A new method of surface subsidence prediction for natural gas storage cavern in bedded rock salts

Liu, Wei; Yinping, Li; Chunhe, Yang; Deyi, Jiang; Daemen, J. J. K.; Jie, Chen; Junfeng, Kong

A new method of surface subsidence prediction for natural gas storage cavern in bedded rock salts

2016

The surface subsidence above underground natural gas caverns in salt formations is mainly induced by the volume shrinkage of the cavern. In this paper a new method, based on the Mogi model, to predict the subsidence above bedded rock salts gas storage cavern is proposed. Firstly, the equivalent elastic boundary deformation of the cavern volume decrease is assumed to be the first-order approximation of the real subsidence induced by creep shrinkage. Secondly, the cavern shape is simplified to be a spherical one with the same depth and volume, subjected to the pressure change of hydrostatic pressure in the sphere. And then, solving for the subsidence above, the storage is analyzed as the boundary displacement problem of the spherical cavern subjected to pressure change of hydrostatic pressure in the sphere in semi-infinite space. Based on the equivalent elastic model, the Mogi model, which has been developed for subsidence prediction in volcano seismology, is introduced to solve the boundary displacement problem. Then the expressions for subsidence and for horizontal displacement are obtained. The advantage of the new method is that the ground displacements can be calculated directly from the cavern volume shrinkage, thus the calculation has much been simplified. The validity of the method is verified by comparing to numerical simulation results, which show that the Mogi model has high validity for subsidence prediction for the gas cavern in salt formations. In the end, some constructive discussions on the application and improvement of the Mogi model are presented for its further applications.

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