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Description
Heat transfer in fractured rock systems plays a fundamental role in the exploitation of deep geothermal resources. Fractures act as the primary conduits for fluid flow and advective heat transport, whereas heat exchange with the surrounding rock matrix occurs mainly through diffusion. These mechanisms operate over markedly different spatial and temporal scales, and their combined effect is strongly governed by fracture and rock heterogeneity, which ultimately determines geothermal system performance.
This study examines two transient mechanical processes that may modify fracture geometry during fluid circulation, thereby influencing heat transport and the overall efficiency of geothermal installations. The first process concerns flow channeling generated by shear slip in mechanically activated fractures. This mechanism is investigated at the single-fracture scale. Through a combination of analytical modeling and numerical simulations, we analyze the thermal response to the injection of a cold fluid pulse into a rough fracture characterized by both synthetic and natural heterogeneous aperture distributions. Our results indicate that fracture roughness exerts a strong control on heat transport dynamics. Specifically, the post-peak tailing of temperature breakthrough curves displays an anomalous transient decay, which precedes the emergence of the asymptotic regime with a −3/2 decay exponent associated with fracture–matrix diffusion. This transient behavior is highly sensitive to aperture field modifications induced by relative shear displacement between fracture walls, with increasing slip promoting earlier temperature breakthroughs and postponing the transition to the diffusive asymptotic regime.
The second process addresses thermally induced cooling and contraction of the rock mass surrounding the fractures. This contraction leads to fracture opening, with direct consequences for fluid flow and advective heat transport. We investigate this effect at the scale of fractured rock masses using a hybrid approach that couples an analytical formulation with particle tracking simulations in Discrete Fracture Networks (DFNs). Numerical results demonstrate that thermal contraction of the host rock enhances advective transport, leading to a more rapid arrival of cold fluid at the system outlet.
Together, these findings highlight the key fractured rock properties that govern heat transport when fracture slip and aperture changes occur. Such insights are essential for improving the control, efficiency, and long-term sustainability of geothermal energy exploitation.
| Country | Spain |
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