Importance

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Abstract

A dual string high pressure riser system is disclosed for use in drilling a deepwater well through a subsea wellhead. An outer riser extends from the surface and sealingly engages the wellhead and an inner riser extends from the surface downwardly, concentrically through the outer riser to communicate with the well. A surface BOP provides well control at the top of the dual high pressure riser. In another aspect of the present invention, a method is disclosed for conducting deepwater drilling operations in which a surface BOP and a lightweight outer riser are installed in communication with a subsea wellhead and a first interval is drilled through the outer riser. Casing is run through the outer riser into the first interval, cemented within the borehole and sealed at wellhead. As drilling proceeds toward subterranean intervals at which high pressure might be encountered, an inner riser is deployed concentrically within the outer riser, engaging to the wellhead at its lower end and communicating with the surface facilities through the BOP at the upper end. Subsequent intervals are drilled through the inner riser.

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First Claim