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Evaluating Silica Scaling in Enhanced Geothermal Systems Under Dispatchable Scenarios for Both Conventional and Waste Heat Injection Scenarios
Georgia CARUSO CARTER, Esuru Rita OKOROAFOR, Roman J. SHOR
[Texas A&M University, USA]
With the development of technology for enhanced geothermal energy, there is a growing potential for its application in dispatchable geothermal energy. Dispatchable energy has the added benefit of optimized economics, with the ramping up of production during high energy demand and high energy prices and reduction of production during low demand and energy prices. As enhanced geothermal systems tend to target granite layers for their reservoir, silica scaling is a growing concern. The injection of cold water in the fractured system causes the silica to precipitate out of solution in the reservoir, decreasing flow and accelerating the thermal drawdown as silica scaling acts as an insulator. This paper evaluates the subsurface effects of the cyclical pressure and temperature changes, that are a result of the nature of dispatchable geothermal energy, and its effect on silica scaling in the reservoir. A non-isothermal reservoir numerical simulator was applied to develop a reservoir model of an enhanced geothermal system in an artificially stimulated granite reservoir. The model evaluates thermal-hydraulic flow, time-dependent heat transport, and geochemical equilibrium calculations for silica solubility. A variety of multiple production-rest cycles are evaluated, as well as waste heat storage to evaluate optimal production scenarios. The simulation results stress the importance of accounting for silica scaling in enhanced geothermal systems, particularly in dispatchable production cases. Optimal operational thresholds are defined for the typical multiple production-rest case, as well as for the waste heat storage case. These thresholds decrease the need for scaling intervention and decrease the production losses associated with the scaling.
Topic: Enhanced Geothermal Systems