FURTHER ADVANCES IN COILED-TUBING DRILLING

The use of coiled tubing (CT) to drill horizontal re-entry wells has r eceived considerable interest in the industry over the last two years. The benefit of being able to drill at balance, safely and in a contro lled manner, with nitrogen to reduce downhole pressure while drilling highly depleted reservoirs, provides an advantage over conventional te chniques, particularly in reducing formation damage. This paper descri bes such a horizontal re-entry drilled in the shallow depleted waterfl ooded reservoir Barenburg in northern Germany. The scope of work for t his 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. slotte d liner. The entire program was executed with no intervention from a c onventional rig or workover hoist. A special structure to be positione d 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 substructu re. The development of a surface-controlled orienting tool and an adju stable motor provided excellent directional capabilities on a 2 3/8-in . CT. This program represents a significant extension of the capabilit ies of drilling with CT.