Abstract:

During the last years the demand for high frequency storage of natural gas increased dramatically. The new operation modes for gas storage caverns in rock salt mass require a more detailed rock mechanical consideration of thermal induced stress-es in the vicinity of the caverns. This means that the change of gas temperatures dur-ing operation and the consequences of these temperature changes on the stressing of the salt rock mass cannot be neglected any more, i.e. thermo-mechanical coupled cal-culations are necessary. As rock salt has a time dependent material behavior stress redistributions in the rock salt mass take place even under constant internal pressure conditions. Therefore not only the phases with different pressure change rates but also the duration of phases with nearly constant internal pressure have an influence on the resulting state varia-bles. Within the paper on principle two different loading scenarios are taken into ac-count. The first scenario is a cyclic pressure change with different withdrawal and injection rates, the second scenario includes idle time periods under maximum pres-sure. The main differences are demonstrated and discussed with respect to recommen-dations for the rock mechanical design rock salt has a time dependent material behav-ior stress redistributions in the rock salt mass take place even under constant internal pressure conditions.

1 INTRODUCTION

The seasonal storage of natural gas in salt caverns has been practiced since some dec-ades successfully. Nowadays new operation modes are aimed at, which are character-ized by high withdrawal rates and possibly more than one pressure cycle per year. The main differences between seasonal and cyclic storage operations have been pointed out by Staudtmeister & Zapf (2010). This is important because no gas flow doesn't mean that the state variables like cavern temperature and stresses in the rock mass remain un-changed during this period.

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