EP0244542A1 - Lifting method and device, especially for an oil production platform - Google Patents

Abstract

This method of lifting a platform comprising an actual platform or bridge carried by legs resting on the seabed, consists of: fixing on each of the legs (2) of the platform a lifting device (4) forming a reinforcing device, the fixing zones on the legs (2) are located on either side of a region of the leg to be cut; cutting the leg to separate it into a lower portion (2a) and an upper portion (2b); when all the legs are cut, actuate the lifting devices associated with each of the legs to move the platform on a stroke corresponding to the desired lifting while controlling the attitude of the platform, and to be fixed between the ends of the portions (2a, 2b) of each leg an extension (5) again joining the two portions of the leg together, and to remove the lifting means.

Description

The present invention relates to oil rigs and relates more particularly to the lifting of offshore oil rigs.

It has been found that in certain regions of the globe and in particular in the North Sea, certain oil sites on which fixed operating platforms are installed, tend to sink due in particular to the instability of certain layers of the underground caused by cavities left in the underground by pumping large quantities of oil out of the geological pockets that contain it.

The sinking of the site results in a subsidence of the seabed on which the pylons of the oil platforms rest so that their height above sea level decreases dangerously and risks within a few years from making these plates - dangerous forms for operating personnel, especially in heavy weather.

The invention aims to create a method and a device for ensuring the lifting of an oil platform of a sufficient height to allow the platform to be used despite the depression of the sea floor on which it is, until the exhaustion of the deposit it exploits.

• a) à fixer sur chacune des jambes de la plate-forme un dispositif de relevage formant disposi­tif de renforcement dont les zones de fixation sur les jambes sont situées de part et d'autre d'une région de la jambe à découper et à mettre le dispositif de rele­vage sous charge;
• b) à pratiquer dans ladite région (12) un découpage de la jambe (2) pour la séparer en une por­tion inférieure (2a) prenant appui sur le sol marin et une portion supérieure (2b) solidaire du pont;
• c) lorsque toutes les jambes de la plate-­forme sont découpées, à actionner les dispositifs de relevage associés à chacune des jambes pour déplacer la plate-forme sur une course correspondant au rele­vage désiré tout en contrôlant l'assiette de la pla­te-forme, et à fixer entre les extrémités des portions (2a,2b) de chaque jambe une rehausse (5) solidarisant à nouveau les deux portions de la jambe entre elles, et
• d) à retirer les moyens de relevage.

It therefore relates to a method of lifting an oil platform for exploitation at sea comprising an actual platform or bridge, carried by legs resting on the seabed, characterized in that it consists:

• a) to fix on each of the legs of the platform a lifting device forming a reinforcement device whose fixing zones on the legs are located on either side of a region of the leg to be cut and to put the lifting device under load;
• b) practicing in said region (12) a cutting of the leg (2) to separate it into a lower portion (2a) bearing on the sea floor and an upper portion (2b) integral with the bridge;
• c) when all the legs of the platform are cut, actuating the lifting devices associated with each of the legs to move the platform on a stroke corresponding to the desired lifting while controlling the attitude of the platform, and to fix between the ends of the portions (2a, 2b) of each leg a riser (5) again joining the two portions of the leg together, and
• d) to remove the lifting means.

• - la Fig.1 est une vue schématique en éléva­tion d'une plate-forme pétrolière avant relevage selon le procédé de l'invention;
• - la Fig.2 est une vue analogue à celle de la Fig.1 de la plate-forme après relevage;
• - la Fig.3 est une vue partielle en éléva­tion à plus grande échelle d'une jambe de plate-forme pétrolière sur laquelle est posé un dispositif de re­levage suivant l'invention avant relevage;
• - la Fig.4 est une vue correspondant à celle de la Fig.3 montrant le dispositif de relevage suivant l'invention en position de fin de relevage;
• - la Fig.5 est une vue partielle à plus grande échelle d'une jambe de plate-forme pétrolière montrant une première phase du procédé de relevage suivant l'invention;
• - la Fig.6 est une vue analogue à celle de la Fig.5 montrant une seconde phase du procédé de re­levage suivant l'invention;
• - la Fig.7 est une vue analogue à celles des Fig.5 et 6 montrant la jambe de la plate-forme après relevage.
• - les Figs.8 et 9 sont des vues schématiques en élévation montrant les phases de mise en place de la tête du dispositif de relevage autour d'une jambe de plate-forme;
• - les Fig.10 à 12 sont des vues analogues à celles des Fig.8 et 9 montrant la mise en place des supports du dispositif de relevage;
• - les Fig.13 et 14 sont des vues schémati­ques montrant l'installation des vérins hydrauliques dans les supports du dispositif de relevage;
• - la Fig.15 est une vue partielle de dessus montrant le support intermédiaire du dispositif de re­levage en place sur une jambe de plate-forme;
• - la Fig.16 est une vue en plan du support intermédiaire du dispositif de relevage suivant l'invention;
• - la Fig.17 est une vue en plan du support inférieur du dispositif de relevage suivant l'inven­tion;
• - la Fig.18 est une vue en coupe montrant un détail du support intermédiaire; et
• - les Fig.19 et 20 sont des vues schémati­ques en élévation montrant la mise en place d'une réhausse formant entretoise après relevage de la plate-forme.

In the accompanying drawings, given solely by way of example:

• - Fig.1 is a schematic elevational view of an oil platform before lifting according to the method of the invention;
• - Fig.2 is a view similar to that of Fig.1 of the platform after lifting;
• - Fig.3 is a partial elevational view on a larger scale of an oil platform leg on which is placed a lifting device according to the invention before lifting;
• - Fig.4 is a view corresponding to that of Fig.3 showing the lifting device according to the invention in the end of lifting position;
• - Fig.5 is a partial view on a larger scale of an oil platform leg showing a first phase of the lifting process according to the invention;
• - Fig.6 is a view similar to that of Fig.5 showing a second phase of the lifting process according to the invention;
• - Fig.7 is a view similar to those of Fig.5 and 6 showing the leg of the platform after lifting.
• - Figs.8 and 9 are schematic elevational views showing the phases of placing the head of the lifting device around a platform leg;
• - Fig.10 to 12 are views similar to those of Fig.8 and 9 showing the establishment of the supports of the lifting device;
• - Fig.13 and 14 are schematic views showing the installation of hydraulic cylinders in the supports of the lifting device;
• - Fig.15 is a partial top view showing the intermediate support of the lifting device in place on a platform leg;
• - Fig.16 is a plan view of the intermediate support of the lifting device according to the invention;
• - Fig.17 is a plan view of the lower support of the lifting device according to the invention;
• - Fig.18 is a sectional view showing a detail of the intermediate support; and
• - Fig.19 and 20 are schematic elevational views showing the establishment of an extension forming a spacer after lifting the platform.

The platform shown diagrammatically in FIG. 1 comprises a platform proper or deck 1, supported by tubular legs 2 joined together by lattice 3 of metal beams and bearing on the seabed. On each of the legs 2 is fixed in a manner that will be described later, a lifting device 4 consisting of a set of hydraulic cylinders. The lifting devices 4 are intended, after cutting each of the legs in an intermediate region between the fixing zones of each of the lifting devices on the leg 2 with which they are associated, to cooperate to ensure the movement of the bridge 1 towards the top of an appropriate distance.

In Fig.2, there is shown the platform of Fig.1 after lifting. It can be seen that the lifting devices 4 are in the extended position.

Between the leg portions 2a and 2b resulting from the cutting of each of the legs 2 and the ends of which are separated by a gap resulting from the lifting operation, tubular extensions 5 are interposed ensuring the reconstruction of the continuity of each of the legs.

In Fig.3, there is shown on a larger scale, a leg 2 of the platform on which is set up a lifting device 4 consisting of two hydraulic cylinders 6 whose cylinders 7 are secured to each other by supports 8 and 9 welded to leg 2 in areas below the leg region to be cut. The rods 10 of the jacks 6 are supported by a head 11 welded below the lower part of the deck 1.

In Fig.3, the cylinders 7 of the lifting device 4 are shown in the retracted position. Between the first support 8 which assembles the upper ends of the cylinders 7 and the head 11 for supporting the rods 10 of the jacks, there is shown in phantom a region 12 in which the leg 2 must be cut. Before cutting, the cylinders 6 of the device 4 are loaded, which then plays the role of reinforcement device by taking up the forces exerted by the mass of the bridge on the corresponding leg.

In Fig.4, the jacks 6 of the lifting device 4 are shown in the extended position, the rods 10 of the jacks being extended and having provided by means of the head 11 of support of their free ends, a displacement towards the top of the upper portion 2b of the leg 2, the lower portion 2a thereof which bears on the seabed itself serving as a support by means of the supports 8 and 9 for assembling the cylinders 7 jacks 6 during the application of the lifting force to the deck 1 by said jacks.

The stroke of the cylinder rods 10 corresponds to the lifting height of the platform. This lifting height is materialized by an interval 13 resulting from the relative displacement of the parts 2a and 2b of the leg 2 after cutting of the latter in the zone 12.

We will now refer to Figs. 5 to 7 to describe in more detail the various phases of the rewashing operation of the platform by considering one of the legs thereof.

We see in Fig.5, a first phase of the operation during which after the installation of the lifting device 4 and pressurization of the jacks 6 thereof, we cut in the leg 2 a section of tube in region 12 and we removed it so that the lower leg portions upper 2a and upper 2b are now separated by an interval. The portions 2a and 2b are held in place by the lifting device which thus constitutes, during the initial phase of the operations, a device for strengthening the leg 2.

As shown in Fig.6, in the gap between the lower porta 2a and upper 2b of the leg 2, a connecting part 14 is inserted in two parts provided with end flanges 15, 16 joined together by assembly bolts 17. Each of the parts 15, 16 of the part 14 is welded to the end of the corresponding portion 2a, 2b of the leg 2. With this operation, the integrity of the leg 2 is restored while making it separable and therefore ready to undergo the lifting operation of the platform.

The two parts 15, 16 of the part 14 are provided with complementary centering cones (not shown) intended on the one hand to center the flanges relative to the other and on the other hand, to support the lateral forces .

Such a technique makes it possible to proceed in turn to the preparation of all the legs of the platform without compromising the stability of the latter and, when all the legs have undergone the insertion of a corresponding connecting piece 14, d '' wait for favorable weather conditions to carry out the actual lifting in a minimum of time.

Fig.7 is a view corresponding to those of Figs.6 and 5 and on which we see that the lifting operation is completed. The rods 10 of the jacks 6 are extended and have caused the leg portion 2b to move upward relative to the por tion 2a and a tubular riser 5 has been inserted in the gap between the ends of the portions 2a and 2b to reconstitute the integrity of the leg 2. The riser 20 has at its ends flanges 21, 22 which are secured to the respective collarettes 15, 16 of the part 14 in two parts which had been inserted in place of the section of tube removed by cutting, during the phase of the operations shown in Fig. 6. The flanges 21, 22 are also provided with centering cones (not shown) complementary to the cones of the flanges 15 and 16 of the part 14 with which they are intended to cooperate.

The flanges 15 and 21 on the one hand and 16 and 22 on the other hand, are joined by assembly bolts similar to the bolts 17.

We will now describe the installation of the lifting device according to the invention on a platform leg.

This implementation begins with the installation of the head 11 for supporting the ends of the rods 10 of the jacks 6 against the lower part of the bridge 1 surrounding the corresponding leg 2.

As shown in Fig.8, the bridge 1 has a lower floor 25 provided in the region surrounding the leg 2 with hooking means 26 for cables 27 each wound on a winch 28. Each winch 28 is arranged in a half beam or jaw 29 intended to form after mounting the head 11. Each of the jaws is made in the form of a box of mechanically welded sheet metal and comprises on its side intended to come into contact with the leg 2, a semi-cylindrical recess.

In Fig. 8, the two mas choirs 29 intended to constitute the head 11, respectively hooked to their suspension cable 27. Each of the jaws is provided with a hook 30 intended to cooperate with a cleat 31 provided on the leg 2. When the winches 28 located are actuated in each of the jaws 29, the jaws are caused to move upwards until they are in positions facing one another, so that the edges of their semi-cylindrical recesses are in mutual contact and that their hook 30 is engaged with the cleat 31. It is then possible to carry out the edge-to-edge welding operations of the jaws 29 in diametrically opposite regions 31.

When the welding is finished, the head 11 consisting of its two jaws welded together is still suspended on the cables 27. The hooks 30 are then cut and the winches 28 are actuated again to cause the movement of the head 11 along of the leg 2 until it is pressed against the floor 25 of the deck 1 as shown in Fig.10.

When this operation is complete, the head 11 is fixed by welding to the leg 2 on the one hand and to the bridge 25 on the other hand.

The cables 27 can then be released from the hooking elements 26 of the floor 25.

The winches 28 are then used for the establishment of the intermediate support 8 which is also formed by two half-beams or jaws 32 in the form of a box of mechanically welded sheet metal with a structure similar to that of the jaws of the head 11 and which includes, like these, hooks 33 cooperating with a cleat 34 provided on the leg 2 and disposed at a suitable distance below the cleat 31, intended for the positioning of the head 11. This then serves as a suspension element for the jaws 32 which are placed and welded together edge to edge and also to leg 2 in the position shown in Fig. 12. When the welding operations are finished, the hooks 33 are cut.

The lower support 9 which will only have to support vertical forces due to its own weight is made of sheet steel. It is much lighter than the head 11 and the intermediate support 8, so that it can be put in place on the leg 2 by lifting means commonly provided on a ship.

Referring again to FIG. 3, it can be seen that the head 11 is placed around a vertical portion of the leg 2 while the intermediate support 8 or first support and the lower support 9 or second support are attached to an inclined part of this leg.

The position of the intermediate support 8 on an inclined part of the leg 2 is shown in plan in Fig.15, on which we have also shown some of the beams of the lattice of metal beams 3 connecting the legs together.

The intermediate support 8 is shown more clearly in FIG. 16. This support consists, as indicated above, of two jaws 32 whose facing sides welded together comprise semi-cylindrical recesses 35 together defining a passage for the leg 2, the axis of which is parallel to the axis of the inclined part of the leg on which the support 8 is mounted.

Each of the jaws 32 which constitute the support 8 comprises a fork 36 intended for receiving the cylinder 7 from a corresponding jack 6.

The support 8 advantageously contains a main hydraulic control device, cylinders supply pumps 6 as well as corresponding hydraulic connection pipes (not shown). On the sides of the support 8 are arranged hydraulic fluid reservoirs 37 shown in phantom in Fig. 15.

The positioning of the cylinder 7 of a jack in a fork 36 of the support 8 is ensured, as shown in FIG. 18 by means of an annular wedge 39 placed on top of the fork 36 and comprising a seat annular 40 of spherical profile of large diameter with which cooperates a bearing 41 of corresponding shape provided on a shoulder 42 of the outer surface of the cylinder 7 of the corresponding cylinder.

Such an arrangement makes it possible to make up for any inaccuracies in mounting the jacks with a view to ensuring a thrust thereof in a very vertical direction.

The lower support 9 which is of a lighter structure than the intermediate support 8, has a semi-circular lateral recess 43 in which the leg 2 is engaged on a portion of its periphery.

The support 9 also comprises forks 44 intended to receive the lower ends of the cylinders 7 of the jacks 6.

In the embodiment which has just been described, the lifting devices each comprise two jacks. It will be understood, however, that for a platform of greater structure and weight, it it is also possible to provide lifting devices comprising a larger number of jacks. In such a case, the support head of the rods of the jacks and the intermediate and lower supports will be designed in a similar manner to the corresponding elements of this embodiment but so as to receive the desired number of jacks.

In Figs. 13 and 14, the handling phase of a jack 6 is shown with a view to its positioning in the supports 8 and 9 and under the head 11.

To this end, in the bridge 25 is mounted a rail 45, a part of which projects in cantilever with respect to the bridge and in which is movably mounted a carriage 46 driven by an electric motor 47 and provided with means for suspending the cylinder 6 via a cable 48.

Fig.13 shows the cylinder 6 suspended before its installation, while Fig.14 shows the cylinder brought by the carriage 46 in the desired position below the head 11, the upper end of the cylinder 7 of the cylinder 6 being engaged in the corresponding fork 36 of the intermediate support 8.

This same handling device is used for the installation of the risers 5 once the lifting operations are completed (Fig. 19 and 20).

The lifting operations are carried out under the control of a central computer which at all times receives information relating to the position of all the jacks associated with the legs of the platform and which develops the hydraulic circuit for controlling the pumps. supply of the actuators to the control signals intended to cause the acceleration or the slowing of the rise of the rods of the corresponding cylinders according to the attitude reference data of the platform to be observed.

The instantaneous position of each of the jacks is given for example by sensor systems of the electromagnetic type incorporated in the jacks.

Thanks to the arrangement which has just been described, it is possible to ensure in good conditions and within a few hours the lifting and consolidation in the raised position of an oil platform of very high tonnage. The cylinders used in the lifting devices are very long stroke cylinders up to six meters.

In the embodiment which has just been described, the ends of the cylinder rods bear on a head 11 fixed below the lower part of the bridge. It is also possible to envisage bringing the ends of the rods of the jacks directly against the lower wall of the bridge by providing therein sufficient reinforcing elements to withstand the lifting efforts of the jacks.

Claims (12)

1. Lifting method in particular of an oil platform for exploitation at sea comprising an actual platform or bridge, carried by legs bearing on the seabed, characterized in that it consists: a) to fix on each of the legs (2) of the platform a lifting device (4) forming a reinforcement device whose fixing zones on the legs (2) are located on either side of a region (12) of the leg to be cut and to put the lifting device under load; b) practicing in said region (12) a cutting of the leg (2) to separate it into a lower portion (2a) bearing on the sea floor and an upper portion (2b) integral with the bridge; c) when all the legs of the platform are cut, actuating the lifting devices associated with each of the legs to move the platform on a stroke corresponding to the desired lifting while controlling the attitude of the platform, and to fix between the ends of the portions (2a, 2b) of each leg a riser (5) again joining the two portions of the leg together, and d) to remove the lifting means. 2. Method according to claim 1, characterized in that the cutting made in each leg (2) consists in cutting and removing a section of said leg to form a gap between the ends of the lower (2a) and upper (2b) portions ham (2). 3. Method according to claim 2, characterized in that it further consists in inserting in said interval formed by the withdrawal of said leg section, a part (14) in two parts (15, 16) joined together by removable assembly means (17) to weld each of the two parts of said part respectively to a end of the corresponding portion (2a, 2b) of the leg, to temporarily restore the integrity of said leg and to remove the removable assembly means (17) immediately before actuating the lifting devices. 4. Lifting device for implementing the method according to any one of claims 1 to 3, characterized in that it comprises associated with each leg (2) of the platform, at least one first support ( 8) fixed to said leg below the region (12) to be cut and at least two hydraulic cylinders (6) whose cylinders (7) are engaged in said support (8) and whose rods (10) bear against the bottom wall of the deck (1) of the platform. 5. Lifting device according to claim 4, characterized in that it further comprises a second support (9) fixed to the leg (2) below the first support (8) and in which are engaged the lower ends of the cylinders (7) of the cylinders (6). 6. lifting device according to one of claims 4 and 5, characterized in that it further comprises a head (11) fixed to the leg (2) against the bottom wall of the bridge (1) of the platform , against which the ends of the rods (10) of the jacks (6) bear. 7. Lifting device according to one of claims 4 to 6, characterized in that said pre mier support (8) is formed of two half-beams or jaws (32) each provided with a semi-cylindrical recess (35) and assembled together and to the leg (2) by welding, the semi-cylindrical recesses (35 ) constituting a passage for the leg (2) and and the pins (44) for receiving the cylinders (7) of the jacks (6). 8. lifting device according to claim 7, characterized in that the cylinder (7) of each cylinder (6) bears on the corresponding fork (44) of said first support by means of an annular wedge (39) comprising a seat (40) of spherical profile and cooperating with a bearing (41) of corresponding shape provided on a shoulder (42) of said cylinder. 9. lifting device according to one of claims 6 to 8, characterized in that said head (11) is formed of two half-beams or jaws (29) assembled together and to the leg (2) by welding and provided semi-cylindrical recesses which together form a passage for said leg. 10. Lifting device according to claim 9, characterized in that in each jaw (29) of said head (11) is disposed a winch (28) for handling said jaw by means of a cable (27), the free end is fixed to a hooking means (26) integral with the bridge (1), and in that said winches also constitute means for handling the jaws (32) of the first support (8) after the fixing of said head against the bottom wall of the bridge (1). 11. Lifting device according to one of claims 4 to 9, characterized in that said jaws (32) of the first support (8) and said jaws (29) of the head (11) are provided with respective hooks (30, 33) carried by the leg to ensure the maintenance of said jaws in position on the leg (2) for the operations of welding the jaws together and to the leg (2). 12. Lifting device according to one of claims 5 to 11, characterized in that said second support (9) comprises a semi-circular lateral recess (43) in which is engaged the leg (2) and forks (44) receiving the lower ends of the cylinders (7) of the corresponding cylinders (6).

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