FR2916795A1 - BACKFILL-BOND INSTALLATION COMPRISING AN ELASTIC DAMPING ARRANGEMENT REPRESENTING THE TENSION OF THE UPPER END OF A RIGID DUCT IN SUBSURFACE - Google Patents

Abstract

The present invention relates to a bottom-surface connection installation of an underwater pipe resting on the sea bottom comprising a rigid pipe (1) rising from the sea bottom where it rests, up to the subsurface where its top end (11) is connected to a floating support (10), characterized in that the said top end (11) of the rigid duct is connected to the said floating support by: 1) a flexible pipe (2) capable of allowing fluid transported by the said rigid pipe (1) to be transferred to the floating support, and 2) a flexible link comprising at least one elastic damping device (4) to provide the connection between the top end of the riser and a coupling point (5, 41c) on the said floating support, the said elastic damping device (4) absorbing the tension of the said rigid pipe at its top end, and allowing the distance between the top end of the rigid pipe and the floating support to vary in a controlled manner.

Description

Background-to-surface bonding arrangement comprising an elastic device

  of damping taking up the tension of the upper end of a rigid pipe subsurface. The present invention relates to a bottom-surface connection installation comprising at least one underwater pipe providing the connection between a floating support and the seabed, particularly at great depth. These rigid subsea pipes are called "risers" or "risers" as explained below, these risers consisting of unitary tubular elements welded together end to end, made of steel.

  More particularly, the present invention relates to a bottom surface connection installation of a submarine pipe resting at the bottom of the sea comprising a rigid pipe rising from the seabed where it rests, to the subsurface where its upper end is connected to a floating support. The technical sector of the invention is therefore the field of the manufacture and installation of subsea pipelines and more particularly bottom-surface production links for the underwater extraction of oil, gas or other soluble material. or fuse, or a suspension of mineral material, from submerged wellhead for the development of production fields installed offshore at sea. The main and immediate application of the invention being in the field of oil production, as well as in the re-injection of water and the production or re-injection of gas. A floating support generally comprises anchoring means to remain in position despite the effects of currents, winds and waves. It also generally comprises means for drilling, storage and treatment of oil and means of unloading to removing tankers, the latter occurring at regular intervals to perform the removal of production. The name of these floating supports is the Anglo-Saxon term "Floating Production Storage Offloading" (meaning "floating means of storage, production and unloading") which will be used the abbreviated term "FPSO" throughout the description FDPU or Floating Drilling & Production Unit), where the floating support is also used to carry out drilling operations with deviated wells in the height of the slice. of water.

  An underwater pipe, or a riser, according to the invention can be either a "production line" of crude oil or gas, or a water injection pipe, ensuring the connection with a sub-wellhead. marine installed at the bottom of the sea, is still a "drill riser" ensuring the connection between the floating support and a head of 5 wells located at the bottom of the sea. In the FPSO where we install in general a multiplicity of lines it is necessary to implement either bottom-surface links of the hybrid-tower type, or catenary type links in the form of a "chain". When the bottom-surface connection pipe is of the catenary type, it directly ensures the connection between a floating support and a point of contact at the bottom of the sea which is offset with respect to the axis of said support, said pipe takes by its own weight a so-called "chain" configuration, forming a curve whose radius of curvature decreases from the surface to the point of contact at the bottom of the sea, and the axis of said pipe forms an angle with the vertical whose value generally varies from 15 to 20 degrees at the floating support up to, theoretically, 90 degrees at the seabed corresponding to a theoretical position substantially tangential to the horizontal as will be explained below . Chain linkages are generally carried out using flexible pipes, but their cost is extremely high due to the complex structure of the pipe. Thus, it has been necessary to develop risers that are substantially vertical, so as to bring the flexible link in the chain configuration closer to the surface towards the floating support, which makes it possible to minimize the length of said flexible pipe, as well as the forces which are applied, thus considerably minimizing its cost. As soon as the water depth reaches and exceeds 500-1000m, it becomes possible to make said bottom-surface connection using a thick-walled rigid pipe, because the length of the pipe being considerable, its flexibility allows to obtain a satisfactory chain configuration while remaining within acceptable stress limits.

  These rigid risers made of strong, thick, chain-shaped materials, are commonly referred to by the English term "Steel Catenary Riser" meaning "chain-shaped steel riser" whose abbreviated term "SCR" or "SCR" will be used. catenary riser "in the present description, whether steel or other material such as a composite material. These "SCR" or "catenary risers" are much simpler to achieve than flexible pipes and therefore less expensive. The geometric curve formed by a conduct of uniform weight in suspension subjected to gravity, called "chain" is a mathematical function of hyperbolic cosine type (Cosx = (ex + eX) / 2, connecting the abscissa and the ordinate of any point of the curve according to the following formulas: y = Ro (cosh (x / Ro) -1) R = Ro (Y / Ro + 1) 2 in which: x represents the distance in the horizontal direction between said point of contact and a point M of the curve, y represents the altitude of the point M (x and y are therefore the abscissae and ordinates of a point M of the curve with respect to an orthonormal coordinate system whose origin is point of contact) - Ro represents the radius of curvature at said point of contact, ie at the point of horizontal tangency - R represents the radius of curvature at the point M (x, y) Thus, the curvature varies continuously along the chain from the surface, or its radius has a maximum value Rmax, to the point of contact, or its radius has a minimum value Rmjn (or Ro in the formula above). Under the effect of waves, wind and current, the surface support moves laterally and vertically, which has the effect of lifting or resting the chain-shaped pipe at the bottom of the sea. the pipe has a maximum radius of curvature at the top of the chain, in general of at least 1500, in particular from 1500 to 5000m, that is to say at

  point of suspension on the FPSO, and decreasing to the point of contact with the ground. At this point, the radius of curvature is minimal in the suspended portion. But, in the adjacent part resting on the bottom of the sea, said pipe being theoretically in a straight line, its radius of curvature is theoretically infinite. In fact, this radius is not infinite but extremely high, because there remains a residual curvature. Thus, according to the movements of the floating support surface, the contact point moves back and forth and, in the area raised or rested on the bottom, the radius of curvature successively passes from a minimum value Rmin to a value extremely high, even infinite in the case of a theoretical configuration where the underwater pipe rests on the bottom of the sea substantially in a straight line. These alternative flexures create fatigue phenomena concentrated throughout the chain foot area and the life of such pipes is greatly reduced and generally incompatible with the desired lifetimes for the bottom-surface bonds, ie 20-25 years or more.

  In addition, it is observed that during these reciprocating movements of the contact point, the stiffness of the pipe, associated with the residual curvature mentioned above, will in time dig a groove over the entire length raised and then rested and create a transition zone in which will have a point of inflection where the radius of curvature, minimum at the foot of the chain, will then change direction in said transition zone, and will increase to finally reach an infinite value in the underwater pipe portion resting in a straight line on These repeated movements at the top of the riser for long periods create a groove that is all the more important in the poorly consolidated soils that are commonly encountered at great depth, which has the effect of modifying the curvature of the sea. the chain and lead, if the phenomenon is amplified, to the risk of damaging the pipes, either at the level of the submarine pipes resting at the bottom of the sea, or at the level of the SCRs linking the underwater pipes lying at the bottom of the sea to the surface. The movements are of two very different types occurring with very different periodicities and consequences as shown in FIG. 2. Indeed, the floating support is anchored in general by 8 or 16 lines of anchors in general.

  distributed and located in the corners. Under the effect of wind and current, the floating support moves within a surface called excursion circle, substantially elliptical or circular and substantially centered with respect to its rest position. And, we try to minimize the size of this circle excursion by playing on the stiffness of the anchors. Thus, it is common to provide the anchors to limit the excursion of the floating support in a radius of 5-6% of the water height. Thus, for a water depth of 1500m, the excursion circle will have a radius of 75-90m. These movements due to the wind are usually very slow and their period is 200 to 300 seconds, that is to say that the chain foot moves relatively slowly back and forth and in normal conditions the movements are of very low amplitude. We speak of quasistatic state, that is to say that the system is always in quasi-equilibrium, which makes it possible to neglect the efforts due to the inertia of the whole. In fact, this type of long-period movement is not very detrimental to the resistance of the foot to fatigue during its lifetime.

  The second type of movement is due to the heave of the floating support which occurs over several meters and then generates vertical movements of the riser. These dynamic movements are much more prejudicial because they have a much shorter period, between 3-5 seconds and 15-18 seconds. And in addition, certain frequencies between the extreme values, correspond to the resonance frequencies of the riser in the chain configuration, which has the effect of considerably amplifying the deformations of said chain, and thus the movements and risks of damage to the foot chain, at the point of contact. At the surface, at the level of the connection of the riser head with the floating support, a flexible flexible joint device called flex joint is generally installed, so as to absorb the angular variations of the top of the riser, during the movements of the floating support. These flexjoints consisting mainly of elastomers, especially in the form of laminated abutments with a surface of revolution, not only serve to take up the traction forces generated by the riser, but also to transfer the crude oil to the rigid pipes integral with the floating support. These laminated abutment hinge devices are very expensive and delicate to manufacture and the risks of elastomer leakage are important because the life of such installations reaches and exceeds 20-25 years or more.

  The object of the present invention is to provide an improved bottom-surface connection facility comprising a rigid pipe or riser rising from the seabed to a floating support to overcome the above-mentioned drawbacks.

  More particularly, an object of the present invention is to provide a bottom-surface connection facility as defined above for attenuating the movements of the riser, so as to minimize the consequences of movements of the floating support and more particularly the heave movements, thereby to increase radically the fatigue strength of said bottom-surface bond.

  To do this, the present invention provides a bottom surface connection facility of a submarine pipe resting at the bottom of the sea comprising a rigid pipe rising from the bottom of the sea where it rests, to the subsurface where its upper end is connected to a floating support, charac ~ erized in that said upper end of the rigid pipe is connected to said floating support by: 1) a flexible pipe capable of allowing the transfer of the fluid carried by said rigid pipe to the floating support, and 2) a flexible link comprising at least one elastic damping device to ensure the connection between the upper end of the riser and a point of attachment on said floating support, said resilient damping device taking up the tension of said rigid pipe to its upper end, and allowing the variation of the distance between the upper end of the rigid pipe and the floating support, in a controlled way. It will be understood that: the elastic damping device according to the invention, by its extension or retraction, induces an increase or a decrease in the distance between the upper end of the rigid pipe and the floating support, said flexible link being kept taut, and this variation of distance is controlled within limits pre-established by the characteristics and elastic properties of the elastic damping device; and the variation in distance between the upper end of the rigid pipe and the floating support induced by the elastic damping device is a function of the variation of tension exerted on it.

  by the upper end of the rigid pipe, with an increase in the distance in case of traction and a decrease in case of relaxation of the tension exerted on the elastic damping device. In view of the fact that the variation of tension at the upper end of the rigid pipe is essentially related to the movements of the rigid pipe and the floating support under the effect of the swell and the wind and / or the sea currents, the device damping elastic according to the invention allows to soften the connection between the upper end of the rigid pipe and the floating support by reducing the tension at the upper end of the rigid pipe by increasing or decreasing the distance between the upper end of the rigid pipe and the floating support. The present invention makes it possible to reduce the fatigue and wear of the rigid pipe at its point of contact with the seabed and at its point of attachment with the floating support and in particular allows the possibility of eliminating or avoiding the use of a flexible articulation device of the flexjoint type at the junction between the rigid pipe and the floating support. More particularly still, the elastic damping device according to the invention makes it possible to limit the movements in the zone of the riser foot, and thus to limit the formation of a groove at the bottom of the sea, which makes it possible to reduce cumulative fatigue in the foot zone of the riser in a considerable way.

  The installation according to the present invention makes it possible to dissociate: on the one hand, the fluid transfer function from the upper end of the rigid pipe to its floating support, the transfer function exerted by the said flexible pipe, and on the other hand, the mechanical connection function between the upper end of the rigid pipe and the floating support, a function exerted by said link combined with said elastic damping device. Advantageously, said flexible link comprises a first cable or chain cooperating with said elastic damping device such that said elastic damping device allows the variation of the distance between the upper end of the pipe and the floating support while maintaining said first cable or chain stretched over a substantially constant length.

  In this case, it is understood that the elastic damping device is: - either integral with the floating support to which it is rigidly attached, said first cable or chain then ensuring the connection between the damping device and the upper end of the pipe rigid, - is secured to the upper end of the rigid pipe to which it is directly fixed rigidly, said first cable or chain then ensuring the connection between the floating support and the damping device. In both cases, the displacement of the upper end of the rigid pipe is related to the possible extension or retraction of the elastic damping device by its elastic properties. As will be explained in the detailed description which follows, the inventors have discovered that an elastic damping device according to the invention essentially reduces the vertical movements of the upper end of the rigid pipe induced by heave movements. floating support, and the shortest period of most damaging voltage variations resulting therefrom. But, an elastic damping device according to the present invention has substantially little effect on so-called quasi-static movements of the head of the riser related to lateral or horizontal excursion of the floating support as described above. More particularly, said rigid pipe is a catenary type pipe 20 rising from the seabed to said subsurface in a chain curve having a curvature substantially continuously variable to its upper end. In an alternative embodiment, said flexible pipe is a dip pipe having a low point situated between its two ends connected respectively to the upper end of the rigid pipe and to said floating support, said flexible pipe being connected to the upper end of the pipe. the rigid pipe by means of a gooseneck device of the gooseneck type. In known manner, the connection between the upper end of the rigid pipe and the flexible pipe is done: through an angled device called gooseneck, so as to allow the flexible pipe to dip below the level from the end

  top of the rigid pipe before going up to the floating support. The loop thus created allows the flexible pipe to withstand the excursions of the floating support without ever having to take up the tensions exerted on the floating support or the riser head following the movements of the lurch head and heave of the floating support, only said flexible link combined with the elastic damping device taking up most of the tension at the top of the riser associated with these lurching and pounding of the floating support. In a first embodiment, said elastic damping device comprises a mechanical elastic device or a hydro-pneumatic elastic device. More particularly, an installation according to the invention comprises a resilient mechanical damping device comprising biconical elastic elements comprising frustoconical washers of the Belleville type, preferably consisting of pairs of frustoconical washers of belleville type arranged axially and inversely, suitable for to deform elastically axially, threaded around a first axial rigid rod contained in a cylindrical chamber to a prestressing state, so as to form a stack of said washers retained on one side by a stop at one end of said first rigid rod axial and on the other side by one of the end walls of said cylindrical enclosure, end wall through a perforation of which the other end of said first rigid rod is able to move, said other end of the first rigid rod being connected to said upper end e rigid driving. Said frustoconical washers called belleville washers are grouped in pairs forming biconical elements, the said successive washers being arranged alternately axially reversed, that is to say the small bases of the two frustoconical washers of the pair being one against the other. while the large bases of the two frustoconical washers of one pair are adjacent to other large frustoconical washer bases of an adjacent pair slipped on the same rod. It is understood that when said washers are compressed axially, because of their elastic properties, they exert traction on said first rod and therefore on the upper end of the rigid pipe which takes up the tension at the upper end of the rigid pipe, watery pulls said first rod of the damping device into

  outside said enclosure following the descent of the upper end of the riser deeper subsurface under the effect of heave floating support. More particularly, the number and dimension of said frustoconical washers called belleville are such that: • in their initial prestressing state inside said enclosure, with a minimum extension of said first rod outside said enclosure, the elastic device of 'damping allows to resume a voltage corresponding to the voltage of the upper end of the rigid pipe when the floating support is at rest, and ^ in their state of maximum stress of abutment against said end wall, during the extension possible maximum of said first rod outside said rigid enclosure, the elastic damping device allows to take up the maximum possible tension exerted at the upper end of the rigid pipe in case of excursion of said floating support in particular under the effect of swell, wind and / or strong ocean currents. This cushioning device with frustoconical washers will thus always have an exit rod length capable of giving the required flexibility between the floating support and the upper end of the rigid pipe. Advantageously, in this resilient damping device comprising frustoconical washers, said initial prestressing tension and maximum abutment tension of said elastic damping device substantially correspond to the tension values delimiting a flattening zone of the force / displacement curve representing the voltage variation in the damping device as a function of the length of said first rod output from said chamber, flattening zone in which the variation of the displacement of said first rod is maximum for a given voltage variation exerted on said first rod .

  In another advantageous embodiment, said elastic mechanical damping device comprises a spring combined with a return pulley and a counterweight, one end of said spring being rigidly attached to a said point of attachment on said floating support and the other end of said spring being fixed to said counterweight, said flexible link ensuring the connection between said counterweight and said upper rigid pipe end passing through said first deflection pulley.

  This embodiment makes it possible to implement springs taking up only part of the tension at the upper end of the rigid pipe, the remainder, namely the greater part of said tension being taken up by said counterweight, said spring allowing only to soften the voltage variations by variations in distance between the upper end of the rigid pipe and the floating support, the tension at the end of the rigid pipe when the floating support is at rest being taken up by said counterweight . In another advantageous embodiment, said elastic damping device is a hydro-pneumatic device comprising a hydraulic jack fixed on the floating support, combined with a hydro-pneumatic energy storage system, for controlling the movement of the rod. of the cylinder, said first cable or chain being fixed to the upper end of said rigid pipe and cooperating with the ends of said rigid cylinder rod, and at least one second return pulley, so that a traction exerted by the upper end of the rigid pipe on said first cable or chain is taken up by a thrust exerted by the rod of the jack under the effect of the hydraulic pressure supplied by said hydraulic energy storage system, said thrust of the rod of jack exerting an opposite traction on said first cable or chain taking up the tension exerted by the upper end of the called rigid pipe.

  It will be understood that the average extension of the jack rod corresponds to a thrust resuming the tension exerted on the upper end of the rigid pipe when the floating support is at rest and the maximum extension, respectively minimum, of the cylinder rod. corresponds to a thrust taking again the tension exerted by the upper end of the rigid pipe corresponding to the movements of maximum distance of the barge, respectively of maximum approach in the direction of the point of contact in foot of riser. More particularly, in said pneumatic elastic damping device according to the invention, said jack rod cooperates with at least one second return pulley secured to the end of the cylinder rod, said second return pulley cooperating with said first cable or chain.

  It is understood that said second return pulley sends a return of the flexible link between its first end fixed to the upper end of the rigid pipe and its second end fixed to the floating support. Even more particularly, the elastic hydro-pneumatic damping device according to the invention is characterized in that: said accumulator system consists of a plurality of tanks filled partly with liquid and partly with gas; said gas under the effect of the transfer of the liquid from the jack to said tanks is according to the movements of the cylinder rod and imparting elasticity properties to said resilient damping device, and - the control of the pressure losses by means for varying the pressure drop during the transfer of the liquid between said reservoirs and said jack for controlling and damping hydraulic pressure variations in the accumulator system and in the jack, so that it is possible to obtain maximum variations in cylinder rod displacement for corresponding minimum variations in hydraulic pressure in the system accumulator and hydraulic cylinder. In a preferred embodiment, an installation according to the invention comprises a safety device providing a second connection of variable size between the upper end of the rigid pipe and the floating support constituted by at least two safety bars articulated to their ends, varying the inclination of said bars relative to each other to vary the distance between the point of attachment and articulation of said second connection on the floating support and the upper end of said rigid pipe, the maximum length of said second connection corresponding to the cumulative length of said bars being less than the length of said flexible pipe and preferably greater than the maximum displacement length of the upper end of said rigid pipe relative to said support; floating as controlled by said damping device. It is understood that this safety device protects said flexible pipe in the event of breakage or damage of said flexible link or of said elastic damping device according to the present invention.

  Advantageously, said safety device comprises a bar articulated on said floating support which is a telescopic bar. This embodiment makes it possible to keep the elastic damping device substantially in a straight line with the other security bar articulated on the upper end of the rigid pipe. In a particular embodiment, said elastic damping device is fixed at one end to said floating support and at the other end to the upper end of the pipe or, where appropriate, the articulation between said two safety bars. (51a, 51b) of a safety device. It is understood that this particular embodiment not including said first cable or chain implies that the flexible link according to the invention does not cooperate with any return pulley. In practice, said damping device is capable of taking up tensions at the upper end of said rigid pipe from 50 to 750 T, preferably 100 T to 250 T.

  More particularly, said damping device allows said displacements of the upper end of said rigid pipe, capable of damping voltage variations at the upper end of said rigid pipe, said variations representing up to 20% of the voltage at the rest at said upper rigid pipe end, that is to say when the floating support and the upper end of the rigid pipe are at rest. More particularly, said elastic damping device is able to allow variations in distance between the upper end of the rigid pipe and the floating support or displacements in the axial direction XX of the upper end of the rigid pipe of 1 at 10 m, preferably from 2 to 5 m, preferably for voltage variations at the upper end of the rigid pipe 5 to 150 T. In one embodiment, the upper end of said rigid pipe is located in subsurface at a depth of 20 to 60 m. More particularly, said flexible pipe has a length of 20 to 140 m.

  Other features and advantages of the present invention will appear in the detailed light of the embodiments which follow, with reference to the following figures, in which: FIG. 1 is a side view of an underwater rigid pipe in Simple chain configuration, suspended on a floating support 10 of the FPSO type, and whose lower end rests on the bottom of the sea 13, represented in three different positions 1a, 1b, 1c, according to the prior art. - Figure 1A is a sectional side view detailing the trench 12 dug by the foot 11 of chain during the lifting movements of the pipe 1 on the seabed. FIG. 2 is a curve detailing the voltage variations in the riser in quasi-static motion and in dynamics. - Figure 3 is a side view of a damping device according to the invention installed between a fixed point of a barge and the upper end of a riser. - Figure 3A is a variant of Figure 3, wherein the damping device is disposed in a well inside the barge. - Figure 4 is a side view of a barge and a riser connected to a counterweight associated with a damping device installed wedge of the barge in a well. FIGS. 5A-5D are cross-sectional views of a damping device according to the invention consisting of conical washers, respectively in the configuration of assembly, prestressing and operation. - Figure 5D is a diagram of the forces generated during the variation of the rod length H of said device. - Figure 6 shows a damping device according to the invention consists of a hydraulic cable tensioner, in a passive operating configuration and active operation. FIG. 6A represents a view of the rod head of the jack of FIG. 6. FIGS. 7A-7C show a side view of a preferred embodiment of the invention in which the end of the riser is guided by relative to the barge 10 by means of articulated bars. In FIG. 1, there is shown in side view a bottom-surface connection 1, of the SCR type, suspended on a floating support 10 of the FPSO type anchored at 11, and resting on the bottom of the sea 13 at the point The curvature varies along the chain from the surface, or its radius has a maximum value, to the point of contact, or its radius has a minimum value R. Under the effect of waves, wind and of the current, the floating support 10 moves, for example from left to right as shown in the figure, which has the effect of lifting or resting the chain-shaped pipe at the sea floor. position 10c, the floating support deviates from the normal position 10a, which has the effect of straightening the chain 1c by lifting it, and move the point of contact 14 to the right of 14a to 14c; the radius of curvature at the foot of chain increasing from Ro to R2, as well as the horizontal tension in the pipe generated at said point of contact at the bottom of the sea, as well as the tension in the pipe at the head of riser at said floating support. In the same way, in the opposite position 10b, the displacement to the right of the floating support has the effect of relaxing the chain lb and resting a portion of the pipe on the seabed. The radius Ro at the point of contact 14a decreases to the value R1 at 14b, as is the horizontal tension in the pipe at the same point 14b, as well as the tension in the pipe at said floating support. At the point of contact 14 with the ground 13, the radius of curvature of the pipe is minimal in the suspended portion, but in the adjacent portion resting on the bottom of the sea, said pipe being theoretically in a straight line, its radius of curvature is theoretically infinite. In fact, this radius is not infinite but extremely high, because it generally remains a residual curvature. Thus, as previously explained, at the mercy of the movements of the surface floating support 10, the contact point 14 moves from right to left and, in the area raised or rested on the bottom, the radius of curvature passes successively from one minimum value Rn,; n at an extremely high value, even infinite in the case of a substantially straight line configuration.

  The variation of the radius of curvature at 14 creates considerable internal stresses within the structure of the pipe, which generates cumulative fatigue phenomena that can eventually lead to the ruin of the bottom-surface bond. These alternative flexures create fatigue phenomena concentrated throughout the chain foot area and the life of such pipes is greatly reduced and generally incompatible with the desired lifetimes for the bottom-surface bonds, ie 20-25 years or more. In addition, as illustrated in FIG. 1A, it is observed that during these reciprocating movements of the point of contact, the stiffness of the pipe, associated with the residual curvature mentioned above, will in time dig a groove 12 over the entire raised length and then rested. A transition zone is thus created in which there exists a point of inflection 11, where the curvature changes direction in the transition zones, to finally reach an infinite value in the underwater conduct portion resting in a straight line on the bottom of the sea, said portion being lifted only exceptionally, for example during the maximum cumulation in the same direction, to the left, of all the disturbing elements (swell-wind-current) acting on the floating support and on the chain, or during the appearance of resonance phenomena at the level of the chain itself. When the pipe lifts, the inflection point disappears and the materials of the pipe previously in traction are then found in compression which creates considerable fatigue in this portion of pipe. Said fatigue is then of one or two orders greater than the fatigue in current section where there is no change in the curvature, which is incompatible with a desired service life of 25-30 years or more. The elastic damping device according to the invention makes it possible to radically limit the movements in the zone of the riser foot, as well as the formation in time of the furrow 12, and consequently to reduce the cumulative fatigue in this zone, of a factor 4 to 6 or more in some preferred embodiments. FIGS. 3 and 4 show a bottom surface connection installation of an underwater pipe resting at the bottom of the sea, comprising a rigid pipe (1) going up from the bottom of the sea where it rests, to subsurface where its upper end (11) is connected to a floating support (10) in which said rigid pipe is a catenary type pipe (SCR) rising from the bottom of the

  sea (13) to said subsurface in a chain curve having a curvature substantially continuously variable up to its upper end, and said upper end 11 of the rigid pipe is connected to said floating support by: 1) a flexible pipe 2 fit to allow the transfer of the fluid conveyed by said rigid pipe 1 to the floating support, said flexible pipe being a dip pipe having a low point 2a located between its two ends respectively connected to the upper end of the rigid pipe and said floating support, said flexible pipe being connected to the upper end of the rigid pipe by a gooseneck-type device 6, and 2) a flexible link comprising a first cable 3 cooperating with an elastic damping device 4 to ensure the connection between the upper end of the riser and a point of attachment 5 on said floating support t above the level of the sea surface, said elastic damping device 4 taking up the tension of said rigid pipe at its upper end, and able to allow the variation of the distance between the upper end of the pipe rigid and the floating support, so as to control, while maintaining said flexible link stretched. It is understood that said flexible pipe 2 has one end 21 connected to the upper end of the gooseneck 6 at the upper end of the rigid pipe and the other end 22 connected to pipes 53b on board the floating support.

  In FIG. 3, the elastic damping device 4, 20 is integral with the upper end of the rigid pipe to which it is directly fixed rigidly, said first cable 3 providing the connection between a point of attachment 5 of the floating support. and the other end of the elastic damping device 4, 20. In FIG. 4, the elastic damping device 4, 30 comprises a spring 301 associated with a counterweight 302, said spring 301 being fixed at one end to a point 5 of the solid support, said first cable 3 providing the connection between the other end of the resilient damping device 4, 30 and the upper end of the rigid pipe 11. More particularly, the upper end of said pipe Rigid is located in subsurface at a depth of 20 to 60m. Said flexible pipe has a length of 20 to 140m.

  FIG. 2 shows the diagram of the variations in time of the tension at the head 11 of riser under the effects of quasi-static movements and dynamic movements of the floating support. Curve 2 represents the combination of quasi-static 2a and dynamic 2b variations over a quasi-static period of 200-300 seconds. Initially, the floating support is in the center of the excursion circle, that is to say that the riser is in the position la of Figure 1, corresponding to a voltage in the riser of F0 = 100t. Then, the barge deviates to the left towards the maximum position 1c, where the tension is then maximum with Finax value = 110t. The position is reached after T / 4 = 50-75 seconds. Then, the floating support returns to the right and the tension decreases to a minimum Fmin = 90t, position reached at 3T / 4, ie 150-225 seconds. To these variations of tension, are superimposed dynamic variations 2b due to the vertical heave movement of the barge. These dynamic variations are of shorter period, from 3-5 seconds to 15-20 seconds, and of variable amplitude according to said movements of the FPSO. In the case where the excitation frequency corresponds to a resonant frequency of the riser, the amplitude of the voltage variation is considerably amplified as indicated in 2c-2d, which causes an extremely important detrimental movement in the foot of chain. On the left side (first half-period of T = 0 to T / 2) of the diagram is shown the variations 2a, 2b, 2c of the voltage at the head of the riser, for a riser of the prior art, simply hooked on the edge of the FPSO, through a flexjoint. And on the right (second half-period of T = T / 2 to T), there is shown the voltage variations 2e at the riser head provided with a damping and softening device 20, 30, 40 according to the invention installed between the upper end 1 of the riser and the floating support. Thus, the damping device according to the invention 20, 30, 40 acts as a filter for the high frequencies corresponding to the dynamic movements, but has substantially little effect on the low frequencies corresponding to quasi-static movements. . In a preferred version of the invention, shown in Figure 3, the damping device comprises a pre-compressed spring 20 consisting of a stack of elastic frustoconical washers 20a, known as belleville washers (or conical spring washer ). The operation of the device 20 is explained with reference to FIGS. 5A-5E. The belleville washers 20b are arranged axially in alternately reversed manner, thus forming a succession of pairs 20a of washers.

  frustoconical 20b threaded by their axial perforation around a said first rod 22. The 2 small bases of each frustoconical washer 20b of the same pair 20a being turned towards one another and the two large opposite bases of the washers of the pair being turned towards the large base of a next or previous washer threaded thereafter on said first rod 22. The washers threaded on the rod 22 are inserted into a cylindrical tube 21 provided with a bottom 21a pierced with way to let the rod 22 provided at its lower end with an attachment point 22a. Said washers are threaded around said rod in sufficient number to be put into compression in a state of pre-stress as shown in Figure 5B. A washer or end stop 22b is then secured to said rod, so that if one pulls down on the attachment 22a, one increases the compression of the spring and therefore the return force F , creating a bH elongation that gives flexibility to the upper end of the riser. In the diagram of FIG. 5E, the variations of the voltage in the device 20 are represented as a function of the length of the rod 22 output 6H. The peculiarity of the belleville washers is that the curve 23 force / displacement is substantially linear until a certain value of flattening or crushing of the washers, then the curve 23 flattens in a second time between 23b and 23c. In this zone 23b-23c, a slight increase in compression creates a large displacement. Thus, during the assembly of the device 20 and its prestressing to reach the state shown in FIG. 5B, the number of washers 20a is adjusted so as to reach the point 23b of the diagram of FIG. 5E with a rod 22 practically fully retracted into the chamber 21. In this position 23b, the prestressing is 90t taking up the tension at the head of riser when the floating support 10 is at rest in 10a, that is to say that if one draws towards down on the end 22a of the rod 22, no movement occurs. If the voltage increases at the riser head, the rod 22 moves downwards thus giving flexibility to the device 20, until reaching 23c the maximum voltage value F corresponding substantially to a maximum rod output 22. If we go beyond point 23c, the set of washers is almost flat and then we reach a quick stop 23d which then blocks the device, thus making it completely rigid. Thus, the preload of the device 20 at 23b is adjusted to a minimum value lower than the minimum of the quasi-static voltage accumulated with the dynamic variation, as represented in FIG. 2, and the upper voltage of the device 20 is advantageously limited to 23c. at a maximum value greater than the maximum of the quasi-static voltage cumulated with the dynamic variation,

  As is shown in FIG. 2. By doing so, the device 20 according to the invention will always have its output rod length 22 located between the two points 23b-23c of the diagram 5E, and will thus give the required flexibility between the structure of the barge and the upper end of the riser. To increase the stiffness of the device by two, three or more, advantageously the belleville washers are advantageously arranged by a first group of two or three or more, oriented in the same direction, the second group comprising the same number of identical washers oriented in reverse. In FIG. 3A the end of the riser is connected by a cable 3 rotated around a first deflection pulley 7, and connected to the device 20 installed inside a well 15 extending over the height of the barge 10, that is to say on 25-30m. FIG. 4 shows in partial section and in side view, a preferred version of the invention in which the riser tension is counterbalanced by a counterweight 302 connected to a first cable 3 rotated around a said first pulley. return 7 secured to the barge. Thus, when the tension increases or decreases, the counterweight rises upwards or downwards thus giving flexibility to the connection between the barge and the riser, thus avoiding transmitting the movements to the foot of the said riser chain. Advantageously, an additional elastic device 301, for example a spring, or a belleville washer device 20 with a capacity lower than that described with reference to FIGS. 5A-5E is advantageously added. Indeed, the tension of the riser being counterbalanced by the counterweight 302, for example of a value of 80 tons, the capacity of the device 20 or spring 301 can then be reduced to 10 tons in prestressing configuration corresponding to point 23b of the FIG. 5E, and at a maximum value of 35 tonnes corresponding to point 23c of the same FIG. 5E. FIG. 6 shows a hydraulic elastic tensioning device 40 consisting of a cylinder body 41 supported at 41a by the barge 10. The cylinder rod 42 supports at its end at least one upper pulley 43 (or said second pulley the first cable 3 being turned around the upper and lower pulleys 43b and 41b, the end of said cable being fixed at 41c to a support 41d integral with the structure of the barge 10. The hydraulic cylinder is connected by a line 46 of the cylinder body 30 to a first set of three hydraulic storage tanks 44a constituting a first passive system. Indeed, when the voltage at the riser increases, the pressure in the hydraulic circuit increases and the oil 44b compresses the

  gaseous upper part 44c. The decrease in the volume of gas put in compression allows the rod 42 of the jack then down and the first cable 3 rotated around the pulleys 43-41b is unfolding down thus drastically reducing the increase in tension at the top of the riser. Advantageously added in the hydraulic circuit are adjustable regulators associated with check valves 44e-44f, which make it possible to create, in a manner known to those skilled in the art, and independently, a damping of the movements of oil in the rising direction of the cylinder rod (lowering of the voltage: regulator 44e), and in the downward direction of the cylinder rod (increase of the voltage: regulator 44f). Advantageously, batteries 46a are advantageously installed as a dynamic device 45 consisting of a gas accumulator 45a preloaded at a higher pressure, for example P + 30 bars, at the maximum pressure 44d of the three accumulators 44a. A 45e-45f slave valve isolates the second accumulator 45a from the bypass 46a. A calibrated discharge valve 45d directs the oil to a tank 45b when the pressure in the hydraulic circuit 46-46a exceeds a defined value, thus causing a rapid discharge of the pressure, therefore a reduction of the voltage in the first cable 3. In the event of a significant drop in the voltage in the cable, the accumulators discharge and the pressure drops, the 45e-45f slave valve of the active device then opens and releases the oil from the second preloaded accumulator to a higher pressure. and thus restores the desired pressure level. A hydraulic pump 45c recharges the second accumulator as needed to maintain the overpressure, by drawing the oil into the discharge tank 45b. By doing so, the passive system 44 provides the desired flexibility for small voltage variations, while the active device 45 closes the voltage peaks by releasing oil in the tank 45b in case of voltage increase beyond of a fixed first upper threshold, or by re-injecting the oil through the 45e-45f servo valve in the event of a drop in voltage below a second lower threshold set to maintain the displacement of the cylinder rod within limits controlled. Said device 40 has been shown installed on board the barge with a 6-strand squirrel and three sets of pulleys 43 as shown in FIG. 6A, but a similar device comprising only the jack and the hydraulic circuit previously described is advantageously installed in place and placing the device 20 of FIG. 3 or the device 30 of FIG. 4. In FIGS. 7A-7C, a preferred version of the invention is shown.

  facilitating the installation of the assembly on site, as well as the safety in case of partial or complete rupture of one of the elements. In the prior art, the installation of the risers requires the installation on board of the barge towing gear extremely powerful and bulky so as to transfer the end of the riser to its support secured to the barge. In addition, because a plurality of risers is generally installed side by side along the plating, said device must be successively moved from one location to riser to the location of the next riser, which greatly complicates the organization this area is already heavily congested by various pipes, as well as reinforced structural structures capable of resuming efforts of several hundred tons. For this purpose, a safety device 51 comprising two safety bars 51a-51b hinged at 51c are suspended at a hinge 51d integral with the plating of the barge. The installation vessel 50 has just completed the assembly of the riser 1, suspended from the ship by a cable 50a. A cable 51e makes it possible to bring the hinged busbar 51a-51b towards the upper end of the riser to make their connection to each other as detailed in FIG. 7B, in position 1c of the riser 1. Once the connection is complete, the cable 50a is deviated and the riser takes the position 1d. As illustrated in FIG. 7C, the damping and softening device, for example the device 20 of FIG. 3, is then installed, or a hydraulic cylinder 40 associated with accumulators 44-45 as described with reference to FIG. secured to a hooking point 5 fixed to the structure of the barge, and whose second end is connected to the hinge 51c between the two bars 51a and 51b by means of a first cable 3. A flexible pipe 2 connects the upper end of the riser rigid pipes 53 of the barge 10, said flexible pipe being guided 54a- 54b respectively at the bars 51a-51b. By doing so, the installation vessel is used to perform all the phases requiring significant traction, and in case of breakage of the softener device 4 or the first cable 3, the assembly is found then substantially in the configuration ld of FIG. 7B, the connecting hose 2 being always connected at its two ends, thus avoiding interrupting production, the assembly remaining safe in a configuration similar to the prior art, although temporarily without the device of FIG. damping and softening 4, pending repair of the latter and restarting the device according to the invention.

  In a preferred version of the invention, shown in FIG. 7D, the first bar 51a is telescopic, and comprises two elements 51a1, 51a2, a first said element 51a1 being integral with the hinge 51d, a second element 51a2 sliding on the other side. 51a1 interior and coming into full stop in case of complete extension, the second end being articulated at 51c on the second bar 51b, the resilient damping device being connected at the same joint 51c. Thus, in normal operation, the elastic damping device induces no compression force within the telescopic bar 51a1-51a2, and the damping elastic device is substantially in a straight line with respect to the end of the riser 1 and at the second bar 51b. During the installation previously detailed with reference to FIGS. 7A-7B-7C, as well as in case of breakage of one of the elements of said resilient elastic device, the sliding element 51a2 of the first bar 51a comes into abutment with the 51a1 element integral with the hinge 51d on the floating support, which then gives the entire device the configuration 1d shown in Figure 7B, thus simplifying the installation procedure, or making safe the riser in case of breakage one of the elements of said resilient elastic device. The invention has been described in multiple configurations based on elastic damping devices, either in direct line with the end of the riser (FIGS. 3, 7A-7D) or with idler pulley (FIGS. 3A, 4), but It remains in the spirit of the invention when one associates with any one of these devices a muffling whose function is to amplify or reduce the available stroke, the force within the elastic device. damper is accordingly amplified or reduced in the same proportions, insofar as it neglects internal friction within the pulleys and bearings. The hydro-pneumatic device described with reference to FIGS. 6-6A, has a 6-strand blowing, which, for a stroke of about 12m between the riser head and the floating support, requires a jack of 2m stroke; against the efforts at the head of the riser will be, at the rod 42 of the cylinder, multiplied by the same factor 6. In the same way, gear devices can increase or decrease the stroke by increasing or decreasing respectively in the same report the efforts at the damping elastic device, insofar as one can neglect the friction within the system. The various devices have been described in connection with a barge anchored in a fixed manner on multiple anchors, but they have the same advantage when they are

  installed on FPSO anchored on reel. In this type of anchorage, the drum is anchored on the seabed by 6-8-12 anchors, and the FPSO freely turns around said drum and is thus naturally positioned according to the winds and currents, in the position creating the minimum effort between FPSO and reel, so the minimum effort in the anchoring system, which increases the stability of the FPSO and all the less disrupts the risers in chain configuration connected to said reel. The device according to the invention makes it possible, by adjusting for example the length of the flexible link 3, to modify the sensitive zone in the foot of riser subjected to fatigue. Thus, during the first years of operation the length of said flexible link will for example be 5m, then after five years, it will be increased to 10m, the sensitive area at the foot of the chain then being substantially displaced, an area critical cumulative fatigue then resting permanently on the ground, and therefore not being subjected to fatigue. The operation will advantageously be repeated at regular intervals, insofar as the length of the flexible connection has been provided long enough to absorb these variations in the position of the upper end of the riser in a chain configuration. If necessary, the flexible link will simply be changed and a new longer flexible link will replace the length that has become too short. It remains in the spirit of the invention when one uses as elastic damping device a hawser made of thermoplastic fibers of high capacity and of great length. Such hawsers, 100 to 300mm in diameter are capable of withstanding loads of several hundred tons and are commonly used for docking floating structures. They have a high elasticity and their length advantageously from 100 to 200m to provide the necessary travel of several meters in the desired voltage range. The end of the riser being thus further away from the plating of the barge, it will be necessary to adjust the flexible link length which, in this configuration will be much greater than in the variants described above.

Claims (20)

  1. A bottom-surface connection installation of a submarine pipe resting at the bottom of the sea comprising a rigid pipe (1) rising from the bottom of the sea where it rests, to the subsurface where its upper end (11) is connected to a floating support (10) characterized in that said upper end (11) of the rigid pipe is connected to said floating support by: 1) a flexible pipe (2) capable of allowing the transfer of the fluid conveyed by said rigid pipe ( 1) to the floating support, and   2) a flexible link comprising at least one elastic damping device (4) to ensure the connection between the upper end of the riser and a point of attachment (5.41c) on said floating support, said elastic damping device (4) taking up the tension of said rigid pipe at its upper end, and allowing the variation of the distance between the upper end of the rigid pipe and the floating support, in a controlled manner. 2. Installation according to claim 1, characterized in that said flexible link comprises a first cable or chain (3) cooperating with said resilient damping device (4) such that said elastic damping device allows the variation of the distance between the upper end of the pipe and the floating support, while maintaining said first cable or chain (3) stretched over a substantially constant length.   3. Installation according to claim 1 or 2, characterized in that said rigid pipe is a catenary-type pipe rising from the seabed to said subsurface in a chain curve having a curvature substantially continuously variable to its upper end.   4. Installation according to claim 1 to 3, characterized in that said flexible pipe (2) is a dip pipe having a low point (2a) located between its two ends respectively connected to the upper end of the rigid pipe and said support floating, said flexible pipe being connected to the upper end of the rigid pipe by means of a gooseneck-type pipe device (6).   5. Installation according to one of claims 1 to 4, characterized in that said elastic damping device comprises a mechanical elastic device (20, 30) or a hydro-pneumatic elastic device (40).   6. Installation according to claim 1 to 5, characterized in that said resilient damping device comprises biconical elastic elements (20a) comprising frustoconical washers of belleville type, preferably consisting of pairs of frustoconical washers of belleville type arranged axially and in an inverted manner, able to deform elastically axially, threaded around a first axial rigid rod (22) contained in a cylindrical chamber (21) in a prestressed state, so as to form a stack of said washers retained by a side by a stop (22b) at one end of said first axial rigid rod (22) and at the other side by one of the end walls (21a) of said cylindrical enclosure (21), end wall (21a) through a perforation of which the other end (22a) of said first rigid rod (22) is able to move, said other end of the first rigid rod e being connected to said upper end of the rigid pipe.   7. Installation according to claim 6, characterized in that the number and dimension of said frustoconical washers called belleville are such that: in their initial prestressing state inside said enclosure (21), with a minimum extension of said first rod (22) outside said enclosure (21), the resilient damping device (20) allows to resume a voltage corresponding to the tension of the upper end of the rigid pipe when the floating support is at rest, and ^ in their state of maximum abutment stress against said end wall (21a), during the maximum possible extension of said first rod (22) outside said rigid enclosure (21), the resilient damping device ( 20) makes it possible to take up the maximum possible tension exerted on the upper end of the rigid pipe in the event of an excursion of said floating support, in particular under the effect of waves, wind and / or marine currents. orts.   8. Installation according to claim 7, characterized in that said initial prestressing tension and maximum abutment tension of said resilient damping device (20) substantially correspond to the tension values delimiting a zone of lower slope of the force / stress curve. displacement representing the variation of tension in the damping device (20) as a function of the length of said first rod (22) output from said chamber (21), zone of weakest slope in which the variation of the displacement of said first rod is maximum for a given voltage variation exerted on said first rod.   9. Installation according to one of claims 5 to 8, characterized in that said elastic mechanical damping device (30) comprises a spring (20, 301) combined with a first deflection pulley (7) and a counterweight (302). ), one end of said spring being fixed rigidly to a said point of attachment (5) on said floating support and the other end of said spring being fixed to said counterweight (302), said flexible link (3) ensuring the connection between said counterweight (302) and said rigid pipe upper end passing through said first deflection pulley (7).   10. Installation according to one of claims 2 to 4, characterized in that said elastic damping device is a hydro-pneumatic device (40) comprising a hydraulic cylinder (41-42) attached to the floating support, combined with a system hydro pneumatic energy accumulator (44-45), for controlling the displacement of the cylinder rod (42), said first cable or chain (3) being fixed to the upper end of said rigid pipe and cooperating with the ends of said rigid cylinder rod (42), and at least one second deflection pulley (43), such that traction exerted by the upper end of the rigid pipe on said first cable or chain (3) is taken up by a thrust exerted by the cylinder rod under the effect of the hydraulic pressure supplied by said hydraulic energy accumulator system (44-45), said thrust of the cylinder rod exerting an opposite traction on said first a cable or chain (3) taking up the tension exerted by the upper end of said rigid pipe.   11. Installation according to claim 10, characterized in that said cylinder rod (42) cooperates with at least one second return pulley (43) integral with the end of the cylinder rod (42), said second return pulley. (43) cooperating with said first cable or chain (3).   12. Installation according to claim 10 or 11, characterized in that: - said accumulator system (44-45) consists of a plurality of reservoirs (44a, 45a) partially filled with liquid (44b, 45b) and for part of gas (44c, 45c), - the compression of said gas under the effect of the transfer of the liquid from the cylinder (41-42) to said tanks is as a function of the movements of the cylinder rod (42) and conferring elasticity properties to said resilient damping device, and -the control of the pressure drops by pressure drop variation devices (44e-44f) during the transfer of the liquid between said reservoirs and said jack for controlling and controlling damping hydraulic pressure variations in the accumulator system and in the cylinder, so that maximum variations in the displacement of the cylinder rod can be achieved for corresponding variations in the minimum hydraulic pressure in the system; me of hydraulic accumulator and hydraulic cylinder.   13. Installation according to one of claims 1 to 12, characterized in that it comprises a safety device (51) providing a second connection of variable size between the upper end of the rigid pipe and the floating support constituted by at least two safety bars (51a, 51b) hinged (51c) at their ends, varying the inclination of said bars relative to each other to vary the distance between the point of attachment and d hinge (51d) of said second link on the floating support and the upper end of said rigid conduit, the maximum length of said second link corresponding to the cumulative length of said rods being less than the length of said flexible pipe (2) and preferably, greater than the maximum displacement length of the upper end of said rigid pipe relative to said floating support as controlled by said device damping (4).   14. Installation according to claim 13, characterized in that said safety bar (51a) articulated on said floating support is a telescopic bar.   15. Installation according to one of claims 1 to 14, characterized in that said elastic damping device is fixed at one end to said floating support and at the other end to the upper end of the pipe or where appropriate the hinge (51c) between said two safety bars (51a, 51b) of a safety device (51).   16. Installation according to one of claims 1 to 15, characterized in that said damping device is capable of taking up tensions at the upper end of said rigid pipe from 50 to 750 T, preferably 100T to 250 T.   17. Installation according to one of claims 1 to 16, characterized in that said damping device allows said movements of the upper end of said rigid pipe, adapted to dampen voltage variations at the upper end of said pipe rigid, said variations representing up to 20% of the resting voltage at said rigid pipe upper end.   18. Installation according to one of claims 1 to 17, characterized in that said elastic damping device is adapted to allow variations in distance between the upper end of the rigid pipe and the floating support or displacements in the direction axial () OX) of the upper end of the rigid pipe from 1 to 10 m, preferably from 2 to 5 m, preferably for voltage variations at the upper end of the rigid pipe 5 to 150 T .   19. Installation according to one of claims 1 to 18, characterized in that the upper end of said rigid pipe is located in the subsurface at a depth of 20 to 60 m.   20. Installation according to one of claims 1 to 19, characterized in that said flexible pipe has a length of 20 to 140 m.