Fluid assist bearing for telescopic joint of a RISER system

In a floating offshore drilling vessel having a riser system with an axis extending between the sea floor and the drilling vessel, a telescopic joint in the riser system having a rotary bearing, and a plurality of riser tensioners extending from the drilling vessel to an outer barrel of the joint for exerting an upward force to apply tension to the riser system, the rotary bearing comprising:

• a first annular member which is stationarily mounted to the outer barrel of the telescopic joint;
• a second annular member slidingly engaging the first annular member, the second annular member being rotatable and axially movable relative to the first annular member for a limited amount;
• a sealed chamber located between the first annular member and the second annular member and defined by a downward facing portion of the first annular member and an upward facing portion of the second annular member, the chamber containing hydraulic fluid for keeping said portions of the annular members apart from each other and providing a fluid cushion for allowing the second annular member to rotate relative to the first annular member while the second annular member exerts an upward force on the first annular member through the tensioners;
• a primary seal located between the first and second annular members for sealing the chamber;
• and
• a passage extending from the chamber to an external port, the passage communicating hydraulic fluid from the external port to the chamber.

A method for rotating a telescopic joint in a riser system for a floating offshore drilling vessel, the riser system extending between the sea floor and the drilling vessel, comprising:

• (a) providing a rotary bearing in the telescopic joint having a chamber defined between first and second annular members, the chamber being filled with hydraulic fluid to provide a fluid cushion therebetween and being sealed with a primary seal, and the first annular member being nonrotational relative to the riser system;
• (b) securing a plurality of riser tensioners to the second annular member, the tensioners extending from the drilling vessel;
• (c) exerting an upward force on the tensioners to apply tension to the riser system;
• and
• (d) rotating the drilling vessel relative to the riser system such that the second annular member rotates relative to the first annular member while the second annular member exerts an upward force on the first annular member through the fluid cushion.