Research on Tubing and Casing Anti-Bending Technology for Salt Cavern Gas Storage Cavity Construction

Abstract

Abstract Benefiting from its outstanding gas injection-production capability and fully recoverable cushion gas, salt cavern gas storage technology was developed rapidly in recent years. Wangchang salt cave gas storage is characterized by deep burial depth and multiple interlayers. The project of water-soluble cavity construction faces problem of serious tubing and casing bending and deformation. Therefore, development of effective tubing and casing string damage-prevention and risk control method remains an ongoing challenge. Both theoretical study and field tests are presented in this article. Through field observation, mechanical analysis and production data analysis, it was identified that the main reasons causing tubing and casing bending are liquid-solid coupling instability, interlayer rock impact and smashing, as well as pipe string wear and corrosion. By optimizing the tubing and casing strings design and adjusting production parameters, tubing and casing bending problem could be effectively improved. Besides, remedial measures to deal with bending pipe string were proposed. Critical destabilizing flow rate of the tubing and casing was calculated under different diameter and wall thickness conditions. Analysis of calculation results showed that the current water injection volume of the Wangchang gas storage well was higher than the critical displacement. It was verified that the liquid-solid coupling instability was the main reason causing tubing and casing bending in the gas storage well. Field data analysis showed that large water injection displacement and high water injection pressure fluctuation was more likely to cause bending and damage of tubing and casing. Technical measures are listed as following: (1) strengthening the steel grade wall thickness of intermediate casing; (2) equipping the central tubing column with a drop connector to optimize the distance between the central tubing shoe and the middle casing shoe; (3) Optimizing the cavity water circulation method to stabilize the water injection pressure and displacement. The anti-bending technology presented in this study unlocks a critical bottleneck during the salt cave building progress, which is the tubing and casing bending and deformation problem. With the application of this method, efficiency of water-soluble cavity building can be greatly improved. More importantly, this technology might pave a new way for the deep multi-interlayer salt cavern gas storage design.