Stability and optimization of small-spacing two-well (SSTW) gas storage salt caverns in bedded salt formation

Abstract

Many rock salts in China have a bedded structure, consisting of several thin interlayers and salt layers. To eliminate the limitations of the conventional single-well gas storage caverns, the small-spacing two-well (SSTW) salt caverns can be utilized. In this paper, under the geological conditions of Pingdingshan salt formation in Henan province, China, a geomechanical model was established to evaluate the stability of the SSTW salt cavern. The deformation, volume shrinkage rate, and safety factor were used for the cavern stability evaluation. The optimal cavern roof shape, two-well spacing, and cavern roof height were determined by analyzing the salt cavern stability under constant pressure conditions. Based on the optimal salt cavern morphology, the stability of the salt cavern and interlayers under various injection and withdrawal cycle frequencies are investigated. The results show that the rampant arch-shaped SSTW salt cavern has good feasibility in Pingdingshan salt formation. The cavern roof vertical displacement and volume shrinkage decrease with the increase of cavern roof height, and it is suggested that the ratio of cavern roof height to cavern height is at least 0.26. With the continuous increase of the two-well spacing, the cavern volume shrinkage also increases. It is recommended that the ratio of the two-well spacing to the single cavern radius should be no more than 0.625. The increase in cycle frequency reduces the duration of salt caverns under low-pressure conditions, thus improving the mechanical stability of the cavern and interlayers. This paper provides design and operation parameters for the SSTW salt cavern in Pingdingshan salt formation and can also be a reference for the construction of other SSTW salt caverns.