Technology for Cementing Deep Reservoirs in Yingxi Area, Qinghai Oilfield

Qinghai Oilfield has in recent years found deep petroleum reservoirs in the Block Yingxi Shizigou. This is a major breakthrough in oil and gas exploration in the Qaidam Basin. This block not only has huge potential of oil and gas reserves, the complex drilling and geological conditions also bring about great challenges to well cementing operation and subsequent production. Since the horizontal wells in this block is stimulated with multistage fracturing, to establish effective zonal isolation and to maintain long-term seal integrity of the cement sheath, a special cement slurry and prepad fluid have been selected, based on the analyses of difficulties encountered in well cementing. The cement slurry, the prepad fluid and an improved set of well cementing techniques together formed a set of well cementing technology suitable for the horizontal wells drilled in block Shizigou. Using a self-healing agent, the micro-fractures generated inside set cement were filled and the set cement was thus rendered elasticity, ensuring the long-term seal integrity of the cement sheath. The anti-invasion anti-channeling cement slurry also has some thixotropic property and internal viscous force, which are beneficial to cement slurry loss control and channeling mitigation. Since 2018, this set of well cementing technology has been applied with great success in Shizigou for more than 20 times/wells, with average well depth of 5,000 m and average horizontal length of 1,000 m. Wells cemented with this technology satisfied the needs of subsequent spatial fracturing operation. As a key technology for the development of deep reservoirs in Yingxi, this technology will find wide application in the future.