ABSTRACT
The Ellis model for constitutive behavior, as implemented for rock salt, defines the displacement rate as the sum of a linear term and a power-law term with respect to the deviatoric stress. This combination represents a superposition of dislocation creep and solution-precipitation creep (pressure solution). The linear term constitutes a considerable contribution to the creep rate at small stresses. It must therefore be taken into account when salt cavern closure is considered, in particular at large distances from the cavern wall. In the present contribution we formulate an analytical solution for the quasi-steady-state cavern convergence in a 2D plane strain field. We have compared the outcome with numerical calculations with a Finite Element simulator, with good results. The calculations show that the increased strain rate/shear stress ratio at large distances from the cavern have a profound influence on the cavern squeeze rate, even while the strains and stresses in the cavern vicinity are dominated by the power-law creep branch of the constitutive model.
