Abstract
This paper presents and discusses the results of the field application where a new integrated expandable under reamer technology was implemented in the North Sea. An operator faced issues with wellbore stability and equivalent circulating density (ECD) while drilling a 12¼-in. section in a challanging formation. Placing the reamer close to the bit removed the need for an additional rathole elimination run, avoiding the risks associated with it and saving rig time.
The on-command digital, expandable under reamer is fully integrated into the bottom hole assembly (BHA) and can be monitored and controlled from the surface. The under reamer tool has unlimited activation cycles that provide the capability of selective reaming. The flexible placement of multiple reamers in the BHA enables near-bit and main reaming applications, and a combination of both. When used for near-bit reaming service, the reamer can reduce the rat-hole length to 4 m. Significant time savings and safety improvements can be achieved by simultaneously operating the main and the near-bit reamer.
In one run, the entire section was simultaneously drilled and underreamed to TD. The first 3,491 ft (1064m) were drilled while simultaneously opening the hole to 13½-in. with the main underreamer. The remaining 233 ft (71m) were drilled and reamed with both the main and the near-bit reamers activated. The rathole length was reduced to 33 ft (10m) in the same drilling run, saving 3 days of rig time. The 10¾-in. liner was then run to the desired depth. Minimal vibrations were recorded in the interval where both reamers were activated and stick/slip was nominal. After the run, an inspection of the reamer blades showed good performance and little wear.
The paper will summarize and describe the results and features in detail, and demonstrate how they can help the operators to reduce operational risks and save cost.
