MXPA06008393A - Structure for transporting, installing and dismantling the elements of a fixed oil platform and methods for using said structure - Google Patents

Abstract

The invention relates to a structure for transporting, installing and dismantling a fixed oil platform provided with framework elements which are substentially formed by a bridge and at least one supporting pillar. The inventive structure comprises a floating U-shaped shell (11) provided with at least three lifting legs (12) adapted for resting upon the bottom of the sea and a shuttle (30) movable along the lifting legs (12) for displacing a platform element. Said shuttle consists of at least three elements (31) each of which is associated with the lifting leg (12) and is provided with mechanical means for driving on the corresponding lifting leg (12) in a manner independentof the shell (11) of the structure (10) and with means for connecting to displaceable framework element. Methods for transporting, installing and dismantling the bridge or the supporting pillar of a fixed offshore oil platform are also disclosed.

Description

STRUCTURE OF TRANSPORTATION, INSTALLATION AND DISMANTLING OF ELEMENTS OF FIXED OIL PLATFORM AND METHODS OF USE OF SUCH STRUCTURE Description of the Invention The present invention relates to a structure for transportation, installation and dismantling of a fixed oil exploitation platform in the sea that carries frame elements formed especially by a bridge and at least one support column. It also refers to transport procedures, installation and dismantling of the framework elements of a fixed oil platform. For the oil exploitation, it is already known the placement above an oil field, of a fixed oil platform that includes a bridge that takes especially the exploitation equipment and the room premises. The bridge is supported by a support column anchored on the seabed. At present, there are two major methods of transportation, installation and dismantling of the framework elements of a fixed oil platform. The first method consists of using lifting cranes mounted on flat boats to deposit the support column on the seabed and to transfer the bridge of the platform of the transport ship - on this Ref.174654 support column. This method, which is the most widespread until now, has limitations. In fact, the first of these limitations is the capacity of the lifting cranes that may prevent the bridge from obtaining several elements, which significantly increases the manufacturing cost of this bridge and the cost of installing and dismantling the bridge. oil rig. The second limitation lies in the fact that this method requires having a relatively important time interval to be able to perform different transfer operations at sea in good conditions. Thus, this method is hardly applicable without a considerable increase in the cost in the areas where the time intervals are relatively short, as per. example in the North Sea. The second method is to install the support column on the seabed by the lifting cranes and install the bridge of the oil platform in a single block on the support column and floating it on top of it. Next, the bridge is placed on this support column either by a ballasting / deballasting system, or by a mechanical system. In the case of a ballasting system, the bridge of the platform is supported either by a floating support constituted for example, by a flat boat, pontoons or by a U-shaped floating support, or by the intermediation of an associated structure to this floating support. In the case where the superstructure can be subjected to ballasting or deballasting, it is already known to use, for the dismantling of the bridge of the oil platform, the debonding of the floating support and the ballasting of the superstructure. When the superstructure has a large ballasting capacity, the dismantling operation can be developed relatively quickly. In the case of a superstructure anchored on the seabed, only the capacity of the floating support can be demolished. When this capacity is limited, the operation develops slowly. Systems that use ballasting or deballasting have drawbacks that mainly lie in the fact that they impose a complex structure at the level of the drawers or pumps and a very precise control of the replacement and emptying of the drawers to maintain the stability of the floating support during the operation. The speed of operation depends on the capacity of ballasting and deballasting of these drawers of the floating supports, which is generally relatively small, although the speed of operation is limited especially when the superstructure is anchored on the seabed. further, in the course of this operation, the conditions of the sea must be favorable to carry out this operation in good conditions. An alternative to the ballasting / deballasting system is the use of a mechanical system to raise or lower the oil platform bridge. These systems allow the operation of installing or dismantling the oil platform bridge more quickly than the systems mentioned above. For this purpose, a system comprising two flat boats that support the bridge of the oil platform by the intermediation of two oscillating structures is already known. In addition, a system of hand winches and cables is used to ensure the stability of the system and control the up and down movement of the oil platform bridge. By actuating these hand winches, the departure of the flat boats is controlled, allowing the ascent or descent of the bridge. However, this type of mechanical system presents a very precarious stability and is often incompatible with use in the open sea. Another mechanical system consists of a rack-and-pinion system to raise or lower the oil platform bridge.

In a general way, the mechanical systems used so far to carry out the installation and dismantling of a bridge of an oil rig are faster than the ballasting or deballasting systems, but they depend on the sea conditions that make it difficult. its use in areas where favorable time intervals are relatively short. It is also known in the application WO 03/080425 a structure for supporting, installing and dismantling a bridge of a fixed oil platform carrying a floating U-shaped hull and a bridge support naveta and movable to along the legs by the helmet. The object of the invention is to propose a transport, installation or dismantling structure of a fixed oil exploitation platform in the sea, which is known because it simplifies and decreases the duration of the dismantling of said platform, allowing to obtain an important time gain and avoid all risks of environmental contamination and increase the safety of the personnel in charge of carrying out the different operations. For this purpose, the invention has as its object a structure for dismantling and transporting a fixed oil exploitation platform in the sea that carries frame elements formed especially by a bridge and at least one support column, said structure comprises: "U" floating hull equipped with at least three lifting legs of this C SCO and adapted to provide support on the seabed, each lifting leg is associated with mechanical movement means housed in a carrier frame of said hull, and - a naveta movable along the lifting legs and intended to move one of the elements of the platform frame, characterized in that the naveta is formed of at least three associated elements each. one to one lifting leg and each carrying, on the one hand, mechanical means of dragging on the corresponding lifting leg independently of the hull of the structure and, on the other hand, means of connection with the frame element for the displacement of the platform. Following the particular modes of use: - each element of the naveta comprises a vertical guide arm on the corresponding carrier frame of the helmet and carries on its upper part a horizontal support arm for the mechanical means of dragging the element -on the corresponding leg , - the mechanical means of dragging each element comprise, on the one hand, two opposing plates carried by each vertical frame of the corresponding lifting leg and each bearing, on each side face, a series of teeth and, on the other hand , at least two opposing assemblies, carried by the horizontal arm of said element and each formed by a pinion carried in rotation and cooperating with one of the series of teeth, - the means of connection with the frame element formed by the bridge of the platform comprises at least one horizontal support plate of this bridge and placed in the lower part of the vertical arm of each element of the naveta, - the joining means with the frame element formed by a column supporting the platform comprise, at the level of each element of the naveta, a linear and vertical traction element, formed by a chain or a cable and two interlocking assemblies of the traction element, one of said assemblies is carried by the element and the other of these assemblies is carried by the helmet for a vertical step-by-step displacement of the support column by the successive interlocking of said interlocking assemblies, - each interlocking assembly is formed by two opposite bolts and oscillating vertically towards each other in a position of release of the traction element and a locking position of this traction element, - the structure has an independent arm for sealing the opening of the helmet and that can be nailed on said helmet. Another object of the invention is a dismantling and transport method as well as a method for transporting and installing a frame element of a fixed oil platform, formed by a bridge. Another object of the invention is a dismantling and transport method as well as a method for transporting and installing a frame element of a fixed oil platform, formed by a section of a support column. The invention will be better understood with the reading of the description that follows, given only as an example and made with reference to the attached figures, in which: - Figure 1 is a schematic elevation view of a fixed oil platform in the operating position, Figure 2 is a schematic perspective view of a transport, installation and dismantling structure according to the invention, - Figure 3 is a schematic sectional view of an element of the naveta of the structure according to the invention, - figure 4 is a sectional view according to line 4-4 of figure 3, - figure 5 is a sectional view according to the line -5 of Figure 3, Figure 6 is a schematic perspective view of an interlocking assembly of an organ of. Linear traction and equipping the structure according to the invention, - Figure 7 is a schematic top view of the structure according to the invention, - Figure 8A, Figure 8B, Figure 3C, Figure 8D, 8E, FIG. 8F, FIG. 8G, and FIG. 8H are diagrams showing the different stages of the process of dismantling and transporting a bridge of a fixed oil platform by means of the structure according to the invention, Figure 9A, Figure 9B, Figure 9C, Figure 9D, Figure 9E, Figure 9F, Figure 9G, Figure 9H, Figure 91, Figure 9J, and Figure 9K, are diagrams showing the different stages of the process of dismantling and transporting a supporting column of a fixed oil platform by means of a structure according to the invention. 1, schematically represents a fixed oil platform designated as a whole by reference 1 and comprising frame elements formed especially by a bridge 2 provided with operating equipment and the usual room and a support column 3 on which the bridge 2 rests. The base of this column 3 is anchored on the seabed 4 by the anchoring elements 5. To ensure transport, installation ("executed" at angles) and dismantling, ("disarmed "at angles" of the bridge 2 and the support column 3 of the fixed oil platform 1 of an operation site to a dismantling spring of these frame elements or conversely, a structure designated by the general reference 10 and represented is used schematically in figure 2. On this figure 1, the general dimensions of the structure as well as the proportions of the different elements that make up this is 10 have not been respected forcibly in order to simplify the understanding of the design. In a general manner, the structure 10 comprises a floating hull 11 in the "U" shape equipped with lifting legs 12 of this hull 11 and adapted to provide support on the seabed 4. The hull 11 comprises two lateral portions lia and a connecting portion 11b connecting the two lateral portions Iaa. In the embodiment shown in Figure 2, the helmet 11 is equipped with three lifting legs 12 distributed according to a triangle, a leg 12 is placed on each side portion lia and a leg 12 is placed on the joint portion 11b. According to a variant, the helmet 11 can be equipped with four lifting legs 1.2 deposited in pairs on each lateral arm Ia of said helmet 11. Each leg 12 is terminated, at its lower end, by a shoe 13 intended to provide support on the marine-bottom 4. As shown in FIGS. 2, 4 and 5, each of these legs 12 has, in this embodiment, a triangular section. These legs 12 can also have a square or circular section. Each leg 12 is formed of three members 14 connected to each other by a lattice of metal beams 15. As shown in figures 3 and 4, each leg 12 is associated with mechanical means 20 for moving the helmet 11. For each leg 12 , the mechanical displacement means 20 are housed in a carrier frame 16, also called by the "Jack-house" specialists, which is supported by the helmet 11.

As it is represented on these figures 3 and 4, each member 14 of each leg 12 carries two opposite plates 21 each carrying, on each side face, a series of teeth 22 forming with the two members 14 a double rack. The mechanical displacement means 20 of the helmet 11 comprise several assemblies 25 distributed on one side and the other on each plate 21., following the height of it. Each assembly 25 comprises a motor-reducer group 26 which ensures the drive of a pinion 27 which meshes with a series of teeth 22 of the corresponding plate 21. In the embodiment shown on FIGS. 3 and 4, the two series of teeth 22 of each plate 21 are associated with six pinions 27 each driven in rotation by a motor-reducer group 26. The structure 10 also carries a designated naveta by the general reference 30 which is displaceable along the legs 12 independently of the hull 11 of the structure 10 and which is intended to move the frame elements of the platform 1, that is to say either the bridge 2, or the column of support 3, as will be seen later. As shown in Figure 2, the naveta 30 is composed of independent elements 31 whose number corresponds to the number of legs 12 of the structure 10. Thus, in the embodiment shown on the figures, the naveta 30 is composed of three elements independent 31, each associated with a lifting leg 12. In general, each element 31 of the naveta comprises the mechanical means 40 for driving on the corresponding lifting leg 12, independently of the hull 11 of the structure, as well as joining means with the frame element 2 or 3 for moving the platform 1. Referring now to figures 3 and 5, an element 31 of the naveta 30 is described, the other elements 31 are identical. The element 31 comprises a vertical guide arm 32 on the carrier frame 16 of the helmet 11 and which is thus supported on a vertical wall 16a of this carrier frame 16. The element 31 also comprises a horizontal arm 33 carrying a central opening 34 for the passage of the corresponding leg 12. This horizontal arm 33 is placed on the upper part of the vertical arm 32 and supports the mechanical means 40 for driving said element 31 on the leg 12. The mechanical means 40 for driving each element 31 on the corresponding leg 12 operate independently of the mechanical means 20 for moving the helmet 11 and these means 40 of the set of elements 31 work in synchronization with each other so that the same displacement of each element 31 is obtained on the corresponding leg 12. The mechanical means 40 for moving each element 31 of the naveta 30 comprise several assemblies 41 distributed on one side and the other of each plate 21 of the frame 14, following the height thereof. Each assembly 41 comprises a motor-reducer group 42 which ensures the drive of a pinion 43 which meshes with a series of teeth 22 of the corresponding plate 21. In the embodiment shown on FIGS. 3 and 5, the two series of teeth 22 of each plate 21 are associated with four pinions 43 each driven in rotation by a motor-reducer unit 42. As shown in FIG. 3 , the vertical wall 16a of the carrier frame 16 forming the guide for the vertical displacement of the corresponding element 31 is prolonged, in its upper part, by a vertical plate 17 on which the element 31 slides so as to increase the vertical displacement height of this element 31. On the other hand, the joining means of each element 31 of the naveta 30 with the frame element 2 or 3 to be moved, are for each of said elements 31 of two classes. Referring now to Figure 3, the joining means associated with an element 31 of the naveta 30 will be described, the joining means of the other elements 31 of this naveta 30 are identical. The first of these means for displacing the bridge 2 of the oil platform 1 is constituted by a horizontal plate 50 supporting the bridge 2 in the course of its transport, as will be seen later. The second of these means for displacing the support column 3 is constituted by a linear and vertical detraction element 51, formed by a chain or a cable. In the exemplary embodiment shown on the figures, the traction element 51 is constituted by a chain. As shown in Figure 3, the chain 5 can be wound on a drum 52- placed on the hull 11 of the structure 10 and carries a first mounting part 51a passing through the carrier frame 16 of the helmet 11, the horizontal arm 33 of the element 31 and ends in the upper part of the vertical arm 31 of the element 30. At this level, the chain 51 passes over a transmission pulley 53 and carries a descending part 51b that passes through the vertical arm 32 of the element 31 and extends to along the hull 11 where it is guided by a pulley 54 fixed on this hull 11. The end of the chain 51 is equipped with a hooking system 55, of the known type, on the support column 3 at the moment of his displacement. The chain 51 is associated with two interlocking assemblies € 0 and 65, one 60 is mounted on the element 31 and the other 65 is mounted on the helmet 11. These two sets 6-0 and 65 operate independently of one another thus allowing join the chain 51 with the element 31 or with the helmet 11. Referring now to figure 6, an example of an interlocking assembly is described, for example, the interlocking assembly 60, the interlocking assembly 65 is identical. As shown on this figure, the interlocking assembly 60 is formed of two subsets respectively, 61a and 61b, identical or symmetrical. The first subassembly 61a is formed by a bolt 62a oscillatingly mounted on a pedestal 63a about a horizontal axis 64a carried by the pedestal 63a. The oscillation of the bolt 62a between an elevated position and a lowered position is commanded by a jack 65a, for example hydraulic or pneumatic, whose extremity is integral with the pedestal 63a and whose other extremity is integral with the bolt -62a. In the same way, the second subassembly 61b is constituted by a bolt 62b oscillatingly mounted on a pedestal 63b around a horizontal axis 64b carried by said pedestal 63b. The oscillation of the bolt 62b between a lowered position and a raised position is commanded by a jack 65b, for example hydraulic or pneumatic, whose end is integral with the pedestal 63b and whose other end is integral with the jack 62b. The displacement of the bolts 62a and 62b is simultaneous. In the lowered position, the bolts 62a and 62b block the chain 51, as was shown on figure 6. Finally and as shown in figure 7, the opening of the "U" of the hull 11 of the structure 10 can be closed by an independent arm 70 optionally carrying a crane 71 that allows the modules of the oil platform 1 or another platform to be moved to one side of which the transport structure 10 can be installed. Classically, this arm -70 can. to be installed by a flat boat, not shown, ballasted / unlayable and can be nailed, then unlocked from the hull 11 of the structure 10. The transport of the bridge 2 of the oil platform 1 by the structure 10 between an exploitation site and the A port's dock is made as follows. First and as it is represented in the figure 8A, the structure 10 without the complementary arm 70 is carried by flotation under the bridge 2 of the platform 1 by placing the support column 3 of this bridge 2 in the U-shaped space carried between the lateral portions Ia of the helmet 11 In the course of its placement, the positioning legs 12 are in the retracted position and the shoes 13 are placed below the helmet 11. The horizontal arms 50 of the elements 31 of the naveta 30 are in the low position substantially at the level of the helmet 11, as shown in figure 2. Next, the gear-reducing units 26 and 42, respectively of the hull 11 and the elements 31 of the naveta 30, are driven to rotationally drive the pinions 27 and 43 that they engage with the series of teeth 22 of the plates 21 of each lifting leg 12 in order to bring the shoes 13 in contact with the seabed 4, as shown in Figure 8B. Since the shoes 13 are in contact with the seabed 4, the hull 11 and the elements 31 of the naveta 30 move upwards along the length of the legs 12, under the effect of driving in rotation of the pinions 27 and 43 which mesh with the series of teeth 22 of the plates 21 of the lifting legs 12. Moving upwards, the elements 31 of the naveta 30 come to be applied against the underside of the bridge 2 and the drive of the pinions 27 and 43 is stopped (Figure 8C). Next, the support column 3 is separated from the bridge 2 and the elements 31 of the naveta 30 are lifted to divert the bridge 2 from the support column 3 that remains in vertical position as shown in Figure 8C. Several variants can be contemplated. The first consists in interlocking the elements 31 of the naveta 30 on the lifting legs 12, in bringing the hull 11 in flotation to reduce the stresses in these, lifting legs 12 and the sea bottom 4, in separating the support column 3 of the bridge 2 and in raising the elements 31 of the naveta 30 by the pinions 43 that mesh with the series of teeth 22, as shown in Figure 8E. In an alternative, the elements 31 of the naveta 30 can only be lifted by the pinions 43, but locked on the lifting legs 12. The elevation of the elements 31 and of the bridge 11 can then be carried out passively in the moment of the lifting of these lifting legs 12. The second variant consists in locking the elements 31 of the naveta 30 on the lifting legs 12, in trimming a section of the supporting column 3 of sufficient length, in removing this section to separate the bridge 2 of the rest of the support column 3 and in bringing the helmet 11 in flotation. The third variant consists of separating the supporting column 3 from the bridge 2, in raising the elements 31 of the naveta 30 by means of the pinions 43 which mesh with the series of teeth 22, then in locking these elements 31 on the legs of the latter. lifting 12 and, finally, in lowering the hull 11 in flotation (figure 8D). Finally, the fourth variant consists in separating support column 3 from bridge 2, in elevating the elements 31 of the naveta 3 and the hull 11, in locking these elements 31 on the lifting legs 12 and in wearing the helmet 11 float. After having carried the hull 11 in float, the pinions 27 are always driven in rotation which causes, by reaction, due to the collapse of the hull 11 in the water, the lifting of the lifting legs 12 (FIG. 8E). The hull 11 supporting the bridge 2 by the intermediation of the naveta 30, is uncoupled from the exploitation site on which the support column 3 is always in place. Then, the elements 31 are unhooked from the lifting legs 12 and are lowered by the drive in the opposite direction of the pinions 43 which mesh with the series of teeth 22 to carry these elements 31 that support the bridge 2 substantially at the level of the hull 11 (figure 8F). Structure 10 transports bridge 2 by flotation, as shown in Figure 8G. In the course of this transport the lateral stabilization of the bridge 2 on the elements 31 of the naveta 30 can be ensured by the jacks, not shown, which are in contact with the lateral faces of this bridge 2. In the exemplary embodiment shown on Figure 8H, the hull 11 supporting the bridge 2 is transported by flotation, to a spring of a port and the lifting legs 12 are applied on the bottom to stabilize this hull 11. A connecting piece 6 is placed between the hull 11 and the port to ensure a continuity between the surface of this hull 11 and said port. Next, bridge 2 is unloaded on this port. According to a variant, the bridge 2 can be previously unloaded on a flat boat that ensures the transport of this bridge to the port. The structure 10 according to the invention can also be used for the installation of a bridge 2 on a support column 3 substantially making the same operations in a reverse direction. The structure 10 also allows the dismantling of a support column 3. After the bridge 2 has been removed from the support column 3, the structure 10 is carried by flotation around the support column 3, as shown in Figure 9A . Next, the motor-reducing groups 26 and 42 are driven to be driven in rotation by the pinions 27 and 43 which mesh with the series of teeth 22 of the plates 21 of each lifting leg 12 to bring the shoes 13 in contact with the seabed 4. Since the shoes 3 are in contact with the seabed 4, the helmet 11 and the elements 31 of the ship 30 move upwards, along the legs 12, under the effect of dragging in rotation of the pinions 27 and 43 which mesh with the series of teeth 22. The hull 11 and the elements 31 of the naveta 30 are also placed above the water level. The free ends of the chains 51 are connected by the latching systems 55 to the support column 3 and this support column 3 is separated to the level A (FIG. 9B), from its part anchored to the sea floor 4. The upper extremity of the fragment of the support column 3 is hooked by the cables 56 to the helmet 11 and these cables 56 are wound on the drums 57 so that their extension is allowed. After these different stages, the interlocking assembly 60 of each element 31 of the naveta 30 is driven by the oscillating movement of the bolts so as to be in solidarity with the chains 51 and, due to this, with the support column 3 of This elements. The interlocking assemblies 65 are in the open position to allow the chains 51 to slide. Next, the elements 31 of the naveta 30 are lifted by rotating the pinions 43 by means of the gear-reducing units 42 and engaging with the series of teeth 22 of the plates 21 of each leg - of lifting 12. Due to the solidarity of the chains. With these elements 31, the fragment of the support column 3 is also raised. In the course of this displacement, the elements 31 of the shuttle 30 are first sent to the vertical wall 16a of the carrier frame 16 of the hull 11 and to the plates 17, as shown in Figure 9C. After this first operation of lifting the fragment of the support column 3, the interlocking assemblies 65 are driven to lock the chains 51 and to attach these chains 51 of the helmet 11. The interlocking assemblies 60 are opened by the oscillating movement of the locks so that the chains 51 of the elements 31 of the naveta 30 are released. These elements 31 are lowered to bring them substantially to the level of the hull 11, as shown on Figure 9D. The chains 51 are again secured to the elements 31 by the interlocking of the assemblies 60 and these chains 51 are released from the hull 11 by the opening of the assemblies 65. The elements 31 of the naveta 30 are raised so that they also rise the fragment of the support column 3 and these operations are renewed to progressively elevate this fragment, as shown on Figure 9E. Next, the elements 31 of the naveta 30 carrying the fragment of the support column 3 are brought substantially to the level of the hull 11 (figure 9F) and the set formed by the naveta 30 and the hull 11 is lowered to carry this helmet 11 in flotation, as shown in Figure 9G. The legs 12 are lifted and the structure 10 carrying the support column 3 is removed from the operation site by flotation (Figure 9G). The structure 10 carrying the fragment of the support column 3 is carried by flotation to a loading site of this fragment on a flat boat 80. For this, the lifting legs 12 are applied on the seabed 4 by rotating the sprockets 27 and 43 by the motor-reducers 26 and 42 and when the lifting legs 12 are in contact on the seabed 4, the hull 11 and the elements 31 of the naveta 30 are raised to bring the lower extremity of the fragment of the support column 3 above the water level as shown on figure 9H. The flat boat 80 is brought under this fragment and said fragment is placed on the flat boat 80, then the chains 51 as well as the cables 56 are disconnected from the fragment of the support column 3 (figure 91). The helmet 11 is then carried in flotation (Figure 9J) and the legs 12 are raised to allow the structure 10 to be used for a new transfer operation of the remaining part of the support column 3. The flat boat ßO carrying the fragment from the support column 3 is taken to a disassembly port and this fragment is transferred onto this port, as shown in Figure 9K. The structure 10 can also be used to raise the lower part of the support column 3 or, if this is possible, to raise the assembly of the support column 3 in a single operation. Finally, this structure 10 can also be used for the placement of a support column 3 of an oil platform on a holding site possibly carrying out the same operations in reverse rent. In a general manner, the order of certain stages of dismantling the bridge or the supporting column can be reversed according to the dismantling conditions. The structure according to the invention has the advantage of being able to transport both the bridge and the supporting column of an oil platform directly from the operating site on a fixed site where the assembly can be carried out safely, without the risk of contamination of the environment marine or vice versa between a fixed site and a site of exploitation. In addition, the different transfer and transport stages are carried out without any ballasting operation, thus allowing to obtain an important time gain that is appreciable in the regions where the atmospheric conditions are changing very rapidly. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (11)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. 1. A dismantling and transport structure of a fixed oil exploitation platform in the sea that carries frame elements formed especially by a bridge and at least one supporting column, comprising: a floating "U" shaped hequipped with at least three lifting legs of this helmet and adapted to provide support on the seabed, each lifting leg is associated with the mechanical means of movement housed in a frame carrying said h and - a naveta movable along of the legs and intended to displace one of the frame elements of the platform, characterized in that the naveta is formed by at least three elements each associated with a lifting leg and each carrying, on the one hand, mechanical means of dragging on the corresponding lifting leg independently of the hof the structure and, on the other hand, the means of connection with the element of frame, to move said platform.
2. 2. The structure according to claim 1, characterized in that each element of the naveta comprises a vertical guide arm on the corresponding carrier frame of the hand that bears, on its upper part, a horizontal arm for supporting the mechanical means of driving said element on the corresponding leg.
3. 3. The structure according to claim 1 or 2, characterized in that the mechanical means of driving each element comprise, on the one hand, two opposing plates carried by each frame of the corresponding lifting leg and carrying each. one, on each lateral face, a series of teeth and, on the other hand, at least two opposed assemblies carried by the horizontal arm of said element and each formed by a pinion driven in rotation and cooperating with one of the series of teeth . The structure according to one of claims 1 to 3, characterized in that the connection means with the frame element formed by the bridge of the platform comprise at least one horizontal support plate of this bridge and placed in the lower part of the vertical arm of each element of the naveta. 5. The structure according to any of claims 1 to 3, characterized in that the means of connection with the frame element formed by a column supporting the platform comprise, at the level of each element of the naveta, a traction element linear and vertical, formed by a chain or a cable and two interlocking sets of the traction element, one of said sets is carried by the element and the other of these sets is carried by the hfor a vertical displacement step by step of the support column by the. successive interlocking of said interlocking assemblies. The structure according to claim 5, characterized in that each interlocking assembly is formed by two opposite bolts and that can be moved vertically swinging towards each other between a release position of the tension element and a blocking position. of this traction element. The structure according to any of claims 1 to 6, characterized in that it has an independent arm for sealing the opening of the helmet and can be locked on said helmet. 8. A procedure for dismantling and transporting a framework element of a fixed oil platform, formed by a bridge, between an operation site and a bridge dismantling port, characterized in that it consists of the following stages: - placing under the bridge a transport structure carrying a floating U-shaped hequipped with at least three lifting legs of this hand a movable halong these legs regardless of the hull, - apply the lifting legs on the seabed, - lift the hull and the naveta to bring said naveta in contact with the bridge, - lock the naveta on the legs - lifting, - lower the hull to carry it in flotation, - separating the bridge from its support column, raising the bridge by the intermediation of the naveta under the action of raising the lifting legs, moving the structure supporting the bridge to decouple said bridge from the support column, to lower the naveta that supports the bridge to carry it on the hull, - to carry by flotation the structure that supports the bridge to the dismantling port or to a discharge site on a flat boat, - to apply the lifting legs on the bottom to stabilize the hull, - release the bridge from the structure, and - unload the bridge over the harbor or over the flat boat. 9. A method of transport and installation of a frame element of a fixed oil platform, formed by a bridge, between a port or a flat boat and a site of exploitation, characterized in that a structure is used in accordance with any of the . claims 1 to 7. The process of dismantling and transporting a frame element of a fixed oil platform, formed by a fragment of a support column, between an operating site and a disassembly port of the support column. , characterized in that it consists of the following steps: - placing around the supporting column a floating U-shaped hull equipped with at least three lifting legs of this hull and a naveta made up of at least three movable elements, each one along one of these legs, regardless of the hull, apply the lifting legs on the seabed, - lift the hull and the elements of the naveta, - connect each element of the naveta to the fragment of the support column by a linear pull element, - separating the fragment from the support column from the rest of said column, - locking each traction element to each element of the naveta, - elevating the elemeof the naveta to lift the fragment of the support column, locking the traction elemealternatively to the elemeof the naveta and the hull and to lower and raise said elemefor the step-by-step lifting of the fragment of the support column, - to carry the naveta that carries the fragment of the support column in contact with the hull, - lowering the naveta and the hull to carry them in flotation, - continuing the descent of the hull to provoke by reaction the lifting of the legs lifting the structure, - displacing the structure that carries the fragment of the support column to uncouple this fragment of the exploitation site and take it on a loading site on a flat boat, - apply on the unloading site the lifting legs on the bottom marine, - lift the hull and the naveta for the lifting of the fragment of the support column above the water level, - place the flat boat in the structure below said fragment, _ - lower the hull and the naveta to place the fragment of the support column on the flat boat, - disengage the traction elemefrom the fragment of the support column, and - take the flat boat that carries the fragment of the support column to the dismantling port and repeat these stages for the other fragmeof said support column. 11. A method of transporting and installing a framework element of a fixed oil platform, formed by a fragment of a support column between a port and a site of exploitation, characterized in that a structure is used in accordance with any of the claims 1 to 7.