Analysis and Research on Technical Challenges and Countermeasures for Cementing in Large-Diameter Boreholes of Ultra-Deep Wells

With the advancement of oil and gas exploration into deeper formations, cementing operations in large-diameter boreholes of ultra-deep wells face technical challenges such as high casing stiffness, narrow safe density windows, and significant risks of annular channeling. Under complex wellbore structures, the safety and quality of cementing in large-diameter boreholes have become increasingly prominent. This paper takes the third section of Well S in the northwestern Sichuan Basin (total depth of 3,608.55 m) as an example. Addressing issues such as high casing running friction (casing sizes Φ492.13 and Φ485.78 mm), an 81% occurrence of lost circulation, low casing centralization leading to difficulties in casing running, high risk of lost circulation, and insufficient displacement efficiency, this study successfully achieved safe cementing in the ultra-large-diameter borehole of the third section through optimized borehole preparation techniques, customized casing running tools, and optimized cementing the structure of the slurry column and construction processes. The cementing quality of this well achieved a first-interface excellence rate of 91.73% and a qualification rate of 98.38%, while the second-interface excellence rate reached 91.03% with a qualification rate of 99.88%. This study has developed a set of key technologies for cementing in ultra-deep, large-diameter boreholes with independent intellectual property rights, providing a Chinese solution for the efficient development of global deep oil and gas resources.