Hydro-thermal coupling in rough fractures using lattice Boltzmann (LB) methods

In a context where developing carbon-free energies answers a very important societal and environmental demand, the present development of the so called "Enhanced Geothermal Systems'', like the one developed over a 30-year-long European project in Soultz-s ous-Forêts (France) or in the Cooper Basin (Australia), requires basic research to better understand heat exchanges occurring when a cold fluid is injected into a hot fractured rock. This in turn requires the modeling of both mass and energy transport. No te that the understanding of hydraulic flow in single fractures and in fracture networks is also a key for other topics like oil exploration, supercritical CO2 injection, pollutant flow, or storage of radioactive wastes in crystalline rocks. While the com plexity of the fracture morphology is seldom taken into account, it has been shown that the fracture roughness is likely to inhibit the temperature exchange, because of channeling effects on the fluid flow. The previously cited studies are based on a stro ng hypothesis called the lubrication approximation, which stipulates in particular that the hydraulic flow is laminar. It was however shown that even at low Reynolds number, recirculation, such as eddies, may happen because of a sharp morphology. This ef fect may have large consequences on any process which depends on fluid convection, like thermal exchanges. The aim of our study will be to characterize the influence of realistic shapes of the fracture asperities, complex pressure gradients, and fluid vis cosity on the hydro-thermal behavior. To do so, numerical simulations will be carried out using a coupled lattice Boltzmann (LB) method, that we have already started to develop.