A brief overview of the underground storage of natural gas in salt caves

The creep behaviour of natural rock salt is of special interest for underground repositories for radioactive and toxic wastes. For the long-term safety analysis of a permanent repository a creep law is required which allows, on the base of laboratory results, to predict the thermomechanical behaviour of the surrounding host rock for long time periods (thousands of years) with high reliability. For this reason the model should be based on the physical processes governing the deformation. Speisesalz (stratigraphic notation) serves as a reference material for other types of rock salt, which show considerable differences in the deformation behaviour mainly due to different impurity content and distribution.A procedure to be used in order to determine a general constitutive equation for stationary creep, aiming at describing the volumetric compressibility, needs special care in the mathematical formulation in order not to contradict the physical evidence. Long-term creep failure can also be introduced using an energetic criterion. The model can be used in order to predict the slow closure of underground openings, where around the opening the rock mass becomes dilatant and compressible, where a fast failure will occur and where a creep failure is to be expected. Also one can show how the slowly produced damage steadily spreads from the opening surface into the rock mass.

Keywords:

Salt cavern , Underground gas storage , Creep behavior , shrinkage