Formula omitted]-plume geothermal in fluvial formations: A 2D numerical performance study using subsurface metrics and upscaling

Abstract

CO2-plume geothermal (CPG) operations are considered for sufficiently permeable formations due to their superiority compared to conventional water-based geothermal systems. The fluvial heterogeneity in sedimentary reservoirs can significantly affect the pumping energy losses and heat extraction from hot sedimentary aquifers. In the present study, we have implemented the braided type of fluvial channels to account for the geological uncertainty, and investigated the subsurface performance metrics of a CPG system with a checkers-board pattern. An optimization of doublet/well spacing is performed based on the coefficient of performance (CoP), energy sweep parameter, and an objective function (f) defined specifically for optimization of the process. In addition, a sensitivity analysis on the grid resolution, braided channel thickness and orientation, and the injection flow rate and span of the supercritical (sc)-CO2 is performed. The upscaled grid resolution mainly affects the pressure-related parameters, including CoP and f, resulting in an average error of 80% and 60% between the fine- (120 × 120) and the coarse-scale (15 × 15), respectively. As a result, the grid resolution of 60 × 60 with dx≈16.5 m is found to have both acceptable average error and optimum runtime. The optimum doublet/well spacing for the present case is about L=450 m, in which the CPG system provides about 9 to 13 times higher values of f compared to cases with doublet/well spacing higher or lower than the optimum value. Moreover, injection wells with I1-I2 line parallel to channels’ orientation, provide about 30% higher f compared to the perpendicular case. However, channels’ orientation does not change the optimum doublet/well spacing (L=450 m).