Judy Maksoud
International Editor
Offshore
GlobalSantaFe applied a new method of drilling riser management to overcome current conditions and enable drilling off northern Brazil. James Brekke, manager of marine technology at GSF, told participants at the annual Offshore Mechanics and Arctic Engineering conference in Halkidiki, Greece, that drilling offshore northern Brazil traditionally has posed problems because of the high speed of the North Brazil current.
"GlobalSantaFe is proud of the accomplishment of drilling a well in this area," Brekke said.
GSF'sJack Ryan drillship drilled the Algodoal wildcat well in 2,450 ft water depth in the Foz do Amazonas basin off northern Brazil last summer, Brekke said. The vessel drilled the well despite currents as high as five knots.
During another operator's attempt to drill in this area in 1980, the 20-inch casing experienced numerous fatigue failures during open-water running operations due to vortex-induced vibration (VIV), Brekke said. This helped identify the need for special procedures and equipment to cope with the high currents.
Following BP's internal process, the two companies worked to identify specific risks and to appraise the drilling conditions. They selected a key issue to evaluate and defined an operational plan that would allow GSF to drill the well despite the anticipated high current.
Several things led to the successful drilling, Brekke said. A key component was drift-running the riser. The process required the drillship to drift with the current toward the well site while it ran the riser. "The vessel drifts with the current, so the riser hangs vertically through the rig floor," Brekke said. This condition would not be possible if the rig were stable, he explained.
Riser fairings reduced drag and contended with VIV, Brekke said. The optimal riser configuration employed fairings on the top third, alternating bare and buoyant joints in the middle third, and exclusively bare joints on the bottom third, Brekke said. This arrangement minimized VIV, provided extra weight needed for drift running, and reduced the risk of riser recoil, he said.
Brekke enumerated disadvantages of this approach, noting increased top tension and a high hook load requirement. Because theJack Ryan is a deepwater vessel rated for 9,000 ft, it was more than capable of handling the extra weight, Brekke said.
Brekke attributed the operation's success to planning, cooperation, and a software package called Deepdrift, which allowed the crew to optimize drilling performance under the extreme current conditions.
06/14/05
