Ships – Ballasting – Water tanks
Patent
1993-05-24
1994-11-15
Sotelo, Jesus D.
Ships
Ballasting
Water tanks
114267, B63B 4306
Patent
active
053637887
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a floating oil rig with controllable heave and, more particularly, to such a rig intended to be installed in a calm sea.
Floating oil rigs of the semi-submersible type are subjected to wave motion, which, during the passage of a wave, causes a vertical movement of the rig which tends to maintain its level of flotation with respect to the surface of the sea. Each sea has it own geographical conditions which give the wave motion associated characteristics: mean height of the waves and frequency of the wave motion. The shape and dimensions of a rig give a specific response time during the passage of a wave. Therefore, in order to avoid resonance problems, it is necessary that the natural periods of the wave motion and of the rig are sufficiently different.
The subject of the present invention is therefore a rig of which one can ensure that the natural period is different from that of the wave motion in which the rig is installed.
In order to achieve this, the invention proposes a floating oil rig with controllable heave, comprising a deck and a flotation unit, which,, in order to control the response of the rig to the motion of the sea in which it is installed, comprises a tidal chamber which is open to the sea and connected to a gas tank by a circulation conduit fitted with a restriction device. According to the invention, the flotation unit comprises two gas tanks arranged on either side, in the vertical plane, of the tidal chamber and connected to it by the circulation conduit.
This type of rig is particularly suitable for calm seas in which the wave motion has a long period, for example the Gulf of Guinea.
According to a second aspect, the invention proposes a rig whose deck comprises bearing cages arranged around its periphery, each bearing cage being intended to receive the end of an associated flotation column, the flotation columns being connected to their associated bearing cages only under the effect of their buoyancy thrust, the columns not being connected together.
Such a structure has advantages of manufacture cost and enables the rig to be assembled directly on site, the flotation columns being manufactured in the region of installation and only the deck being constructed in a remote shipyard. In addition, such a rig can be installed without having to use heavy equipment. The deck is an independent barge which arrives on site fully equipped.
The advantages, as well as the operation of the present invention, will emerge more clearly on reading the following description given in a non-limiting manner with reference to the attached drawings in which:
FIG. 1 is a diagrammatical view of an oil rig at sea according to the invention;
FIG. 2 is a longitudinal section of one of the columns used in the rig of FIG. 1; and
FIGS. 3A and 3B are each a longitudinal section of a column according to a second embodiment of the invention.
In FIG. 1, an oil rig with controllable buoyancy is shown overall as 10. The rig 10 comprises a floating deck 12 which is mounted on the upper ends of flotation columns 14 which form a flotation unit. The rig 10 comprises at least four columns 14 and in the example illustrated, it comprises six of them. The six flotation columns are substantially identical and will be described in more detail hereinafter. The columns may have a rectangular cross-section, or, preferably, a circular cross-section. A drilling mast, shown diagrammatically as 16, is mounted on the deck 12.
The deck 12 is fitted with six bearing cages 18 arranged around its periphery, each one intended to receive the upper end of an associated flotation column 14. As shown in FIG. 2, the upper end 20 of the column 14 bears on the lower surface 22 of the cage 18 via a set of blocks 24 made of elastomer and arranged in a circle on the lower surface 18, which make it possible to distribute the load on the end of the column 14 and which form a joint. Other types of joint, for example a spherical bearing surface, can also be used.
Each column 14, having the form of a tube with closed ends, i
REFERENCES:
patent: 4167147 (1979-09-01), Bergman
patent: 4207828 (1980-06-01), Horowitz et al.
Elf Aquitaine Production
Sotelo Jesus D.
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