A Deepwater Riser Emergency Disconnect Antirecoil System
- C.J. Hock (Sonat Offshore Drilling Inc.) | R.D. Young (Stress Engineering Services)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1993
- Document Type
- Journal Paper
- 744 - 751
- 1993. Society of Petroleum Engineers
- 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.6 Drilling Operations, 4.2.4 Risers, 4.3.4 Scale, 4.5.10 Remotely Operated Vehicles, 1.7 Pressure Management, 4.1.5 Processing Equipment, 1.11 Drilling Fluids and Materials, 2.1.7 Deepwater Completions Design, 1.10 Drilling Equipment, 4.1.9 Heavy Oil Upgrading
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During drilling in deep water, very high tensions must be used to control the riser, so a large amount of energy is stored in the riser and tensioning system. If the riser and stored energy are not controlled during an unplanned disconnect of the riser from the subsea blowout preventer (BOP), which would result if a dynamically positioned vessel drifted off location, the rig could be seriously damaged and the costly riser could be lost. This paper presents the design processes, installation, and testing of the riser emergency disconnect antirecoil system added to the drillship Discoverer 534 as part of the upgrade to 6,000-ft water depth. The system controls the riser and its tensioning system during and after an unplanned disconnect. This paper views the initial design analysis of the riser and tensioning system using an existing computer modeling program. It presents modifications to the computer program to simulate a disconnect with mud in the riser and using the telescopic-joint latching riser capture system. We discuss the hardware and the problems experienced during the design and computer analysis phases and their unique solutions. We describe important details of the installation in the shipyard and during sea trials. We discuss the full-scale instrumented emergency-disconnect test of the system in 3,700 ft of water and the results of the test. Finally, we present the post-test fine tuning of the computer modeling and predictions for deepwater/high-mud-weight disconnects.
When the upgrade of Discoverer 534 to drill in 6,000 ft of water in the Gulf of Mexico began, knowledge gained during years of record-setting deepwater drilling by the Discoverer Seven Seas was used in guiding the project. Engineering studies made during the upgrading of the Discoverer Seven Seas indicated that a riser antirecoil system was needed to control the riser during and after an unplanned disconnect from the subsea BOP. Control of the energy stored in the marine riser and its tensioning system was necessary to latch it to the floating vessel mechanically, thereby preventing riser loss.
The Discoverer 534 and the Discoverer Seven Seas are sister drillships with essentially the same hull. However, their riser and riser tensioning systems are different. The Discoverer Seven Seas has an 18 5/8-in.-OD riser system; the Discoverer 534 has a 21 in.-OD riser. The type of drilling planned for the Discoverer 534 called for heavyweight drilling fluids of up to 16 lbm/gal. The Discoverer Seven Seas typically used much lighter muds. These differences meant that, while the experience gained from operating the Discoverer Seven Seas would be invaluable, the engineering and the design of its antirecoil system could not be directly applied to the Discoverer 534. With the Discoverer Seven Seas as a starting point, the design of the Discoverer 534 began.
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