Further Advances in Coiled-Tubing Drilling

Abstract

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 / S -and 9 5 / s -in. casing, (2) drilling a 5 7 / s -in.-medium-radius curve, (3) running a 5-in. liner and a 5Jf2-in. parasitic string for nitrogen injection, (4) drilling a 4 3 / s -in. horizontal with nitrogen to maintain a balanced condition, (5) running openhole logs, and (6) running 3Jf2-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 surfacecontrolled orienting tool and an adjustable motor provided excellent directional capabilities on a 23/ s -in. CT. This program represents a significant extension of the capabilities of drilling with CT.

Underbalanced Drilling with Coiled Tubing

“…Fig. 2 Bottom hole assembly for drilling with coiled tubing [5] To ensure that the coiled tubing is capable of performing the required tasks (to drill, to sidetrack) it must have certain capabilities that are in connection with desired well design.…”