, injection and production now exists resulting in a very low decline rate. The Navy I production wells are the shallowest in the field and steam contributions from other parts of the field and the margins contribute to the steam produced from the steam cap.