LABORATORY STUDY OF GAS-PERMEABILITY CHANGES IN ROCK SALT DURING DEFORMATION

Gas permeability and porosity measurements have been made during hydrostatic and triaxial quasi-static, stress-rate controlled compression tests. The permeability and porosity of the as-received samples decrease significantly as a result of hydrostatic loading. These changes are largely irreversible, and are believed to "heal" or return the rock to a condition comparable to its undisturbed state. The permeability can increase more than 5 orders of magnitude over the initial (healed) state as the samples are deformed during deviatoric loading. The gas permeability and porosity changes are consistent with a flow model based on the equivalent channel concept. A model of microcrack initiation and growth based on the frictional sliding crack suggests the flow paths initially develop along grain boundaries and then along axial intragranular tensile cracks. Post-test visual observations support the model predictions.