Importance

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Abstract

This invention provides a method and apparatus for maintaining safe pressure in the annulus of a deepwater marine riser by preventing the displacement of drilling mud with formation gas. By providing an improved flow diverting control device having an annular sealing device in the riser string below the riser telescopic joint, liquid well fluids under limited pressure can be maintained in the riser despite the impetus of formation gas below the mud column to displace the liquid. Provision of the annular shut-off below the telescopic joint eliminates the necessity to seal well fluid pressure at the telescopic joint packer during kick control circulating operations. The flow diverting control device includes an outlet which opens on the closing of the annular sealing device and which provides a flow path beneath the annular sealing device to a choke line to facilitate bringing the well under control by circulating kill mud. If the BOP stack is on bottom, circulation can be directed down a riser kill line and introduced into the annulus above a closed ram. If the BOP's are open or if the stack is not on bottom, circulation is directed down the drill pipe, up the riser annulus and through the choke manifold. By maintaining a mud column in the riser annulus, the hazard of collapsing the pipe by external hydrostatic head near the lower end of a deepwater marine riser is avoided.

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First Claim