Heterogeneity matters: cooling gains from artificial groundwater circulation in geothermal borehole fields

Artificial groundwater circulation using well doublets can substantially mitigate heat accumulation around borehole heat-exchanger (BHE) arrays, even in geologically heterogeneous settings. We develop a single-platform MODFLOW 6 model that couples the Groundwater Flow and Groundwater Energy packages to simulate a nine-BHE array within a five-layer aquifer system and quantify the cooling benefit of an engineered injection–extraction pair under both confined and unconfined conditions. After a vertical discretization analysis, we adopt a mesh that resolves interlayer temperature structure and use it to assess circulation rates from 0 to 66~ m³\,d⁻¹ . Forced circulation lowers 10-year temperatures near the BHE array by as much as 8.7~^∘ C , with unconfined cases remaining slightly warmer than confined cases at equal rates. Furthermore, we examine the effect of heterogeneity on the efficiency of the well doublet heat-mitigation strategy. Groundwater circulation consistently reduces subsurface temperatures. Unresolved hydraulic-conductivity heterogeneity introduces uncertainty in groundwater temperature predictions, resulting in temperature variations of up to 4~^∘ C among realizations, while the ensemble-mean temperature differs from that of the corresponding homogeneous aquifer by approximately 1~^∘ C . Shorter hydraulic-conductivity correlation lengths yield lower average temperatures. These results provide process-based guidance: (i) high-resolution characterization of the geothermal site is important for the efficient design of geothermal energy systems; (ii) deploy well doublets and tune pumping–injection rates Q to advect heat away from the BHE array, recognizing diminishing returns at high rates; (iii) preferentially site BHE fields along high hydraulic conductivity pathways identified by site characterization; and (iv) account for partially saturated layers where relevant, as they modestly elevate groundwater temperatures.