Directional casing while drilling, using a retrievable bottomhole assembly (BHA) to steer the wellbore, provides a unique solution to the lost circulation and wellbore stability problems commonly encountered during well construction in mature offshore fields. During a press conference at the recent 2008 IADC/SPE Drilling Conference and Exhibition, members of the oil and gas industry press corps were briefed on the latest developments in directional casing-while-drilling technology by Schlumberger and Tesco Corporation.
Kyel Hodenfield, Schlumberger Drilling & Measurements vice president of technology and marketing; Bill Lesso, Drilling & Measurements drilling mechanics advisor; and Nigel Lakey, Tesco Corporation's senior vice president of marketing and business development, described the developing trends and best practices in this market. Rick Watts, drilling engineering fellow and head of ConocoPhillips Upstream Technology Drilling Engineering and Operations, delivered an operator's perspective.
About 80% of casing while drilling is done with a nonretrievable bit attached to the bottom of the casing that is left in the hole at TD, or with a drillable bit for internal runs. Directional casing while drilling, on the other hand, uses a retrievable, steerable BHA. This makes the technique a viable alternative to conventional directional drilling in depleted or mature fields that typically exhibit severe lost circulation and wellbore stability problems.
Successful results in the North Sea
The first offshore directional well drilled with casing and wireline-retrievable BHAs was completed by ConocoPhillips in January 2007. The operator had developed the technique previously in south Texas vertical land wells. Because of its tremendous success in reducing the number of drilling days on these wells, ConocoPhillips decided to deploy this technology offshore on a well drilled from the operator's Eldfisk Bravo platform in the Norwegian sector of the North Sea. Both the 10 3/4-in and 7 3/4-in sections of the well—totaling 10,968 ft were drilled successfully and positioned as planned using retrievable BHAs that incorporated Schlumberger PowerDrive X5 rotary steerable systems, PowerPak straight positive displacement motors, and Pulse telemetry and survey systems. Despite a complex wellpath that included a 70-degree inclination and 170-degree turn, directional objectives were successfully achieved.
Viable and reliable technology offering
Although casing while drilling has a solid track record of success in commercial land wells in which BHAs have been retrieved countless times, this was the first instance of its use in a directional offshore well. Rick Watts of ConocoPhillips fielded questions following the briefing and confirmed the technique's viability and reliability, stating, "Directional casing while drilling in offshore environments has a definite future."
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