Some thmc controls on the evolution of fracture permeability

The significant controls exerted on the evolution of fracture permeability by ambient conditions of stress, temperature, and chemical potential are illustrated for contrasting rock types. Natural and artificial fractures in Berea Sandstone, Arkansas Novaculite, and Bellefonte Limestone are confined within an x-ray transparent pressure cell and water flow-through tests conducted. The samples are monitored for change in permeability that evolves concurrently with the circulation of the water, and for net mineral efflux that accompanies this circulation. Periodic imaging by x-ray CT is used to define source areas of mineral efflux and its redistribution, and to provide constraint to phenomenological models that describe the observed behaviour. Vastly different behaviours are observed between the fractures present within the varied host materials - some gape with net mineral efflux, and some seal. These responses are viewed within the framework of the competition between mass mobilized by pressure solution, and net free-face dissolution or precipitation on the fracture walls, and in the matrix. Viewed in this context, the surprising range of behaviours, observed under similar THMC conditions in these three contrasting material types, may be unravelled.