Identifying and assessing key parameters controlling heat transport in discrete rock fractures

Numerical modeling of heat transfer in low porosity fractured rock is challenging because of the complexity associated with the interactions between fractures, bedrock matrix, groundwater, and heat sources. Possible influential parameters include the heat source configuration, the thermal conductivity of the matrix, the velocity of the fluid, the thermal dispersivity in the fracture, and the aperture of the fracture. In this investigation we use factorial analysis (2K) to define which of the five parameters, or combinations thereof, significantly influence heat migration in a single fracture setting assuming a parallel plate condition. A 3-D numerical model based on the control-volume finite element method is used for the simulations. For the parameter ranges investigated, results indicate that the most influential factor controlling heat propagation in a single fracture setting is the velocity of the fluid in the fracture. The interaction between the thermal conductivity of the matrix and the velocity of the fluid, and between the thermal conductivity of the matrix and the aperture of the fracture, dominantly control the attenuation of the thermal front migration. Depending on the particular system, one or more of these parameters should be given better consideration during site characterization in fractured rock and in the compilation of site-specific models intended to predict heat propagation in fractured systems.