Newly applied BHA elements contribute towards mainstreaming of coiled tubing drilling applications

Coiled tubing drilling (CTD) is coming into the mainstream in a number of locations and applications, and the availability of improved BHA elements is a significant contributor in this regard. This paper describes BHA elements including a hydraulic orienter and MWD system recently employed by ARCO in CTD operations, examines their capabilities, and provides a series of examples in which these tools were successfully employed. The BHA elements formerly utilized in coiled tubing drilling have often not performed as well or as reliably as the industry has become accustomed to in conventional drilling operations. Principle concerns here include the overall ROP, attainment of timely survey and steering data, and directional control of the BHA. The BHA elements utilized in the recent operations represent an improvement in these critical functions. The BHA orienter is a newly engineered, simple, hydraulically actuated device. Its performance attributes affecting overall ROP and directional control of the BHA are examined, including its speed of actuation, and its ability to change the BHA orientation while in a medium radius curve. The MWD system really represents a new application of an existing reliable system, with attributes that are especially important in the CTD environment. Modifications related to downsizing are examined, as well as relevant performance attributes including: steering data update rate; real time gamma log quality; mud pulse detection capability on coil in a range of drilling fluids; and reliability. The BHA is also looked at from an overall system perspective, including its integration with the coiled tubing and other equipment associated with the CTD operation. As of this writing, ARCO Alaska, Inc. and THUMS Long Beach Co. (a wholly owned subsidiary of ARCO) have completed 16 CTD reentry sidetrack jobs utilizing these BHA elements in Alaska and Long Beach, California. Overall performance and reliability from these jobs are summarized. Additionally, specific cases are examined in greater detail, with these BHA elements contributing towards successful CTD window milling, medium radius curves, and laterals.