The Optimized Drilling Techniques Used in Ultra-Deep and Slim-Hole Horizontal Wells of the Shunbei Block

The drilling of ultra-deep slim hole horizontal wells in the Shunbei Block encountered multiple challenges such as formations susceptible to lost circulation, significant friction torque, trajectory control difficulties for borehole with diameter of φ120.6 mm, low ROPs and long drilling time. Accordingly, research has been conducted to develop fast and high-quality drilling techniques. Through comprehensive analyses of drilling, logging, testing and other data, pore pressure, borehole collapse and fracturing pressure gradient profiles were determined. Accordingly, sealing points were identified and the six stage casing program was optimized to four stages. With consideration to specific features of formations susceptible to circulation lost and borehole collapsing, experimental study was performed to clarify technical solutions for those potential problems. Through analyzing build-up capacity of PDM and the deployment of dual-incremental trajectory, difficulties in slimhole trajectory control would be effectively minimized. By reducing the length of directional drilling intervals, minimizing the contact areas between drilling tools and sidewalls and by the utilization of oil-mixed drilling fluid, friction torques would be reduced dramatically. In the investigation, drilling techniques of "torsion impact device+PDC bit" were applied to enhance ROP. Through experimental tests and field testing, fast and high-quality drilling techniques for ultra-deep slim-hole wells in the Shunbei Block were determined. These techniques have been used in five wells in this region. It compared the Well X1 with six-stage casing program, ROP and drilling time for wells drilled with innovative techniques increased 29.36% and reduced for 93 days. Research results and on-site application performance showed that the newly-developed rapid and high-quality drilling techniques for the ultra-deep slim hole can satisfy the safe and high-efficiency drilling of slim hole horizontal wells in Shunbei Block. Generally speaking, the application of these techniques may provide necessary technical support for high-efficiency development of marine carbonate reservoirs in this block.