Geomechanical performance of a novel L-shaped wellbore design for hot dry rock geothermal reservoirs: insights from fully coupled thermo-hydro-mechanical modeling

Enhanced Geothermal Systems (EGSs), developed to extract heat from hot dry rock (HDR) formations, are promising renewable heat resources; however, their long-term performance is governed by coupled thermo-hydro-mechanical (THM) processes. This study introduces a novel L-shaped injection-production wellbore configuration designed to enhance reservoir contact while reducing drilling complexity compared to conventional vertical, multilateral, and closed-loop systems. A fully coupled three-dimensional THM numerical model is developed to evaluate its performance, accounting for conductive-convective heat transfer, pore-pressure evolution, and thermally induced deformation. A sensitivity analysis investigates the effects of horizontal wellbore length, injection pressure, injection temperature, rock thermal expansion coefficient, and fluid compressibility. Extending the horizontal section increases the stable production period from 2.6 to 6 years and doubles reservoir lifetime from 6.3 to 12.4 years compared to a quintuplet vertical system, while delivering more than twice the thermal power output. Reducing injection pressure from 10 to 5 MPa suppresses cold-front migration and extends sustainability beyond 20 years. Increasing injection temperature from 323.15 to 343.15 K raises lifetime from 11 to 12.4 years but reduces power by 20%. The results demonstrate that the proposed configuration provides a balanced solution between thermal efficiency, mechanical response, and operational simplicity for HDR development.