Geothermal power generation and mineral extraction from geothermal brines are affected by chemical processes within the reservoir. Until recently, numerical simulation technology for geothermal systems could not handle most chemical processes, except for tracking total salinity, one or two non-condensable gases, and non-reactive tracers. The Lawrence Berkeley National Laboratory (LBNL) has developed an enhanced version of their geothermal reservoir simulation software TOUGH2, developed with funding from the U.S. Department of Energy. This highly innovative software (TOUGHREACT) includes comprehensive chemical interactions between liquid, gaseous and solid phases that are coupled to the modeling of solute transport and subsurface multiphase fluid and heat flow.

Pressure decline within The Geysers geothermal reservoir has resulted in decreased power output from existing power plants. As a means of partially arresting these ,pressure declines, several field operators and the County of Lake propose to add approximately 13,000 lpm of treated municipal waste water from several small communities into 6 injection wells in the southeastern corner of the field. Water will be carried to the geothermal field via a 50- or 6O-cm diameter pipeline from the vicinity of Clear Lake, a distance of about 45 km. The results of this study suggest that the proposed injection of effluent could help reducing the high rate of pressure and production rate declines without inducing significant geochemistry incompatibility or microseismicity.