VERY LARGE SELF-JACKING PLATFORM FOR PROCESSING GAS OR OIL AT SEA AND METHOD OF ASSEMBLING AND INSTALLING SUCH A PLATFORM The present invention relates to a very large self jacking platform for processing gas or oil at sea. The invention also relates to a method of assembling and installing such a very large self-jacking platform. After the extraction of the gas or oil, this type of product requires numerous processing steps and heavy and very large equipment and installations. In the case of extraction at sea, the equipment and installations are placed on a plurality of oil platforms, for example of the self-jacking type, comprising a hull mounted to be movable between a flotation position and an operating position out of the water on bearer legs by means of drive mechanisms for moving said legs between a raised position and a position bearing on the seabed. But, taking into account the numerous operations carried out, the different items of equipment are distributed on a plurality of platforms. The dimensions of the hulls of the platforms used up to now are in fact limited by the fact of their infrastructure and the operating conditions, thereby making it necessary to distribute the items of processing equipment between the different platforms and to connect the platforms with one another by means of a network of pipes, electrical connections and control systems, obviously increasing the costs of production, installation and processing at sea of the gas or oil. In addition, before setting such platforms in operation, tests must be carried out by the personnel who remain mobilised on the platforms for longer or shorter periods. One solution lies in increasing the dimensions of the hulls of the platforms.
H: \ext\lnterwoven\NRPortbl\DCC\EXT\5003554_1.DOC- 19/03/2013 -2 But in this case serious problems of stability and rigidity of the hull arise, as well as problems of installation at sea. It would be desirable to provide a very large self-jacking platform for processing gas or oil at sea which enables these problems to be solved. 5 The invention provides, in a first aspect, a very large self-jacking platform for processing gas or oil at sea, comprising a hull movable between a flotation position and an operating position out of the water, on main bearer legs by means of drive mechanisms for moving said main legs between a raised position and a position bearing on the seabed, wherein the distance separating two adjacent main legs is 10 greater than 75 m and wherein the hull comprises, between said two adjacent main legs, at least one secondary bearer leg equipped with drive mechanisms for moving said secondary legs between a raised position and a position bearing on the seabed and for moving the hull between the flotation position and the operating position and for improved distribution of the loads on the seabed. 15 According to particular embodiments, the platform may include one or more of the following characteristics: -the hull is in the shape of a quadrilateral having on two opposed sides the main legs and, between each pair of opposed main legs on two sides, a secondary leg, the two opposed sides of the hull bearing the main legs are each formed by a lateral 20 one-piece section, -each main leg is fixed on the corresponding lateral section by means of a bearer framework, -each secondary leg is carried by a connecting section connecting the two lateral sections in alignment with two opposed main legs, and 25 -the drive mechanisms of each of the main legs are associated with means for locking the corresponding main leg. The invention also provides a method of assembling and installing such a very large self-jacking platform, comprising the following consecutive steps: -each lateral section and each connecting section is fabricated independently 30 on an assembly dock, -each lateral section is set down on the water in proximity to the dock, -the bearer framework of each main leg is fixed onto each lateral section in the raised position, -the two lateral sections are maintained facing each other, 35 -by means of at least one barge, the connecting sections, each carrying a secondary leg in the raised position, are brought between the lateral sections, H:\ext\lnterwoven\NRPortbl\DCC\EXT\5003554_ 1 0OC-19/03/2013 -3 -the connecting sections are moved vertically in order to bring the upper face of the connecting sections to the level of the upper face of the lateral sections, -the connecting sections are fixed onto the lateral sections, -said at least one barge is withdrawn, 5 -the hull thus assembled is conveyed by flotation to the installation site with the main and secondary legs in the raised position, -the main and secondary legs are gradually lowered, in synchronisation, as far as the seabed, and -the hull is raised into the operating position out of the water by means of the 10 main and secondary legs, and the main legs are locked. According to embodiments of the method: -each bearer framework is mounted without the main leg and each main leg is placed in a corresponding bearer framework before the flotation of the lateral sections, -each main leg is placed in a corresponding bearer framework after the 15 flotation of the sections, and -the secondary legs are mounted on the connecting sections after the fixing of the connecting sections onto the lateral sections. The invention will become clearer from the following description of preferred embodiments, provided by way of example with reference to the appended drawings, 20 in which: -Figure 1 is a schematic top view of a self-jacking platform according to preferred embodiments of the invention, -Figure 2 is a side view of the self-jacking platform according to preferred embodiments of the invention, 25 -Figure 3 is a schematic view in section along the line 3-3 of Fig. 1, -Figure 4 is a schematic view in cross-section of a main leg of the platform, showing the drive mechanisms of said leg, -Figure 5 is a schematic top view of the two lateral sections of the hull of the self-jacking platform in the course of assembly, and 30 -Figures 6 and 7 are two schematic views in crosssection showing the assembly of the lateral sections with the connecting sections to form the hull of the self-jacking platform. Figures 1 to 3 show a very large self-jacking platform designated as a whole by the reference 1. The platform 1 is intended in particular for processing gas or oil at 35 sea.
H:\ext\Interwoven\NRPortbl\DCC\EXT\5003554_ 1.DOC-19/03/2013 -4 The self-jacking platform 1 comprises a very large hull 10 on which are disposed the different items of equipment and installations for processing gas or oil, as well as customary living quarters.
5 The hull 10 is mounted to be movable between a flotation position and an operating position out of the water (Figs. 2 and 3) on main bearer legs 30 by means of drive mechanisms 35 for moving said main legs 30 between a raised position and a position bearing on the seabed F, as shown in Figs 2 and 3, and also for moving the hull 10 out of the water into the operating position as shown in these drawings. As shown in Figure 1, the distance d separating two adjacent main legs 30 is greater than 75 m and the hull 10 comprises, between said adjacent main legs 30, at least one secondary bearer leg 40 also equipped with drive mechanisms 45 for moving the secondary legs 40 between a raised position and a position bearing on the seabed F (Figs. 2 and 3), and also for moving the hull 10 out of the water into the operating position. According to a preferred embodiment, the hull 10 is in the shape of a quadrilateral and more particularly of a rectangle carrying on two opposed sides the main legs 30 and, between each pair of opposed main legs 30 on the two sides, a secondary leg 40. By way of non-limiting example, the distance d separating two opposed main legs 30, i.e. the width of the hull 10, is 100 m and the length D of the hull 10 is 300 m. The number of main legs 30 is sixteen, eight on each side of the hull 10, and the number of secondary legs 40, each disposed between two opposed main legs 30, is eight. In the exemplary embodiment shown in the drawings, the two opposed sides of the hull 10 bearing the main legs 30 are each formed by a lateral one-piece section 11 and each secondary leg 40 is carried by a transverse connecting section 15 connecting the two lateral sections 11 in alignment with the opposed main legs 30. The inner wall lla of each lateral section 11 comprises a series of protruding portions 12 separated by recessed 6 portions 13. The connecting sections 15 are fixed, as shown in Figure 1, between two protruding portions 12 of the two opposed lateral sections 11. Each main leg 30 is fixed onto the outer wall llb of the corresponding lateral section 11 by means of a bearer framework 38. As shown in Figures 2 and 3, each main leg 30 ends at its lower part in a foot 39, intended to bear on the seabed F. Each of the main legs 30, in the embodiment shown in Figure 1, has a triangular cross-section and the main legs 30 may also have a square or circular cross-section. As can be seen more particularly in Figure 4, each main leg 30 is formed by three booms 31 connected to one another by a latticework of metal girders 32. The booms 31 of the main legs 20 have teeth to form on each boom 31 two diametrally opposed racks 33 intended to co-operate with the drive mechanisms 35 in order to move the main legs 30, then the hull 10 on the main legs 30. Figure 4 shows only one drive mechanism 35, since the other mechanisms 35 are identical. Each drive mechanism 35 is formed by reduction gear units 36 each driving an output pinion 37 co-operating with the racks 33 disposed on the booms 31 of the corresponding main leg 30. In addition, each drive mechanism 35 of each of the main legs 30 is associated with means for locking the main leg in the position in which said main leg 30 bears on the seabed F, and especially in the operating position of the hull 1 out of the water, as shown in Figures 2 and 3. The locking means, not shown, are known and described for example in the documents FR-A-2 653 462, FR-A-2 876 124 and FR-A-2 881 763. Each secondary leg 40 ends, at its lower part, in a foot 41, intended to bear on the seabed F, as shown in Figure 3.
7 In the exemplary embodiment shown in the drawings and more particularly in Figure 1, each of the secondary legs 40 has a square cross-section, and the secondary legs 40 may also be of triangular or circular cross-section. In this case, each secondary leg 40 is formed of four booms 42 connected to one another by a latticework of metal girders. In a manner identical to the main legs 30 and not shown in detail in the drawings, the booms 42 of the secondary Legs 40 have teeth to form on each boom two diametrally opposed racks, intended to co-operate with drive mechanisms 45, identical in principle to the drive mechanisms 35 of each main leg 30. Referring now to Figures 5 to 7, a description will be given of the construction and assembly of the different sections 11 and 12 of the hull 10 of the platform 1. Firstly, the different sections 11 and 12 forming the hull 1 are fabricated independently on an assembly dock of a naval dockyard. Then, on each lateral section 11, the bearer frameworks 38 are fixed with the main legs 30 in a raised position and by suitable means, not shown, the lateral sections 11 equipped with the bearer frameworks 38 with the main legs 30 in the raised position are set down on the water in proximity to the dock, i.e. in a calm and shallow area. The bearer frameworks 38 of the main legs 30 are fixed by suitable means of conventional and known type, not shown, onto the outer wall llb of each lateral section 11, as shown in Figure 5. Each bearer framework 38 is fixed onto the outer wall llb opposite a protruding portion 12 provided on the inner wall lla of the lateral section 11. The main legs 30 are in a raised position, as shown in Figure 6, and each lateral section 11 is floating with a draught of the order of 5 m. According to a first variant, each bearer framework 38 is mounted without the main leg 30 on the outer wall llb of each 8 lateral section 11 and each lateral leg 30 is placed in a corresponding bearer framework 38 before the flotation of the lateral sections 11. According to a second variant, each main leg 30 is placed itn a corresponding bearer framework 38 after the flotation of the lateral sections 11. The two lateral sections 11 are maintained facing each other by suitable means and the connecting sections 15 are brought between the lateral sections 11 by means of at least one barge 50 and, preferably, by means of a plurality of barges 50, each carrying a plurality of connecting sections 15. In the example of assembly shown in Figure 7, each connecting section 15 is previously equipped with a secondary leg 40 disposed in the raised position. In order to bring the upper face of each of the connecting sections 15 to the level of the upper face of the lateral sections 11, the connecting sections 15 are moved vertically by suitable means, such as for example by ballasting or de-ballasting the barges 50. The connecting sections 15 are then fixed onto the lateral sections 11 by systems of known type, then the barges 50 are removed by ballasting them. The different operations of assembly of the sections 11 and 15 having thus been carried out and the hull 10 being equipped with the main legs 30 and the secondary legs 40, the whole of the hull 10 is conveyed by flotation to the installation site at sea with the main legs 30 and secondary legs 40 in the raised position. When the platform 1 is situated on the site, the main legs 30 and the secondary legs 40 are gradually lowered, in synchronisation, by means of the drive mechanisms, respectively 35 and 45, until the feet, respectively 31 and 41, fit on the seabed F. As soon as the feet 39 and 41 of the 9 legs, respectively main legs 30 and secondary legs 40, bear on the seabed F, the drive mechanisms, respectively 35 and 45, still in operation, cause the hull 10 to rise out of the water Lo its operating position shown in Figures 2 and 3. As soon as the hull 10 has reached its operating position, the main legs 30 are locked via the locking means so as to hold the hull 1 in this position. The secondary legs 40 disposed between two opposed main legs 30 participate in the raising of the hull 10 and, taking into account the distance d between the opposed main legs 30, prevent flexing of the hull 10 between the opposed main legs 30 which could cause jamming of the drive mechanisms 35 of said main legs 30 and also heavy loads on the latter as a result of any flexing movement. The synchronous driving of the main legs 30 and also of the secondary legs 40 makes it possible to prevent such jamming and makes it possible above all to maintain the whole of the hull 10 in a stable and substantially horizontal position. According to one variant, the secondary legs 40 may be mounted on the connecting sections 15 after the assembly of the connecting sections 15 with the lateral sections 11. The transverse stresses generated by the very large dimensions of the hull 10 are taken up by the main legs 30 owing to the locking means on the main legs 30. The secondary legs 40 participate only in the raising of said hull 10 and do not take up horizontal loads, taking into account their low inertia compared with that of the main legs 30. By way of example, such a platform without the equipment and installations for processing gas or oil has a mass of the order of 120,000 tonnes, and with the equipment and installations, a total mass of the order of 200,000 tonnes. The method of assembling and installing a very large self-jacking platform according to the invention makes it possible to simplify the operations of fitting and assembly H:\ext\Interwoven\NRPortbl\DCC\EXT\5003554_ 1. DOC- 19/03/2013 - 10 and consequently to reduce the fabrication costs. The very large dimensions of the hull allow the different items of equipment and different installations necessary for processing gas or oil extracted at sea to be grouped on the same platform. 5 The method of assembly and installation according to the invention makes it possible to reduce the maintenance operations and prevent the different operations of assembly of the sections forming the hull being affected by bad weather. In fact, by means of the method of the invention, these operations are carried out in a calm area and in shallow water. 10 Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. The reference in this specification to any prior publication (or information 15 derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 20