Semisubmersible vessel with captured constant tension buoy

Abstract

A floating drilling and production unit comprising two independently floating bodies: (1) an outer, larger, substantially cylindrical buoyant caisson with an enlarged skirt around its lower perimeter to dampen sea-induced motions and (2) a wellhead buoy captured within the central well of the outer caisson. The outer caisson supports the weight of the drilling platform, machinery, storage and living quarters and is ballasted and anchored in a manner similar to a conventional semisubmersible vessel. The constant tension buoy supports the wellheads of completed wells and is held in a constant position relative to the ocean floor much like a tension leg platform by the production risers of completed wells, tendons, or a combination of tendons and risers. Production risers are kept taut by the buoyancy of the constant tension buoy. The constant tension buoy has a tapered shape that minimizes contact and interaction between the wellhead buoy and the caisson. Thus, the wellhead buoy is substantially unaffected by sea-induced motions of the bouyant caisson. Drilling operations with equipment supported by the caisson are carried out through a moonpool extending vertically through the wellhead buoy.

Dependencies are inferred from the claim text.