Ships – Floating platform
Patent
1998-06-04
2000-02-15
Avila, Stephen
Ships
Floating platform
114265, B63B 3544
Patent
active
060240407
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an off-shore production platform, and especially relates to an off-shore oil production platform which includes an upper barge extending above the level of the sea and being connected to a completely submerged hollow lower base by partially submerged connecting legs forming a buoyancy tank and extending substantially vertically.
Platforms of this type are called semi-submersible platforms. In order to make such platforms stable during production, the lower base is ballasted (for example by filling it with seawater). In known platforms, the legs are formed by cylindrical columns with solid walls delimiting along their entire height a closed space forming a buoyancy tank for the platform.
These platforms do not rest directly on the sea bed and are simply anchored by mooring lines. They are thus very sensitive to swelling of the sea, which causes rising and falling vertical movements of the platform. The amplitude of these movements may reach high values. This phenomenon makes oil production from the platform difficult.
In order to attempt to provide a solution to this problem, it has been proposed to extend the length of the legs so that the base is submerged at a great depth. The result obtained by implementing this solution remains imperfect, and such platforms are complicated to manufacture and to install. Furthermore, they are temporarily unstable during installation.
French patent application FR-A-2,713,588 describes a jack-up platform including legs formed of a metal lattice along their entire height. Floats built into the legs allow the platform to be made buoyant. However, they are not intended to reduce the vertical movements of the platform.
SUMMARY OF THE INVENTION
An object of the present invention is to propose an off-shore production platform which is not very sensitive to swelling, and in which the length of legs connecting an upper barge to a lower base is limited.
To this end, an object of the invention is an off-shore production platform, especially an off-shore oil production platform (of the aforementioned type) which comprises legs that include at least two successive portions along their submerged height. A first portion has solid walls delimiting a closed space and forms a buoyancy tank. A second portion has an openwork sidewall that includes an interior space open to a surrounding marine environment.
According to specific embodiments, the invention may have one or more of the following features:
the second portion with the openwork sidewall has a metal lattice structure;
the second portion with the openwork sidewall is arranged between the first portion having solid walls and the base;
the first portion having solid walls extends at least partially immediately below the barge;
the first portion and second portion have dimensions such that over a usual swell range period, a pressure force exerted on the first portion with solid walls substantially compensates for an acceleration force of the platform;
the first portion and second portion have dimensions such that for two values of a swell period lying within the usual swell period range, the pressure force and the acceleration force are equal;
the smallest value of the swell period for which the pressure force and the acceleration force are equal is greater than 4 seconds;
the submerged height of the second portion lies between one quarter and three quarters of the total submerged height of the leg;
the submerged height of the second portion lies between substantially 0.4 and substantially 0.65 times the total submerged height of the leg;
the legs have a cylindrical external overall shape;
the base includes at least one passage passing substantially vertically right through it;
the base is filled with a fluid forming a ballast, and particularly with seawater;
the barge is mounted so that it can be moved along the legs and mechanisms are provided for the relative movement and locking of the barge with respect to the legs; and
the second portion having the openwork sidewall
REFERENCES:
patent: 4784529 (1988-11-01), Hunter
patent: 4864958 (1989-09-01), Belinsky
patent: 5012756 (1991-05-01), Kristensen
patent: 5588369 (1996-12-01), Rizkalla et al.
Avila Stephen
Technip Geoproduction
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