Comparing heat and solute transport in a discrete rock fracture of variable aperture

Abstract

In this study, we have compared heat and solute transport in a discrete fracture using numerical modeling. Fracture aperture heterogeneity was described using geostatistical properties with fracture aperture means of up to 1000 μm, variances of 10,000 µm2 and isotropic correlation lengths up to 10 m. Groundwater flow in the matrix was assumed to be negligible and flow in the fracture was set to values typical for natural groundwater conditions with velocities less than 100 m/day and associated hydraulic gradients of less than 0.05. A uniform isotropic thermal conductivity of 2 W/m °C was set for the matrix. Based on 50 realizations, three-dimensional and two-dimensional conduction in the matrix and in the fracture, respectively, play an important role in controlling the development and the shape of the thermal plume under natural flow conditions. In contrast, solute transport exhibits limited penetration depth in the matrix. The results of this research indicate that, contrary to solute transport in discrete fracture settings where channeling is sometimes a major contributor to solute migration rates, no significant thermal channeling is observed under natural groundwater flow conditions. The use of tracer experiments or the monitoring of solute transport in fractured rock will not therefore provide a reliable prediction of the migration of heat in the same setting.