Numerical modeling of water injection into vapor-dominated geothermal reservoirs

Water injection has been recognized as a powerful technique for enhancing energy recovery from vapor-dominated geothermal systems such as The Geysers. In addition to increasing reservoir pressures, production well flow rates, and long-term sustainability of steam production, injection has also been shown to reduce concentrations of non-condensible gases (NCGs) in produced steam. The latter effect improves energy conversion efficiency and reduces corrosion problems in wellbores and surface lines.This report reviews thermodynamic and hydrogeologic conditions and mechanisms that play an important role in reservoir response to water injection. An existing general-purpose reservoir simulator has been enhanced to allow modeling of injection effects in heterogeneous fractured reservoirs in three dimensions, including effects of non-condensible gases of different solubility. Illustrative applications demonstrate fluid flow and heat transfer mechanisms that are considered crucial for developing approaches to in situ abatement of NCGs