Identifying Key Parameters Controlling Heat Transport in Discrete Rock Fractures

Understanding heat transfer in fractured rocks is necessary for the proper design of thermal remediation of contaminated sites and the design of energy storage. Numerical modeling of heat transfer, in low porosity fractured rock, is challenging because of the complexity associated with the interaction between fracture, matrix, fluid and the heat source. Of particular importance are the following five parameters; the source configuration, the thermal conduction in the matrix, the velocity of fluid in the fracture, the aperture of the fracture, and the thermal dispersion in the fracture. In this investigation we use factorial analyses (2^K) to define which of the five parameters, or combination thereof, significantly influences heat migration in a single fracture setting (parallel plate condition). A 60m block domain was considered with a single horizontal fracture dividing the domain in half. A 10°C uniform temperature was initially set for the model. Two types of constant 11°C heat sources were considered with a point source located in the middle of the fracture, and a line source extending 1 m into the matrix along either side of the fracture. The flow in the matrix was assumed to be extremely small, with isotropic thermal conductivity varying between 0.52 W/m °C and 10.17 W/m °C. The fracture aperture ranged between 100 μm and 2000 μm with velocity varying between 40m/day and 0.5m/day. Thermal dispersivity in the fracture was varied between 1 m and 0.1 m for the longitudinal direction and tenfold less for the traverse direction. HydroGeoSphere was used for the simulations. For the parameter ranges investigated, preliminary results indicate that the most influential factors controlling the heat propagation inside a single fracture setting are the velocity of the fluid in the fracture, fracture aperture size and matrix conduction. Therefore, these parameters should be given better consideration during site characterization.