This study investigates the influence of modeling choices related to the scale of reservoir heterogeneity on the predicted performance of geothermal doublets in fluvial low-enthalpy geothermal reservoirs. Fourteen geocellular grids were created to systematically analyze the impacts of numerical grid resolution, permeability upscaling methodology, and modeled scales of sedimentary architecture, using MODFLOW-2005 and MT3D-USGS to simulate groundwater flow and heat transport for well-doublet operation over a 35-year period. The results reveal complex relationships between these choices and simulated reservoir behavior: the considered factors have significant influence on injection pressures but only a modest effect on production temperatures (with variations within 2 °C after 35 years across all models), likely due, at least in part, to a relative dominance by thermal diffusion over heat advection in the considered scenarios. Simplification of geological architecture through omission of fine-scale features may augment the hydraulic impact of larger flow barriers, such as abandoned-channel mud plugs. The highest injection pressures were simulated on grids that embody sedimentary architectural elements but lack internal facies heterogeneity. The permeability upscaling method also has an effect: simulations on grids upscaled using harmonic averaging consistently yield the highest near-injector pressures, followed by those based on geometric averaging and arithmetic averaging. The dynamic behavior of grids upscaled via flow-based upscaling closely approximates that of grids upscaled using arithmetic averaging, suggesting that bulk hydraulic behavior is dominated by the connectivity of high-permeability units. The performance gap between grids following different upscaling methods decreases significantly for higher grid resolution. Simulations of geological models that incorporate increasingly detailed geological features predict cold-water plumes with slightly more complex shapes and tortuous fronts, as documented by values of plume surface-to-volume ratio. The complexity of the cold-water plume shape, as measured by the surface-to-volume ratio, is slightly higher for well doublets oriented at a high angle to the channel-belt axis, but does not increase systematically with the resolution at which fine-scale features are represented.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)