Theoretical and numerical simulation studies of the self-stabilization capability of salt cavern roofs

Abstract

The self-stabilization capability of the roof structure in salt cavern gas storage is of paramount importance for ensuring cavern stability. In this study, the influences of roof span, roof interlayer thickness, and arch height on the plastic zone, vertical displacement, and volume shrinkage in salt caverns were thoroughly investigated. Through a combination of theoretical analysis and numerical simulations, the shapes of flat and arc-shaped roofs were analysed, leading to the following conclusions. First, equations for the normal stress and limit span of the cavern roof were derived. The limit spans of both flat and arc-shaped roofs were found to be directly proportional to the internal gas pressure but inversely proportional to the buried depth of the salt cavern. The flat roof exhibited a concentration of tensile stress in the middle, whereas compressive stress was mainly distributed on both sides. To assess roof stability for arc-shaped roof structures, the ratio of roof span to arch height was introduced. It was discovered that increasing the roof span resulted in an enlargement of the plastic zone and vertical displacement, with the plastic zone penetrating the salt layers and extending into deeper interlayers. The mismatched deformation between the salt layer and interlayer leads to the penetration effect of the roof plastic zone, causing damage in the deep interlayer and ultimately resulting in roof collapse. Compared to the flat roof, the arc-shaped roof demonstrated a smaller plastic zone, and the stability of an arc-shaped salt cavern roof is maximized when it possesses the minimum span-to-height ratio. As a result, pear-shaped caverns exhibit the smallest plastic zone, and increasing the arch height diminishes both the plastic zone and the maximum vertical displacement. Finally, it was observed that volume shrinkage is predominantly influenced by the centroid depth, with greater depths corresponding to higher values. These findings significantly contribute to the optimization of cavern design aimed at enhancing stability and increasing the long-term storage capacity in underground salt caverns.