High-Angle Directional Drilling With 9 5/8-in. Casing Offshore Qatar
- Karen Bybee (JPT Assistant Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 2009
- Document Type
- Journal Paper
- 45 - 47
- 2009. Society of Petroleum Engineers
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- 84 since 2007
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This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 119446, "High-Angle Directional Drilling With 9⅝-in. Casing in Offshore Qatar," by Michael Avery and Tod Stephens, Occidental Petroleum of Qatar Ltd.; Ali K. Al-Hadad, SPE, Qatar Petroleum; Mounir Turki, SPE, Tesco Corp.; and Malek Abed, SPE, Schlumberger, originally prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17-19 March. The paper has not been peer reviewed.
Horizontal-well programs that require drilling through unstable formations at high angles before entering the productive zone are becoming more common. Casing while drilling (CWD) is becoming a powerful method in mitigating both lost-circulation and wellbore-stability issues in offshore directional wells. As a result of recent advances in tool design, it is now possible to circulate, rotate, and reciprocate the casing during bottomhole-assembly (BHA) retrieval and setting operations without modifications to the rig.
Occidental Petroleum of Qatar currently drills a number of offshore horizontal production and injection wells in the Shuaiba limestone formation. Directly above the Shuaiba is the Nahr Umr formation, which is composed of a nonreactive, but unstable, kaolonitic shale. The 12¼-in. section is drilled conventionally approximately 80 ft into the Shuaiba [20 ft true vertical depth (TVD)] at up to 86° inclination, and a 9⅝-in., 47-lbm/ft L-80 casing string is run and cemented to isolate the shale and sand while drilling the 8½-in. reservoir section.
The Nahr Umr/Shuaiba interface is often a point where highly conductive faults are encountered. Severe losses of drilling mud often occur at this interface, resulting in a dramatic reduction of hydrostatic pressure as the wellbore-annulus fluid level falls. This pressure loss causes the unstable formation to collapse on the drillstring and BHA, packing it off and making it practically impossible to retrieve. The Shuaiba exploitation strategy, however, depends on landing wells at near-horizontal angles so that long sections can be drilled in the reservoir.
A potential solution to this problem is to drill the section with casing and a retrievable BHA. Directional CWD technology uses the casing, in place of drillpipe, to convey rotation and torque and act as a conduit for the drilling fluids. The directional BHA is latched to the lowermost casing joint and extends approximately 85 ft out of the shoe. It is driven by both surface rotation and a downhole motor. For this application, an 8½-in. bit is used to drill a pilot hole, which is opened up immediately to 12¼ in. by an underreamer positioned just below the 9⅝-in. casing-reamer shoe. The BHA can be retrieved through the casing at any point during the drilling operation by running in through the casing with drillpipe and a latch tool.
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