Thermo-Mechanical Effects on Flow Channeling in Single- and Multi-Fracture Enhanced Geothermal Systems

Abstract

Flow channeling is widely recognized as a key mechanism that accelerates thermal drawdown and degrades the long-term performance of enhanced geothermal systems (EGS). In addition to fracture-scale flow channeling, non-uniform flow rate allocation among fractures induced from wellbore-induced pressure loss and thermo-mechanical interactions between fractures can further complicate flow behavior in multi-fracture EGSs. To systematically investigate these coupled effects, we develop field-scale single- and double-fracture EGS models and simulate the fully coupled thermo-hydro-mechanical (THM) processes. Numerical simulations first reveal how injection flow rate governs thermo-mechanical responses and flow channeling within a single fracture. Low injection flow rates lead to localized cooling, strong thermal stress accumulation, and pronounced aperture heterogeneity, resulting in severe flow channeling. In contrast, high injection flow rates generate a broader cooling zone and reduce fracture stiffness over a larger area, producing more spatially distributed aperture evolution and relatively uniform fracture flow, despite faster thermal drawdown. Extending to the double-fracture system, wellbore pressure loss induces persistent asymmetric flow allocation, producing flow behavior in each fracture similar to that in single-fracture cases, while overlapping thermal perturbation zones between closely spaced fractures create strong inter-fracture thermo-mechanical coupling, synchronizing aperture evolution and enhancing flow redistribution.