Analytical and numerical modeling of cavity closure in rock salt

Abstract

Rock salt creeps under shear at the low temperatures encountered close to the surface. Salt flow is problematic for any cavity, like caverns or wells, because of the time dependent closure it induces if the internal hole pressure is less than the far field one. This thesis presents new analytical solutions giving the speed at which hole closure occurs in salt. The solutions are new because they take into account both the effects of intergrain water on salt deformation and far field shear. The deformation of rock salt is often considered to be solely due to the movements of dislocations inside salt grains but pressure solution at grain contacts has also been found to be important. Taking pressure solution and far field shear into account can lead to an increase of several orders of magnitude in the closure velocity of a hole present in the salt formation. Salt is a common rock in the underground and its unique sealing properties makes it involved in many applications. The solutions presented in this thesis will hopefully be used by engineers to better assess hole closure in salt and increase the safety as well as the success rate of operations.