Water Injection Management for Resource Maximization: Observations from 25 Years at the Geysers, California

Abstract

Injection at The Geysers began in 1969 as a way to dispose of excess steam condensate. The steam reservoir was selected as the disposal target because its high injectivity would assure reliable plant operation, and because injection there could be expected to improve steam production after several years. The thermodynamic conditions at the time were such that injection could reduce but did not immediately increase production. Greatly increased injection volumes have accompanied development of the geothermal field, Long-term injection management has been guided by reservoir performance studies, including large scale tests of concentrated injection in the most pressure-depleted areas. Several studies are reviewed, including chemical and radioactive tracer tests, geochemical sampling programs, and seismic monitoring. The results have been successfully combined to determine the flow patterns and boiling rates of injected water. Injected water, either steam condensate or from local creeks, has become a significant source of steam throughout the field. Injection is being used to mine energy from pressure-depleted areas with high rock temperatures. Early reservoir engineering estimates of injectate boiling rate have been confirmed by trends in isotope concentrations in the produced steam.