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We present thermo-hydro-chemical simulations of silicic geothermal reservoirs over ∼20 year durations. For injection of undersaturated or oversaturated water with respect to the solubility of amorphous silica, the highest rates of reactive alteration occur at some distance away from the injection well. This is largely because the temperature dependence of the reaction rate plays a much greater role than temperature dependent solubility. For oversaturated injection, precipitation occurs in a band, confining the flow system to smaller areas. For undersaturated injection, dissolution causes permeability growth far from the injection well, resulting in longer flowpaths that prevent short-circuits, which implies favorable conditions for sustained energy production. Initial permeability heterogeneity influences reservoir response significantly only when the correlation lengths are of the order of 1/10th of the fracture size or more. [ABSTRACT FROM AUTHOR]

Abstract: A fuzzy set overlay model is used to analyze the distribution of moulins (vertical meltwater conduits) on Sermeq Avannarleq (“Dead Glacier”) in West Greenland in 1985 and 2008–09. Input data is derived from a historical topographic map based on airborne visible imagery and more recent WorldView-1 panchromatic imagery, as well as an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation model (DEM). A non-parametric best-fit model approach using a Monte Carlo simulation is used to derive the membership functions for moulin location based on three independent variables – elevation, slope and aspect – and to test for the robustness of the model. We determine that there is a topographic setting independent of time that favors the development of moulins in this region. Using the membership functions, and an optimal alpha cut derived for 1985, we could correctly predict the locations of ~88% of the moulins in 2008–09. The model accounts for increased surface melt in 2008–09 in comparison to 1985. Our results demonstrate the potential of a fuzzy set based approach to improve models of ice sheet hydrology in Western Greenland, by providing more reliable spatial distributions of entry points of meltwater into the ice based on remotely sensed datasets of the ice surface, which are readily available. [Copyright &y& Elsevier]

Highlights: [•] A multispecies transport model of dissolution/precipitation in carbonate reservoir. [•] Rapid alteration of effective transmissivity by reaction kinetics in calcite. [•] Fast reaction rate creates problem for long term operation of geothermal power plant. [•] The evolution of transmissivity is very sensitive to injection concentration and temperature. [Copyright &y& Elsevier]