Development of an Injection Augmentation Program at the Dixie Valley, Nevada Geothermal Field

Abstract

Evaporative cooling at geothermal power plants generally reduces reservoir pressures even if all available geothermal liquids are reinjected. Controlled programs of injecting nongeothermal waters directly into reservoirs have been tested or implemented at only four fields, three of them being vapor dominated. At the liquid-dominated Dixie Valley geothermal field an unsuccessful search for a large volume source of warm, chemically desirable fluid for augmentation was conducted. After determining water treatment was uneconomical, an augmentation program utilizing cold shallow groundwater rich in Ca and Mg was implemented in mid 1997. This required extensive bench testing of various waters for scaling potential, obtaining water rights, rehabilitating an irrigation well, and constructing a polyethylene pipeline to a dedicated injector. During the first two years of this program four different injectors have been utilized and tested. An injection augmentation rate of approximately 30 kg/sec is capable of stabilizing the Dixie Valley reservoir pressure. Higher rates result in increasing reservoir pressure. This program has not resulted in decreased injectivity of the dedicated injectors. One injection well showed a greatly increased injectivity. Monitoring of production chemistry has demonstrated that most, if not all, of the calcium and magnesium injected with the shallow groundwater is precipitating between the injection and production wells. Monitoring of the shallow groundwater aquifer has demonstrated that this aquifer is very large and is capable of supplying water indefinitely. Small drawdowns of this aquifer indicate subsidence is unlikely to be a problem.