Optimizing flow distribution and heat transfer in enhanced geothermal systems: Advances, challenges, and outlook

Enhanced geothermal systems (EGS) offer a scalable pathway for baseload renewable energy, yet their long-term performance is strongly constrained by flow channeling, thermal short-circuiting, and the complex coupling between fracture networks, fluid transport, and heat transfer. This review provides a critical synthesis of recent analytical and numerical studies on fluid flow and heat transfer in fractured geothermal reservoirs, with emphasis on flow partitioning in fracture networks, thermal breakthrough behavior, working fluid selection, and operational controls. The evolution of modeling approaches is summarized, from early analytical and semi-analytical formulations to high-resolution, fracture-resolved numerical frameworks. Key findings consistently show that fracture geometry, connectivity, orientation, and permeability govern reservoir sweep efficiency and the sustainability of heat extraction, while injection strategy strongly influences the onset of thermal decline. Comparative assessments of water and supercritical CO 2 as working fluids indicate that CO 2 can enhance heat extraction and pressure management under regulated operating conditions, although performance remains highly sensitive to fracture-scale transport properties and reservoir heterogeneity. Despite significant progress, most existing models neglect fully coupled thermo-hydro-mechanical–chemical processes, fracture evolution, multiphase flow, and long-term permeability degradation, limiting predictive reliability for multi-decade operation. The review identifies critical research gaps and outlines priorities for next-generation EGS modeling, including fully coupled, field-calibrated frameworks with uncertainty quantification, to support reliable reservoir design and long-term performance assessment.