Vol. 227 No. 12

Rig floor equipment

New diverter technology improves sealing

Drilling offshore in deep water poses unique challenges over drilling on land or from a jackup fixed to the seafloor in relatively shallow water. Whereas fixed platforms allow for little to no vertical movement of equipment, in deep water floating drilling and production structures must be able to move, while the drillstring remains fixed and in tension. These floating systems are differentiated in two ways: 1) wellheads are attached to the seafloor instead of the platform and 2) vertical movement, heave and rotation, occurs.

This drill pipe section with two auxiliary lines at 180o is cylindrically encased inside the diverter.

When an offshore drilling rig heaves or rotates, its position shifts relative to the drill pipe. A diverter attached to the vessel's drillfloor moves up and down around the drill pipe with the rig, possibly 30 ft or more. In the past, if a floating rig experienced a blowout, the diverter would be closed around the pipe and return lines to send gas to the atmosphere.

Often, there are auxiliary lines running parallel to the drill pipe. The immense force required to seal the spaces between the drill pipe and auxiliary lines often crushes these lines. In some cases, the diverter cannot completely seal the blowout. The gas kick then vents improperly and dangerously out the diverter's top.

The Hydril Seal-All Diverter Insert solves this problem. The insert features an interior elastomer that is custom-molded to form around the drill pipe and the auxiliary lines, while maintaining a smooth, cylindrical exterior. The inserts are manufactured in nominal 8-ft sections, which can be stacked to accommodate expected heave height. For example, three 8-ft sections would be stacked to accommodate an expected 20-ft heave.

If the diverter is activated due to a gas kick, the packing unit closes around the insert's smooth outer shell, creating a positive seal. The packing unit will then move up and down with the vessel's motion on the exterior of the insert, while the interior elastomer seals the drill pipe and auxiliary lines. The internal rubber and the round exterior create a positive seal in any configuration.

These units are presently on a BP-operated drillship and will soon be installed on Chevron-operated drillship projects. The units can be disassembled and reinstalled on other platforms as needed.