Emergency dump apparatus for buoyancy air tanks on buoyant riser systems

Abstract

An apparatus for rapid venting of the compressed air and deballasting of a buoyant air tank in a positively buoyant riser system in the event of a premature drive off or a riser section parting is shown. The rapid venting of the compressed air ensures that the riser section cannot rapidly ascend to the surface and damage the drilling rig positioned above. In a first embodiment, the buoyancy tank or housing includes a circumferentially shaped channel positioned on its upper end. An annularly shaped ring is placed over the circumferentially shaped channel and sealed in place by a frangible weld. A tether line attaches to the annularly shaped ring and extends to an anchor point on the BOP stack below. In the event of a catastrophic parting of the riser, as the riser sections and attached buoyancy tank or housings begin ascending, the tether line is drawn tight. Further ascension of the buoyancy tank or housings, causes the frangible weld joints to break and peel back the annularly shaped ring, exposing the circumferentially shaped channel. This causes an immediate and complete venting of the buoyancy tank or housings, rendering them negatively buoyant. Alternate embodiments using an annularly shaped flange releasable by toggle clamps or retainer pins are also shown.

Dependencies are inferred from the claim text.