Abstract:
This method comprises connecting a downstream point ( 40 ) of a pipe ( 24 ) to a buoy ( 26 ) and completely submerging the buoy ( 26 ). It comprises deploying in the body of water ( 12 ) an intermediate section ( 30 ) of the pipe ( 24 ) from the downstream point ( 40 ) to at least as far as an upstream point ( 38 ), anchoring the upstream point ( 38 ), and tensioning the intermediate section ( 30 ) to keep it vertical. The connecting step includes activating a traction unit ( 96 ) to raise the downstream point ( 40 ) on the buoy ( 26 ). During the connecting step, the buoy ( 26 ) is carried in the body of water ( 12 ) virtually exclusively by its own floatability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This present application is a 35 U.S.C. §§371 national phase conversion of PCT/FR2009/052124, filed Nov. 3, 2009, which claims priority of French Patent Application Nos. 08 57521 and 09 52388, filed Nov. 5, 2008, and Apr. 10, 2009 respectively, the contents of which are incorporated herein by reference. The PCT International Application was published in the French language. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method for installing an operating rig for a fluid in a body of water, of the type comprising the following steps:
         bringing a buoy to the surface of the body of water substantially facing an anchoring region on the bottom of the body of water; the buoy comprising a floatability can;   connecting a downstream point of a fluid transport pipe to the buoy, the connecting step comprising the actuation of a traction unit for raising the downstream point on the buoy;   completely immersing the buoy under the surface of the body of water before or after the connection step;   deploying in the body of water an intermediate section of the transport pipe from the downstream point to at least as far as an upstream point;   anchoring the downstream point on an anchoring element attached to the bottom of the body of water in the anchoring region;   tensioning the intermediate section of the transport pipe between the downstream point and the upstream point under the effect of the buoyancy of the buoy, in order to maintain the intermediate section substantially vertical in the body of water.       

     Such rigs are intended for transporting a fluid produced in the bottom of a body of water up to the surface through the body of water. This fluid notably consists of liquid and/or gas hydrocarbons and of water collected in production wells made in the bottom of the body of water. 
     Such a rig generally comprises a lower pipe for connecting to the production assembly positioned on the bottom of the body of water, a substantially vertical rising column, made on the basis of a flexible pipe or a rigid tube, a buoy for maintaining under tension the rising column in its vertical position, and an anchoring element of a lower point of the rising column. 
     The rig further comprises an upper flexible connecting pipe connecting the rising column to a floating surface assembly. 
     Thus, the hydrocarbons produced by the bottom assembly are successively transported through the lower connecting pipe, the rising column and the upper connecting pipe up to a surface assembly such as a ship, a platform or a barge, where they may be recovered or transported. 
     This type of rig has a relatively simple structure, since maintaining it in a vertical position is exclusively ensured by the anchoring element in the bottom of the body of water, and by the tension generated by the buoyancy of the maintaining buoy connected to the upper point of the rising column. 
     However, such rigs remain difficult to install, notably because of the depth of the body of water, as well as movements at the surface of the body of water due to swell and/or wind. 
     Thus, the lifting buoy, after having been transported on a ship as far as the site for installing the rig, has to be immersed at a sufficient depth so as not to experience the effects of the swell and of the current. For this purpose, the buoy is gradually lowered in the body of water by lifting it out of the ship with a handling crane as for example described in FR 2 911 907. 
     In order to allow the pipe to be held vertically in the body of water, the buoy has to be very voluminous, taking into account the weight of the rising column. Thus, the buoy may have a diameter of more than several meters for a height of several tens of meters. 
     The buoy generally has an elongated cylindrical shape along a vertical axis, notably for facilitating connection of the rising column to the upper connecting pipe, when this connection is carried out under the buoy. 
     Such an installation method therefore requires the availability of a ship having a lifting crane with very large capacity and a great height. 
     Such a ship is not always available. Further, the vertically elongated buoys are very unstable upon their immersion in the body of water. 
     SUMMARY OF THE INVENTION 
     An object of the invention is therefore to obtain a method for installing a rig comprising a lifting buoy, which is simple to apply, notably with ships which do not have any lifting cranes of great capacity. 
     For this purpose, the object of the invention is a method of the aforementioned type, characterized in that during the connecting step, the buoy is borne in the body of water substantially essentially by its own buoyancy. 
     The method according to the invention may comprise one or more of the following features taken individually or according to any technically possible combination(s):
         the traction unit is borne by the floatability can at least during the connecting step;   the intermediate section is flexible over substantially the whole length between the downstream point and the upstream point, the intermediate section being gradually deployed in the body of water between the downstream point attached on the buoy and a laying structure floating on the body of water during the deployment step;   the step for connecting the downstream point comprises the immersion of the downstream point from the floating laying structure in the body of water, and traction of the downstream point towards the buoy, the intermediate section occupying a chain configuration between the floating laying structure and the buoy during the deployment step;   the traction of the downstream point is achieved after complete immersion of the buoy under the surface of the body of water;   the buoy delimits a lumen for letting through the transport pipe opening out upwards and downwards, the step for connecting the downstream point comprising the introduction from bottom to top of the downstream point through the passage lumen;   the buoy has a height, taken along a vertical axis when the intermediate section is tensioned, of greater than or equal to 1.5 time its maximum transverse dimension, taken transversely with respect to the vertical axis, the step for bringing it comprising the displacement of the buoy between a remote position located away from the anchoring region and a placement position located facing the anchoring region, while maintaining the buoy partly immersed at the surface of the body of water;   the displacement of the buoy comprises the towing of the partly immersed buoy in the body of water between its remote position and its placement position by at least one floating towing structure;   the method comprises connecting on the intermediate section, a lower section intended to be connected to the bottom assembly and an upper flexible section intended to be connected to the surface assembly;   the method comprises an additional step for connecting an auxiliary connecting point located on the upper flexible section downstream from the downstream connecting point between the transport pipe and the buoy with a connecting point located on the buoy; and   the additional connecting step comprises the placement of a flexible link between the auxiliary connecting point located on the upper flexible section and the connecting point located on the buoy; and   the buoy has a height, taken along a vertical axis when the intermediate section is tensioned, of greater than or equal to 1.5 time its maximum transverse dimension, taken transversely with respect to the vertical axis.       

     Further the object of the invention is an operating rig for a fluid through a body of water, of the type comprising the following steps:
         bringing a buoy to the surface of the body of water substantially facing an anchoring region on the bottom of the body of water; the buoy comprising a floatability can;   connecting a downstream point of a fluid transport pipe to the buoy;       

     completely immersing the buoy under the surface of the body of water before or after the connection step;
         deploying in the body of water an intermediate section of the transport pipe from the downstream point to at least as far as an upstream point;   anchoring the downstream point on an anchoring element attached to the bottom of the body of water in the anchoring region;   tensioning the intermediate section of the transport pipe between the downstream point and the upstream point under the effect of the buoyancy of the buoy, in order to maintain the intermediate section substantially vertical in the body of water;   connecting onto the intermediate section a lower section intended to be connected to the bottom assembly and an upper flexible section intended to be connected to the surface assembly.   additionally connecting an auxiliary connecting point located on the upper flexible section downstream from the downstream connecting point between the transport pipe and the buoy with a connecting point located on the buoy or upstream from the buoy;       

     The method according to the invention may comprise one or more of the optional features of the method defined above, as well as one or more of the following feature(s), taken individually or according to any technically possible combination(s):
         the additional connecting step comprises the placement of a flexible link between the auxiliary connecting point located on the upper flexible section and the connecting point located on the buoy or upstream from the buoy;   the flexible link is positioned as a chain between the connecting point and the auxiliary connecting point;   the flexible link comprises an upstream region attached on the auxiliary connecting point, a downstream region attached on the connecting point and a ballast element connecting the downstream region to the upstream region;   the additional connecting step comprises rigid attachment of the auxiliary connecting point located on the upper flexible section on the connecting point located on the buoy.       

     The object of the invention is also an operating rig for a fluid through a body of water, of the type comprising:
         a fluid transport pipe immersed in a body of water, the transport pipe comprising a lower connecting section intended to be connected to a bottom assembly producing fluid, an upper flexible connecting section intended to be connected to a surface assembly and an intermediate section placed between the upper flexible section and the lower section;   an anchoring element of the transport pipe in the bottom of the body of water, connected to an upstream point of the intermediate section;   a completely immersed buoy under the surface of the body of water, the buoy including a floatability can,       

     the buoy being connected to a downstream point of the intermediate section in order to maintain the intermediate section located between the downstream point and the upstream point in a substantially vertical tensioned configuration, 
     characterized in that an auxiliary connecting point located on the upper flexible section downstream from the downstream connecting point between the buoy and the transport pipe is connected with a connecting point located on the buoy or upstream from the buoy. 
     The rig according to the invention may comprise one or more of the optional features defined above, as well as one or more of the following feature(s), taken individually or according to any technically possible combination(s):
         the buoy has a height, taken along a vertical axis when the intermediate section is tensioned, of greater than or equal to 1.5 time its maximum transverse dimension taken transversely with respect to the vertical axis,   the buoy has a height, taken along a vertical axis of less than 1.5 time relatively to its maximum transverse dimension taken transversely to the vertical axis,   the intermediate section of the transport pipe is flexible over substantially the whole of its length between the upstream point and the downstream point;   an auxiliary connecting point located on the upper flexible section downstream from the downstream connecting point between the buoy and the transport pipe is connected with a connecting point located on the buoy, advantageously through a flexible link;   it comprises a flexible link between the auxiliary connecting point located on the upper flexible section and the connecting point located on the buoy or upstream from the buoy;   the flexible link is positioned as a chain between the connecting point and the auxiliary connecting point;   the flexible link comprises an upstream region fixed on the auxiliary connecting point, a downstream region fixed on the connecting point and a ballast element connecting the downstream region to the upstream region;   the auxiliary connecting point located on the upper flexible section is rigidly attached onto the connecting point located on the buoy;   the buoy comprises an attachment arm protruding laterally from the floatability can, the connecting point being located on the attachment arm;   the buoy comprises at least one stabilization unit capable of protruding downwards from a lower surface of the floatability can;   the stabilization unit is mobile with respect to the floatability can between an upper retracted configuration in the floatability can and a lower configuration deployed downwards from the floatability can.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the following description, given only as an example, and made with reference to the appended drawings wherein: 
         FIG. 1  is a schematic view taken as a partial sectional view along a median vertical plane of a first operating rig for a fluid according to the invention; 
         FIG. 2  is a schematic perspective view of an exemplary buoy intended for the rig of  FIG. 1 ; 
         FIG. 3  is a view similar to  FIG. 1  during a first step for setting into place the rig of  FIG. 1  with the method according to the invention; 
         FIG. 4  is a similar view to  FIG. 3  during a second step of the method according to the invention; 
         FIG. 5  is a similar view to  FIG. 3  during a third step of the method according to the invention; 
         FIG. 6  is a similar view to  FIG. 3  during a fourth step of the method according to the invention; 
         FIG. 7  is a schematic side view along a median vertical plane of a second operating rig for a fluid according to the invention; 
         FIG. 8  is an enlarged schematic view of a detail of a third operating rig for a fluid according to the invention; 
         FIG. 9  is a similar view to  FIG. 8  of a fourth operating rig for a fluid according to the invention; 
         FIG. 10  is a similar view to  FIG. 8  of a fifth operating rig according to the invention; 
         FIG. 11  is a partial top view of an alternative buoy for an operating rig according to the invention; 
         FIG. 12  is a schematic perspective view of another alternative buoy for a rig according to the invention, the buoy being installed on the rig and comprising a stabilization unit in a deployed configuration; 
         FIG. 13  is a similar view to  FIG. 12 , before the installation of the rig, the stabilization unit occupying a retracted configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the whole of the following, the terms of “upstream” and “downstream” are meant relatively to the normal direction of circulation of the fluid in a pipe. 
     A first operating installation  10  for a fluid in a body of water  12 , installed by a placement method according to the invention, is schematically illustrated in  FIG. 1 . 
     This installation is intended to convey a fluid collected in the bottom  14  of the body of water  12  toward the surface  16  of the body of water. 
     The collected fluid is for example a hydrocarbon gas or liquid stemming from a well (not shown) made in the bottom  14  of the body of water. 
     The body of water  12  is a lake, a sea or an ocean. The depth of the body of water  12 , taken between the surface  16  and the bottom  14  facing the installation  10  is greater than 30 m and is for example comprised between 30 m and 3,500 m. 
     The installation  10  comprises a fluid production assembly  18  located on the bottom of the body of water, a first rig  20  according to the invention and a surface assembly  22  intended for recovering and storing the fluid collected in the fluid production assembly  18  conveyed through the rig  20 . 
     The fluid production  18  for example comprises at least one well head and/or production line (not shown) located on the bottom  14  of the body of water. 
     The surface assembly  22  in this example is a floating assembly. For example it is formed by a ship, a barge, a floating platform or a floating unit for recovering, storing and treating hydrocarbons, designated by the acronym of &lt;&lt;FPSO&gt;&gt; (Floating Production Storage and Offloading). The surface assembly alternatively is a Floating Storage and Regasification Unit designated by the acronym of &lt;&lt;FSRU&gt;&gt;. 
     The surface assembly  22  floats on the body of water in the vicinity of the fluid production assembly  18 . 
     The rig  20  according to the invention comprises a fluid transport pipe  24  connecting the bottom assembly  18  to the surface assembly  22 , an anchoring element  25  of the pipe  24 , attached in the region of anchoring on the bottom  14 , and a buoy  26  for maintaining under tension at least one intermediate section of the transport pipe  24  in a substantially vertical configuration in the body of water  12 . 
     The transport pipe  24  comprises, from bottom to top in  FIG. 1 , a lower section  28  for connecting to the fluid production assembly  18 , an intermediate section formed by a substantially vertical rising column  30 , a fitting  32  and an upper section  34  for connecting to the surface assembly  22 . 
     In this example, the transport pipe  24  is flexible over substantially the whole of its length, taken between the fluid production assembly  18  and the surface assembly  22 . 
     The lower section  28  is for example formed with a lower connecting pipe  36  extending in a bent or tilted way with respect to the bottom  14  of the body of water  12 . The lower connecting pipe  36  is connected upstream to the fluid production assembly  18  and is connected downstream to the rising column  30 . 
     The rising column  30  extends substantially vertically along a vertical axis A-A′ in the body of water  12 , between a lower upstream point  38 , connected to the anchoring element  25  and an upper downstream point  40  connected to the buoy  26 . 
     In this example, the rising column  30  is formed with a flexible pipe  42  over substantially the whole of its length. 
     By &lt;&lt;flex&gt;&gt; or &lt;&lt;flexible pipe&gt;&gt; is meant in the sense of the present invention a pipe as described in the normative documents published by the American Petroleum Institute (API), API 17J and API RP17B, well known to one skilled in the art. This definition equally encompasses flexible pipes of the unbounded or bounded type. 
     More generally and alternatively, the flexible pipe  42  may be a composite bundle of the &lt;&lt;bundle&gt;&gt; type comprising at least one fluid transport tube and one set of electrical or optical cables capable of conveying electrical or hydraulic power or a piece of information between the bottom  14  and the surface  16  of the body of water. 
     An exemplary flexible pipe is described in French application FR 2 911 907. 
     Such a flexible pipe has a relatively small minimum radius of curvature in flexure without any damage (MBR or minimal bending radius), for example of a few meters which makes it particularly able to be wound and unwound reversibly without any significant plastic deformation on a drum or a basket, the drum or the basket being borne by a laying ship, as this will be seen below. 
     The length of the rising column  30 , taken between the upper downstream point  40  and the lower upstream point  38  is greater than 20 m and for example is comprised between 500 m and 3,500 m. 
     The fitting  32 , typically a goose neck, is in this example attached on the buoy  26 . It is connected upstream to the upper downstream point  40  of the rising column  30 . It is connected downstream to the upper section  34 . 
     In this example, the fitting  32  is formed with a rigid tube with the shape of a goose spout. 
     Alternatively, the fitting  32  is formed with a flexible pipe as described above, for example provided with curvature limiters or floatability elements. 
     The upper section  34  is formed with an upper flex  50  extending between the fitting  32  and the surface assembly  22 . 
     The upper flex  50  has a substantially J-shaped catenary configuration. 
     The upper flex  50  is deformable in order to absorb the movements of the surface assembly  22  due to the perturbations of the body of water such as due to the swell, current or wind. The upper section  34  thus substantially prevents transmission of these movements from the surface assembly  22  to the rising column  30 , the upper downstream point  40  of which remains substantially motionless in the body of water. 
     The lower section  28 , the rising column  30 , the intermediate fitting  32 , and the upper section  34  interiorly define a continuous passage  52  for fluid circulation extending between the fluid production assembly  18  and the surface assembly  22  in order to allow transport of the fluid between these assemblies  18 , 22 . 
     In this example, the anchoring element  25  comprises an anchoring unit  60  attached in the anchoring region on the bottom  14  of the body of water and a flexible line  62  connecting the anchoring unit  60  to the upstream point  38  of the rising column. 
     The anchoring unit  60  is for example formed with a stack housed in the bottom  14  of the body of water or with a suction anchor. 
     The flexible line  62  extends vertically along the axis A-A′ between the anchoring unit  60  and the lower upstream point  38 . 
     According to the invention, the buoy  26  is of a substantially flat shape when the rig  20  is mounted in the body of water  12 . 
     The buoy  26  thus has a height, taken along the axis A-A′ of less than its maximum transverse dimension, taken perpendicularly to the axis A-A′. 
     As illustrated by  FIG. 2 , the buoy  26  is advantageously of a cylindrical shape of axis A-A′. The height H of the buoy is advantageously less than 1.5 times, notably less than or equal to once the maximum transverse dimension of the buoy, which in this example is the diameter D of the cylinder. 
     Alternatively, the height H of the buoy is greater than or equal to 1.5 times the maximum transverse dimension of the buoy. 
     The buoy  26  comprises a floatability can  70  interiorly delimiting at least one sealed compartment  72  capable of being selectively filled with gas or liquid, and selective means  74  for filling the compartment  72  with liquid and gas. 
     The buoy  26  further comprises means  76  for connecting to the downstream point  40  of the rising column  30 , visible in  FIG. 1 . 
     In the example illustrated in  FIGS. 1 and 2 , the floatability can  70  delimits a through-lumen  78  of axis A-A′ for letting through the rising column  30 . The lumen  78  opens out upwards and downwards on either side of the can  70 . 
     Said or each compartment  72  extends around the lumen  76  in the can  70 . 
     The filling means  74  are capable of selectively introducing gas or liquid into said or each compartment  72  in order to selectively increase or decrease the buoyancy of the buoy  26 . 
     In the example illustrated in  FIG. 1 , the connecting means  76  comprise at least one attaching collar  80 , attached on the downstream point  40  of the rising column  30 . 
     The rising column  30  is introduced into the lumen  78  as far as its downstream point  40 . The downstream point  40  is firmly attached to the buoy  26  via the collar  80 . 
     The fitting  32  protrudes from an upper surface  82  of the buoy  26 . 
     A first method for setting into place the installation  10  according to the invention will now be described with reference to  FIGS. 3 to 6 . 
     This method is applied by means of a ship  90  for laying the transport pipe  24  and by means of at least one ship  92 A,  92 B for towing the buoy  26 , distinct from the laying ship  90 . In the example illustrated in  FIG. 3 , the method is applied by means of two tug boats  92 A,  92 B. 
     Initially, the pipe elements namely, connecting pipe  36 , flexible pipe  42 , and upper flex  50  intended to form the transport pipe  24  are brought to the vicinity of the fluid production assembly  18  by means of the laying ship  90 . 
     For this purpose, the connecting pipe  36 , the upper flex  50  and the flexible pipe  42  are transported by the laying ship  90  while for example being wound on a laying drum or in a basket. 
     The anchoring element  25  is installed in the bottom of the body of water in the vicinity of the fluid production assembly  18 . For this purpose, the anchoring unit  60  is attached in the bottom  14  of the body of water. 
     According to the invention, the buoy  26  is towed while being partly immersed, with its upper surface  82  located out of the body of water  12 , between a remote position away from the anchoring region of the element  25  and a placement position substantially located facing and above the anchoring region of the element  25 . 
     During this transport, the buoy  26  extends substantially horizontally with its axis A-A′ being vertical. 
     As the buoy  26  has a substantially flat shape, it is not very sensitive to the movements of the surface  16  of the body of water  12 , and notably to the swell, to the current or to the wind, so that it may be transported safely while only being partly immersed in the body of water  12 , by means of the tug boats  92 A,  92 B. It is also a work station by means of its wide flat upper surface  82 . 
     The towing distance of the buoy  26 , which horizontally separates the remote position from the placement position is greater than a few hundreds of meters, or even several hundreds of kilometers. 
     In one alternative, the buoy  26  is loaded on board a partly submersible barge, and is then immersed in the water by immersion of the barge, before being towed. 
     Next, when the buoy  26  occupies its placement position illustrated in  FIG. 3 , it is maintained in the horizontal position by the tug boats  92 A,  92 B by means of deployable mooring lines  94 . 
     A traction device  96  is then mounted on the buoy  26 , for example on its upper surface  82 . This traction device  96  is notably formed by a winch  96  including a deployable traction line  98 . 
     The line  98  is unwound so as to be introduced from top to bottom through the central lumen  78  of the buoy  26 . The line  98  is then brought as far as the laying ship  90  in order to be connected to the flexible pipe  42  at the upper downstream point  40 . 
     The winch  96  is then actuated in order to bring the upper downstream point  40  closer to the buoy  26 , by retracting an increasing length of the line  98  onto the winch  96 . Simultaneously, an increasing length of the flexible pipe  42  is unwound out of the laying ship  90 . The flexible pipe  42  adopts a substantially U catenary shape between the laying ship  90  and the buoy  26 . 
     As the distance separating the laying ship  90  from the buoy  26  is relatively large, for example of more than 50 m, the radius of curvature of the flexible pipe  42  in this configuration is large in order to prevent any damage of the flexible pipe  42 . 
     Further as the weight of the flexible pipe  42  is distributed among the laying ship  90  and the buoy  26 , it is not necessary to provide the buoy  26  or the laying ship  90  with a large capacity winch  96 . 
     Traction of the line  98  is continued until the fitting  32  and the upper downstream point  40  enter the lumen  78  from the bottom, and then move upwards along the lumen  78  before being extracted out of the lumen  78  from the top. 
     In this configuration, the fitting  32  protrudes upwards from the upper surface  82 . The upper downstream point  40  is substantially located at the upper surface  82 . 
     The attaching collar  80  is then set into place in order to immobilize the upper downstream point  40  relatively to the buoy  26 . 
     The traction line  98  is then disconnected from the upper downstream point  40  and the winch  96  is disassembled away from the buoy  26 . 
     The mooring lines  94  are then released and the filling means  74  are actuated in order to introduce liquid into the compartments  72  in order to reduce the buoyancy of the buoy  26 . 
     The buoy  26  is then moved down and completely immersed in the body of water  12 , down to a depth of more than several tens of meters, in a region of the body of water  12  which is not affected by the swell or the waves, as illustrated in  FIG. 5 . 
     The buoy  26  retains its horizontal orientation upon moving down, with its axis A-A′ substantially vertical along its height. 
     A corresponding length of the flexible pipe  42  is unwound out of the laying ship  90 . 
     The increasing weight of the deployed flexible pipe  42  promotes the moving down of the buoy  26  into the body of water  12 . 
     Next, the deployment of the flexible pipe  42  is continued until the lower upstream point  38  is located in the vicinity of the surface  16  of the body of water. 
     The flexible pipe  42  is then completely immersed and the lower upstream point  38  is moved down under the upper downstream point  40  as far as the vicinity of the bottom  14  facing the anchoring element  25 . 
     The lower upstream point  38  of the flexible pipe  42  is then attached on the anchoring unit  60  via the anchoring line  62 . 
     A connecting pipe  36  is moved down with a deployed release line  100  from the laying ship  90 , as illustrated by  FIG. 6 . 
     The connecting pipe  36  is then connected to the rising column  30  and onto the bottom assembly  18  in order to form the lower section of the transport pipe  24 . 
     Next, the buoyancy of the buoy  26  is optionally modified in order to apply between the upper downstream point  40  and the lower upstream point  38 , via the buoy  26 , a tractive force directed upwards, this force being compensated by the retaining force provided by the anchoring line  62 . 
     The flexible pipe  42  thus forms, between the lower upstream point  38  and the upper downstream point  40 , a rising column  30  extending vertically along the axis A-A′, maintained in a vertical position and tensioned along the axis A-A′ between the buoy  26  and the anchoring element  25 . 
     Next, the upper flex  50  is moved down into the body of water  12  in order to be connected to the fitting  32  and to the surface assembly  22 , thereby forming the upper section  34  of the pipe  24 . 
     The continuous passage  52  for circulation of hydrocarbons between the fluid production assembly  18  and the surface assembly  22  is then successively established through the lower section  28 , the rising pipe  30 , the fitting  32  and the upper section  34 . The fluid collected by the fluid production assembly  18  is then transported up to the surface assembly  22  through the passage  52 . 
     In an alternative installation method described earlier, the buoy  26  is immersed under the body of water, before the upper downstream point  40  of the rising column  30  is attached onto the buoy. 
     The buoy  26  is then provided with an actuatable winch  96  while being immersed under the body of water  12 . 
     A second installation  120  according to the invention is illustrated in  FIG. 7 . Unlike the rig  20  of the first installation  10 , the rig  20  of the second installation  120  comprises a buoy  26  positioned above the upper downstream point  40  and above the fitting  32 . 
     The connecting means  76  comprise a ring  122  firmly attached to the flexible pipe  42  at the upper downstream point  40  and a flexible chain  124  connecting the ring  122  to a lower surface  126  of the buoy  26 . 
     By means of the invention which has just been described, it is possible to tow the buoy  26  from the rig  20  as far as its placement position by having it float on the body of water  12 . It is therefore not necessary to convey it on a laying ship equipped with a large capacity crane and to lower it into the body of water with the large capacity crane. 
     Further, the method for placing the rig  20  is notably facilitated by the placement of a large capacity winch on the buoy  26  in order to pull the upper downstream point  40  of the rising column  30  and to deploy this pipe as a chain between the laying ship  90  and the buoy  26 . 
     The buoy  26  is moreover stable upon its immersion into the body of water  12 . It substantially retains its orientation during its downward motion, which facilitates its handling. 
     In an alternative (not shown), the lower section  28  of the pipe  24  is formed by a rigid tubular element which cannot be wound onto a drum or in a basket without any substantial plastic deformation. 
     In this case, the rising column  30  is flexible over substantially the whole of its length. 
     In another embodiment, the upstream point  38  of the flexible pipe  42  is directly attached on the anchoring unit  60  immobilized in the bottom of the body of water  12  without using any flexible anchoring line  62 . 
     According to the invention and as illustrated in  FIGS. 3 and 4 , during the connecting step, the buoy  26  is borne in the body of water  12  substantially exclusively by its own buoyancy, either at the surface  16  of the body of water  12 , while being partly immersed, or under the surface  16 , away from the bottom  14 , while being completely immersed. 
     This means that during this step, for example at least 90% of the vertical force directed upwards, opposing the weight of the buoy  26  is generated by the specific floatability of the buoy  26 , resulting from the pressure force, the so-called buoyancy force. 
     During this step, the buoy  26  is therefore not suspended while being retained upwards by a traction line attached on its upper surface, such as for example a line of a crane borne by a ship. 
     A third operating installation  130  according to the invention is illustrated in  FIG. 8 . 
     Unlike the first installation  10 , the upper section  34  is connected onto the rising column  30  at the buoy  26 , for example on the upper surface of the floatability can  70 . The rig  20  is without any gooseneck spout rigid fitting  32 . 
     The upper section  34  comprises, from upstream to downstream, a first substantially vertical section  132  connected to the buoy, a second curved section  134  with the shape of a U with its concavity directed downwards, a third curved section  136  with the shape of a U with its concavity directed upwards  136  and a fourth substantially vertical section  138  connected to the surface assembly  22 . 
     The first section  132  and the second section  134  are provided with floats  140  distributed over their length in order to ensure that the flexible upper section  34  is maintained in a wave configuration, designated by the term of “steep-wave”. 
     The rig  20  further comprises a means  142  for limiting the torsional movements of the rising column  30 . In this example, the means  142  is formed by a continuous flexible link  144  connecting a first connecting point  146  located on the buoy  26  to an auxiliary connecting point  148  located on the upper flexible section  34  away from the connection point between the rising column  30  and the upper section  34 , and away from the upper downstream point  40  on the buoy  26 . 
     In the example illustrated in  FIG. 8 , the link  144  is substantially continuous over the whole of its length. It is hung as a chain between the points  146 ,  148 . 
     The connecting point  146  is located on a side surface of the floatability can  70  located on the same side as the third section  136  of the flexible upper section  34 . 
     The auxiliary connection point  148  is located on a rising portion of the third U-shaped section  136  away from the lowest point. 
     The buoy  26  further comprises a ballast element  149  located opposite the connecting point  146  with respect to a vertical axis of the can  70 , in order to compensate the weight of the flexible link  144 . 
     At least one portion of the transport pipe  24  with non-zero length extends between the upper downstream point  40  located on the buoy and the auxiliary connecting point  148  located above and away from the buoy  26 . 
     During the manufacturing method, the flexible link  144  is mounted between the connecting point  146  and the auxiliary connecting point  148 , once the upper section  34  is connected to the rising column  30 . 
     The flexible link  144  then generates a frictional force in the water, substantially perpendicular to the vertical axis A-A′ of the rising column  30  preventing or limiting torsion of this column  30 . 
     A fourth installation  150  according to the invention is illustrated in  FIG. 9 . Unlike the third installation  130 , the flexible link  144  forming the means  142  for limiting torsion includes an upstream flexible region  152  attached on the connection point  146 , a downstream flexible region  154  attached on the auxiliary connecting point  148  and a ballast element  156  connecting the upstream flexible region  152  and the downstream flexible region  154  to their lower points. 
     Thus, the flexible link  144  substantially has the shape of a V. 
     The mounting and operation of the fourth installation  150  is moreover identical with that of the third installation  130 . 
     A firth installation  160  according to the invention is illustrated in  FIG. 10 . 
     Unlike the third installation  130  illustrated in  FIG. 8 , the transport pipe  24  comprises a gooseneck spout fitting  32  interposed above the buoy  26 . 
     The auxiliary connection point  148  is located at the upstream end of the flexible upper section  34 , or slightly downstream from this end. It is rigidly attached to a connection point  146  defined on the periphery of the floatability can  70 . 
     In this configuration, the upper flexible section  34  has a catenary shape with a lower section  162  substantially with the shape of a U with concavity directed downwards and an upper substantially vertical section  164  connected to the surface assembly  22 . 
     In this case, the limiting means  142  are formed by the rigid connection between the auxiliary connecting point  148  and the connecting point  146 . 
     In the alternative illustrated in  FIG. 11 , the buoy  26  has two connecting side arms  170 A,  170 B which are connected to the floatablility can at  171  and protrude laterally away from the floatability can. Each side arm  170 A,  170 B has a free end  172  connected to the other arm at  173  in order to thereby define a support with a general triangular shape. 
     The attachment point  146  is located at the free ends  172 , radially away from the periphery of the floatability can  70 . 
     In another alternative, illustrated in  FIGS. 12 and 13 , the buoy  26  comprises a stabilization unit  180  moveably mounted in the central lumen  78  of the floatability can  70 . 
     The stabilization unit  180  is formed with a vertical rigid hollow tube  182  provided at its ends with abutment flanges  184 ,  186 . It interiorly defines a channel  188  for letting through the transport pipe  24 . 
     The stabilization unit  180  is moveably mounted in the floatability can  70  along a vertical axis A-A′ between a retracted upper configuration, illustrated in  FIG. 13  and a deployed lower configuration illustrated in  FIG. 12 . 
     In the retracted upper configuration, used during the transport of the can  70  on the ship, the rigid tube  182  protrudes upwards from an upper surface  190  of the floatability can  70 . The length of the rigid tube  182  protruding downwards from a lower surface  192  of the floatability can  70  is minimal or even zero. The draught of the buoy  26  is thus substantially equal to that of the floatability can  70 . 
     In the deployed configuration illustrated in  FIG. 12 , the tube  182  has been moved downwards. Its protruding length from the lower surface  192  is maximum. The draught of the buoy  26  is then much larger than that of the floatability can  70 , which increases the stability of the buoy  26  when it is partly immersed in the body of water. 
     The end flange  184  is positioned so as to bear upon the upper surface  190  in order to retain the tube  182 . 
     In this configuration, the transport pipe  24  is positioned through the channel  188  as illustrated in  FIG. 12 .