Mechanical Stability of a CavernSubmitted to High-Frequency Cycles

Storage of natural gas in salt caverns had been developed mainly for seasonal storage,resulting in a small number of yearly pressure cycles and moderate gas-production rates. Theneeds of energy traders are changing toward more aggressive operational modes. Gas temperaturechanges and additional stresses generated by high-frequency cycling in a storage cavern arediscussed. It is proved that, when short-period gas pressure cycles are performed, the thickness ofthe thermally disturbed zone at the cavern wall is relatively small. Refined meshes of the disturbedzone are required when performing numerical computations. The case of an actual cavern isdiscussed. In addition to the Munson-Dawson constitutive law, reverse creep is considered. Theno-tension and dilation criteria are used to discuss numerical results. It is proved that tensilestresses may develop when cavern pressure is low. The evolution of the state of stresses in the(the formula is in the text) plane; i.e., the bumble-bee flight, as suggested by Kurt Staudtmeister and Zapf(2010) [1] is discussed, and it is proved that the dilation criterion is met at an early stage.

Keywords:

Cycling loading , gas cavern design , rock mechanics , numerical analysis