Numerical and Experimental Analysis of Heat Transport at Fracture Intersections

Heat transport in fractured media concerns various hydrogeology and subsurface engineering applications, such as heat transfer in enhanced geothermal systems (EGS), thermal energy storage in fractured rocks, or the effect of heat on rock properties near nuclear waste repositories. The main factors influencing heat transport in fractured media are the thermal and hydraulic properties of the rock matrix and the presence and magnitude of fluid flow, which depends on the connectivity, geometry, and hydraulic properties of the fracture network.

This study analyzes coupled flow and heat transport processes at fracture intersections based on numerical simulations and laboratory experiments. The numerical simulations are conducted with OpenFoam, solving the mass, momentum, and energy conservation equations in the fractures coupled to heat conduction in the impermeable rock matrix. The numerical simulations are complemented by high-resolution temperature measurements in quasi-two-dimensional fracture intersection geometries. This is accomplished by the phosphor thermometry measurement technique. Phosphor particles are seeded into the fluid and act as tracers for the fluid temperature thanks to their temperature-dependent luminescence. The simulations and experiments are conducted under different volumetric flow rates to vary the thermal Péclet number.

Coupled flow and thermal transport in the numerical simulations and laboratory experiments are analyzed from the thermal breakthrough curves, the thermal front in the fractures, and the overall heat transfer coefficient between the fractures and the rock. The results characterize the effect of the fracture aperture, the angle under which the fractures intersect, and the thermal conductivity of the matrix on the heat transport at fracture intersections.