Directional Casing

Directional Casing while Drilling Combining TESCO CASING DRILLING and Schlumberger PowerDrive* rotary steerable systems to deliver a viable well construction option for mature offshore fields TM

Directional Casing while Drilling advantages OF Directional casing while drilling in OFFSHORE FIELDS ■ ■

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Directional Casing while Drilling, using a retrievable BHA to steer the wellbore, provides a unique solution to the lost circulation and wellbore stability problems commonly encountered during mature field well construction offshore.

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ost Casing while Drilling —about 80%—is done by attaching a nonretrievable bit to the bottom of the casing and leaving the bit in the hole. Directional casing while drilling (DCwD) uses a steerable BHA that is retrieved—not left in the hole. That makes DCwD a viable alternative to conventional directional drilling in depleted or mature fields that have severe lost circulation and wellbore stability problems. IMPROVES WELL CONTROL AND WELLBORE STABILITY

Well construction in mature fields with standard drillpipe sometimes requires extra casing strings to avoid well stability problems caused by depleted formation

pressures. Because they improve wellbore stability, the DCwD techniques developed through close collaboration between Schlumberger and Tesco under the sponsorship of ConocoPhillips may reduce the number of casing strings needed. When circulation is lost or the wellbore collapses and excessive cuttings come to the surface during conventional drilling, the usual—and often ineffective— remedy is to condition the mud and ream the hole. If an hour is spent conditioning and reaming for every 2 hours spent drilling conventionally, DCwD techniques can very likely save rig time and reduce well construction cost.

Reduced well construction costs Improved personnel safety because of reduced pipe handling Circulation while tripping, which enhances well control Proven and tested technology Reduction in number of casing strings Higher-quality wellbores Trained and experienced Schlumberger and TESCO personnel working in close collaboration

SOLVES PREVIOUSLY UNSOLVABLE PROBLEMS

Well construction in mature fields where persistent drilling mechanics and wellbore stability problems occur at very predictable times or depths

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Hole sizes from 6 to 171⁄2 in

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PROVIDES UNIQUE SOLUTIONS

BHA retrievable at will using wireline or drillpipe

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Available for most-popular casing sizes: 7, 95⁄8, and 133⁄8 in

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Rugged, robust rotary steerable system: 43⁄4 to 8 in

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Technique of casing rotation that actually strengthens wellbore

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DCwD techniques also improve well control because they allow circulating while the BHA is being retrieved or run into the well. They also leave the casing at or very near bottom while the BHA is out of the well. During drilling, DCwD rotation strengthens the borehole wall because of the plastering effect, also referred to as smear or stress cage, that occurs in the narrow annulus. USED SUCCESSFULLY IN NORTH SEA

The first deployment of unique DCwD technology offshore was on a well drilled from the ConocoPhillips-operated Eldfisk Bravo platform in the Norwegian sector of the North Sea. Both the 103⁄4-in and 73⁄4-in sections of Well 2/7B-16A— totaling 10,968 ft—were drilled successfully and positioned as planned using retrievable BHAs that incorporated PowerDrive X5* rotary steerable systems (RSSs), PowerPak* straight positive displacement motors (PDMs), and Pulse* telemetry and surveying systems. The casing strings were rotated at 20 to 30 rpm from the surface, and the PDMs provided an additional 130 rpm to the RSS, polycrystalline diamond compact (PDC) bits and under-reamer. ROP varied, but was as high as 80 ft/h. All directional objectives for the complex wellbore were achieved, with a maximum dogleg severity of 4.83°/100 ft.

Drill Lock Assembly (DLA)‡ connecting BHA to Casing Profile Nipple‡ Internal tandem stabilizer‡

PowerPak† straight PDM

Casing shoe‡ Offers VIABLE AND RELIABLE success

Casing while drilling has a long track record of success in commercial land wells in which BHAs have been retrieved at least a thousand times. To prove its viability and reliability for offshore use, DCwD technology was tested extensively before its deployment to the North Sea. For additional information, see SPE papers 79862, 79914, 92195, 99248, and 112560, or contact your Schlumberger or TESCO representative.

Vibration sensor sub

Motor bit box Under-reamer‡

Roller reamer

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Drillpipe

Casing

Pulse† telemetry and surveying MWD system

Annulus

Because directional casing while drilling minimizes annulus size, casing rotation causes a plastering effect—also called smear or stress cage—that mechanically strengthens the borehole wall.

PowerDrive X5† RSS

PDC bit The steerable BHAs for directional casing while drilling are usually run and retrieved on wireline, but drillpipe also can be used.

†Provided by Schlumberger ‡Provided by TESCO

Directional Casing while Drilling DCwD, using a retrievable BHA to steer the wellbore, is a viable alternative to conventional directional drilling in depleted or mature fields that have severe lost circulation and wellbore stability problems.

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