Bedded salt formations are located throughout the United States, providing valuable storage capacity for natural gas and other hydrocarbons. In order to increase gas storage capabilities and provide operators with improved geotechnical design and operating guidelines for these caverns, stability analyses of single bedded salt cavern have been completed and are described in this paper. This work is a part of integrated efforts initiated and sponsored by the US Department of Energy, Gas Technology Institute, and Pipeline Research Council International, Inc.

Numerical geomechanical models have been developed to investigate single cavern deformation and bedding plane slip for a variety of cavern configurations. A viscoplastic salt model has been developed based on an empirical creep law developed for the Waste Isolation Pilot Plant (WIPP) Program and combined with a Drucker-Prager model for damage and failure. The non-salt materials are described with either a traditional Mohr-Coulomb model, or an elastic model, depending on layer properties.

A baseline model with specified geometric dimensions is first selected and subjected to one year cyclic pressure operations. The amount of damage around the cavern wall and roof is evaluated and used as a comparison in the study. Then the operations are extended to 15 years to study cavern stability for long term gas storage and operations. In addition to the baseline model, parametric studies have been performed to investigate cavern damage as a function of salt roof thickness, overburden stiffness, interface properties, and cavern geometries. Each cavern simulation includes one year of pressure cycling with a minimum, mean, and maximum cavern pressure of 6.1 MPa (884.5 psi), 8.8 MPa (1276 psi) and 14.9 MPa (2160.5 psi), respectively. Different operation conditions, e.g. hydrostatic, cyclic, and a direct pressure drawdown, are compared and evaluated in terms of cavern stability.

These analyses can serve as a basis to select the best salt cavern candidate for gas storage and operations. They can also help to assess critical cavern design parameters for thin bedded salt formations.

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