Journal of Petroleum Technology, Vol.47, No.5, 403-408, 1995
Further Advances in Coiled-Tubing Drilling
The use of coiled tubing (CT) to drill horizontal re-entry wells has received considerable interest in the industry over the last two years. The benefit of being able to drill at balance, safely and in a controlled manner, with nitrogen to reduce downhole pressure while drilling highly depleted reservoirs, provides an advantage over conventional techniques, particularly in reducing formation damage. This paper describes such a horizontal re-entry drilled in the shallow depleted waterflooded reservoir Barenburg in northern Germany. The scope of work for this project included (1) cutting windows through 6 5/8- and 9 5/8-in. casing, (2) drilling a 5 7/8-in.-medium-radius curve, (3) running a 5-in. liner and a 5 1/2-in. parasitic string for nitrogen injection, (4) drilling a 4 3/8-in. horizontal with nitrogen to maintain a balanced condition, (5) running openhole logs, and (6) running 3 1/2-in. slotted liner. The entire program was executed with no intervention from a conventional rig or workover hoist. A special structure to be positioned over the well to support the CT injector head and to provide a work platform had to be constructed for this type of operation. A dedicated mast for lifting pipe and downhole tools was placed on the substructure. The development of a surface-controlled orienting tool and an adjustable motor provided excellent directional capabilities on a 2 3/8-in. CT. This program represents a significant extension of the capabilities of drilling with CT.