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. When dealing with 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. However, to the best of our knowledge, gels have not been applied to EGS to enhance heat extraction. In the current study, we explore the benefit of using gels as a means to alter the flow field in a fracture network, to create fluid circulation cells, and to design alternating sweeping zones for maximum heat extraction. As a first step, we present results relevant to a single smooth and rough surface fracture where flow and gel-transport equations are simultaneously solved using finite element methods. The effect of gelation on the hydraulic properties of the geo-fluid, e.g., viscosity and fracture aperture, are also considered. Several scenarios based on different in-situ conditions were simulated. As a second step, a fracture network composed of a few fractures was used to illustrate the design of several injection and production scenarios with an emphasis on maximizing the heat extraction and minimizing geo-fluid losses. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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