Geochemical consequences of treated waste water injection at the geysers, USA geothermal field

• Published in: Geothermics 1989, Vol.18 (1), p.65-72
• Main Authors: Crecraft, Harrison R., Koenig, Brian A.
• Format: Article
• Language: English
• Subjects: 150302 - Geothermal Exploration & Exploration Technology- Geochemical Techniques & Surveys; 150303 - Geothermal Exploration & Exploration Technology- Exploratory Drilling & Well Logging; 152001 - Geothermal Data & Theory- Properties of Aqueous Solutions; CALIFORNIA; CHALCOGENIDES; CHEMICAL REACTIONS; COMPUTERIZED SIMULATION; DATA ANALYSIS; DISSOLUTION; ENERGY TRANSFER; FEDERAL REGION IX; FLUID INJECTION; GEOTHERMAL ENERGY; GEOTHERMAL FIELDS; GEYSERS GEOTHERMAL FIELD; HEAT TRANSFER; HYDROGEN COMPOUNDS; INJECTION WELLS; LIQUID WASTES; MINERALS; NORTH AMERICA; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; PERMEABILITY; QUARTZ; SILICON COMPOUNDS; SILICON OXIDES; SIMULATION; STEAM GENERATION; USA; WASTE WATER; WASTES; WATER; WATERFLOODING; WELLS
• ISSN: 0375-6505; 1879-3576
• DOI: 10.1016/0375-6505(89)90011-4

Injection of treated waste water (SRWW) from the City of Santa Rosa, CA, was considered as a means to increase liquid reserves in The Geysers, a vapor-dominated geothermal field in Northern California. We conducted a study to evaluate the geochemical effects of this process. Computer modelling using EQ3/6 permitted comparison of mineral precipitation/dissolution effects between SRWW and two current injectates: produced steam condensate, and meteoric water from Big Sulfur Creek (BSCW). Total dissolved solids content of SRWW (400 ppm) is intermediate to those of BSCW (142 ppm) and steam condensates (140–4500 ppm). Suspended solids contents of three injectates range from 4 to 187 ppm; their effects are also considered. Although TDS and TSS contents are low, large injection volumes coupled with fracture dominated flowpaths suggest a potential for significant permeability reduction. A conceptual model involving injectate propagation, heat transfer, and chemical processes provides the framework for evaluating simulation results. Computer modeling indicates that, prior to substantial boiling, injection of any of the liquids examined can result in a net porosity increase. This result reflects the fact that in each case modeled volumes of dissolved quartz exceed modeled precipitate mineral volumes. Several questions must be addressed to evaluate the applicability of this conclusion. Foremost among these are: 1) the availability of quartz within fractures, 2) the rate of injectate heating, 3) the kinetics of mineral precipitation/dissolution reactions, and 4) the nature of suspended solids deposition. Thus, geochemical modelling does elucidate potentially important processes, but additional data are required to realistically evaluate the consequences of fluid injection.