Effects of Plastic Deformation on the Transport Properties of Rocksalt

Abstract

It has recently been suggested that plastic deformation of rocksalt in nature can lead to the development of significant permeability to fluids, even under fully ductile deformation conditions. It is proposed that the key mechanisms controlling this permeability development are (1) reconnection of occluded grain boundary brine inclusions to form a fluid network, and (2) passive stretching and intersection of fluid inclusions in deforming salt. The creation of such fluid pathways would lead to migration of brine and hydrocarbons through the rocksalt formation, despite the usual assumption that salt is practically impermeable. We combine new and previous work to assess the impact of these two mechanisms on the transport properties of deforming salt. Our analysis shows that, for natural brine contents and microscale distributions, the permeability of a connected pore network remains very low, as brine-filled pore and film apertures are too small to support significant fluid flow. Furthermore, stretching of fluid inclusions is fully counteracted by surface-energy-driven, solution-precipitation transfer. We therefore infer that the previously proposed mechanisms are very unlikely to render rocksalt permeable in a Darcian sense, on either engineering or geological timescales.