Current Status and Development Suggestions in Drilling and Completion Technology of Underground Gas Storage in China

As one of the most important facilities in natural gas storage and peak regulation in the world, underground gas storage (UGS) shows the advantages of large storage capacity, low cost and high safety factor. Because wellbore integrity directly affects the safety and reliability of the long-term operation of UGS, drilling and completion are the most expensive and time consuming process in the construction of UGS. Up to now, China has built 32 depleted gas reservoir and salt-cavern UGSs in total and has preliminarily formed characteristic technical systems in UGS drilling and completion, including well type optimization design for depleted gas reservoir UGS, prevention and control of circulation loss and reservoir protection in ultra-low pressure formation, toughness slurry cementing, large flow rate injection and production completion, existing well evaluation and reuse. For salt-cavern UGS, those technical systems include drilling and completion, cavity construction and cavity shape control, existing cavern modification and utilization, injection and production wellbore integrity, etc. However, there still exist large gaps comparing with foreign counterparts in terms of hole size, well type design and technological level. Researches on horizontal well with large hole size in depleted gas reservoir UGS, directional cluster well drilling technology in salt-cavern UGS, drilling and completion of aquifer UGS, and injection and production wellbore integrity technology are required to form a complete UGS drilling and completion technical system, and to meet the needs of realizing high-quality development of UGS and the national energy strategy of China.