Estimating Water Saturation at the Geysers Based on Historical Pressure and Temperature Production Data

Abstract

Available historical data from 503 wells at the Geysers geothermal field were analyzed to estimate in-situ water saturation in the reservoir. The pressure and temperature performance data of most of the wells demonstrate "dry-out" due to the formation of superheated steam. The in-situ water saturation of the reservoir can be inferred by using zero-dimensional models derived from mass and energy conservation equations. Techniques to identify the initial reservoir temperature and the dry-out temperature were developed and used in the saturation calculations. Effects of reinjection of the Geysers were analyzed and compared to models of depleted reservoirs. Regional trends of the saturation values plotted in the Cartesian plane were also investigated.