EP2318267B1 - Floating support comprising a drum equipped with two buoys to which to fasten tethers and pipes connecting between the sea bed and the surface - Google Patents

Description

The present invention relates to a floating support anchored on a disconnectable drum.

The technical sector of the invention is more particularly the field of underwater oil production in extreme weather-ocean weather zone and more particularly in the Arctic and Antarctic, from floating supports.

A floating support for oil production generally includes anchoring means to remain in position despite the effects of currents, winds and waves. It also generally comprises means for drilling, storage and treatment of oil and means of unloading to removing tankers, the latter occurring at regular intervals to perform the removal of production. The usual name for these floating supports or vessels is the Anglo-Saxon term "Floating Production Storage Offloading" (meaning "floating medium of storage, production and unloading") which we use the abbreviated term "FPSO" as a whole of the following description, or "FDPU" or "Floating Drilling & Production Unit" (meaning "buoyant means of drilling and production"), when the floating support is also used to perform drilling operations with well deviated in height of the slice of water.

When the ocean-weather conditions, ie swell, wind and current are important, even extreme, in the case of storms, it is preferable to anchor the FPSO at a reel, usually located at known manner in the forward third of the ship and in the axis, the vessel being free to turn around said drum in the wind, the current and the swell. Thus, wind, current and waves exert specific forces on the hull and the superstructures, the FPSO because of its degree of freedom of rotation around the vertical axis ZZ, coming naturally to the position of least resistance. The pipes connecting the wellheads are connected in generally on the underside of the drum and connected to the FPSO via a rotary joint integrated in the axis of said drum. When weather conditions can become extreme, such as in the North Sea, in the Gulf of Mexico or in the Arctic or Antarctic zone, the FPSO is generally disconnectable so that it can be sheltered waiting for acceptable operational conditions.

The present invention relates more particularly to a floating support for submarine oil production in the Arctic or Antarctic zone equipped below its hull with a disconnectable drum from which anchor lines extend to the seabed and pipes. connecting bottom / surface, said shell having in its longitudinal direction substantially flat lateral edges and vertical, and optionally, with, known manner of the proues (front part of the ship) and, preferably stern (rear part of the ship), inclined relative to the horizontal and preferably profiled to form a reinforced pointed bow, capable of breaking the pack ice by simple bending when said pack ice engages force under said reinforced bow.

The floating supports advantageously have a hull with longitudinal edges substantially vertical to give them optimum oil storage capacity, and better behavior in case of high sea. But a hull with vertical edges is particularly disadvantageous in terms of behavior. facing the pack ice. So in US 4102288 and US 4571125 floating supports are proposed which, among other means, have curved or angled curved planks to promote ice breakage, as is the case with the known bow ship profiles with bow inclined relative to the horizontal.

• une bouée d'amarrage desdites lignes d'ancrage et conduites de liaison fond/surface de préférence ladite bouée étant une bouée annulaire, et
• ladite bouée d'amarrage étant fixée dessous la coque du support flottant, à un dispositif rotatif comportant une structure en forme de tour appelé « touret », ledit touret coopérant avec la coque au sein d'une cavité traversant la coque du support flottant sur toute sa hauteur, ledit touret étant articulé en rotation par rapport à ladite coque par l'intermédiaire d'au moins un palier de roulement ou de frottement, de préférence un palier de roulement de manière à autoriser la rotation dudit support flottant autour d'un axe sensiblement vertical ZZ' dudit touret et de ladite cavité, sans entraîner la rotation de ladite bouée d'amarrage par rapport au même axe vertical ZZ', et
• lesdites conduites de liaison fond/surface remontant au sein de la cavité jusqu'à un raccord d'une pluralité de dites conduites, ledit raccord étant solidaire du support flottant au niveau du pont du support flottant, ledit raccord étant articulé en rotation de manière à autoriser la rotation dudit support flottant sans entraîner la rotation dudit raccord du type raccord à joint tournant.

A floating oil production support comprising a disconnectable mooring system of anchoring lines at the bottom of the sea and bottom / surface connection pipes comprises in known manner:

• a mooring buoy of said anchor lines and bottom / surface connection lines, preferably said buoy being an annular buoy, and
• said mooring buoy being fixed below the hull of the floating support, to a rotary device comprising a tower-shaped structure called "reel", said reed cooperating with the hull within a cavity passing through the hull of the floating support on any its height, said drum being articulated in rotation relative to said shell by means of at least one rolling or friction bearing, preferably a rolling bearing so as to allow the rotation of said floating support about an axis substantially vertical ZZ 'of said drum and said cavity, without causing rotation of said mooring buoy with respect to the same vertical axis ZZ', and
• said bottom / surface connection pipes going up within the cavity to a connection of a plurality of said pipes, said connection being integral with the floating support at the level of the floating support bridge, said connection being articulated in rotation so as to allowing rotation of said floating support without causing rotation of said rotary joint type fitting.

In the prior art described above, the rolling bearing is either located at the level of the floating support bridge or located in the lower part in a wet zone, that is to say that the bearing is immersed, or else in combination of the two previous configurations.

Embodiments in which the rolling bearing is located exclusively at the level of the bridge are valid only for floating supports of relatively low height, especially less than 15 m. Beyond this, for the floating supports, in particular 20 to 25 m high, the horizontal force on the drum resulting from the rotation of the floating support creates a bending on the structure of the drum in its length, which forces the mechanical resistance of the upper bearing of rolling and therefore affects the mechanical reliability of operation. On the other hand, when the rolling bearing is immersed in the lower part of the drum, this immersion affects the reliability of operation and the durability of said rolling bearing and in addition creates difficulties in carrying out maintenance operations. In fact the on-site interventions require the use of divers and considerable technical means, and one is generally led to perform these operations in a protected area, such as a fjord, or preferably a dry dock, after disconnection of the FPSO. Thus, when the FPSO is intended to remain in position for several decades without scheduled disconnection for maintenance in dry dock or protected site, this type of drum is not suitable.

Media of the type defined above are known in GB 2291389 and EP 259072 .

In WO 94/15828 a connection and quick disconnection system for a mooring buoy is described, in which the mooring buoy comprises an upper part connected to the bottom of the hull of the floating support, more precisely at a mooring cavity. extending annularly at the lower end of a cavity passing through the hull of the floating support over its entire height and through which the bottom / surface connection lines rise. The mooring buoy also includes a lower portion to which anchor lines are anchored and lower portions of bottom / surface connection lines extending to the bottom of the sea, this lower portion of the mooring buoy. is rotatable through a completely immersed rolling bearing, allowing the rotation of this lower part relative to the upper part of the mooring buoy secured to the hull.

This type of system with a fully submerged rotating part and fully immersed rolling bearings is not suitable for mooring a large number of bottom / surface connection pipes, for which it is desirable to provide a system in which at least part of the rolling bearings is located in the area out of water, so that it can be easier to maintain and operate in less demanding operating conditions.

In WO 94/15828 at the bottom of the shell, there are provided internal tanks having a large area in horizontal section in which the atmospheric pressure is established or preferably the vacuum. These internal tanks have a large contact surface in horizontal section with the upper part of the mooring buoy, against which the latter is intended to be fixed. To do this, an annular interstitial zone is created between the mooring buoy and the atmospheric pressure vessel at the bottom of the hull of the vessel, delimited by two concentric O-rings, an annular zone of reduced volume which is brought into contact with the atmospheric pressure chamber at the bottom of the hull of the ship to create a positive buoyancy of the entire mooring buoy and anchor lines and bottom / surface connection lines which are pressed against said contact surface.

Under certain conditions, it may be desirable to disconnect only the bottom-surface connection lines, maintaining said floating support moored at the bottom by said anchor lines, these being moored to said mooring buoy.

This type of circumstance occurs especially when it is necessary to provisionally shelter the bottom-surface connection pipes which are more fragile than the anchor lines, especially when the bottom-surface connection pipes comprise flexible pipes ensuring the connection between said mooring buoy and a buoy immersed in the subsurface, without the need to drop said anchor lines.

In mooring systems with a single annular mooring buoy attached to a drum such as in GB-2,321,631 , and on which are fixed both said anchor lines and said lines of link, it is not possible to drop the bottom-surface connection lines without first disconnected and lowered the mooring buoy on which they are moored, when the sea is agitated surface and subsurface. First of all, it is necessary to drop the mooring buoy to descend it to a sufficient depth where the sea is quieter and where there is no risk of damaging the bottom / surface connection lines when their release from the buoy. Otherwise, there is a risk of damaging the upper end connectors of the bottom / surface link pipe portions connected to the buoy. But, the disconnection of the buoy then involves disbanding the floating support at least momentarily, which is not always desirable.

In EP-0 831 023 a mooring buoy consisting of two independent parts consisting of a first annular buoy on which are exclusively anchored said anchoring lines of the floating support and a second coaxial buoy secured to said first buoy in a reversible manner is described; that is disconnectable, within the central orifice of said first buoy, said bottom / surface connection lines being moored exclusively to said second buoy. However, in the embodiment as described in EP-831,023 , the two buoys are entirely contained in a cavity within the hull of the floating support and are thus connected and therefore disconnectable, exclusively by complicated mechanical locking means and very difficult to implement when the forces become considerable, the latter being able to reach and exceed 5 to 6000 tons.

The object of the present invention is to provide a mooring device reversibly connected to the floating support comprising at least one mooring buoy, device on which are fixed said anchoring lines and bottom / surface connection lines, said mooring device cooperating with a drum, the structure and operation of said mooring device being such that the device allows independent disconnection of the bottom / surface connection lines, without risk of damaging them, while maintaining the floating support anchored by said anchor lines.

Another object of the present invention is to provide a system for connection / disconnection of said mooring device, which is fast and based on the principle of creating a positive buoyancy between a mooring buoy and the anchor lines and and / or mooring / mooring connecting lines moored thereto, the buoy connection / disconnection system to be further adapted to an embodiment in which said mooring device is secured under a rotating drum within a cavity extending preferably over the entire height of the hull of the ship, said docking device being articulated in rotation relative to said hull with the aid of at least one rolling bearing, preferably which is not susceptible to be immersed in operation.

• un dispositif d'amarrage de lignes d'ancrage au fond de la mer et de premières conduites de liaison fond/surface s'étendant depuis ledit dispositif d'amarrage où elles sont amarrées, jusqu'au fond de la mer, ledit dispositif d'amarrage comprenant au moins une bouée annulaire d'amarrage, ledit dispositif d'amarrage étant connecté de manière réversible à un touret, et
• ledit touret comprenant au moins une structure tubulaire étanche, de préférence à section circulaire selon ledit axe vertical ZZ', comportant une paroi de fond assemblée de manière étanche à l'extrémité inférieure de la paroi tubulaire latérale de ladite structure tubulaire étanche, ledit touret s'étendant au sein d'une cavité traversant la coque du support flottant de préférence sur toute sa hauteur, ledit touret étant articulé en rotation par rapport à ladite coque par l'intermédiaire d'au moins un palier de roulement ou de frottement situé de préférence au-dessus de la ligne de flottaison et/ou hors d'eau, de préférence un palier de roulement, de manière à autoriser la rotation dudit support flottant autour d'un axe sensiblement vertical ZZ' dudit touret et de ladite cavité, sans entraîner la rotation dudit dispositif d'amarrage par rapport au même axe vertical ZZ', et
• des secondes conduites de liaison s'étendant entre l'extrémité supérieure desdites premières conduites de liaison fond/surface auxquelles elles sont connectées et le pont du support flottant, lesdites deuxièmes conduites de liaison traversant de manière étanche la paroi de fond du touret et remontant au sein de la cavité jusqu'à un raccord d'une pluralité de dites secondes conduites, ledit raccord étant solidaire du support flottant au niveau du pont du support flottant, ledit raccord du type raccord à joint tournant, étant articulé en rotation de manière à autoriser la rotation dudit support flottant sans entraîner la rotation dudit raccord, les extrémités inférieures desdites secondes conduites de liaison en sous-face de ladite paroi de fond du touret étant connectées aux extrémités supérieures desdites premières conduites de liaison fond/surface par l'intermédiaire de connecteurs coopérant avec des vannes, caractérisé en ce que :
• ledit dispositif d'amarrage comporte deux bouées disposées coaxialement l'une par rapport à l'autre et par rapport à l'axe ZZ' de la paroi de fond dudit touret, une première bouée étant une bouée annulaire sur laquelle sont amarrées lesdites lignes d'ancrage, et ladite bouée annulaire comportant un orifice central contenant une deuxième bouée d'amarrage sur laquelle sont amarrées lesdites premières conduites de liaison fond/surface, ladite deuxième bouée d'amarrage comprenant une paroi tubulaire supérieure, à l'intérieur de laquelle sont situées lesdites vannes et connecteurs à l'extrémité supérieure desdites premières conduites de liaison, et
• ledit support flottant comprend un système de connexion/déconnexion de ladite première et/ou respectivement deuxième bouée(s) d'amarrage par rapport à ladite paroi de fond du touret, permettant la connexion/déconnexion de chacune desdites première ou respectivement deuxième bouée d'amarrage indépendamment l'une de l'autre, comprenant :
  • deux joints d'étanchéité sur la face supérieure de ladite première bouée annulaire, lesdits joints étant de préférence coaxiaux par rapport à l'axe ZZ' de l'orifice central de ladite première bouée, délimitant une première chambre étanche ou chambre annulaire interstitielle entre la paroi de fond dudit touret et la face supérieure de ladite première bouée, lorsque ladite face supérieure de ladite première bouée est plaquée contre la paroi de fond dudit touret, et
  • ladite paroi supérieure tubulaire de ladite deuxième bouée délimitant avec la paroi de fond dudit touret une deuxième chambre étanche dite chambre des vannes, lorsque un joint d'étanchéité sur le bord supérieur de ladite paroi supérieure tubulaire de la deuxième bouée est appliqué contre la paroi de fond dudit touret, en sous-face de celui-ci, et
  • une pluralité de liens, tels que des câbles de levage fixés à chaque dite bouée d'amarrage, de préférence au bord supérieur de la dite paroi supérieure tubulaire de ladite deuxième bouée d'amarrage, lesdits liens s'étendant de préférence à l'intérieur du touret en traversant de manière étanche la paroi de fond du touret, et
  • au moins deux tubes d'évent s'étendant verticalement à l'intérieur du touret, depuis un niveau situé au-dessus de la ligne de flottaison jusqu'à la paroi de fond du touret qu'ils traversent de manière étanche au niveau de chacune desdites première et respectivement deuxième chambre, et
  • des moyens de pompage d'eau dans chacune desdites première et respectivement deuxième chambres, lorsque ladite première et respectivement deuxième bouée correspondante est appliquée contre la paroi de fond du touret, et
  • le poids propre de ladite première bouée d'amarrage et lignes d'ancrage et respectivement le poids propre de ladite deuxième bouée d'amarrage et desdites premières conduites de liaison fond/surface est inférieur au poids du volume d'eau V_i tel que V_i=S_ix(H₀-H_2i), dans laquelle:
• H₀ est la hauteur d'eau du niveau de flottaison,
• H_2i est la hauteur de la partie de la paroi de fond du touret délimitant ladite première chambre ou respectivement deuxième chambre, et
• S_i étant la surface de la section transversale de ladite première chambre ou respectivement dite deuxième chambre,
• i = a pour ladite première bouée et dite première chambre et i = b pour ladite deuxième bouée et dite deuxième chambre.

To do this, the present invention provides a floating support for oil production comprising:

• an anchoring device anchoring lines to the seabed and first bottom / surface connection lines extending from said docking device where they are moored, to the bottom of the sea, said device mooring comprising at least one annular mooring buoy, said mooring device being reversibly connected to a drum, and
• said drum comprising at least one sealed tubular structure, preferably of circular section along said vertical axis ZZ ', having a bottom wall sealingly assembled at the lower end of the tubular side wall of said tubular waterproof structure, said drum extending within a cavity passing through the hull of the floating support preferably over its entire height, said drum being articulated in rotation with respect to said shell by means of at least one rolling or friction bearing preferably located above the waterline and / or out of water, preferably a rolling bearing, so as to allow rotation of said floating support about a substantially vertical axis ZZ 'of said reel and of said cavity, without causing rotation of said docking device with respect to the same vertical axis ZZ', and
• second connecting lines extending between the upper end of said first bottom / surface connection conduits to which they are connected and the bridge of the floating support, said second connecting lines sealingly passing through the bottom wall of the drum and going back to the within the cavity to a connection of a plurality of said second conduits, said connection being integral with the floating support at the level of the floating support bridge, said connection of the rotary joint type connection being articulated in rotation so as to allow rotating said floating support without causing said coupling to rotate, the lower ends of said second connecting lines on the underside of said bottom wall of the drum being connected to the upper ends of said first bottom / surface connection conduits via connectors cooperating with valves, characterized in that:
• said mooring device comprises two buoys arranged coaxially with respect to one another and with respect to the axis ZZ 'of the bottom wall of said drum, a first buoy being an annular buoy on which said lines are moored; anchoring, and said annular buoy having a central orifice containing a second mooring buoy to which said first bottom / surface connection lines are moored, said second mooring buoy comprising an upper tubular wall, within which are located said valves and connectors at the upper end of said first connecting lines, and
• said floating support comprises a connection / disconnection system of said first and / or respectively second mooring buoy (s) with respect to said bottom wall of the drum, allowing the connection / disconnection of each of said first or second mooring buoy independently of each other, comprising:
  • two seals on the upper face of said first annular buoy, said seals being preferably coaxial with respect to the axis ZZ 'of the central orifice of said first buoy, delimiting a first interstitial chamber or interstitial annular chamber between the bottom wall of said drum and the upper face of said first buoy, when said upper face of said first buoy is pressed against the bottom wall of said drum, and
  • said tubular upper wall of said second buoy delimiting with the bottom wall of said drum a second sealed chamber known as the valve chamber, when a seal on the upper edge of said tubular upper wall of the second buoy is applied against the wall of bottom of said drum, on the underside of it, and
  • a plurality of links, such as lifting ropes attached to each said mooring buoy, preferably to the upper edge of said tubular upper wall of said second mooring buoy, said links preferably extending inside. of the drum by sealingly passing through the bottom wall of the drum, and
  • at least two vent tubes extending vertically inside the drum, from a level above the waterline to the bottom wall of the drum which they pass through in leaktight manner at each level said first and second chambers, and
  • means for pumping water into each of said first and second chambers, when said first and respectively corresponding second buoy is applied against the bottom wall of the drum, and
  • the dead weight of said first mooring buoy and anchor lines and respectively the dead weight of said second mooring buoy and said first connecting lines bottom / surface is less than the weight of the volume of water V _i such that V _i = S _i x (H ₀ -H _2i ), in which:
• H ₀ is the water level of the water level,
• H _2i is the height of the part of the bottom wall of the drum delimiting said first chamber or respectively second chamber, and
• S _i being the surface of the cross section of said first chamber or so-called second chamber,
• i = a for said first buoy and said first chamber and i = b for said second buoy and said second chamber.

The weight of the volume of water V _i corresponds to the buoyancy force applied to the horizontal section S _i of said first or second chamber.

No part of the drum and / or mooring device is fixedly secured to the hull.

The mooring device of the present invention makes it possible to disconnect and descend to a certain immersion depth below the floating support the second buoy alone, in order to put the first lines of bonds away from turbulence surface and subsurface, while now connected the first buoy on which the anchor lines are moored and thus without undoing the floating support.

On the other hand, it is understood that in extreme conditions, it is safer to disconnect preventively and to descend to a certain depth the second buoy carrying only the first bottom / surface connection lines, without disconnecting the first buoy. on which are moored the anchor lines, which exert a greater return tension on the first buoy on which they are moored.

In addition, the connection / disconnection system is particularly easy to implement, according to the following principle.

When applying the upper face of the first buoy or the upper edge of the upper tubular wall of the second buoy in contact against the underside of the bottom wall of the drum, said first or second chamber being filled with water, a connection of said buoy is made to said bottom wall of the drum by creating a positive buoyancy of all of said first buoy and said anchor lines or said second buoy respectively and said first bottom / surface connection lines . To do this, the water is pumped inside said first or second chamber until the level of water in said guide tubes is between H _1i and H _2i , H _1i corresponding to the height at which the volume of water V _1i = S _i x (H ₀ -H _1i ) is equal to the self weight of said first buoy and said anchor lines or respectively said second buoy and said first connecting bottom pipes, with i = a for the first buoy and first chamber, and i = b for the second buoy and second chamber. For the disconnection of said buoy with respect to the drum, said first or second chamber is filled with water, said vent and guide tube or tubes keeping said first or second chamber substantially at atmospheric pressure during filling, until the level of water in said guide tubes is at a height slightly greater than H _1i . When the self-weight of the assembly consisting of the buoy and said first connecting pipes or anchor lines, exceeds the value of the weight of the volume of water V _1i = S _i x (H ₀ -H _1i ), the buoy begins to release naturally from the reel and begins to descend down. Indeed, as soon as the buoy is detached from the bottom of the drum, it is found with a level of hydrostatic pressure corresponding to the level of depth of the sea, said buoy being then precipitated down with a considerable force corresponding to its own weight, that is to say 500 to 1500 tons, thus freeing the floating support from its anchorage on reel almost instantaneously.

Preferably, the floating support comprises a plurality of said hoisting cables extending from winches preferably arranged at the deck of the ship or at the top of said reel, above the waterline, said hoisting ropes. optionally extending into a plurality of vent and guide tubes extending vertically within the drum, from a level above the waterline to the bottom wall of the drum which they cross in a sealed way.

More preferably, for at least one of said first or second buoy, preferably for each of said first or second buoy, said connection / disconnection system comprises at least three said cables and at least three said guide tubes, arranged, preferably, symmetrically with respect to the center of the circular bottom wall of said drum and, preferably, along and near the outer surface of said tubular structure of said drum for said first buoy or respectively close to the inner surface of said tubular structure of said reel for said second buoy, the lower ends of said cables being fixed at the upper face of said first buoy or respectively at the upper edge of said upper tubular wall of said second buoy.

This arrangement of said cables during the reconnection phases makes it possible to progress in a controlled and stable manner, the approach of said buoy against the underside of the bottom of the reel, synchronizing the operation of the winding winches of said hoisting ropes. .

More particularly, the diameter of said guide tubes and the depth of immersion of the bottom wall portion of the drum on which said guide tubes rest, with i = a or b, are such that the internal volume of the guide tubes is less than 15 m ³ , of preferably less than 5 m ³ , for a reel height immersed within said cavity of at least 20 m, more particularly preferably from 20 to 50 m.

More particularly still, said upper tubular bottom wall of said second buoy comprises, at its lower end, a bottom wall to which it is sealingly assembled, forming the bottom wall of the chamber of the valves supporting said valves and / or automatic connector parts, and said second buoy comprises, in the lower part, a box constituting a float on the underside of the bottom wall of the valve chamber.

It is understood that the upper tubular wall of the second buoy has a height necessary and sufficient to install said valves and connectors automatic connection of the first and second pipes.

More particularly still, the floating support comprises at least one said pump located preferably in the lower part inside said sealed tubular structure constituting the drum, said pump cooperating with a suction pipe sealingly passing through said bottom wall of the drum, said suction pipe arriving close to the wall of each said first or second chamber when said first or second buoy is in position against said bottom wall of the drum, and said pump cooperating with a discharge pipe for each said first or second chamber, each said discharge pipe opening into said cavity preferably through the tubular side wall of said tubular waterproof structure constituting the drum, preferably in the lower part of said drum.

• une partie centrale de préférence circulaire assemblée de manière étanche avec ladite paroi tubulaire latérale dudit touret à l'intérieure de celle-ci et au-dessus de l'extrémité inférieure de ladite paroi tubulaire latérale et une partie périphérique entourant ladite partie centrale, de préférence une partie périphérique annulaire assemblée de manière étanche à l'extrémité inférieure de ladite paroi tubulaire latérale ou sur la face externe de ladite paroi tubulaire latérale du touret, décalée en hauteur vers le bas par rapport à ladite partie centrale de telle sorte que les extrémités inférieures desdites deuxièmes conduites de liaison comprenant de préférence des parties de connecteurs, en sous-face de ladite partie centrale de la paroi de fond, soient situées au-dessus de l'extrémité inférieure de la paroi tubulaire latérale de la structure tubulaire étanche du touret.

Advantageously, the bottom wall of said drum comprises:

• a preferably circular central portion sealingly connected with said tubular side wall of said drum inside thereof and above the lower end of said lateral tubular wall and a peripheral portion surrounding said central portion, preferably an annular peripheral portion sealingly assembled at the lower end of said lateral tubular wall or on the outer face of said tubular side wall of the drum, shifted in height towards the low relative to said central portion such that the lower ends of said second connecting lines preferably comprising connector portions, on the underside of said central portion of the bottom wall, are located above the end lower part of the tubular side wall of the tubular tight structure of the drum.

This embodiment is particularly advantageous in that it allows that said first buoy is not likely to damage, when disconnected, the lower end of the second connecting lines, including the part of automatic connectors, when the said first buoy is dropped, given the considerable booster forces to which said first buoy is subjected, when the FPSO undergoes significant horizontal displacements due to swell, wind, current, or drifting ice. The first buoy is thus disconnected only after disconnecting and releasing said second buoy relative to the central orifice of said first buoy.

Indeed, the lower ends of the second pipes, including connector parts at the lower end of the second pipes are thus protected, protected by the lower part of the side tubular wall located below said central portion of the wall of bottom of the drum.

This offset between the central portion and the peripheral portion of said bottom wall forms a cavity delimited by the lower end of the inner surface of the tubular side wall of the drum and the underside of the central portion of the bottom wall.

This cavity forms a centering catch so that it can hold and wedge in position said second mooring buoy when it is pressed on the underside of said bottom wall to allow the connection of said first and second lines of connection using said connectors.

It will be understood that said centering means make it possible to facilitate the centering of the upper tubular wall of said mooring buoy with respect to said drum, in approaching movement against the underside of said bottom of the drum and, if necessary, facilitate the connection. male and female connector portions at the upper ends of said bottom / surface connection conduits overlying the bottom of said second chamber and at the lower ends of said second connecting lines.

Advantageously, the floating support comprises means for retaining or reversible mechanical safety lock of each of said first and second mooring buoys against the underside of the bottom wall of said drum.

More particularly, each of said first or second mooring buoy comprises abutments or protective cleats limiting the crushing of said seal and ensuring the vertical load transfer between said first or second buoy and the drum when said first or second buoy is applied. against the bottom wall of said drum, said O-rings being compressed between the underside of the bottom wall of said drum and said first or second mooring buoy, said protective catch being able to cooperate with an articulated movable safety lock secured to the underside of the bottom wall of said drum, such that said first or second mooring buoy is secured to said drum when said safety lock is engaged below said protective catch.

Thus, in the event of undesired invasion of said first or second chamber by seawater, in the event of a leak, the total loss of buoyancy of the mooring buoy will be compensated for by the fixing made with the aid of said locks. safety and there will be no risk of inadvertent and destructive release of said mooring buoy.

Preferably, said upper tubular wall of the second buoy and / or the tubular side wall of the sealed tubular structure of said reel comprises (s) a filling valve cooperating with filling pipes connecting the sea water and the interior of said valve chamber, and, preferably, said tubular wall of said valve chamber having a large-sized watertight hatch, adapted to allow an almost instantaneous filling of said valve chamber with seawater when one opens said hatch.

More particularly, the bottom wall of the drum comprises a inspection hatch of said valve chamber.

Since it is possible to empty the valve chamber, this allows the personnel to intervene dry in said chamber for maintenance and, if necessary, the implementation of the valves and automatic connectors ensuring the connection between said first and second conduits.

1. a- on immerge une dite première ou deuxième bouée d'amarrage, à laquelle sont amarrées desdites lignes d'ancrage ou respectivement dites premières conduites de liaison fond/surface, et
2. b- on accroche l'extrémité inférieure des câbles de levage à ladite première ou respectivement deuxième bouée, ledit support flottant étant positionné de telle sorte que ladite première ou respectivement deuxième bouée soit sensiblement axé dans l'axe vertical ZZ' de ladite cavité, et
3. c- on actionne lesdits treuils pour relever ladite première ou deuxième bouée jusqu'à ce que lesdits joints d'étanchéité, notamment joints toriques pour la première dite bouée d'amarrage ou ledit joint pour ladite deuxième bouée d'amarrage soi(en)t appliqué(s) contre et en sous-face de la paroi de fond dudit touret, formant ainsi une dite première ou respectivement deuxième chambre remplie d'eau de mer, lesdits tubes de guidage coopérant avec ladite première ou respectivement deuxième chambre étant également remplis d'eau de mer sur une hauteur H₀ correspondant sensiblement au niveau de la surface de l'eau de la ligne de flottaison, et
4. d- on pompe l'eau à l'intérieur de ladite première ou respectivement deuxième chambre à l'aide de dits moyens de pompage jusqu'à ce que le niveau de l'eau dans lesdits tubes de guidage coopérant avec ladite première ou respectivement deuxième chambre soit inférieur à la hauteur H_1i , de préférence inférieur ou égal respectivement à la hauteur H_2i, la hauteur H_1i étant telle que la poussée d'Archimède correspondant au poids du volume d'eau V_1i=S_ix(H₀-H_1i), avec i = a pour la première bouée et première chambre et i = b pour la deuxième bouée et deuxième chambre, soit supérieur au poids de l'ensemble de ladite première bouée d'amarrage et desdites lignes d'ancrage pour ladite première chambre étanche ou respectivement le poids de l'ensemble de ladite deuxième bouée d'amarrage et desdites conduites de liaison pour ladite deuxième chambre étanche., et
5. e- de préférence on vide complètement ladite première ou respectivement deuxième chambre que l'on rend ensuite étanche.

The present invention also provides a method of implementing a floating support according to the invention, wherein the connection is made of a said first or second buoy on the underside and against the bottom wall of a said reel , and the following steps are performed:

1. a said first or second mooring buoy is immersed, to which are anchored said anchoring lines or respectively said first bottom / surface connection lines, and
2. b- attaching the lower end of the hoisting ropes to said first or second buoy, said floating support being positioned so that said first or second buoy is substantially oriented in the vertical axis ZZ 'of said cavity, and
3. c. said winches are actuated to raise said first or second buoy until said seals, in particular O-rings, for the first said mooring buoy or said seal for said second mooring buoy; applied (s) against and on the underside of the bottom wall of said drum, thereby forming a said first or second chamber filled with seawater, said guide tubes cooperating with said first or second chamber also being filled with sea water over a height H ₀ corresponding substantially to the level of the water surface of the waterline, and
4. d- the water is pumped inside said first or second chamber by means of said pumping means until the level of water in said guide tubes cooperating with said first or second respectively chamber is less than the height H _1i , preferably less than or equal to the height H _{2i respectively} , the height H _1i being such that the buoyancy force corresponding to the weight of the volume of water V _1i = S _i x (H ₀ -H _1i ), with i = a for the first buoy and first chamber and i = b for the second buoy and second chamber, greater than the weight of all of said first buoy and said anchor lines for said first sealed chamber or the weight of all of said second mooring buoy and said connecting lines for said second sealed chamber., and
5. e- preferably it completely empties said first or second chamber that is then sealed.

As mentioned above, H _2b represents the height with respect to the seabed of the upper edge of the upper tubular wall of the second buoy and that of the underside of the portion of the bottom wall of the drum when in contact and S _b is the cross-sectional area of the upper tubular wall of said second buoy or the surface of the bottom wall of the drum delimited by the upper edge of the upper tubular wall of the drum when in contact. Similarly, H _2a represents the height, with respect to the seabed, of the upper face of the first buoy and that of the underside of the peripheral portion of the bottom wall of the reel when in contact, and S _a is the section of the annular surface of the cross section of said second chamber delimited by the two joints of the upper face of the first buoy when in contact with the underside of the peripheral portion of the wall of bottom of the drum.

More particularly, after emptying said first or second chamber, the lower ends of said lifting cables are detached from said first or second mooring buoy and, preferably, mechanical locking means of said first or second buoy are engaged. mooring, making it integral with the bottom wall of said drum, preferably with the aid of an articulated movable safety lock adapted to cooperate with protective stops preventing crushing of said seals or said compressed gasket between said first or respectively second mooring buoy and the underside of the bottom wall of the drum.

1. a- on fait rentrer de l'eau dans ladite première ou respectivement deuxième chambre étanche, de manière à ce que le niveau de l'eau dans lesdits tubes de guidage coopérant avec ladite première ou respectivement deuxième chambre arrive juste au-dessus dudit niveau H_1i avec i = a pour la première chambre et i = b pour la deuxième chambre, et
2. b- Pour la déconnexion de ladite deuxième bouée, on déverrouille les connecteurs automatiques entre lesdites première et deuxième conduites de liaison et,
3. c- on libère lesdits moyens de retenue mécaniques pour désolidariser mécaniquement ladite première ou respectivement deuxième bouée d'amarrage et ladite paroi de fond du touret, et
4. d- on finit de remplir les tubes de guidage en communication avec la chambre, ce qui provoque la déconnexion de ladite bouée.

The present invention also provides a method of implementing a floating support according to the invention, in which the disconnection of a said first or second buoy connected to a said reel, wherein the lower ends of said hoisting ropes have been detached from said first or second buoy, comprising the following steps wherein:

1. water is introduced into said first or second sealed chamber, so that the level of water in said guide tubes cooperating with said first or second sealed chamber; respectively second chamber arrives just above said level H _1i with i = a for the first chamber and i = b for the second chamber, and
2. b- For the disconnection of said second buoy, the automatic connectors are unlocked between said first and second connecting lines and,
3. c- freeing said mechanical retaining means to mechanically separate said first or respectively second mooring buoy and said bottom wall of the drum, and
4. d- it finishes filling the guide tubes in communication with the chamber, which causes the disconnection of said buoy.

1. a- on dépressurise lesdites premières et secondes conduites de liaison fond/surface, et
2. b- on remplit ladite deuxième chambre ou chambre de vannes jusqu'à ladite hauteur H₂b de la sous-face de la paroi de fond du touret, et on arrête le remplissage dès que ladite chambre des vannes est intégralement remplie d'eau, et
3. c- on déverrouille les connecteurs automatiques entre lesdites premières et deuxièmes conduites de liaison,
4. d- on déverrouille, le cas échéant, lesdits verrous de sûreté mécaniques, et
5. e- on continue le remplissage de ladite chambre de vannes, de manière à réaliser le remplissage des tubes de guidage jusqu'à la hauteur H_1b, ce qui provoque la déconnexion de ladite seconde bouée.

Preferably, for the disconnection of said second buoy, the following steps are carried out in which:

1. said first and second bottom / surface connection lines are depressurized, and
2. b- filling said second chamber or valve chamber to said height H ₂ b of the underside of the bottom wall of the drum, and stop fueling when said valve chamber is fully filled with water, and
3. c- the automatic connectors are unlocked between said first and second connection lines,
4. d-unlocking, if necessary, said mechanical safety locks, and
5. e-it continues filling of said valve chamber, so as to perform the filling of the guide tubes to the height H _1b , which causes the disconnection of said second buoy.

This two-stage disconnection mode is advantageous because, at the end of step b- and up to step d-included, the second buoy is is held in position by the hydrostatic thrust and the release process of the second buoy is always reversible by simply emptying the chamber. This allows to provide a phase of intermediate disconnection or waiting phase, in case we are not sure of wanting to disconnect the second mooring buoy but that, if necessary, we want to be ready to be able to do this disconnection as quickly as possible, by simply filling the guide tubes in accordance with step e-above. Thus, in case of imminent but not certain danger, such as the drift of an ice floe or an iceberg, the preparatory phase which is still reversible (stages ad) is calmly carried out, this phase possibly taking several hours in the case of burning of the iceberg. depressurization gas by the edge flare. Upon confirmation of the disconnection, the second phase (step e-), the latter being irreversible, lasts only a few tens of seconds, or even a few minutes, to obtain the release of the buoy, and therefore the almost instantaneous release of the FPSO of its bottom / surface links, or in the case of the first mooring buoy, its anchorage.

1. 1) on déconnecte ladite deuxième bouée par rapport audit touret tout en maintenant connectée ladite première bouée sur ledit touret, et
2. 2) on descend ladite deuxième bouée à une certaine profondeur d'immersion dessous ledit support flottant en gardant les premières conduites de liaison amarrées sur la deuxième bouée.

Advantageously, in a method according to the invention, the following steps are carried out in which:

1. 1) disconnects said second buoy relative to said reel while keeping said first buoy connected to said reel, and
2. 2) lowering said second buoy to a certain depth of immersion below said floating support keeping the first connection lines moored to the second buoy.

• la figure 1 représente en coupe et en vue de côté d'un support flottant du type FPSO ancré sur touret au sein d'une banquise,
• la figure 2 représente en coupe et en vue de côté un FPSO soumis à une poussée horizontale extrême de la part d'une banquise dérivante 31,
• la figure 3 représente en vue de côté le largage d'une deuxième bouée supportant les conduites de liaisons flexibles 14, le FPSO étant maintenu en position grâce aux lignes d'ancrage solidaires d'une dite première bouée,
• la figure 4 représente en vue de côté le largage subséquent de ladite première bouée en vue de libérer le FPSO de la banquise,
• la figure 5 représente en vue de côté un FPSO reprenant position à la verticale desdites premières et secondes bouées, en vue de se reconnecter à ladite première bouée comportant les lignes d'ancrage 13, puis à ladite deuxième bouée solidaire desdites premières conduites de liaisons fond-surface de type conduites flexibles,
• la figure 6 représente en coupe et en vue de côté, le touret traversant de part en part le FPSO, la paroi de fond du touret supportant une dite première bouée annulaire auxquelles sont amarrées les lignes d'ancrage et une deuxième bouée 1-2 comportant une chambre des vannes dans lesquelles sont connectées lesdites première conduites de liaisons fond-surface, ladite chambre des vannes en opération continue étant rendue accessible aux personnels 10₂ car elle se trouve alors à la pression atmosphérique,
• la figure 7 représente en coupe et en vue de côté la déconnexion de ladite deuxième bouée du touret par envahissement de ladite deuxième chambre des vannes par de l'eau de mer, en cours de procédure de largage avec accompagnement de câbles de manutention 20b,21b,
• la figure 8 représente en coupe et en vue de côté la reconnexion de la deuxième bouée sur le touret au moyen de treuils et de câbles,
• la figure 9 représente une vue en coupe selon I-I de la figure 8 au niveau d'un palier de roulement supérieur 5₂,
• la figure 10 représente en coupe et en vue de côté le touret et le déballastage au moyen d'une pompe de cale, de la partie supérieure de la deuxième bouée correspondant à la chambre des vannes 30,
• la figure 11 représente en coupe et en vue de côté de l'étape initiale de la déconnexion de la deuxième bouée par rapport au touret par envahissement de la chambre des vannes par de l'eau de mer, en cours de procédure de largage,
• la figure 12 représente en coupe et en vue de côté les éléments de fixation entre la sous-face du touret et la partie supérieure de la deuxième bouée, ainsi que des moyens pour inonder la chambre des vannes par l'eau de mer.
• la figure 13 représente en coupe et en vue de côté le dispositif de déballastage au moyen d'une pompe de cale, de la partie supérieure de la chambre de la première bouée,
• la figure 14 représente en coupe et en vue de côté le dispositif d'envahissement de la chambre de la première bouée, la déconnexion de ladite deuxième bouée ayant eu lieu.
• la figure 15 représente une vue de dessus des deux première et deuxième bouées disposées coaxialement.

Other features and advantages of the present invention will become more apparent in the light of the detailed description which follows, given in an illustrative and nonlimiting manner, with reference to the drawings in which:

• the figure 1 represents in section and in side view of a FPSO type floating support anchored on a reel within an ice floe,
• the figure 2 represents in section and in side view an FPSO subjected to extreme horizontal thrust from a drifting pack ice 31,
• the figure 3 represents in side view the release of a second buoy supporting the flexible connection lines 14, the FPSO being held in position by the anchoring lines integral with a said first buoy,
• the figure 4 represents in side view the subsequent release of said first buoy to release the FPSO from the pack ice,
• the figure 5 represents in side view an FPSO taking up position vertically of said first and second buoys, in order to reconnect to said first buoy comprising the anchor lines 13, then to said second buoy secured to said first bottom-surface connection lines of type flexible pipes,
• the figure 6 represents in section and in side view, the drum passing right through the FPSO, the bottom wall of the drum supporting a said first annular buoy to which anchoring lines are moored and a second buoy 1-2 having a chamber of valves in which are connected said first bottom-surface connection pipes, said valve chamber in continuous operation being made accessible to personnel _{2 2} because it is then at atmospheric pressure,
• the figure 7 represents in section and in side view the disconnection of said second buoy of the drum by flooding said second valve chamber with seawater, during the release procedure with accompanying handling cables 20b, 21b,
• the figure 8 represents in section and in side view the reconnection of the second buoy on the drum by means of winches and cables,
• the figure 9 represents a sectional view along II of the figure 8 at an upper rolling bearing 5 ₂ ,
• the figure 10 represents in section and in side view the drum and déballastage by means of a bilge pump, the upper part of the second buoy corresponding to the valve chamber 30,
• the figure 11 represents in section and in side view of the initial step of the disconnection of the second buoy with respect to the reel by invasion of the valve chamber by sea water, during the drop procedure,
• the figure 12 represents in section and in side view the fastening elements between the underside of the drum and the upper part of the second buoy, and means for flooding the valve chamber with seawater.
• the figure 13 represents in section and in side view the deballasting device by means of a bilge pump, of the upper part of the chamber of the first buoy,
• the figure 14 represents in section and in side view the device for flooding the chamber of the first buoy, the disconnection of said second buoy having taken place.
• the figure 15 represents a view from above of the first and second two buoys arranged coaxially.

On the figure 1 is shown in section and in side view, an FPSO type floating vessel or support 10 anchored on a disconnectable mooring system 1 fixed on the underside of a drum 2 comprising a first buoy 1-1 on which are moored anchoring lines 13 and a second buoy 1-2 connected to submarine wellheads, not shown, by flexible pipes called first bottom-surface connection lines 14 in a plunging chain configuration 14a to a float In subsurface supporting said hose. The float 15 is held by a cable 15a connected to a dead body 15b at the bottom of the sea, then said flexible pipe 14a is extended in chain configuration 14b to the bottom of the sea 50, then to said wellheads.

The structure and the connection / disconnection modes of said first and second buoys on the underside of the drum 2 independently of each other are described below.

On the figure 2 a side FPSO pushed by a drifting ice-floe 31 is shown in side view, which causes an offset δL which has the effect of modifying the configuration of the chains 14a of the connecting lines 14 on the left, at the extreme, a force F applying at the level of the first buoy 1-1 is transmitted to the drum 2 of the FPSO, now the latter in position.

On the figure 3 , the disconnection of the second buoy 1-2 which drifts somewhat and is stabilized at a height Ha above the bottom of the sea 50. A dead body 16 connected to the second buoy 1-2 stabilizes the second buoy 1-2 at the height Ha when the dead body 16 rests at the bottom of the sea 50. The first buoy is still integral with the FPSO and keeps the latter in position.

On the figure 4 the dropping of the first mooring buoy 1-1 is carried out. The latter also drifts and stabilizes at a height Hb above the bottom of the sea 50. The FPSO is then free and can emerge from the pack ice to shelter.

On the figure 5 , there is shown in side view an FPSO coming to take position vertically from the first and second stabilized buoys at Hb-Ha heights respectively above the seabed 50, the FPSO will recover and connect successively the first mooring buoy 1-1, then the second buoy 1-2.

The figure 6 represents in section and in side view the mooring device 1. It comprises two buoys 1-1, 1-2 arranged coaxially with respect to each other and with respect to the axis ZZ 'of the bottom 2b of said drum, a first buoy 1-1 being an annular buoy on which are anchored said anchoring lines 13, and said annular buoy having a central orifice 1-3 containing a second buoy 1-2 on which are moored said first bottom-surface connection lines 14, said second mooring buoy 1-2 comprising an upper tubular wall 1a, hereinafter referred to as a valve chamber, within which said valves 8 and connectors 7 to the upper end of said first connecting lines 14.

Said docking device 1 is reversibly connected to a drum 2. Said drum comprises a sealed tubular structure 2, with a circular section along said vertical axis ZZ ', comprising a bottom wall 2b sealingly assembled at the lower end. of the tubular side wall 2a of said tubular waterproof structure. Said drum 2 extends within a cavity 4 passing through the hull of the floating support over its entire height. Said drum is articulated in rotation relative to said shell by means of 3 rolling bearings 5 ₁ , 5 ₂ , 5 ₃ , a 5 ₁ is located above the waterline 32 and / or out of water . These rolling bearings allow the rotation of said floating support around a substantially vertical axis ZZ 'of said drum and said cavity, without causing the rotation of said docking device with respect to the same vertical axis ZZ.

Second connecting lines 14c extend between the upper end of said first bottom / surface connection conduits 14 to which they are connected and the bridge of the floating support 10 ₁ . Said second connecting ducts 14c pass sealingly through the bottom wall 2b of the drum 2 and up through the cavity 4 to a coupling 3 of a plurality of said second pipes 14c, said coupling 3 being integral with the floating support at the bridge 10 _{1 of} said floating support. Said connector 3 is of the type with a rotating joint, articulated in rotation on the bridge so as to allow the rotation of said floating support without causing the rotation of said coupling. The lower ends of said second connecting lines on the underside of said bottom wall of the drum are connected to the upper ends of said first connecting pipes 14 via connectors 7 cooperating with isolation valves 8.

The seawater is present inside said cavity 4 of the FPSO and outside the drum.

The drum 2 comprises at its upper end an upper platform 2c, of larger diameter than the lateral tubular wall 2, said platform bearing, in its peripheral parts protruding from the lateral tubular wall 2, against the step 10a at the end upper cavity 4.

• un palier supérieur de supportage 5₁, et
• un palier supérieur de guidage latéral 5₂, et
• un palier inférieur de guidage latéral 5₃.

The mooring system at the reel has 3 rolling bearings, namely:

• an upper support bearing 5 ₁ , and
• an upper lateral guide bearing 5 ₂ , and
• a lower lateral guide bearing 5 ₃ .

• la paroi interne 4₁ de la cavité 4 et la surface externe de la paroi tubulaire latérale 2, en ce qui concerne les rouleaux ou les roulettes latéraux de guidage 5₂ et 5₃, et
• le redan 10a et la plateforme supérieure 2_c du touret 2, en ce qui concerne le palier de supportage 5₁.

Said bearings 5 ₁ , 5 ₂ , 5 ₃ are friction or rolling bearings, preferably rolling bearings. It may be more particularly rollers or rollers interposed between:

• the inner wall 4 ₁ of the cavity 4 and the outer surface of the lateral tubular wall 2, with regard to the rollers or the lateral guide rollers 5 ₂ and 5 ₃ , and
• the recess 10a and the upper platform 2 _c of the drum 2 with respect to the bearing Bracketing _May 1st.

It is understood that the level of said bearings at least said tubular structure 2 and said inner wall 4 of cavity ₁ have a circular section. The rollers or rollers of the lower and upper lateral guide bearings 5 ₂ and 5 ₃ are more particularly arranged with their axes of rotation in a vertical position. In the case of the upper support bearing 5 ₁ , said rollers or rollers are arranged with their axes of rotation in a horizontal position bearing on the step 1a, the platform 2 ₁ resting on the edge of said rollers 5 ₁ .

By way of example, to install a large number of pipes, gases, raw products, hydraulic umbilicals and electrical cables, for example 36 or 48 conduits 14, with all their security and control elements, the diameter outside said tubular structure of the drum 2 may exceed 25m, more particularly from 10 to 20m and its wet height is generally greater than 20 m, can reach 25 m, or more in the case where the hull of the floating support extends over a height of 50 m as in some cases.

The connection / disconnection system of said first and / or respectively second mooring buoy (s) 1-1, 1-2 with respect to said bottom wall 2b of the drum, allows the connection / disconnection of each of said first and / or respectively second mooring buoy independently of one another.

• une partie centrale 2b1 circulaire assemblée de manière étanche avec ladite paroi tubulaire latérale 2a dudit touret à l'intérieure de celle-ci et au-dessus de l'extrémité inférieure 2c de ladite paroi tubulaire latérale et
• une partie périphérique annulaire 2b2 entourant ladite partie centrale 2b1, assemblée de manière étanche à l'extrémité inférieure 2c de ladite paroi tubulaire latérale 2a ou sur la face externe de ladite paroi tubulaire latérale du touret, décalée en hauteur vers le bas par rapport à ladite partie centrale 2b1 de telle sorte que les extrémités inférieures desdites deuxièmes conduites de liaison 14c comprenant de préférence des parties de connecteurs 7b, en sous-face de ladite partie centrale 2b1 de la paroi de fond 2b, soient situées au-dessus de l'extrémité inférieure 2c de la paroi tubulaire latérale de la structure tubulaire étanche du touret 2.

The bottom wall 2b of said drum comprises:

• a circular central portion 2b1 sealingly assembled with said lateral tubular wall 2a of said drum inside thereof and above the lower end 2c of said lateral tubular wall and
• an annular peripheral portion 2b2 surrounding said central portion 2b1, sealingly assembled at the lower end 2c of said side tubular wall 2a or on the outer face of said tubular side wall of the drum, offset upwardly with respect to said central part 2b1 so that the ends lower portions of said second connecting lines 14c preferably comprising connector portions 7b, on the underside of said central portion 2b1 of the bottom wall 2b, are situated above the lower end 2c of the lateral tubular wall of the tight tubular structure of the drum 2.

Two concentric seals 200a, 200b, preferably O-rings, located on the upper face 40a of said first annular buoy 1-1, said seals being coaxial with respect to the axis ZZ 'of the central orifice 1-3 of said first buoy, delimit a first sealed chamber or interstitial annular chamber 40 between the peripheral portion 2b2 of the bottom wall 2b of said reel and the upper face 40a of said first buoy, when said upper face of said first buoy 1-1 is pressed against the bottom wall of said drum.

The FPSO is in cold waters in which icebergs or large, large ice sheets floating on the surface of the sea can move. 32 In extreme situations, such as storms or in the case of sea ice. thick that the bow of the ship in the form of icebreaker is not able to break during its progression, it is then necessary to disconnect the FPSO to protect it while waiting for a return to a normal situation. For this purpose, said second buoy is disconnected to lower the said first pipes to a certain depth And, disconnects the said first buoy, commonly called "spider buoy", that is to say "spider buoy".

More particularly, the internal buoyancy of said first and second buoys, that is to say the volume of the annular chamber 40b empty inside the first buoy 1-1 and the volume of the chamber 30b on the underside of the chamber valves 30 of the second buoy are adjusted in such a way that said first and second buoys stabilize at depths Ha and Hb, respectively, above the seabed, corresponding, for example, to distances of 50 to 100m from the surface of the sea 32, thus putting all the anchor lines and hoses under cover, as shown on the same figure 5 .

However, according to the invention, it is sufficient to disconnect the only second buoy to put the lines 14 safe without disconnecting the first buoy and thus without disengaging the floating support, as shown in FIG. figure 3 .

As shown on the figure 2 when the ship is under heavy stress, either by ice, wave, wind or current, its anchoring system 13 connected to annular mooring buoy 1 ₁ keeps it in position. Given the large dimensions of the FPSO, the anchor reaction forces create considerable variations in the horizontal tension F at the level of the drum base, which can reach 5000 to 7500 tonnes in the case of a pack ice progressing perpendicular to the bordered by the FPSO, and 1500 to 3000 tons in extreme conditions of swell, wind and current. These horizontal forces are directly transmitted by said first annular mooring buoy to said base of the drum.

On the Figures 6 to 11 , for the sake of clarity, there is shown the second buoy 1-2 with a single said second conduit 14c passing through the inside of the drum from a female part 7b of automatic connector 7 on the underside of the bottom wall 2b of the drum .

As illustrated on the figure 7 the second buoy is handled by the cables 20b, at least two cables, preferably three cables, preferably regularly and evenly distributed inside said drum close to the internal cylindrical surface of the wall of the tubular structure 2, and connected to winches 20a, integral with the drum and installed in the upper part, largely above the waterline 32, preferably on the platform 2c. Said cables 20b each pass through a guide tube 20c-2, the latter protruding several meters, for example 5m, the level maximum of the maximum swell hitting the side of the ship, said maximum level being largely above the level of the sea at rest 32 as shown on said figure 7 . Said guide tube 20c-2 extends vertically downwards and passes in a sealed manner through the central portion 2b1 of the bottom wall 2b of the drum 2. Thus, the level of the seawater inside the tubes 20c-2 guide remains substantially the same as at the side of the ship, that is to say at the corresponding level H ₀ , in said figure, at sea level 32. In case of heavy swell or storm, the level of the water in the guide tube 20c-2 can not reach the top of the tube 20c-2, and the seawater is thus not likely to invade the inside of the drum 2.

The tubular side wall 2a of the drum is traversed in its structure by guide tubes 20c-1, preferably at least 3 regularly distributed, which extend from the platform 2c to the lower end of the side tubular wall 2a through the peripheral portion 2b2 of the bottom wall 2b of the drum. Within these guide tubes extend 21b cables hung at their upper end on winches 21a resting on the platform 2c and hooked at their lower ends on the upper face 40a of said first flat ring buoy.

The first mooring buoy is therefore handled by the cables 21b, at least two cables, preferably three cables, preferably regularly and evenly distributed inside the tubular wall 2a of said drum.

As illustrated on the figure 5 , the first mooring buoy 1-1 being in the rest position at an altitude Ha above the seabed, and the second buoy 1-2 being in the rest position at an altitude Hb, the FPSO is positioned substantially at the vertical of the two buoys, and a ROV (automatic submarine intervention driven from the surface) is connected to said first buoy 1-1, the end of the cables 21b down to the desired depth by deviating the winches 21a. The first buoy is then raised towards the bottom 2b of the drum by synchronized winding of all the winches, until the upper part of the buoy comes into contact with the lower part 2b2 of the drum. Then deballaste the first chamber 40 as detailed on the figure 13 using a pump 22 and said first buoy is then secured to the drum due to the buoyancy force exerted on the surface delimited by the two seals 200a-200b, since said first chamber 40 is then substantially under pressure atmospheric.

In the same way, the second buoy 1-2 being in the rest position at an altitude Hb above the seabed, the ROV connects the upper edge 1b of said second buoy 1-2, the lower end of the cables. 20b, descended to the desired depth by unscrewing the winches 20a. The second buoy is then raised towards the bottom of the drum by synchronized winding of all the winches, until the upper part of the buoy comes into contact with the lower part of the drum. The valve chamber 30 is then unpacked as detailed on the figure 10 using a pump 22 and said second buoy is then secured to the drum by the buoyancy force acting on the surface defined by the seal 100, since said chamber 30 is then substantially at atmospheric pressure.

The modes of connection and disconnection of the first and second buoys are similar and in the following description, the case of the second buoy is explained in more detail.

The upper part of the second buoy 1-2 is constituted by an upper tubular wall 1a, preferably of circular section, delimiting a first chamber or chamber of the valves 30 enclosing the upper ends of the first pipes 14 sealingly crossing the bottom 30a of the chamber 30, as well as the buoyancy chamber 30b located on the underside of said chamber of the valves 30. Said upper ends of the first ducts 14 being equipped with valves 8 and / or male 7a or female 7b automatic connectors 7. The valves 8 and male portions 7a of automatic connectors 7 at the upper end of the first conduits 14 are supported by the bottom of the valve chamber 30a.

The circular seal 100, preferably an O-ring, is applied to the upper edge 1b forming the edge of the upper tubular wall of the second buoy 1-2.

The circular elastomer seal 100 integral with the buoy 1-2 is compressed between the under-face of the drum of the upper part of the second buoy, a tab 101 secured to said second buoy, limits the crushing of said seal and ensures the transfer vertical load due to buoyancy, between said second buoy and the drum.

These cleats 101 are applied against the outer surface of the tubular wall 1a and extend below it, that is to say below the level of the underside of the bottom wall 2b of the tubular structure 2, in order to allow the recovery of the horizontal forces experienced by the mooring buoy 1-2.

The lower end 27 of the tubular side wall 2a of the drum below the central portion 2b2 of the bottom wall serves as a guide means 27 for centering the second buoy relative to the drum, and thus facilitate the connection male parts 7a and female 7b automatic connectors.

The lower end 27 of the tubular side wall 2a of the drum allows the recovery of horizontal forces experienced by the mooring buoy 1-2.

When the docking of the second buoy 1-2 on the reel is completed, the tension is maintained in the cables 20b, 21b and the deballasting of the valve chamber 30a is carried out as detailed on the figure 10 .

For this purpose, a pump 22 draws water through a suction pipe 22a sealingly through the bottom 2b of the drum and discharging the water into the sea via the discharge pipe 22b sealingly through the reel 2. At the beginning of the pumping, the water inside the guide tubes 20c-1 is at level H ₀ , corresponding substantially to sea level, but as soon as the pump has evacuated a few hundred liters, the The water will reach the level H ₁ b, because the diameter required for the pipes is related to the diameter of the lifting cables 20b and is advantageously reduced to a minimum. For example, a guide tube of 300mm internal diameter and a height H ₀ -H _2b of 20m, inside which is installed a lifting cable of 150mm in diameter corresponds to a volume of water d about 1m3, i.e., an overall volume of about 4m3 for a four-strand lifting system. A deballasting pump of 500m3 / h will thus empty the entire height of the said guide pipes in approximately 30 seconds, and then begin to empty the valve chamber whose volume is approximately 2,000 m3 for a 5m chamber. height and 22.5 m in diameter.

Thus after evacuation of the first 4 m 3 of water, so after about 30 seconds, the second buoy is placed under the face of the drum with a vertical force directed upwards corresponding to the section of the inner surface S _b delimited by the seal sealing 100 multiplied by the hydrostatic pressure corresponding to the level H _2b , that is to say corresponding to the buoyancy of Archimedes, and therefore to the weight of the volume of water V _b = S _b x (H ₀ -H _2b ). By way of example, the annular buoy previously described has a valve chamber 22.5 m in diameter at the level of the seal 100, and situated at a depth H _2b = 20 m, which corresponds substantially to a pressure of 2 bars, is pressed against the drum with a vertical force upwards of about 8000 tons. When the valve chamber 30 is empty, it is at atmospheric pressure and is made accessible by a manhole 24 provided with a watertight trapdoor 24a in the closed position when the second buoy is disconnected, or that the valve chamber is being purged or filled.

When the valve chamber 30 is purged, the hoisting ropes are no longer needed and are preferably disconnected to further facilitate the release of the second buoy when necessary. Advantageously, under the face of the drum there is a safety lock device figure 14 consisting, for example in an articulated movable portion 102 secured to said underside of the drum, cooperating with a tab 101 integral with the annular buoy, said tab being for example common with the stop limiting the crushing of the elastomer seal 100. Thus, in the event of flooding of the valve chamber, the loss of buoyancy of the ring buoy will be compensated by the safety locks and there will be no risk of unintended and destructive release of said ring buoy.

• on ferme de manière étanche la trappe d'accès 24b à la chambre des vannes, et
• les câbles de levage 20b sont déconnectés de la bouée annulaire et le cas échéant sortis intégralement des tubes guides 20c-2, les verrous de sûreté 102 étant toujours enclenchés, on ouvre la vanne 25, représentée sur la figure 11, qui met en communication, par le biais des conduites de remplissage 25a-25b traversant respectivement la paroi latérale tubulaire 2 en partie basse du touret et la partie centrale 2b1 de la paroi de fond 2b du touret, la mer et ladite chambre des vannes, et ainsi commence le remplissage de la chambre des vannes, les tubes guides 20c-2 servant d'évent en maintenant la chambre des vannes sensiblement à la pression atmosphérique pendant tout ledit remplissage, et
• on arrête le remplissage en refermant la vanne 25, lorsque la chambre des vannes 30 est intégralement remplie, ce qui représente un volume d'eau de mer d'environ 2000m3 dans l'exemple précédemment décrit, c'est à dire lorsque la cote H2b du niveau de l'eau à l'intérieur de la chambre des vannes est atteinte.

If it is necessary to disconnect the second buoy of the FPSO, for example due to a storm, an iceberg or an ice pack threatening all the installations, the disconnection is advantageously carried out according to the following preferred procedure described in reference to Figures 6 to 12 :

• the access hatch 24b is sealed in the chamber of the valves, and
• the hoisting ropes 20b are disconnected from the annular buoy and if necessary completely out of the guide tubes 20c-2, the safety locks 102 being always engaged, the valve 25, shown in FIG. figure 11 , which communicates, through the filling lines 25a-25b respectively passing through the tubular side wall 2 at the bottom of the drum and the central portion 2b1 of the bottom wall 2b of the drum, the sea and said valve chamber, and thus begins the filling of the chamber of the valves, the guide tubes 20c-2 serving as vent by maintaining the valve chamber substantially at atmospheric pressure during all said filling, and
• the filling is stopped by closing the valve 25, when the chamber of the valves 30 is completely filled, which represents a volume of sea water of about 2000m3 in the example described above, that is to say when the dimension H2b the water level inside the valve chamber is reached.

In this position, the second buoy is always held in position by the hydrostatic thrust (F = weight of the volume of water V _2b = S _b x (H ₀ -H _2b ), and the release process is reversible by simple emptying of the chamber as previously explained: Before or during this filling phase, which can last from 10 to 45 minutes depending on the number of valves 25 and filling lines 25a-25b and their respective diameters, all the flexible lines 14 are advantageously depressurized. to the wellheads, and more particularly the gas lines under very high pressure, the gas is sent to the flare of the FPSO for burning.

• on déverrouille les verrous de sûreté 102 en les faisant pivoter de leur position engagée 102a à leur position rétractée 102b, et
• on ouvre en grand au moins l'une des vannes 25 de manière à finir le remplissage des tubes guides 20c-2, ce qui représente un volume faible, de l'ordre quelques m3 dans l'exemple décrit précédemment.

When the disconnection is definitively confirmed:

• the safety latches 102 are unlocked by pivoting them from their engaged position 102a to their retracted position 102b, and
• at least one of the valves 25 is opened in large so as to complete the filling of the guide tubes 20c-2, which represents a small volume, of the order of a few cubic meters in the example described above.

As soon as the level H _1b is reached, the buoyancy of the second buoy is reduced by the value F _3b = Weight of the volume of water V _3b = S _b x (H ₀ -H _3b ) with H ₃ b = level of the bottom wall 30a of the chamber of the valves 30, up to the value F _1b = Weight of the volume of water V _1b = S _b x (H ₀ -H _1b ). When the self-weight of the assembly consisting of the second buoy, flexible pipes exceeds the value of F _1b , the second buoy begins to naturally release the drum and the fact that said second buoy begins its descent down, the seal 100 is no longer waterproof and then leaves between the sea water with a almost infinite flow. Instantly, the second buoy is found with a hydrostatic level corresponding to sea level, that is to say at the H0 level, and said second buoy is precipitated down with a considerable force corresponding to its own weight, c that is, 500-1500 tons, thus freeing the FPSO from its anchorage on a drum, almost instantaneously.

This ultimate phase, between its triggering and its result, requiring the transfer of 3-4m3 in the previously described example to fill the guide tubes 20c-2 acting as vents, takes only a few seconds, or even a few tens of minutes. seconds in the worst case. Indeed, when the hydrostatic level H _1b is reached, the second buoy begins its descent, but the seal 100 being in a compressed state is always sealed. To continue the process of dropping, it is necessary to continue the entry of water until the seal is decompressed and begins to let the sea water, which then causes the brutal release of the second buoy. By way of example, a gasket with a thickness of 25 mm will require, in the above-mentioned example of a chamber with valves of 22.5 m in diameter, a complementary supply of seawater of approximately 10 m 3, which does not dramatically increase the disconnection time.

It is also possible to fill the valve chamber 30a with valves 26 and lateral filling lines 26a-26b passing through said upper tubular wall 1a of the second mooring buoy 1-2, as shown in FIG. figure 12 .

To obtain an almost instantaneous disconnection, it is advantageous to use a leaktight trapdoor in the upper tubular wall 1a of the valve chamber 30, a large hatch 103 that is kept in the closed position 103a during normal operation and in the preliminary disconnection phase by a control device. trigger, or by explosive bolts, not shown, and then actuated remotely in a known manner to release said sealed door, which in position 103b then allows the seawater to pass freely. The release is then almost instantaneous.

In the foregoing description, said tubular upper wall 1a of the second mooring buoy has been described as being defined by a cylindrical surface of vertical axis ZZ ', preferably of circular section. But it is understood that said upper tubular wall 1a can be defined by a surface of revolution of vertical axis ZZ 'whose right generator is inclined relative to the axis ZZ', said upper tubular wall then having a frustoconical shape, or said generator may be curved, the essential part being to define a side wall whose upper edge 1b is adapted to come into contact with the underside of the central portion 2b2 of the bottom wall 2b of the drum 2, on the one hand , and, on the other hand, whose lower end is sealingly assembled on the periphery of the bottom wall of the chamber 30, so as to define a chamber of the valves 30a sealed when the upper edge of the side wall of said valve chamber comes into contact with the central portion 2b1 of the bottom wall 2b of the drum 2.

In the descriptions of the various figures, the winches 20a-21a are installed at the deck of the FPSO and the corresponding lifting cables 20b-21b pass through the guide tubes 20c-1,20c-2, the latter also playing the role of vent, but it remains in the spirit of the invention if we integrate the winches in the structure of the drum at its bottom. The winches are then directly in the water and the cables connected directly to the buoy: it then has at least one pipe 20c-1,20c-2 which then has a role of vent.

The system and method for connecting / disconnecting said first buoy 1-1 is similar to that of the second buoy described above.

For the connection of the first buoy 1-1, the pumping means cooperating with a suction pipe 22a passing through the peripheral portion 2b2 of the bottom wall 2b and a discharge pipe 22b passing through the tubular side wall 2a and opening into the cavity 4, make it possible to empty the interstitial chamber 40 between the two seals 200a and 200b delimiting said second chamber 40, when the first buoy is pressed against the bottom wall of the drum.

The two elastomeric seals 200a-200b, integral with the first ring buoy 1-1 are compressed between the underside of the drum and the upper part of the first buoy.

Cleats 101a, 101b comprising a male portion 101a integral with the upper face 40a of the first buoy cooperates with complementary female portions 101b in which they can be wedged under the side of the peripheral portion 2b2 of the bottom wall 2b of the drum.

Similarly also the stops or lugs 101a, 101b can limit the crushing of the seals 200a and 200b and these tabs can cooperate with safety locks (not shown) making the first buoy integral with the peripheral portion 2b2 of the bottom wall 2b of the drum.

These cleats 101a, 101b serve as centering means of the first buoy relative to the bottom wall of the drum and allow to take up at least part of the horizontal forces experienced by the first buoy.

And, for the disconnection of the first buoy 1-1, a valve 25 and pipes 25a, 25b passing through the side wall 2a of the drum allow to fill the chamber 40 with the water coming from the inside of the cavity 4.

In both buoys, the Archimedes thrust is applied on the limited surface respectively by the seal 100 in the case of the second buoy, and limited by the joints 200a-200b in the case of the first buoy. The upward thrust is a function of the difference H ₀ -H, where H is the level of the free water within the guide tubes 20c-1,20c-2.

In the case of the first buoy, as illustrated on the figure 6 , the level H = H _1a corresponds to a balance between the Archimedes thrust (upward) and the self-weight (downward) of the mooring buoy 1-1 provided with its anchoring system. Thus, during the connection of said first buoy, the pump 22 will very quickly lower the water level in the guide tubes 20c-1, and as soon as the level H _1a is reached, said buoy 1-1 is located the continuation of the pumping will have the effect of increasing the buoyancy of Archimedes and the security factor of the system is then a function of the height H _1a -H _2a .

In the same manner, during a quiet time disconnection of the first buoy, as long as the level of the water inside the guide tubes 20c-1 is below the level H _1a , said buoy remains plated in the underside of the drum, but it is released as soon as said level H _1a is exceeded and approaches the surface. In the case of extreme conditions, as shown in figures 2 & 3 , the disconnection will take place for a level H between the level H _1a and the level H _2a .

It is the same for the second buoy which will be, in calm weather, connected or disconnected at a level H _1b , and in case of extreme conditions will be dropped to a level H between level H _1b and level H _2b . For example, a first buoy 1-1 having a seal inner peripheral diameter 200a of 25m and a seal outer peripheral 200b of 42m, a value of H ₂ was 22m, is subjected, when the plan of the joints is at a depth of 20m, with an Archimedes thrust of about 20,000 tonnes directed upwards.

Claims (16)

1. An oil production floating support (10), comprising:

   • a mooring device (1) for mooring anchor lines (13) at the bottom of the sea and first bottom-to-surface connection pipes (14) extending from said mooring device where they are moored down to the bottom of the sea, said mooring device comprising at least one annular mooring buoy (1-1), said mooring device (1) being connected reversibly to a turret (2); and

   • said turret comprising at least one watertight tubular structure (2), preferably of circular section about said vertical axis (ZZ'), having a bottom wall (2b) assembled in watertight manner to the bottom end of the tubular side wall (2a) of said watertight tubular structure, said turret (2) extending in a through cavity (4) passing within the hull of the floating support, preferably up its entire height, said turret being rotatably mounted relative to said hull by means of at least one rolling or friction bearing (5₁, 5₂, 5₃) preferably situated above the water line (32) and/or out of the water, preferably a rolling bearing, so as to allow said floating support to turn about a substantially vertical axis ZZ' of said turret and of said cavity without causing said mooring buoy to turn relative to the same vertical axis ZZ'; and

   • second connection pipes (14c) between the top ends of said first bottom-to-surface connection pipes (14) to which they are connected and the deck of the floating support (10₁), said second connection pipes (14c) passing through the bottom wall (2b) of the turret (2) in watertight manner and rising within the cavity (4) to a coupling (3) for coupling a plurality of said second pipes (14c), said coupling (3) being secured to the floating support level with the deck (10₁) of the floating support, said coupling (3), of the rotary joint coupling type, being rotatably mounted so as to allow said floating support to turn without turning said coupling, the bottom ends of said second connection pipes under said bottom wall of the turret being connected to the top ends of said first connection pipes (14) by means of connectors (7) co-operating with valves (8);

   the support being characterized in that:

   • said mooring device (1) comprises two mooring buoys (1-1, 1-2) disposed coaxially one relative to the other and about the axis (ZZ') of the bottom wall (2b) of said turret, a first buoy (1-1) being an annular buoy having said anchor lines (13) moored thereto, and said annular first buoy including a central orifice (1-3) containing a second mooring buoy (1-2) having said first bottom-to-surface connection pipes (14) moored thereto, said second mooring buoy (1-2) having a top tubular wall (1a) within which said valves (8) and connectors (7) are situated at the top ends of said first connection pipes (14); and

   • said floating support includes a connection/disconnection system for connecting/disconnecting said first and/or said second mooring buoy(s) (1-1, 1-2) respectively relative to said bottom wall (2b) of the turret, enabling each of said respective first or second mooring buoys to be connected/disconnected independently of the other, the connection/disconnection system comprising:

   • two sealing gaskets (200a, 200b) on the top face (40a) of said annular first buoy (1-1), said gaskets being coaxial about the axis (ZZ') of the central orifice (1-3) of said first buoy, defining a first watertight chamber or interstitial annular chamber (40) between the bottom wall (2b) of said turret and the top face (40a) of said first buoy when said top face of said first buoy (1-1) is pressed against the bottom wall of said turret; and

   • said tubular top wall (1a) of said second buoy co-operating with the bottom wall (2b) of said turret to define a second watertight chamber (30) referred to as the valve chamber, when a sealing gasket (100) on the top edge (1b) of said tubular top wall of the second buoy is pressed against the bottom wall (2b) of said turret, against the underface thereof; and

   • a plurality of links (20b, 21b), such as hoist cables fastened to said mooring buoy, preferably to the top edge (1b) of said tubular top wall (1a) of said second mooring buoy, said links preferably extending inside the turret and passing through the bottom wall (2b) of the turret in watertight manner; and

   • at least two vent tubes (20c-1, 20c-2) extending vertically inside the turret from a level above the water line (32) to the bottom wall (2b) of the turret through which they pass in watertight manner via each of said first and second chambers (40, 30) respectively; and

   • pump means (22) for pumping the water in each of said first and second chambers (40, 30) respectively when said first and second corresponding buoy is respectively pressed against the bottom wall (2b) of the turret; and

   • the dead weight of said first mooring buoy (1-1) and anchor lines (13) and respectively the dead weight of said second mooring buoy (1-2) and of said first bottom-to-surface connection pipes (14) is less than the weight of the volume of water corresponding to the volume (V_i) of said first and second chambers, where Vi=Si×(H₀-H_2i) in which:

   • H₀ is the height of water at the water line;

   • H_2i is the height of the top portion of the bottom wall (2b) of the turret defining said first chamber (H₂a) or said second chamber (H₂b) respectively;

   • S_i is the area of the cross-section of said first chamber (S_a) or of said second chamber (S_b) respectively; and

   • i=a for said first buoy and said first chamber and i=b for said second buoy and said second chamber.
2. A floating support according to claim 1, characterized in that said plurality of said hoist cables extends from winches (20a, 21a) preferably located on the deck of the floating support or at the top of said turret, above the water line (32), said cables where appropriate extending inside a plurality of vent and guide tubes (20c-1, 20c-2) extending vertically inside the turret from a level above the water line down to the bottom (2b) of the turret through which they pass in watertight manner.
3. A floating support according to claim 1 or claim 2, characterized in that, for at least one of said first and second buoys, preferably for each of said first and second buoys, said connection/disconnection system includes at least three said cables (20b, 21b) and at least three said guide tubes (20c) preferably disposed symmetrically about the center of the circular bottom (2b) of said turret, and preferably along and close to the outside surface of said tubular structure of said turret for said first buoy or close to the inside surface of said tubular structure (2) of said turret for said second buoy, respectively, the bottom ends of said cables (20b, 21b) being fastened of the top face (50) of said first buoy, or respectively to the top edge (1b) of said top tubular wall (1a) of said second buoy.
4. A floating support according to any one of claims 1 to 3, characterized in that the diameter of said guide tubes (20c-1, 20c-2) and the immersion depths (H₀-H_2i) of the portion of the bottom wall (2b) of the turret on which said guide tubes rest, where i=a or b, are such that the inside volume of the guide tubes is less than 15 m³, preferably less than 5 m³, for a turret having an immersed height H₀-H₂ within said cavity of at least 20 m, and more particularly preferably 20 m to 50 m.
5. A floating support according to any one of claims 1 to 4, characterized in that said top tubular wall (1a) of said second buoy (1-2) includes, at its bottom end, a bottom wall (30a) to which it is assembled in watertight manner, forming the bottom wall of the valve chamber supporting said valves (8) and/or automatic connector portions (7a), and said buoy includes, in its bottom portion, a buoyancy tank (30b) constituting a float against the underface of the bottom wall (30a) of the valve chamber.
6. A floating support according to any preceding claim, characterized in that it includes at least one said pump (22) preferably situated in the bottom portion inside said watertight tubular structure constituting the turret (2), said pump co-operating with a suction pipe (22a) passing in watertight manner through said bottom wall (2b) of the turret, said suction pipe coming close to the wall of each of said first and second chambers (40-30) when said first or second buoy is respectively in position pressed against said bottom wall (2b) of the turret, and said pump (22) co-operating with a delivery pipe (22b) for each of said first and second chambers (40, 30), each said delivery pipe (22b) opening out into said cavity (4), preferably passing through the tubular side wall of said watertight tubular structure (2) constituting the turret, preferably in the bottom portion of said turret.
7. A floating support according to any one of claims 1 to 6, characterized in that the bottom wall (2b) of said turret comprises:

   • a preferably circular central portion (2b1) assembled in watertight manner with said side tubular wall (2a) of said turret inside it and above the bottom end (2c) of said side tubular wall, and a peripheral portion (2b2) surrounding said central portion (2b1), preferably an annular peripheral portion (2b2) assembled in watertight manner to the bottom end (2c) of said side tubular wall (2a) or to the outside face of said side tubular wall of the turret, being offset downwards relative to said central portion (2b1) in such a manner that the bottom ends of said second link pipes (14c), preferably including connector portions (7b) at the underface of said central portion (2b1) of the bottom wall (2b), are situated above the bottom end (2c) of the side tubular wall of the watertight tubular structure of the turret (2).
8. A floating support according to any preceding claim, characterized in that it includes reversible mechanical safety locking or retaining means (101, 102) for locking or retaining each of said first and second mooring buoys against the underface of the bottom wall (2b) of said turret.
9. A floating support according to claim 8, characterized in that each of said first or second mooring buoys includes abutments or protective guide members (101, 101a-101b) for limiting the flattening of said gaskets and for transferring vertical loads between said first or second buoy and the turret when said first or second buoy is pressed against the bottom wall (2b) of said turret, said annular gaskets (100, 200a-200b) being compressed between the underface of the bottom wall (2b) of said turret and said first or second mooring buoy, said protective guide member (101a-101b) being suitable for co-operating with a hinged movable safety latch (102) secured to the underface of the bottom wall (2b) of said turret, whereby said first or second mooring buoy (1) is secured to said turret when said safety latch (102) is engaged under said protective guide member (101, 101a-101b).
10. A floating support according to any preceding claim, characterized in that said top tubular wall of the second buoy (1-2) and/or the tubular side wall (2a) of the watertight tubular structure (2) of said turret include(s) a filler valve (25-26) co-operating with filler pipes (25a-25b and 26a-26b) for putting sea water into communication with the inside of said valve chamber (30), and said tubular wall (1a) of said valve chamber (30) preferably includes a watertight hatch (103) of large dimensions suitable for enabling said valve chamber to be filled almost instantaneously by sea water when said hatch is opened.
11. A floating support according to any preceding claim, characterized in that the bottom wall (2b) of the turret includes an inspection hatch (24, 24a) for inspecting said valve chamber (30).
12. A method of operating a floating support according to any one of claims 1 to 11, wherein a said first or second mooring buoy is connected to the underface against the bottom wall (2b) of a said turret by performing the following steps:

    a) immersing a said first or second buoy, said anchor lines (13) or said first bottom-to-surface connection pipes (14) being moored respectively thereto; and

    b) securing the bottom ends of hoist cables (20b, 21b) to said first or second buoy, respectively, said floating support being positioned in such a manner that said first or second buoy, respectively, is substantially on the vertical axis (ZZ') of said cavity; and

    c) actuating said winches to raise said first or second mooring buoy until said sealing gaskets for said first mooring buoy or said sealing gasket for said second mooring buoy is/are pressed against the underface of the bottom wall (2b) of said turret, thereby forming a said first or second chamber (40, 30) respectively that is filled with sea water, said guide tubes (20c-1, 20c-2) co-operating with said first or second chamber respectively being likewise filled with sea water up to a height H₀ corresponding substantially to the level of the water surface at the water line (32); and

    d) pumping out the water from inside said first or second chamber (40, 30) respectively, using said pump means (22) until the level of water in said guide tubes co-operating with said first or second chamber, respectively, is less than the height H_1i' or preferably less than or equal to the height H_2i, respectively, the height H_1i being such that the buoyancy corresponding to the weight of the volume of water V_1i=S_i×(H₀-H_1i) where i=a for the first buoy and the first chamber and i=b for the second buoy and the second chamber, is greater than the weight of the assembly of said first mooring buoy (1) and said anchor lines (13) for said first watertight chamber or respectively greater than the weight of the assembly of said second mooring buoy and said link pipes (14) for said second watertight chamber; and

    e) preferably completely emptying said first or second chamber (40, 30) respectively and then making it watertight.
13. A method according to claim 12, characterized in that after said first or second chamber (40, 30) has been emptied, the bottom ends of said hoist cables (20b, 21b) are detached from said first or second mooring buoy, respectively, and preferably retaining means (101, 102) for mechanically retaining said first or said second mooring buoy, respectively, are engaged, thereby securing it to the bottom wall (2b) of said turret (101, 102), preferably using a hinged movable safety latch (102) suitable for co-operating with protective guide members (101, 101a-101b) preventing said sealing gaskets (200a-200b) or said sealing gasket (100) that is/are compressed between said first or second buoy respectively and the underface of the bottom wall (2b) of the turret from being flattened.
14. A method of operating a floating support according to claim 12 or claim 13, wherein a said first or second buoy (1) connected to a said turret (2) is disconnected, wherein after the bottom ends of said hoist cables (20b) have been separated from said first or second mooring buoy (1-1, 2-2), the method comprises the following steps:

    a) causing water to enter at least into said first or second watertight chamber (40, 30) respectively in such a manner that the level of water in said guide tubes (20c-1, 20c-2) co-operating with said first or second chamber respectively comes just above said level H_1i with i=a for the first chamber and i=b for the second chamber; and

    b) for disconnecting said second buoy, unlocking the automatic connectors (7) between said first and second link pipes (14, 14c); and

    c) releasing said mechanical retaining means (101, 101a-101b, 102) to separate said first or second mooring buoy respectively from said bottom wall (2b) of the turret; and

    d) ending by filling the guide tubes in communication with the chamber, thereby causing said buoy to be disconnected.
15. A method according to claim 14, characterized in that for disconnecting from said second mooring buoy, the following steps are performed:

    a) depressurizing said first and second bottom-to-surface connection pipes; and

    b) filling said second chamber or valve chamber (30) up to said height H₂b from the underface of the bottom wall of the turret, and stopping filling as soon as said valve chamber (30) is completely filled with water; and

    c) releasing the automatic connectors (7) between said first and second link pipes (14, 14c);

    d) where appropriate, releasing said mechanical safety latches (102); and

    e) continuing to fill said valve chamber so as to fill the guide tubes (20c-1, 20c-2) up to said height H_ib.
16. A method according to claim 14 or claim 15, characterized in that the following steps are performed:

    1) disconnecting said second buoy relative to said turret while keeping said first buoy connected to said turret; and

    2) lowering said second buoy to a certain depth of immersion below said floating support while keeping the first link pipes moored to the second buoy.

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