Key technologies in drilling engineering of Wen 23 underground gas storage

The Wen-23 gas storage features low formation pressure, complex formation systems and high formation fluid salinity. The long-term alternating injection-production tends to trigger the failure of production casing and cement sheaths, which brings a series of challenges to drilling and well completion engineering. From the perspectives of the casing program, drilling fluid system, reservoir damage prevention and wellbore integrity of wells in the Wen-23 gas storage, the design schemes of the third and fourth casing sections were optimized, and the micro-foam lost circulation-preventive drilling fluid system suitable for low-pressure and highly-permeable reservoirs of the Wen-23 gas storage was developed. The reservoir damage prevention basic formula was presented, which mainly consists of self-degradable ultrafine calcium, deformable plugging agents and micro-fibers as main temporary plugging agents, and the cement slurry systems suitable for non-salt intermediate casing section, salt-rock intermediate casing section and production casing section were developed. Such slurry systems together with the matching cementing practices form the cementing technology of salt caprock and low-pressure thief zones. Field applications showed that this technology effectively protects the depleted reservoir of the Wen-23 gas storage, improves the well integrity, and thus, ensures the safe and stable operations of the gas storage.