Numerical modelling of thermal transport and quartz precipitation/dissolution in a coupled fracture–skin–matrix system

Abstract

This paper describes a numerical model for the analysis of chemical reactions in a coupled fracture–matrix system at the scale of a single fracture in the presence of fracture–skin. The quartz concentration is computed using simple linear reaction kinetics. Heat transfer within the fracture–skin and rock matrix is modelled as conduction, while heat transport within the fracture includes thermal advection, conduction, and dispersion in the horizontal plane. Fluid is assumed to be injected at a constant rate at the inlet of the fracture. Heat transfer at the interface of the high permeability fracture and low permeability fracture–skin is modelled on a varying grid at the interface. Sensitivity studies have been conducted using different skin thermal conductivities, fluid velocities, and half fracture apertures. We have also analysed the behaviour of the system when there is fluid loss from the fracture into the adjacent fracture skin. Results suggest that, when fluid loss is considered, the rate at which fluid is injected at the inlet of the fracture plays a major role in the heat transfer and chemical reaction within the fracture. When there is fluid loss, the effect of fracture skin formation on the heat transfer mechanism is reduced and this effect becomes much less sensitive to changes in the size of the fracture aperture. The fracture skin thickness affects the attainment of equilibrium temperature within the fracture in terms of its magnitude and distance from the fracture inlet.