Permeability of layered rock salt at different stresses and geometries

Permeability tests were conducted on layered salt samples at room temperature under stepped increase of differential stress, using a confining pressure of 10 MPa representing in-situ conditions. These layered salt samples were obtained from formations in the Hubei province China at a cavern depth of similar to 800 m, with halite as main constituent, together with glauberite and sulphates interbedded with argillaceous material. The samples were tested for three different geometries of bedding orientation with respect to deformation direction. For a geometry with a vertical interface, the permeability was found to increase permanently with increasing differential stress from 4.54E-20 to 6.1E-19 m(2). The permanent permeability change with stress in case of a horizontal interface was very small (6.13E-18 to 1.26E-17 m(2)) and followed a predominantly elastic response. The permeability change in the geometry with an obliquely oriented interface showed a permanent decrease from 6.09E-16 to 7.06E-17 m(2), despite evidence of localised dilatancy at the interface. The change in bulk permeability with differential stress is thought to be mainly due to collapse of pre-existing pore networks, as no macroscopic failure of samples were observed and bulk volume changes were all towards compaction.