EGS: The Geysers: Why is water injection necessary at The Geysers?
Geothermal Plant Water injection into geothermal systems has become a nearly universal and often required strategy at The Geysers for extended and sustained production of geothermal resources. For example, to reduce a trend of declining pressures and increasing non-condensable gas concentrations in steam produced, operators have been injecting steam condensate, local rain and stream waters, and most recently treated wastewater piped to the field from neighboring communities. Figure 1 shows the injection pattern from two main sources of water—the Santa Rosa, California, wastewater pipeline (~11 million gallons per day) and the Lake County, California, wastewater pipeline (~7 million gallons per day). Also shown in this figure are the seismic stations used to monitor the seismicity and the injection points.
Figure 1. Location of water injection pipelines and injection points. Also shown are the locations of the seismic monitoring stations.
Without this injected water, the thermal capacity of The Geysers would be underutilized, and The Geysers would not be able to provide California with as much low-cost electricity as possible. By their very nature, vapor-dominated and very hot “tight” geothermal reservoirs such as The Geysers are water-short systems. These are prime candidates for enhanced geothermal activities. If The Geysers were produced without simultaneously injecting water, reservoir pressures and flow rates from production wells would decline fairly rapidly, and would reach uneconomically small levels—while enormous heat reserves would still remain in the reservoir rock. Furthermore, in some of these systems, a significant portion of the recoverable geothermal energy is currently underutilized due to high concentrations of non-condensable gas and corrosive HCl. Mitigation of these deleterious components through water injection would significantly increase the resource.