Thermal permeability enhancement of blocky rocks: One-dimensional flows

A conceptual model is presented to describe permeability enhancement within competent blocky rock masses subjected to temperature changes. The model accomodates a ubiquitously jointed, isothermal and initially stressed mass into which fluid of a different temperature is injected. The transient behaviour of the coupled fluid flow and transport system is described using a 1-D or radial upwind weighted, conductive-advective transport model. Heat production from, and thermal volume change of, the surrounding matrix blocks is described analytically via a convolution product with individual blocks represented as equivalent spheres. The assumption of full lateral restraint for control volumes within the blocky mass results in stress redistribution not being explicitly represented. No attempt is made to satisfy stress equilibrium conditions. The model is used to identify the manner and rate at which fluid permeability enhancement processes develop within a representative granite rock mass. Thermal effects are shown to be significant.