Reservoir response to injection in the Southeast Geysers

A 20 megawatt (MW) increase in steam flow potential resulted within five months of the start-up of new injection wells in the Southeast Geysers. Flow rate increases were observed in 25 wells offset to the injectors, C-11 and 956A-1. This increased flowrate was sustained during nine months of continuous injection with no measurable decrease in offset well temperature until C-11 was shut-in due to wellbore bridging. The responding steam wells are located in an area of reduced reservoir steam pressure known as the Low Pressure Area (LPA). The cause of the flowrate increases was twofold (1) an increase in static reservoir pressure and (2) a decrease in interwell communication. Thermodynamic and microseismic evidence suggests that most of the water is boiling near the injector and migrating to offset wells located ''down'' the static pressure gradient. However, wells showing the largest increase in steam flowrate are not located at the heart of the pressure sink. This indicates that localized fracture distribution controls the preferred path of fluid migration from the injection well. A decrease in non-condensible gas concentrations was also observed in certain wells producing injection derived steam within the LPA. The LPA project has proven that steam suppliers can work together and benefit economically from joint efforts with the goal of optimizing the use of heat from The Geysers reservoir. The sharing of costs and information led directly to the success of the project and introduces a new era of increased cooperation at The Geysers.