Abstract:
A method includes the positioning of a rising column ( 22 ) in a vertical configuration and the total immersion of a buoy for retaining the rising column ( 22 ). 
     The method includes the insertion of a male connecting member ( 62 ) borne by the buoy in a female connecting member ( 64 ) borne by the rising column ( 22 ) and the immobilization of the male connecting member ( 62 ) in a receiving passage ( 92 ) defined by the female connecting member ( 64 ). 
     The female connecting member ( 64 ) includes at least one surface ( 98 ) for guiding the male connecting member ( 62 ) towards the receiving passage ( 92 ). The insertion step including the guiding of the male connecting member ( 62 ) towards the receiving passage ( 92 ) by contact with a guiding surface ( 98 ) of the female connecting member ( 64 ) which has a vertical section diverging away from the receiving passage ( 92 ) towards the male connecting member ( 62 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a 35 U.S.C. §371 National Phase conversion of PCT/FR2009/051214, filed Jun. 25, 2009, which claims benefit of French Application No. 08 54337, filed Jun. 27, 2008, the disclosure of which is 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 setting up a hybrid tower in an expanse of water, of the type comprising the following steps:
         positioning and temporarily retaining a rigid rising column in a substantially vertical configuration in the expanse of water,   totally immersing a buoy for retaining the rising column and displacing the retaining buoy facing the rising column;   inserting a male connecting member borne by a first of the rising column and of the retaining buoy, into a female connecting member borne by a second of the rising column and of the retaining buoy;   immobilizing the male connecting member in a receiving passage defined by the female connecting member       

     Such a hybrid tower is for example mounted in an expanse of water such as a lake, a sea or an ocean in order to connect fluid exploitation wells opening out into the bottom of the expanse of water to an assembly for storing and/or discharging this fluid, located at the surface. 
     For this purpose, the hybrid tower generally comprises a substantially vertical rigid rising column anchored on the bottom of the expanse of water. The rising column is maintained in a vertical configuration by a buoy totally immersed under the expanse of water and attached to the upper end of the column. 
     A flexible member connects the upper end of the rising column to the surface assembly. 
     The fluid to be exploited is thereby conveyed between the bottom of the expanse of water and the surface, successively through the rising column and the flexible pipe. 
     Such a hybrid tower is generally set up in the expanse of water by first of all positioning on the bottom of the expanse of water, a lower connecting assembly comprising a foundation, such as a suction pile or a gravity baseplate and a bent connecting joint which is mounted at the end of an exploitation line stemming from the fluid wells. 
     And then the rising column, provided with an upper connecting joint is immersed in the expanse of water and is positioned in a vertical position. It is then maintained temporarily in a vertical position by mooring to the laying surface ship. 
     This column is for example lowered by a so-called J-laying method or by an S-laying method. Alternatively, this column may be made onshore and towed onto the installation site before being immersed. 
     Next, the retaining buoy is immersed and then tilted into the vertical position, before connecting it onto a connecting joint at the upper end of the rising column. 
     For this purpose, the connecting means between the buoy and the rising column for example comprise a rod borne by the buoy, and connected to the latter through a chain, and a mandrel for tightening the rod, borne by the rising column. During the connection of the buoy, the rod is introduced into the mandrel before being immobilized in position. 
     The floatability of the buoy generates a force pulling the rising column upwards, which retains the pipe in its vertical configuration. The temporary mooring means on the laying ship are then released. 
     Such a method does not give entire satisfaction. Indeed, the connection of the buoy on the rising column is carried out in an immersed medium at several tens of meters under the sea level. As the high portion of the rising column is subject to currents and to swell, it generally oscillates around a vertical central position. 
     Further, the buoy is often very bulky, since the hybrid towers are capable of having a height of more than 1,500 meters. Thus the buoy should have a diameter of more than several meters for a height of several tens of meters. It is therefore very difficult to maneuver it specifically under the expanse of water. 
     SUMMARY OF THE INVENTION 
     An object of the invention is therefore to provide a method for setting up a hybrid tower which is simpler to apply, notably when the current or/and the swell are strong. 
     For this purpose, the object of the invention is a method of the aforementioned type, characterized in that the female connecting member comprises at least one surface for guiding the male connecting member towards the receiving passage, the guiding surface opening out around the receiving passage and having a vertical section diverging away from the receiving passage towards the male connecting member upon introducing the male connecting member into the female connecting member, the insertion step comprising the guiding of the male connecting member towards the receiving passage by contact with the guiding surface. 
     The method according to the invention may comprise one or more of the following features, taken individually or according to all technically possible combinations:
         the one of the male connecting member and of the female connecting member borne by the retaining buoy is mounted so as to be transversally mobile relatively to the retaining buoy between an axial rest configuration substantially parallel to a vertical axis A-A′ and a guiding configuration tilted by a non-zero angle relatively to the vertical axis A-A′, the insertion step comprising the displacement of the one of the male connecting member and of the female connecting member borne by the retained buoy between its axial configuration and its tilted configuration during the contact of the male connecting member with the guiding surface,   the retaining buoy is connected to the one of the male connecting member and of the female connecting member borne by the retaining buoy by a substantially vertical line, the one of the male connecting member and of the female connecting member borne by the retaining buoy being pivotally mounted around a transverse axis on the line,   the immobilization step comprises the clamping of the male connection member by an immobilization clamp mounted on the female connecting member,   the method comprises, after the immobilization step, a step for connecting on the rigid rising column a flexible pipe for connecting to a surface assembly, the flexible connecting pipe being connected in the vicinity of the male connecting member and of the female connecting member.       

     The object of the invention is also a hybrid tower intended to be positioned in an expanse of water, comprising:
         an rising rigid column intended to be positioned according to a vertical configuration in the expanse of water;   a retaining buoy of the rising column, the retaining buoy being intended to be totally immersed in the expanse of water,   means for connecting the retaining buoy to an upper end of the rising column, the connecting means comprising a male connecting member borne by a first of the retaining buoy and of the rising column, and a female connecting member borne by a second of the retaining buoy and of the rising column;       

     the male connecting member and the female connecting member being mobile relatively to each other between a disconnected position and a connected position in which the male connecting member is received in a receiving passage defined by the female connecting member; 
     characterized in that the female connecting member delimits a surface for guiding the male connecting member opening out into the receiving passage, the guiding surface diverging away from the receiving passage towards the male connecting member upon introducing the male connecting member into the female connecting member. 
     The hybrid tower according to the invention may comprise one or more of the following features, taken individually or according to all technically possible combinations:
         the guiding surface is a solid surface.   the guiding surface is of a substantially frusto-conical shape.   the one of the male connecting member and of the female connecting member borne by the retaining buoy are mounted so as to be transversally mobile relatively to the retaining buoy between an axial rest configuration substantially parallel to a vertical axis A-A′ and a guiding configuration tilted by a non zero angle relatively to the vertical axis A-A′,   the retaining buoy is connected to the one of the male connecting member and of the female connecting member borne by the retaining buoy by a substantially vertical line, the one of the male connecting member and of the female connecting member borne by the retaining buoy being pivotally mounted around a transverse axis on the line,   the connecting means comprise a clamp for immobilizing the male connecting member in the receiving passage, the immobilization clamp being mounted on the female connecting member,   the hybrid tower comprises a flexible pipe connecting with a surface assembly, the flexible connecting pipe being connected to the rigid rising column in the vicinity of the connecting means.       

     The object of the invention is also an installation for exploiting a fluid in an expanse of water, which comprises:
                    a surface assembly;              a hybrid tower as defined above, the rigid rising column being fixed on the bottom of the expanse of water, the retaining buoy being connected to an upper end of the rigid rising column by immobilization of the male connecting member in the female connecting member.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood upon reading the description which follows, only given as an example, and made with reference to the appended drawings, wherein: 
         FIG. 1  is a partial side schematic view of a first hybrid tower according to the invention, connected to a surface assembly with view to exploiting a fluid; 
         FIG. 2  is a view analogous to  FIG. 1 , during the connection of the buoy on the rising column of the hybrid tower of  FIG. 1 ; 
         FIG. 3  is an enlarged view, taken as a partial sectional view along a median vertical plane, of connection means between the buoy and the rising column during a first connection step; 
         FIG. 4  is a view analogous to  FIG. 3 , during a second connection step; 
         FIG. 5  is a view analogous to  FIG. 3  during a third connection step; 
         FIG. 6  is a view analogous to  FIG. 3  at a larger scale during a fourth connection step; 
         FIG. 7  is a sectional view along the horizontal plane VII of  FIG. 6 , before immobilization of the male connecting member in the female connecting member; 
         FIG. 8  is a view analogous to  FIG. 7  after immobilization of the male connecting member in the female connecting member. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first installation  10  for exploiting a fluid in an expanse of water  12 , set up by an installation method according to the invention is schematically illustrated in  FIG. 1 . 
     This installation  10  is intended to convey a fluid collected at the bottom  14  of the expanse of water  12  towards the surface  16 . The collected fluid is for example a hydrocarbon gas or liquid from a well (not shown) made in the bottom  14  of the expanse of water. 
     The expanse of water  12  is a lake, a sea or an ocean. The depth of the expanse of water  12 , taken between the surface  16  and the bottom  14  is greater than 30 meters and is for example comprised between a 1,000 meters and 3,000 meters. 
     The installation  10  comprises an assembly  18  for recovering and storing hydrocarbons at the surface and a hybrid tower  20  according to the invention connecting a well head or a production line (not shown) located on the bottom  14  of the expanse of water to the surface assembly  18 . 
     The surface assembly  18  is for example a ship, a barge or a floating platform for recovering, storing or treating hydrocarbons. 
     According to the invention, the hybrid tower  20  comprises a rigid rising column  22  substantially extending along a vertical axis A-A′ between the bottom  14  and an upper end  24  located under the surface  16  of the expanse of water  12 . 
     It also comprises a totally immersed floatability assembly  26  in order to permanently maintain the rigid rising column  22  in its vertical configuration, and means  28  for connecting the floatability assembly  26  on the upper end  24  of the rigid rising column  22 . 
     The hybrid tower  20  further comprises a flexible pipe  30  for connection with the surface assembly  18  connecting the rising column  22 , in the vicinity of its upper end  24 , to the surface assembly  18 . This flexible pipe  30  is for example of the bonded or unbonded type as described in the normative documents published by the American Petroleum Institute (API), API 17J and API 17B. 
     The rigid rising column  22  comprises a vertical fluid transport pipe  32 , means  34  for anchoring the lower end of the pipe  32  in the bottom  14  of the expanse of water  12 , and an upper gooseneck connection  36  defining the upper end  24  of the rising column  22 . The upper connection  36  is mounted on an arm  37 . 
     The transport pipe  32  is a rigid pipe for example made by assembling metal tubes mounted end to end. 
     The pipe  32  interiorly defines a vertical passage  38  for transporting hydrocarbons. 
     The anchoring means  34  for example comprise a foundation, such as a suction pile or a gravity baseplate fixed in the bottom  14  of the expanse of water  12  and a bent connecting joint (not shown) connected to a line for collecting hydrocarbons and/or to a production well. 
     The upper connecting joint  36  comprises a main section  40  obturating the vertical passage  38  upwards and a mounting bypass  42  of the flexible pipe  30 . 
     The flexible pipe  30  extends as a catenary between the surface installation  18  and the upper connecting joint  36 . 
     The flexible pipe  30  delimits an inner lumen (not shown) for the circulation of hydrocarbons, hydraulically connected to the vertical passage  38  through the upper connecting joint  36 . 
     The floatability assembly  26  comprises a buoy  50  for retaining the pipe  32 , totally immersed under the expanse of water  12 , the buoy  50  delimiting at least one inner floating compartment  52  at least partly filled with air. 
     The buoy  50  is for example made on the basis of a hollow metal or plastic box delimiting one or more compartments  52 . 
     The retaining buoy  50  extends vertically along the axis A-A′ when it is attached onto the column  22 . It is dimensioned in order to exert through its floatability, a tractive force upwards on the rising column  22  opposing the weight of the column  22  in order to maintain it in its vertical configuration along the axis A-A′ autonomously, in the absence of other upward traction means. 
     The height of the buoy  50  taken along the axis A-A′, is thus greater than several meters, or even several tens of meters, and its width is greater than one meter. 
     According to the invention, the connection means  28  comprise a flexible line  60  attached under the retaining buoy  50 , a male connecting member  62  attached to the lower free end of the flexible line  60  in order to be borne by the retaining buoy  50 , a female connecting member  64 , integral with the upper end  24  of the rising column  22 , and a clamp  66  for immobilizing the male connecting member  62  in the female connecting member  64 . 
     As illustrated by  FIGS. 1 and 2 , the flexible line  60  comprises a chain  70  which has at its lower end a Cardan joint  72 , on which the male connecting member  62  is jointed. 
     When the male member  62  is immobilized in the female member  64  and when the buoy  50  exerts a tractive force upwards, the flexible line  60  is tensioned between its ends so as to extend coaxially with the rising column  22  along the axis A-A′. 
     As illustrated by  FIGS. 3 to 6 , the male connecting member  62  is formed by a torpedo which comprises, from top to bottom in the figures, a fork joint  74  on the Cardan joint  72 , an upper guiding portion  76 , an intermediate portion  78  for insertion into the female member  64 , a thinned lower portion  80  and a retaining endpiece  82 . 
     The fork  74  is pivotally mounted around a transverse axis in the Cardan joint  72  via a pivot  83 . 
     The upper portion  76  has a cylindrical upper region  84  and a chamfered lower region  86  intended to bear against the female member  64 . 
     The diameter of the upper portion  76  in the upper region  84  is greater than the average diameter of the intermediate portion  78 , which is greater than the average diameter of the thinned lower portion  80 . 
     The intermediate portion  78  is also of a generally cylindrical shape extended downwards by a chamfer which converges around the thinned portion  80 . 
     The endpiece  82  has the general shape of a half sphere, with convexity directed downwards. It delimits an upper surface  88  converging upwards around the thinned portion. The upper surface  88  protrudes radially with respect to the thinned portion  80  and forms a retaining abutment intended to co-operate with the immobilization clamp  66 , as this will be seen below. 
     The male connecting member  62  is transversally mobile with respect to the axis A-A′ of the line  60  and of the buoy  50 , by free rotation around the pivot  83 , between an axial rest configuration substantially coaxial with the axis A-A′ and a configuration tilted by a non-zero angle relatively to the A-A′ axis for introducing a male member  62  into the female member  64 , as this will be seen below. 
     The female member  64  comprises, from bottom to top in  FIGS. 2 to 6 , a lower sleeve  90  delimiting a receiving passage  92  for immobilizing the male member  62 , and a funnel  94  for guiding the male member  62  towards the receiving passage  92 . 
     The sleeve  90  is of a generally cylindrical tubular shape. It is attached at its periphery onto the arm. It delimits a lower flange  96  for attaching the immobilization clamp  66 . 
     The passage  92  extends along the axis A-A′ of the rising column  22 . It opens out downwards into the arm  37  and upwards into the funnel  94 . 
     The length of the passage  92  is smaller than the length of the male member  62  so that when the male member  62  is inserted into the passage  92 , upon abutment against the funnel  94 , the retaining endpiece  82  protrudes out of the passage  92 . 
     The passage  92  has a constant cross section over its length, combined with the section of the intermediate portion  78  of the male member  62 . 
     The funnel  94  extends in the axial extension of the sleeve  90 , above the latter. In the example illustrated in the figures, it is made with the sleeve  90  out of the same material. 
     The funnel  94  interiorly defines around the axis A-A′, a surface  98  for guiding the male member  62 . 
     The guiding surface  98  is a solid surface which has a section, taken in a vertical axial plane, which diverges from and away from the passage  92  upwards and towards the male member  62  upon introducing the male member into the female member  64 . Alternatively, the surface  98  is openworked. 
     The guiding surface  98  is thus frusto-conical with an aperture angle α, taken in at least one vertical axial plane, greater than 20° and advantageously substantially equal to 25°. 
     The minimum transverse extent of the guiding surface  98 , taken along its free edge located away from the sleeve  90 , is greater than about 1 meter. 
     As this will be seen in detail below, the male member  62  is axially mobile relatively to the female member  64 , between an upper disconnected position illustrated in  FIG. 2 , in which the male member  62  is located above and axially away from the female member  64 , an intermediate guiding position, illustrated in  FIG. 4 , in which the male member  62  is partly introduced into the funnel  94  and a lower connected position, illustrated in  FIG. 6 , in which the male member  62  is inserted into the passage  92 . 
     As illustrated by  FIGS. 7 and 8 , the immobilization clamp  66  comprises a base  99  attached under the female member  64 , two mobile jaws  100 ,  102  facing each other in order to clasp the retaining endpiece  82  and a controllable screw  104  for tightening the jaws  100 . 
     The jaws  100 ,  102  are jointed on the base  99  around an axis parallel to the vertical axis A-A′ so as to be moved in a substantially horizontal plane. 
     The base  99  and the jaws  100 ,  102  define between them an opening  106  for inserting the endpiece  82 , with variable section and controlled by the displacement of the screw  104 . 
     The screw  104  is transversally mounted between the free ends  108  of the jaws  100 ,  102 . They comprise control thumb-wheels  110 . 
     The thumb-wheels  110  are actuatable, for example by a diver or by a remote-controlled vehicle (designated as “Remote Operated Vehicle” or “ROV”) between an open configuration of the clamp  66 , as illustrated in  FIG. 7  and a closed configuration of the clamp  66 , as illustrated in  FIG. 8 . 
     In the open configuration, the jaws  100 ,  102  and their free ends  108  are far away from each other. The central opening  106  then has maximum section, greater than the maximum cross-section of the endpiece  82 . 
     In the closed configuration, the jaws  100 ,  102  and their free ends  108  are brought closer to each other by pivoting with respect to the base  99  around a vertical axis. The free ends  108  are then substantially in contact. 
     The opening  106  then has a minimum closed cross-section smaller than the maximum cross section of the endpiece  82 , 
     As illustrated by  FIG. 6 , the jaws  101 ,  102  and the base  99  then delimit around the opening  106 , a ring-shaped shoulder  112  for retaining the endpiece  82 . 
     The upper surface  88  of the retaining endpiece  82  is complementarily supported under the shoulder  112 . 
     A first method for setting up the hybrid tower  20  according to the invention will now be described with reference to  FIGS. 2-8 . 
     Initially, the rising column  22  is assembled and is lowered into the expanse of water  12  by means of a laying ship  120 , as illustrated in  FIG. 2 . 
     In order to carry out this assembling and this lowering, a “J-Lay” or alternatively an “S-Lay” method, well known to one skilled in the art, are used for example. 
     The anchoring and connecting means  34  are then fixed on the bottom  14  of the expanse of water  12 . The rigid rising column  22 , provided with its upper connection  36  is releasably moored to the laying ship  120  through mooring lines  122  for maintaining it in a substantially vertical configuration along the axis A-A′, as illustrated by  FIG. 2 . 
     Next, the buoy  50  is immersed into the expanse of water  12  and is brought facing the rising column  22 . To do this, a first technique (not shown) consists of towing the buoy  50  by having it float horizontally on the expanse of water  12 . Next, the buoy  50  is pivoted in order to place it along a vertical axis, by gradually introducing water into the inner space  52 . 
     The buoy  50  is then positioned under the laying ship  120  by a so-called pendular technique up to the vertical configuration illustrated in  FIG. 2 . 
     In an alternative, the buoy  50  is stored on the laying ship  120  and is lowered into the sea vertically via a crane. 
     The buoy  50  is then lowered downwards to the bottom  14  of the expanse of water  12  by gradually bringing the male connecting member  62  in its disconnected position closer to the female connecting member  64 . 
     Taking into account the presence of the guiding funnel  94  delimiting a guiding surface  98  diverging upwards, and taking into account the joint of the male member  62  around the fork  70 , the local vertical axis B-B′ of the buoy  50 , of the line  60  and of the male member  62  does not necessarily coincide with the axis A-A′ of the rising column  22  in the vicinity of the female connecting member  64 , when the male member  62  moves closer to the female member  64  and during the initial contact between these members  62 ,  64 . 
     Thus, a lateral shift by more or less 50 centimeters may be tolerated at the moment of the contact. The connection of the male member  62  and of the female member  64  is thereby considerably facilitated. 
     When the male member  62  comes into contact through its endpiece  82  with the upper edge of the funnel  94 , it pivots from its axial configuration towards its tilted configuration by sliding against the guiding surface  98  in order to occupy its intermediate guiding position in which the upper region  84  of the guiding portion  76  bears against the surface  98 . 
     The male member  62  and its endpiece  82  are then naturally guided towards the passage  92  through contact between the male member  62  and the guiding surface  98 , as illustrated by  FIG. 4 . 
     Next, when the endpiece  82  penetrates into the passage  92 , the buoy  50  is re-aligned with respect to the rising column  22  so that the male connecting member  62  again occupies its axial configuration with an axis coinciding with the axis A-A′ of the column  22 . 
     The downward movement of the male member  62  into the receiving passage  92  delimited by the female member  64  then continues until the lower bevelled region  86  of the upper guiding portion  76  comes into contact with the bottom of the guiding surface  98  around the entrance of the receiving passage  92 . 
     In this inserted lower position, the intermediate portion  78  and the lower portion  80  are positioned in the receiving passage  92  and are blocked in this passage  92  by shapes mating those of the intermediate portion  78  and the sleeve  90 . 
     Further, the endpiece  82  protrudes downwards outside the passage  92  facing the jaws  100 ,  102  into the opening  106 . 
     A diver or a remote-controlled vehicle is then activated for controlling the screw  104  and moving the clamp  66  from its open configuration to its closed configuration. 
     During this passage, the jaws  100 , 102  move closer to the endpiece  82  so as to come into contact with the latter. The upper abutment surface  88  is then received complementarily into the ring-shaped retaining shoulder  112 . 
     Next, the mooring lines  122  connecting the laying ship  120  to the rising column  22  are disconnected from the rising column  22 . Because of its floatability, the buoy  50  tends to move upwards and generate a tractive force directed upwards which is transmitted to the male connecting member  62  through the flexible line  60 . 
     This force is then transmitted to the female member  64  integral with the rising column  22 , by the upper surface  88  bearing upwards against the shoulder  112  in the clamp  66 . 
     As the rising column  22  is retained at its lower end by the anchoring means  34 , the buoy  50  then maintains autonomously the rising column  22  in a substantially vertical configuration, against the weight of the column  22 . 
     Next, the flexible pipe  30  is deployed in the expanse of water  12  and is connected through its lower end  44  to the bypass  42  of the upper connection  36 . 
     Fluid collected in the bottom  14  of the expanse of water is then brought upwards to the surface assembly  18  through the transport passage  38  of the pipe  32  and through the inner lumen of the flexible pipe  30 . 
     In an alternative, the male member  62  is mounted so as to be integral with the upper end  24  of the rising column  22 , while protruding upwards. The female member  64  is jointed on the line  60  with its guiding surface  98  diverging downwards, towards the male member  62  upon introducing the male member  62  into the receiving passage  92 .