Improving Drilling-Operation Efficiency by Use of a Mud Cap
- Chris Carpenter (JPT Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 2015
- Document Type
- Journal Paper
- 128 - 131
- 2014. Society of Petroleum Engineers
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- 165 since 2007
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 167985, “Improving Drilling-Operations Efficiency on an Ultranarrow- Margin HP/HT MPD Well by Use of a Mud Cap,” by Joy Oyovwevotu, SPE, Senergy; Eric Low, SPE, Bowleven; and Steve Nas, SPE, Schlumberger, prepared for the 2014 SPE Drilling Conference and Exhibition, Fort Worth, Texas, USA, 4–6 March. The paper has not been peer reviewed.
This paper describes the planning and execution of use of mud-cap fluid in the drilling of an ultranarrow-margin (0.50-lbm/gal window at the planning stage) high-pressure/ high-temperature (HP/HT) well from a jackup rig. Significant operational efficiency was gained from the use of cap fluids, making it possible to drill a well that otherwise would have been nearly impossible to drill with minimum lost time.
The IM field is located in Block MLHP-7 in the Rio Del Rey basin offshore Cameroon in a water depth of 58 m (Fig. 1). At the target reservoir level, Well IM-5 was predicted to be a marginal HP/HT well with an estimated reservoir temperature of 181°C and a reservoir pressure of 9,971 psi (16.80 lbm/gal) at a depth of 3475-m true vertical depth subsea (TVDSS).
The Middle Isongo sand, intersected by Well IM-3, was the primary gas/ condensate target, consisting of deepwater sands with interbedded shales. The Middle Isongo target package consisted of three reservoir sands, the deepest two of which had not been penetrated in any of the earlier offset wells; this was the primary target of Well IM-5. A secondary target for Well IM-5 was the Intra Isongo, occurring between the Upper Isongo and the Middle Isongo main target.
The well design allowed the 12¼-in.-hole section to be drilled conventionally with statically overbalanced mud weight (MW), but it was impossible to drill the 8½-in. hole without using statically underbalanced MW with managed pressure drilling (MPD). Consequently, it was decided that the 12¼-in. hole would be drilled with MPD so that the crew could become familiar with the procedures and practices that would be needed when the 8½-in.-hole section was drilled. Given the uncertainty in the pore-pressure and fracture-gradient forecast, drilling the 8½-in.-hole section with statically underbalanced MW using MPD was seen as the most efficient means of well construction.
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