The impact of injection on seismicity at The Geysers, California Geothermal Field

Water injection into geothermal systems has often become a required strategy to extend and sustain production of geothermal resources. To reduce a trend of declining pressures and increasing non-condensable gas concentrations in steam produced from The Geysers, operators have been injecting steam condensate, local rain and stream waters, and most recently treated wastewater piped to the field from neighboring communities. If geothermal energy is to provide a significant increase in energy in the United States (the US Department of Energy goal is 40,000 MW by 2040), injection must play a larger role in the overall strategy, i.e., enhanced geothermal systems (EGS). Presented in this paper are the results of monitoring microseismicity during an increase in injection at The Geysers field in California using data from a high-density digital microearthquake array. Although seismicity has increased due to increased injection, it has been found to be somewhat predictable, thus implying that intelligent injection control may be able to control large increases in seismicity.