Drilling-Induced Riser Vibration
- Robert D. Blevins (Consultant) | Charles S. Coughran (Consultant) | Michael E. Utt (Consultant) | Kamaldev Raghavan (Chevron)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- September 2017
- Document Type
- Journal Paper
- 232 - 238
- 2017. The International Society of Offshore and Polar Engineers
- riser, drilling, Vibration, fluid-coupled
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- 148 since 2007
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Significant riser oscillations were observed during deep-water drilling operations. The riser vibrated at frequencies from below to above the rotation speed of the drill pipe. Laboratory tests of a riser section have been conducted for these riser drilling-induced vibrations. The first test consisted of measuring the fluid forces between the rotating drill pipe and the riser. In the second test, the riser was elastically supported. The riser self-excited about the rotating drill pipe. An analytical model is developed for predicting these drilling-induced riser oscillations. The results show that fluid-coupled riser vibrations can result from the fluid forces generated in the annular fluid between the rotating drill pipe and the riser.
A deep-water riser assembly in 6,000 ft (2,000 m) of water is shown in Fig. 1. During drilling, fluid flows downward inside the drill pipe and returns upward in the annulus between the drill pipe and the riser. The drill string rotates at 30 to 120 rpm (0.5 to 2 cycles per second). The drill pipe has a 5-inch (12.5-cm) outside diameter, and the riser has an outside diameter of 13 inches (33 cm). A submerged buoy supports the riser weight. The riser tension is set to about 40% higher than the wet weight of the riser, so the riser is always in tension. The drill pipe is also in tension along the riser section; it goes into compression below the mudline where the riser is cemented into the earth.
Remotely operated vehicle (ROV) field measurements are made of the riser motion during drilling with seawater as the drilling fluid. The riser vibrated between the mudline and the buoy at an unsteady range of frequencies between 40 to 60 cycles per minute, 0.6 to 1 Hz. The vibration occurred only during drilling. Peak-to-peak amplitudes of 1 ft (0.3 m) were observed below the buoy, and currents were nominal on the third and final day of drilling when the vibrations caused fatigue failure of the riser at the buoy.
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