Stewart & Stevenson Services, Inc.

Albert M Regan

Dennis D George

Two types of isolation tools are disclosed for installation between the upward end of the LMRP and the lower end of a riser string in the drilling of a subsea well using dual gradient techniques, one of which is especially adapted for rotation about a rotating drill sling. Each type includes insert packer adapted to be closed about the drill string to divert drilling fluid in the annulus between the drill string and the subsea wellhead into lines extending along the side of the riser to the surface. The insert is selectively removable to permit conventional drilling.

Riser isolation tool

There are disclosed two types of valves connectible in a subsea drilling riser to permit the opening and closing of side ports therein. One such valve is automatically opened when the hydrostatic subsea pressure is greater by a predetermined amount than that of drilling mud in the riser. The other valve is installed in the lower end of the riser and is adapted to be opened to discharge drilling fluid therefrom.

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Cypress, TX, United States of America

Albert M Regan