| Abstract |
Fractures and fracture networks are the principal pathways for migration of water and contaminants in groundwater systems, fluids in enhanced geothermal systems (EGS), oil and gas in petroleum reservoirs, carbon dioxide leakage from geological carbon sequestration, and radioactive and toxic industrial wastes from underground storage repositories. In EGS fracture networks, there are several major issues to consider, e.g., the minimization of hydraulic short circuits and losses of injected geothermal fluid to the surrounding formation, which in turn maximize heat extraction and economic production. Gel deployments to direct and control fluid flow have been extensively and successfully used in the oil industry for enhanced oil recovery, and to divert and contain radioactive and toxic wastes. However, to the best of our knowledge, gels have not been applied to EGS to enhance heat extraction. Inorganic gels, such as colloidal silica gels, may be ideal blocking agents for EGS systems if suitable gelation times and control of gelation behavior can be achieved. In the current study, we explore colloidal silica gelation times, rheology, and gel stability as a function of SiO2 concentration, pH, salt concentration, and temperature up to 300 °C. Results at 25 °C show that it may be possible to choose formulations that will gel in a reasonable and predictable amount of time at EGS temperatures. Results at EGS temperatures indicate that usage of colloidal silica gels may be limited in very high-temperature reservoirs, but may be ideal for reservoir modification at low to medium EGS conditions. |