Abstract:
The invention relates to a structure for transporting, installing and dismantling a fixed oil platform provided with framework elements which are substantially formed by a bridge and at least one supporting pillar. The inventive structure comprises a floating U-shaped shell provided with at least three lifting legs adapted for resting upon the bottom of the sea and a shuttle movable along the lifting legs for displacing a platform element. Said shuttle consists of at least three elements each of which is associated with the lifting leg and is provided with mechanical means for driving on the corresponding lifting leg in a manner independent of the shell of the structure 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:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present patent application is a §371 national stage application of PCT/FR04/03418 filed Dec. 30, 2004 which claims priority from French Application 0400806 filed on Jan. 28, 2004. 
     FIELD OF THE INVENTION 
     The present invention relates to a structure for transporting, commissioning and decommissioning an offshore fixed oil production platform comprising framework elements substantially formed by a deck and at least one supporting column. 
     It further relates to methods for transporting, commissioning and decommissioning the framework elements of a fixed oil platform. 
     DESCRIPTION OF THE RELATED ART 
     It is a known method in oil production to place above an oil field, a fixed oil platform comprising a deck chiefly carrying the production equipment and the living quarters. The deck is supported by a supporting column anchored to the seabed. 
     To date, there are two main methods for transporting, commissioning and decommissioning the framework elements of a fixed oil platform. 
     The first method consists of using barge-mounted lifting cranes for setting down the supporting column on the seabed and for transferring the platform deck from the transport vessel onto this supporting column. This method, which is the most widespread to date, has limitations. 
     The first of these limitations is actually the capacity of the lifting cranes, which may require the deck to be made in several parts, thus significantly increasing the cost of producing this deck and the cost of commissioning and decommissioning the oil platform deck. 
     The second limitation lies in the fact that this method demands a relatively long favorable time window to be able to carry out the various transfer operations at sea under satisfactory conditions. 
     Thus, without a considerable increase in cost, this method is difficult to apply in areas where time windows are relatively short, for example in the North Sea. 
     The second method consists of installing the supporting column on the seabed by lifting cranes and installing the oil platform deck in a single unit on the supporting column by causing it to float above it. The deck is then placed on this supporting column either by a ballasting/deballasting system, or by a mechanical system. 
     In the case of a ballasting system, the platform deck is supported either by a floating support consisting, for example, of a barge, pontoons or a U-shaped floating support, or through the intermediary of a structure associated with this floating support. 
     In the case in which the superstructure can be ballasted or deballasted, a known approach used for decommissioning the oil platform deck is deballasting the floating support and ballasting the superstructure. Since the superstructure has a large ballasting capacity, the decommissioning operation can take place relatively quickly. In the case of a superstructure anchored to the seabed, only the deballasting capacity of the floating support can be used. As this capacity is limited, the operation proceeds slowly. 
     Systems using ballasting or deballasting have drawbacks that lie mainly in the fact that they require a complex structure of caissons or pumps and very precise control of filling and emptying the caissons to maintain the stability of the floating support during the operation. 
     The speed of the operation depends on the ballasting and unballasting capacity of these floating support caissons, which is generally relatively low, thus limiting the operation&#39;s speed, especially when the superstructure is anchored on the seabed. In addition, during this operation, the sea conditions must be favorable in order to carry out this operation under satisfactory conditions. 
     An alternative to the ballasting/deballasting system is to use a mechanical system for raising or lowering the oil platform deck. These systems enable the operation of commissioning or decommissioning an oil platform deck to be carried out faster than the previously mentioned systems. 
     For this purpose, a system is known that includes two barges supporting the oil platform deck using two swiveling structures. In addition, a system of winches and cables is used to ensure the stability of the system and control the descent and ascent of the oil platform deck. 
     Operating these winches controls the barges&#39; clearance, thus enabling the ascent or descent of the deck. But this kind of mechanical system offers very precarious stability and it is very often incompatible with use on the open sea. 
     Another mechanical system consists of a rack and pinion system for raising or lowering the oil platform deck. 
     In general, the mechanical systems used to date for commissioning and decommissioning an oil platform deck are faster than ballasting or deballasting systems, but they are dependent on sea conditions, which makes them difficult to use in areas where favorable time windows are relatively short. 
     A structure is also disclosed in application WO 03/080425 for transporting, commissioning and decommissioning a fixed oil platform deck comprising a U-shaped floating hull and a deck support shuttle that can be displaced along the legs by the hull. 
     BREIF SUMMARY OF THE INVENTION 
     The object of the invention is to provide a structure for transporting, commissioning or decommissioning an offshore fixed oil production platform that is designed to simplify and reduce the time for decommissioning said platform, whilst achieving significant time saving and avoiding any environmental pollution risks and increasing the safety of personnel responsible for carrying out the various operations. 
     For this purpose, the object of the invention is a structure for the decommissioning and transport of an offshore fixed oil production platform comprising framework elements substantially formed by a deck and at least one supporting column, said structure comprising:
         a U-shaped floating hull fitted with at least three lifting legs for this hull, adapted to rest on the seabed, each lifting leg being associated with mechanical displacement means housed in a bearing framework of said hull, and   a shuttle which can be displaced along the lifting legs and intended to displace one of the platform framework elements,
 
characterized in that the shuttle is formed of at least three elements each associated with a lifting leg and each comprising, on the one hand, mechanical drive means on the corresponding lifting leg independent of the structure&#39;s hull and, on the other hand, connecting means with the platform framework element to be displaced.
       

     According to the specific modes of implementation:
         each shuttle element includes a vertical guidance branch on the corresponding hull bearing framework, whose top section comprises a horizontal branch supporting the mechanical drive means of said element on the corresponding leg,   the mechanical drive means of each element comprise, on the one hand, two opposing plates supported by each vertical chord of the corresponding lifting leg each featuring, on each lateral face, a series of teeth and, on the other hand, at least two opposing assemblies, supported by the horizontal branch of said element and each formed of a pinion driven rotationally and cooperating with one of the series of teeth,   the connecting means with the framework element formed by the platform deck comprise at least a horizontal plate supporting this deck and positioned on the bottom part of the vertical branch of each shuttle element,   the connecting means with the framework element formed by a supporting column of the platform comprise, for each shuttle element, a linear, vertical traction device, formed of a chain or cable and two locking assemblies of said traction device, one of said assemblies being supported by said element and the other of these assemblies being supported by the hull for a gradual vertical displacement of the supporting column by successive locking of said locking assemblies,   each locking assembly is formed of two opposing locks that can tilt vertically toward one another between a position releasing the traction device and a position blocking this traction device,   the structure includes an independent branch for sealing the hull opening that is lockable on said hull.       

     The object of the invention is also a method of decommissioning and transporting as well as a method of transporting and commissioning a framework element of a fixed oil platform, formed of a deck. 
     A further object of the invention is a method of decommissioning and transporting as well as a method of transporting and commissioning a framework element of a fixed oil platform, formed of a section of supporting column. 
    
    
     
       BREIF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the description that follows, given solely by way of example and referring to the attached drawings, in which: 
         FIG. 1  is a diagrammatic elevation view of a fixed oil platform in production position, 
         FIG. 2  is a diagrammatic perspective view of a structure for transporting, commissioning and decommissioning according to the invention, 
         FIG. 3  is a diagrammatic side view of a shuttle element of the structure according to the invention, 
         FIG. 4  is a sectional view along the line  4 - 4  in  FIG. 3 , 
         FIG. 5  is a sectional view along the line  5 - 5  in  FIG. 3 , 
         FIG. 6  is a diagrammatic perspective view of a locking assembly of a linear traction device fitted on the structure according to the invention, 
         FIG. 7  is a diagrammatic top view of the structure according to the invention, 
         FIGS. 8A to 8H  are diagrams showing the various stages of the method of decommissioning and transporting a fixed oil platform deck by means of the structure according to the invention, 
         FIGS. 9A to 9K  are diagrams showing the various stages of the method of decommissioning and transporting a fixed oil platform supporting column by means of the structure according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  shows a diagrammatic representation of a fixed oil platform designated as a whole by the reference  1  and including framework elements substantially formed of a deck  2  provided with the usual production equipment and living quarters and a supporting column  3  on which the deck  2  rests. The base of this column  3  is anchored to the seabed  4  by anchorage devices  5 . 
     A structure designated by the general reference  10  and shown diagrammatically in  FIG. 2  is used to ensure the transport, commissioning and decommissioning of the deck  2  and the supporting column  3  of the fixed oil platform  1  from a production site to a disassembly quay for these framework elements or vice versa. 
     The general dimensions of the structure as well as the proportions between the various elements making up this structure  10  have not necessarily been respected on this figure, in order to simplify understanding of the drawing. 
     In general, the structure  10  includes a U-shaped floating hull  11  fitted with lifting legs  12  for this hull  11  and adapted to rest on the seabed  4 . The hull  11  comprises two lateral sections  11   a  and a connecting section  11   b  connecting the two lateral sections  11   a.    
     In the example of embodiment shown in  FIG. 2 , the hull  11  is fitted with three lifting legs  12  arranged in a triangle, one leg  12  being located on each lateral section  11   a  and one leg  12  being located on the connecting section  11   b . According to a variant, the hull  11  may be fitted with four lifting legs  12  arranged in pairs on each lateral branch  11   a  of said hull  11 . 
     Each leg  12  terminates at its bottom end in a shoe  13  intended to rest on the seabed  4 . 
     Each of these legs  12  in this embodiment is triangular in section, as shown in  FIGS. 2 ,  4  and  5 . These legs  12  may also be square or circular in section. Each leg  12  is formed of three chords  14  interconnected by a lattice of metal girders  15 . 
     As shown in  FIGS. 3 and 4 , each leg  12  is associated with mechanical means  20  of displacing the hull  11 . The mechanical means  20  for displacing each leg  12  are housed inside a bearing framework  16 , also called a “jack-house” by specialists, which is supported by the hull  11 . 
     As shown in these  FIGS. 3 and 4 , each chord  14  of each leg  12  comprises two opposing plates  21  each bearing, on each lateral face, a series of teeth  22  forming a double rack with the two chords  14 . The mechanical displacement means  20  of the hull  11  comprise several assemblies  25  arranged on each side of each plate  21 , according to its height. Each assembly  25  includes a geared motor unit  26  driving a pinion  27 , which engages with a series of teeth  22  on the corresponding plate  21 . 
     In the embodiment shown in  FIGS. 3 and 4 , both series of teeth  22  of each plate  21  are associated with six pinions  27 , each driven rotationally by a geared motor unit  26 . 
     The structure  10  also includes a shuttle designated by the general reference  30 , which can be displaced along the legs  12  independently of the hull  11  of the structure  10  and which is intended to displace the platform  1  framework elements, i.e. either the deck  2 , or the supporting column  3 , as will be seen later. 
     As shown in  FIG. 2 , the shuttle  30  is made up of independent elements  31 , whose number corresponds to the number of legs  12  of the structure  10 . Thus, in the example of embodiment shown in the figures, the shuttle  30  consists of three independent elements  31 , each associated with a lifting leg  12 . 
     In general, each element  31  of the shuttle  30  includes mechanical drive means  40  on the corresponding lifting leg  12 , independent of the hull  11  of the structure  10 , together with means of connecting with the framework element  2  or  3  to be displaced on the platform  1 . 
     Referring now to  FIGS. 3 and 5 , one element  31  of the shuttle  30  will be described, the other elements  31  being identical. 
     The element  31  includes a vertical guidance branch  32  on the bearing framework  16  of the hull  11 , which then rests on a vertical wall  16   a  of this bearing framework  16 . The element  31  also includes a horizontal branch  33  that has a central opening  34  for the passage of the corresponding leg  12 . This horizontal branch  33  is positioned on the top part of the vertical branch  32  and supports the mechanical drive means  40  of said element  31  on the leg  12 . 
     The mechanical drive means  40  of each element  31  on the corresponding leg  12  operate independently of the mechanical displacement means  20  of the hull  11  and these means  40  of the assembly of elements  31  operate in synchronization with one another so as to achieve the same displacement of each element  31  on the corresponding leg  12 . The mechanical displacement means  40  of each element  31  of the shuttle  30  comprise several assemblies  41  arranged on each side of each plate  21  on the chord  14 , according to its height. Each assembly  41  includes a geared motor unit  42  driving a pinion  43 , which engages with a series of teeth  22  on the corresponding plate  21 . 
     In the embodiment shown in  FIGS. 3 and 5 , both series of teeth  22  of each plate  21  are associated with four pinions  43 , each driven rotationally by a geared motor unit  42 . 
     As shown in  FIG. 3 , the vertical wall  16   a  of the bearing framework  16  acting as guidance for the vertical displacement of the corresponding element  31  is extended, at its top, by a vertical plate  17  on which the element  31  slides so as to increase the height of vertical displacement of this element  31 . 
     Moreover, the connecting means of each element  31  of the shuttle  30  with the framework element  2  or  3  to be displaced are of two kinds for each of said elements  31 . 
     Now referring to  FIG. 3 , a description will be given of the connecting means associated with one element  31  of the shuttle  30 , the connecting means of the other elements  31  of this shuttle  30  being identical. 
     The first of these means intended for displacing the deck  2  of the oil platform  1  consists of a horizontal plate  50  supporting the deck  2  while it is being transported, as will be seen later. 
     The second of these means intended for displacing the supporting column  3  consists of a linear, vertical traction device  51 , formed of a chain or cable. In the exemplary embodiment shown in the figures, the traction device  51  consists of a chain. 
     As shown in  FIG. 3 , the chain  51  may be wound on a drum  52  positioned in the hull  11  of the structure  10  and comprises a first ascending part  51   a  that traverses the bearing framework  16  of the hull  11 , the horizontal branch  33  of the element  31  and emerges at the top of the vertical branch  31  of the element  30 . At this point, the chain  51  passes over a return pulley  53  and comprises a descending part  51   b  that traverses the vertical branch  32  of the element  31  and runs along the hull  11  where it is guided by a pulley  54  fixed onto this hull  11 . 
     The end of the chain  51  is fitted with a known type of system for coupling  55  onto the supporting column  3  during its displacement. 
     The chain  51  is associated with two locking assemblies  60  and  65 , one  60  being mounted on the element  31  and the other  65  being mounted on the hull  11 . These two assemblies  60  and  65  operate independently of one another thus enabling the chain  51  to be secured to the element  31  or to the hull  11 . 
     Now referring to  FIG. 6 , a description will be given of an example of a locking assembly, for example the locking assembly  60 , the locking assembly  65  being identical. 
     As shown in this figure, the locking assembly  60  is made up of two identical and symmetrical subassemblies,  61   a  and  61   b  respectively. 
     The first subassembly  61   a  consists of a lock  62   a  fitted on a base  63   a , that can be tilted around a horizontal shaft  64   a  borne by the base  63   a . The tilting of the lock  62   a  between a raised position and a lowered position is controlled by a cylinder  65   a , for example hydraulic or pneumatic, whose one end is integral with the base  63   a  and whose other end is integral with the lock  62   a . Likewise, the second subassembly  61   b  consists of a lock  62   b  fitted on a base  63   b , that can be tilted around a horizontal shaft  64   b  borne by said base  63   b . The tilting of the lock  62   b  between a lowered position and a raised position is controlled by a cylinder  65   b , for example hydraulic or pneumatic, whose one end is integral with the base  63   b  and whose other end is integral with the lock  62   b . The displacement of the locks  62   a  and  62   b  is simultaneous. In the lowered position, the locks  62   a  and  62   b  block the chain  51 , as shown in  FIG. 6 . 
     Finally, as shown in  FIG. 7 , the opening of the “U” of the hull  11  of the structure  10  may be closed off by an independent branch  70 , which might possibly support a crane  71  for displacing modules of the oil platform  1  or of another platform next to which the transport structure  10  may be installed. Conventionally, this branch  70  may be installed by a ballastable/deballastable barge, not shown, and may be locked, then unlocked from the hull  11  of the structure  10 . 
     Transporting the deck  2  of the oil platform  1  by the structure  10  between a production site and a port quay is performed in the following way. 
     First of all, as shown in  FIG. 8   a , the structure  10  without the additional branch  70 , is floated beneath the deck  2  of the platform  1  by positioning the supporting column  3  of this deck  2  in the U-shaped space created between the lateral sections  11   a  of the hull  11 . During its positioning, the lifting legs  12  are in a retracted position and the shoes  13  are placed beneath the hull  11 . 
     The horizontal branches  50  of the elements  31  of the shuttle  30  are in a substantially low position at the level of the hull  11 , as shown in  FIG. 2 . Then the geared motor units  26  and  42  respectively of the hull  11  and of the elements  31  of the shuttle  30 , are actuated to rotationally drive the pinions  27  and  43 , which engage with the series of teeth  22  of the plates  21  of each lifting leg  12  to bring the shoes  13  into contact with the seabed  4 , as shown in  FIG. 8B . As soon as the shoes  13  are in contact with the seabed  4 , the hull  11  and the elements  31  of the shuttle  30  move upward along the legs  12 , under the effect of the rotational driving of the pinions  27  and  43 , which engage with the series of teeth  22  on the plates  21  in the lifting legs  12 . 
     By moving upward, the elements  31  of the shuttle  30  come to be applied against the bottom face of the deck  2  and the driving of the pinions  27  and  43  is stopped ( FIG. 8C ). 
     The supporting column  3  is then separated from the deck  2  and the elements  31  of the shuttle  30  are raised in order to separate the deck  2  from the supporting column  3 , which remains in a vertical position as shown in  FIG. 8C . 
     Several variants may be envisaged. 
     The first consists of locking the elements  31  of the shuttle  30  onto the lifting legs  12 , floating the hull  11  so as to reduce the loads on these lifting legs  12  and the seabed  4 , separating the supporting column  3  from the deck  2  and lifting the elements  31  of the shuttle  30  via the pinions  43 , which engage with the series of teeth  22 , as shown in  FIG. 8E . As an alternative, the elements  31  of the shuttle  30  may not be lifted by the pinions  43 , but locked onto the lifting legs  12 . Raising the elements  31  and the deck  11  may then be carried out passively when these lifting legs  12  are brought back up. 
     The second variant consists of locking the elements  31  of the shuttle  30  onto the lifting legs  12 , cutting away a section of the supporting column  3  of sufficient length, removing this section in order to separate the deck  2  from the rest of the supporting column  3  and floating the hull  11 . 
     The third consists of separating the supporting column  3  from the deck  2 , lifting the elements  31  of the shuttle  30  by means of the pinions  43 , which engage with the series of teeth  22 , then locking these elements  31  onto the lifting legs  12  and, finally, lowering the hull  11  into floatation ( FIG. 8D ). 
     Finally, the fourth variant consists of separating the supporting column  3  from the deck  2 , lifting the elements  31  of the shuttle  30  and the hull  11 , locking these elements  31  onto the lifting legs  12  and floating the hull  11 . 
     After floating the hull  11 , the pinions  27  are still rotationally driven, which causes the lifting legs  12  to ascend by reaction due to the downward thrust of the hull  11  into the water ( FIG. 8E ). 
     The hull  11  supporting the deck  2  via the intermediary of the shuttle  30  is removed from the production site where the supporting column  3  is still in place. 
     The elements  31  are then unlocked from the lifting legs  12  and are lowered by the pinions  43  being driven in the reverse direction, which engage with the series of teeth  22  to bring these elements  31  supporting the deck  2  substantially to the level of the hull  11  ( FIG. 8F ). The structure  10  transports the deck  2  by floatation, as shown in  FIG. 8G . During this transport the lateral stabilization of the deck  2  on the elements  31  of the shuttle  30  may be ensured by cylinders, not shown, which are in contact with the lateral faces of this deck  2 . 
     In the example of embodiment shown in  FIG. 8H , the hull  11  supporting the deck  2  is floated up to a port quay and the lifting legs  12  are applied to the bottom to stabilize this hull  11 . 
     A connecting part  6  is placed between the hull  11  and the quay to ensure continuity between the surface of this hull  11  and said quay. The deck  2  is then unloaded onto this quay. 
     According to a variant, the deck  2  may be unloaded beforehand onto a barge that transports this deck up to the quay. 
     The structure  10  according to the invention may also be used for commissioning a deck  2  on a supporting column  3  by substantially performing the same operations in the reverse direction. 
     The structure  10  also enables the decommissioning of a supporting column  3 . 
     After removing the deck  2  from the supporting column  3 , the structure  10  is floated around the supporting column  3 , as shown in  FIG. 9A . 
     The geared motor units  26  and  42  are then actuated to rotationally drive the pinions  27  and  43 , which engage with the series of teeth  22  on the plates  21  of each lifting leg  12  in order to bring the shoes  13  into contact with the seabed  4 . 
     As soon as the shoes  13  are in contact with the seabed  4 , the hull  11  and the elements  31  of the shuttle  30  move upward along the legs  12 , under the effect of the rotational driving of the pinions  27  and  43 , which engage with the series of teeth  22 . The hull  11  and the elements  31  of the shuttle  30  are thus positioned above the water level. The free ends of the chains  51  are connected by coupling systems  55  to the supporting column  3  and this supporting column  3  is separated at level A ( FIG. 9B ) from the part of it anchored to the seabed  4 . 
     The top end of the section of supporting column  3  is coupled via cables  56  to the hull  11  and these cables  56  are wound on drums  57  so as to allow them to be extended. 
     After these various stages, the locking assembly  60  of each element  31  of the shuttle  30  is actuated by the locks tilting so as to secure the chains  51  and accordingly the supporting column  3  of these elements  31 . The locking assemblies  65  are in an open position to allow the chains  51  to slide. 
     The elements  31  of the shuttle  30  are next raised by rotationally driving the pinions  43  by means of the geared motor units  42 , which engage with the series of teeth  22  on the plates  21  of each lifting leg  12 . Due to the chains  51  being integral with these elements  31  the section of supporting column  3  is also raised. During this displacement, the elements  31  of the shuttle  30  are first of all guided towards the vertical wall  16   a  of the bearing framework  16  of the hull  11  and by the plates  17 , as shown in  FIG. 9C . After this first operation of lifting the section of supporting column  3 , the locking assemblies  65  are actuated to lock the chains  51  and secure these chains  51  on the hull  11 . The locking assemblies  60  are opened by the locks being tilted so as to release the chains  51  of the elements  31  of the shuttle  30 . These elements  31  are lowered to bring them down substantially to the level of the hull  11 , as shown in  FIG. 9D . 
     The chains  51  are once again secured on the elements  31  by locking the assemblies  60  and these chains  51  are released from the hull  11  by opening the assemblies  65 . The elements  31  of the shuttle  30  are raised so as to also lift the section of supporting column  3  and these operations are repeated to progressively lift this section, as shown in  FIG. 9E . Next, the elements  31  of the shuttle  30  supporting the section of supporting column  3  are brought substantially to the level of the hull  11  ( FIG. 9F ) and the assembly formed by the shuttle  30  and the hull  11  is lowered to float this hull  11 , as shown in  FIG. 9G . 
     The legs  12  are raised and the structure  10  carrying the supporting column  3  is withdrawn from the production site by floatation ( FIG. 9G ). 
     The structure  10  carrying the section of supporting column  3  is floated up to a site for loading this section onto a barge  80 . 
     For this, the lifting legs  12  are applied onto the seabed  4  by rotationally driving the pinions  27  and  43  by the geared motor units  26  and  42  and when the lifting legs  12  are in contact with the seabed  4 , the hull  11  and the elements  31  of the shuttle  30  are lifted so as to bring the bottom end of the section of supporting column  3  above the water level as shown in  FIG. 9H . The barge  80  is brought beneath this section and said section is placed on the barge  80 , then the chains  51  together with the cables  56  are disconnected from the section of supporting column  3  ( FIG. 9I ). The hull  11  is then floated ( FIG. 9J ) and the legs  12  are raised to enable the structure  10  to be used for another transfer operation of the remaining part of the supporting column  3 . The barge  80  carrying the section of supporting column  3  is brought up to a disassembly quay and this section is transferred onto this quay, as shown in  FIG. 9K . 
     The structure  10  can also be used to remove the bottom part of the supporting column  3  or, if this is possible to remove the whole supporting column  3  in a single operation. 
     Finally, this structure  10  can also be used for installing a supporting column  3  of an oil platform on a production site by substantially performing the same operations in reverse. 
     In general, the order of some stages of decommissioning of the deck or of the supporting column may be reversed according to the decommissioning conditions. 
     The structure according to the invention offers the advantage of being able to transport both the deck and the supporting column of an oil platform directly from the production site onto a fixed site where the disassembly can be carried out in complete safety, without risk of polluting the marine environment or vice versa between a fixed site and a production site. 
     In addition, the various transfer and transport stages are performed without any ballasting operation, thus achieving a considerable saving in time, which is significant in regions where atmospheric conditions change very quickly.