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Efficiently drilling the lateral hole section through the abrasive Granite Wash reservoir sands in western Oklahoma and the Texas Panhandle creates a unique challenge. The highly heterogeneous formation was causing inconsistent PDC bit performance while constructing the 6-1/8" horizontal and thus damaging project economics. A study determined that improved ROI could be achieved by extending bit life in areas where poor drilling performance is expected. A detailed forensic analysis showed extensive cutter damage with abrasive wear being the most common dull characteristic. The cutter wear was causing short runs and frequent trips for bit change-out. To solve the problem required a new approach. A fixed PDC element creates an inherent limitation because only a small portion of the cutter contacts formation and as the cutter wears, drilling efficiency declines. The resulting wear flat generates a high degree of frictional heat which breaks the diamond-to-diamond bond leading to accelerated cutter degradation. The situation is exacerbated by difficulty transferring weight-on-bit due to extended length lateral drilling. An R&D initiative was launched to investigate different methods to enable a PDC shearing element to fully rotate while drilling to increase overall cutting efficiency and bit life. Engineers investigated several different retention methods and developed a specialized fixed housing which is brazed into the bit blade. The PDC cutter is mounted on a circular shaft and fitted within the housing allowing 360° cutter rotation. The robust system holds the cutter/shaft assembly securely in the housing for superior reliability. The rolling cutter assembly has essentially the same OD as a standard PDC cutter for superior design flexibility and cutter placement options. A new-style 6-1/8" PDC (MSiR613/MSiR713) was manufactured with rolling cutters strategically positioned in the shoulder area. It has been run over 45 times in the Granite Wash formation and is delivering positive results. On a steerable motor, the RC equipped bit has increased total footage, hours on bottom and ROP compared to direct offsets drilled with fixed cutter PDC.

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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. 1 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.