Fast Marching Method: A new paradigm for rapid simulation of enhanced geothermal systems

Enhanced Geothermal System (EGS) provide access to thermal energy stored in hot, dry rock formations beyond the reach of conventional hydrothermal systems, yet a significant challenge remains in reliably predicting the flow rate, temperature, and thermal performance of the produced subsurface fluids. Reservoir simulation, widely used in the oil and gas industry for forecasting subsurface fluid production, is also applied to EGS. These simulations must resolve complex non-isothermal, compositional flow through fractured porous media, leading to significant computational demands and runtimes of several hours to days per simulation. We propose a new paradigm for rapid multi-domain, multi-resolution simulation of EGS that accelerates reservoir simulation by orders of magnitude. Our reservoir simulation method uses a finite-volume-based Fast Marching Method (FMM) to efficiently compute Diffusive Time of Flight (DTOF) and transform 3D simulations into equivalent 1D simulations using DTOF as spatial coordinate. The DTOF, which tracks pressure front propagation, guides the discretization of the 1D mesh. To maintain accuracy, the proposed method preserves 3D resolution near the wellbore and hydraulic fractures while converting the rest of the reservoir to 1D grid, resulting in significant computational speed up. The 3D and 1D domains communicate through non-neighbor connections that incorporate both fluid and heat transmissibility. The proposed method was applied to a triplet horizontal well configuration, featuring one horizontal injector positioned between two horizontal producers to optimize heat extraction, with reservoir simulations conducted over 20 years to assess the long-term performance of geothermal projects. The proposed FMM based multi-resolution simulation model provides flow rates, temperature and thermal power output with orders of magnitude (10-25 times) speed up compared to the traditional full 3D numerical simulations. With the accelerated workflow, the proposed approach enables performance assessment and optimization of geothermal projects in hours compared to the typical timeframe of several days using commercial simulators, making such modeling practically feasible for routine applications. • High-fidelity performance of Enhanced Geothermal Systems is quantitatively assessed • FMM-SIM is extended for geothermal applications, incorporating fluid and heat flow • Multi-resolution model accelerates geothermal simulation by orders of magnitude • Applied to EDFM and field-scale fractured model with triplet horizontal wells • Demonstrated rapid simulation studies of well spacing and operational parameters