CAVERN ROOF STABILITY FOR NATURAL GAS STORAGE IN BEDDED SALT

Abstract

This report documents research performed to develop a new stress-based criterion for predicting the onset of damage in salt formations surrounding natural gas storage caverns. Laboratory tests were conducted to investigate the effects of shear stress, mean stress, pore pressure, temperature, and Lode angle on the strength and creep characteristics of salt. The laboratory test data were used in the development of the new criterion. The laboratory results indicate that the strength of salt strongly depends on the mean stress and Lode angle. The strength of the salt does not appear to be sensitive to temperature. Pore pressure effects were not readily apparent until a significant level of damage was induced and the permeability was increased to allow penetration of the liquid permeant. Utilizing the new criterion, numerical simulations were used to estimate the minimum allowable gas pressure for hypothetical storage caverns located in a bedded salt formation. The simulations performed illustrate the influence that cavern roof span, depth, roof salt thickness, shale thickness, and shale stiffness have on the allowable operating pressure range. Interestingly, comparison of predictions using the new criterion with that of a commonly used criterion indicate that lower minimum gas pressures may be allowed for caverns at shallow depths. However, as cavern depth is increased, less conservative estimates for minimum gas pressure were determined by the new criterion.