RIASSUNTO
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 5/8- and 9 5/8-in. casing, (2) drilling a 5 7/8-in.-medium-radius curve, (3) running a 5-in. liner and a 5½-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 3½-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.
Introduction
Over the last 2 years, a number of oil companies have gained experience with CT drilling that has been carried out mainly as re-entry operations. Encouraging results have been reported that generated the idea to develop this technology further as an integrated package capable of carrying out the entire operation without the intervention of a conventional rig or workover hoist. Because no service company on the market could provide the entire scope of work, BEB Erdgas & Erdol GmbH decided to cooperate with two companies on a partnership basis to develop required tools and equipment. A trust was formed between the two service companies for this project.