Current Practices and Research Directions for Drilling and Completion Technologies for Ultra-Deep Wells in Western Sichuan

Western Sichuan, a region rich in oil and gas resources, is confronted with technical challenges in drilling engineering, such as multiple vertical pressure systems, frequent loss of circulation, wellbore instability and collapse, poor drillability of certain formations, high drilling risks, and long drilling duration, due to the complex geological conditions of ultra-deep marine carbonates. Thanks to research conducted in the last few years, drilling and completion technologies for ultra-deep wells, suitable for western Sichuan, have been developed, namely those incorporating casing program optimization for ultra-deep wells, key technologies for rate of penetration(ROP) increase, lost circulation control, managed pressure drilling for high-pressure and low-permeability gas reservoirs, oil-based drilling fluid with high-temperature resistance and strong blocking ability, sidetracking in ultra-deep casings with higher steel grade, cementing based on a pressure control and balance method, cementing in ultra-deep hole with short liner suspension. These technologies contributed to the exploration and development of ultra-deep oil and gas resources in western Sichuan and set many drilling engineering records. However, there are still some technical challenges, such as insufficient understanding of geological conditions in the risky area, great difficulty in controlling serious lost circulation, difficult ROP increase in some hard drilling formations, and fewer associated technologies for safe drilling of formations with narrow mud weight window. In this paper, future research directions were proposed, including casing program design, pilot tests of new technologies for ROP increase, efficient control of lost circulation, and geology-engineering integration, etc. They are expected to boost the rapid development of drilling and completion technologies for ultra-deep wells in western Sichuan and realize economical and effective exploration and development of deep oil and gas resources in the region.