Design, Construction, and Use of a Coiled Tubing Drilling Structure for Onshore and Offshore Operations

Abstract

This paper discusses the design, construction, and Initial application of a structure for supporting a coiled tubing injector head, bottom hole drilling assembly and pressurized lubricator. The paper includes a discussion of the features desired for the structure and how these were addressed during the design. The manufacturing of the support tower and its support platform are then discussed. On site assembly procedures for the movable structure are presented along with photographs of the deployed rig in service. The versatility and usefulness of the structure are discussed from the end users point of view. Introduction In early 1994, during planning for an effort to explore using coiled tubing for drilling operations, the engineers working on the development realized that a structure would be needed to support the weight of the drilling equipment. The objective of the drilling operation was to enter existing wells through the swab valve on the top of the Christmas tree and, while under pressure and blowout prevent (BOP) control, drill laterals into new pay zones. Hence, the BOP was to be mounted on top of the Christmas tree along with a lubricator long enough to contain the entire bottom hole assembly (BHA) and strong enough to contain well pressure. The coiled tubing injector head and pack off would need to be mounted on the upper end of the lubricator. The mechanics of this operation requires that long and heavy pieces of equipment would have to be held vertically over the well with the coiled tubing injector head located at the very top of the equipment stack. It was recognized that a unique and portable structure was needed to hold the coiled tubing drilling equipment. Thus, CAMCO, with the agreement of British Petroleum, a major partner in the drilling project, began a program to design and construct a support tower and a platform on which to locate the tower. This paper is a report on the various phases of the design, construction, and deployment of the drilling structure (DS). Design Requirements The primary purpose of the DS is to prevent bending moments and undue compressive loads from being transmitted to the wellhead while permitting the entire BHA to be lubricated above the wellhead and BOP's. This required that the tower had to be rigid enough to prevent the injector head from moving relative to the wellhead, even under the loads imposed by the down hole coiled tubing weight and the side pull of the coiled tubing reel. Further, the compressive loads from all downward forces had to be eliminated from the long lubricator to prevent buckling. The meant that the downward and overturning forces had to be carried through the tower, into a platform, then via platform supports, to the ground.