Casing Drilling: An Emerging Technology

Abstract

Summary BP America Production Co. used the Tesco Casing Drilling™* process to drill the surface and production intervals of 15 Wyoming gas wells. These wells range in depth from 8,300 to 9,600 ft. This paper provides a case-history discussion of the critical issues encountered and resolved during the planning and operations phases of this project. Oilfield casing was used as the drillstring, along with a wireline-retrievable bottomhole assembly (BHA), to reduce the overall time required to drill, run casing, and cement the surface holes. Drilling with casing matched the rate of penetration (ROP) for conventional wells, and both the downhole and surface tools proved to be reliable. The production-hole interval turned out to be more challenging. Drillstring vibrations were encountered when drilling with the 4½-in. casing, and difficulty was experienced in maintaining a competitive ROP with the wireline-retrievable drilling assembly. The last 11 production holes were drilled with casing and a nonretrievable bit assembly. Nine of these wells were completed without tripping the casing. Drilling times were competitive with conventional drilling in the Wamsutter area. One of the wells was the third-fastest well ever drilled in the field. The project demonstrated that the casing-drilling process can be used successfully but may not be cost-effective in all situations. It is probably better suited to softer formations and larger casing sizes than those used at Wamsutter. The process seemed to improve wellbore stability, reduce lost circulation, and minimize gas influx, even when drilling with a lower mud weight than is typical for conventional drilling.