Hydraulic and earth engineering – Marine structure or fabrication thereof – With anchoring of structure to marine floor
Patent
1996-08-19
1998-08-11
Graysay, Tamara L.
Hydraulic and earth engineering
Marine structure or fabrication thereof
With anchoring of structure to marine floor
4052231, 405205, 114265, B63B 3544
Patent
active
057918198
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a buoyant platform, and to a method of assembling such a platform.
In particular the invention relates to a buoyant platform formed from an existing semisubmersible vessel secured to an upper surface of a purpose built raft.
Semisubmersible vessels have been used for some years in the offshore industry for the purpose of drilling, production and marine operations. These semisubmersible vessels typically have two parallel spaced apart pontoons with buoyant columns upstanding from those pontoons to support a deck. In transit the vessel is deballasted so that it can float on the pontoons with the columns clear of the water. This allows the vessel to operate as a catamaran. For activities which require a stable offshore platform, the vessel is ballasted down so that the pontoons are submerged, and only the buoyant columns pierce the water surface--thus giving the vessel a substantial buoyancy with a small waterplane area.
This configuration--which is illustrated in U.K. Patent Specification 2068439A--provides a more stable platform for offshore operations than would be provided by a conventional ship shaped vessel. However, for severe seastates, even the semisubmersible vessel becomes subject to movements which are unacceptable for many offshore operations, including inter alia drilling and production. This leads to "downtime" during which all the costs of operating the semisubmersible vessel are incurred, but no useful work is done.
Economic development of offshore oil and gas fields in hostile areas (in terms of severe sea states) has led to requirements for drilling, production and marine operations to be carried out in progressively more severe sea states, so to minimise downtimes.
It is known from USSR Certificate of Authorship SU 1303486 to use a ballasted double float with platform as lifting equipment for the assembly or repair of a semisubmersible drilling rig. The ballastable double float with platform may be regarded as a controllably buoyant structure. The ballastable double float with platform is located under the semisubmersible drilling rig, and is then deballasted to lift that semisubmersible drilling rig clear of the water for assembly or repair. This combination is located using anchor chains deployed directly from the semisubmersible drilling rig. This suffers from the disadvantage that the operations can only be carried out in calm water over a limited period of time. For this reason the combination of the semisubmersible drilling rig and the controllably buoyant structure shown in SU 1303486 would be unsuitable as a permanent floating production facility located in a geographic area subject to severe sea states.
Thus there is a requirement for a buoyant platform which is capable of continued operation in more severe sea states than can be tolerated by semisubmersible vessels currently in use. This may be combined with a further requirement for oil storage at an open sea site.
In some cases there may be a requirement to add production facilities to a semisubmersible vessel which is already equipped with power supplies and drilling equipment. Deck load and area limitations, which would normally prevent such production equipment from being carried, can be overcome by supporting the semisubmersible vessel on a raft.
The invention provides a floating platform comprising in combination a semisubmersible vessel having two or more pontoons, buoyant columns upstanding from those pontoons and a deck supported on the columns (the semisubmersible vessel being of a kind known per se); and a raft comprising a hull portion and two or more buoyant caissons arranged so that the raft is capable of floating in a stable configuration with the hull portion of the raft submerged to such a depth that the semisubmersible vessel can float over the hull portion and with only the buoyant caissons piercing the water surface, in which the pontoons of the semisubmersible vessel are secured to upper surfaces of the hull of the raft.
A raft of the kind described in the preceding paragraph will he
REFERENCES:
patent: 3986471 (1976-10-01), Haselton
patent: 4167148 (1979-09-01), Fayren
patent: 4471708 (1984-09-01), Wilson et al.
patent: 4729695 (1988-03-01), Silvestri
patent: 4823719 (1989-04-01), Sarwe
patent: 5292207 (1994-03-01), Scott
87-333556/47 Derwent's abstract of SU-1303-486 SU-869,801 of 15 Apr. 1987.
Graysay Tamara L.
Kaerner AS
Lagman Frederick L.
LandOfFree
Buoyant platform does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Buoyant platform, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Buoyant platform will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-382270