Enhanced Geothermal Systems (EGS) generates geothermal energy without the need for natural convective hydrothermal resources, by enhancing permeability through hydraulic fracturing. EGS involves complex and highly nonlinear multiphysics processes and faces several technical challenges that govern productivity and associated risks in a wide range of reservoir engineering problems. Numerical simulations offer a unique opportunity to improve the hydraulic stimulation design and investigate their long term performance. In this work, we present a thermo-hydro–mechanical coupling based on the fictitious domain method (FDM). FDM allows for nonconforming approaches that rely on the use of different mesh discretization for the solid and the fluid domain. We adopt the governing equations of linear thermoelasticity to model the heat transfer in hot dry rocks, whereas Navier--Stokes equations and heat conductivity equations are adopted to describe the thermal flux in an incompressible fluid. The two problems are then coupled in a staggered manner through the variational transfer. Indeed, the use of the variational transfer allows simplifying the setup of fracture simulations with complex surfaces embedded in the fluid domain, thus overcoming the inconvenience related to the boundary fitted mesh generation. The presented computational framework is first validated by comparing with analytical solutions of two dimensional and three-dimensional benchmarks. Finally, we show that our framework provides high flexibility and allows for simulating the behavior of more complex scenarios including fluid flow and heat transfer in realistic rock geometries.

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