Single column extendable draft offshore platform

Abstract

An extendable draft offshore oil and gas drilling and production platform (“EDP”) includes a buoyant deck having a central opening, an adjustably buoyant pontoon, and a single, adjustably buoyant column. The column is mounted upright on the pontoon, and is vertically movable through the central opening of the deck. The deck is supported on an upper end of the column above a body of water for offshore operations. The pontoon, and optionally, the column, have compartments with a buoyancy that is adjustable by pumps or sea water ballast and pressurized air. In one embodiment, the compartments can comprise a plurality of tubes. In another embodiment, a lower end of the column may comprise an open truss structure. The platform combines the advantages of a SPAR platform with those of a deep draft extendable draft platform.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] (Not Applicable) STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] (Not Applicable) REFERENCE TO APPENDIX [0003] (Not Applicable) BACKGROUND OF THE INVENTION [0004] 1. Field of the Invention [0005] This invention relates to floating vessels useful for offshore oil and gas drilling and production operations in general, and in particular, to a deep-draft, semi-submersible, extendable-draft platform (“EDP”) that incorporates a single, centrally located support column to minimize platform cost, complexity and motions resulting from surface wind and wave forces. [0006] 2. Related Art [0007] The development of deep water offshore oil and gas fields, such as are found in the Gulf of Mexico and the North Sea, present substantial challenges to the petroleum industry. Early production schedule requirements necessitate maximal inshore integration and commissioning, together with a year-round deployment capability. Moreover, th...

AI Technical Summary

Benefits of technology

[0016] In accordance with the present invention, an extendable draft offshore oil and gas drilling and production platform (“EDP”) is provided that combines the structural simplicity, compactness, efficient use of deck space, and reduced resistance to surface level wind, wave and current forces of a SPAR platform with the easy fabrication and self-installing features of a deep draft EDP. The novel platform comprises a buoyant topside, or equipment deck, having a central opening, and an adjustably buoyant pontoon having a center well. A single buoyant support column having a center well is mounted upright on, and concentrically with the center well of, the pontoon, and is vertically movable through the central opening of the deck by adjusting the buoyancy, i.e., the sea water ballast, of the pontoon, and optionally, that of the column as well.

Problems solved by technology

The development of deep water offshore oil and gas fields, such as are found in the Gulf of Mexico and the North Sea, present substantial challenges to the petroleum industry.

While relatively stable, such fixed platforms are typically limited to shallow waters, i.e., depths of about 500 feet (150 m) or less.

Although floating platforms are more complex to operate because of their greater movement in response to wind and wave conditions, they are capable of operating at substantially greater depths than fixed platforms, and are also more mobile, and hence, easier to move to other offshore well sites.

However, the offshore installation of their equipment deck requires the use of a heavy-duty crane barge.

Additionally, they have a relatively low hull efficiency, and their offshore hook-up and connection procedures are relatively time-consuming and expensive.

The motions of these types of semi-submersible platforms are relatively large, and accordingly, they require the use of “catenary” risers (either flexible or semi-rigid), extending from the seafloor to the work platform because they are not capable of supporting the other types of risers, e.g., top-tensioned vertical risers (“TTRs”) that are typically employed in deep water operations.

Additionally, the use of multiple columns entails higher fabrication costs, and the leg wells are relatively wasteful of useful equipment deck area.

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