Construction simulation of large-spacing-two-well salt cavern with gas blanket and stability evaluation of cavern for gas storage

Abstract

The single well or small-spacing two-well technologies with oil blanket has been gradually applied to construct salt cavern storage in recent years. In order to solve the problems of low efficiency, oil blanket sealing failure, cavern deformity, roof collapses, small volume and brine pollution in salt cavern construction. In this study, a large-spacing two-well (Wellhead spacing is greater than 20 m) with gas blanket (LSTW-GB) method was proposed to construct salt cavern. Firstly, through indoor physical simulation experiment, the feasibility of the LSTW-GB to construct cavern is verified and discussed. The experimental results show that increasing the two-well-spacing effectively increases the effective cavern volume, improve the cavern construction rate and obtain clear brine, but the increase of two-well-spacing will also increase the difficulty of connecting the two wells, so more attention should focus on the technology improvement on connecting the two wells. Secondly, combined with the experimental observations and field geological data in Jintan bedded salt rock of China, the stability of the LSTW-cavern for gas storage under different ratios of long axis to height (RLH) was analyzed by numerical simulations. The simulation results show that as the RLH increasing, the stability of the LSTW-cavern gradually decreases. In addition, under low-internal-pressure operation, the cavern is most likely to lose its stability, so much more attention should be paid to designing the value and duration of minimum operating internal pressure (Pmin). Finally, the working conditions of the LSTW-cavern gas storage are optimized, and it is proposed that the Pmin of the gas storage in the LSTW-cavern should be 33% ∼ 38% of the gravity stress at the casing shoe when RLH varies from 1.60 to 3.10. Comprehensive research results show that the LSTW-cavern has a good application prospect in the construction of gas storage of salt rock in China.