Influence of tubing/oil-blanket lifting on construction and geometries of two-well-horizontal salt caverns

Abstract

Underground TWH (Two-well-horizontal) salt caverns are an ideal storage medium for large-scale energy storage, having large usable volumes and high construction efficiency. Different tubing/oil-blanket lifting techniques relate to different solution mining rates and help define cavern geometries based on the previous experience of SWV (Single-well-vertical)-cavern construction. In this study, we present a complete and comprehensive evaluation of the influence of a particular tubing/oil-blanket lifting method on TWH-cavern leaching and geometric shapes. Based on the solution mining numerical simulation original program TWHSMC V2.0 (Two-well-horizontal solution mining cavern V2.0), we carried out a set of numerical simulations, such that the cavern construction process is real-time display and easily recorded. The results demonstrate that with a matching water injection rate, the outlet brine concentration is not sensitive to tubing/oil-blanket lifting. During construction of a horizontal cavern with a volume of 300,000 m3, lifting tubing on both sides simultaneously yields the shortest leaching time (near 307 days). Only lift the tubing on one side will form an asymmetrical cavern, with the height of the cavity near the side being higher than on the opposite side. The lower the frequency of tubing and oil blanket lifting, the smaller the height/length ratio coefficient is, meaning the cavern is closer to the horizontal. Therefore, when constructing TWH-caverns in thinly-bedded rocksalt formations, simultaneously lifting the both sides of tubing and oil-blanket, in addition to a lower lifting rate, are required. This research provides theoretical basis and engineering guidance for TWH-cavern constructing in thinly bedded rocksalt formations.