Study and Application of Low Penetration Cement Slurry for Cementing CCUS Wells in Chuanyu Area

Well cementing in the Chuanyu area (Sichuan and Chongqing) is faced with corrosion, deterioration and failure of sealing of cement sheath in acidic condition. To address these issues, a corrosion-resistant material DST with both filming adsorption and microstructure regulation and control functions was developed, and with DST, a low-permeability corrosion-resistant cement slurry was formulated. Different from conventional corrosion-resistant materials, DST can induce corrosive hydration products to transform from a loose structure to a dense spherical calcium carbonate packing, thereby blocking the deep penetration of the corrosive media. Based on the typical bottomhole temperature and pressure conditions (80 ℃/40 MPa), laboratory acid corrosion experiment and field application were conducted. The results show that after being corroded for 28 days, the compressive strength of the set cement is only reduced by 5%. The permeability of the set cement, although slightly increased, is finally lower than 4 × 10⁻⁵ μm². The diameters of the main pores are kept at 10 – 90 nm, which are harmless or only slightly harmful, and no connected pores and loose structures are observed in the micromorphology of the set cement. This cement slurry has been applied in cementing a CCUS well in the Chuanyu area, and the first and the second bonding interfaces of the cement sheath are qualified at a rate exceeding 94%. In subsequent 300-day injection and production operations, no abnormal sustained pressure and CO₂ leaking were monitored. The key corrosion-resistant material DST developed in this research and the low-permeability corrosion-resistant cement slurry significantly improve the long-term sealing of the CCUS wellbore and lay a solid foundation for cementing CO₂ storage wells.