Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations
  • E21B43/0107—Connecting of flow lines to offshore structures
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/01—Risers
  • E21B17/015—Non-vertical risers, e.g. articulated or catenary-type
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B19/00—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables
  • E21B19/002—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling
  • E21B19/004—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling supporting a riser from a drilling or production platform
  • E21B19/006—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling supporting a riser from a drilling or production platform including heave compensators

Definitions

• a bottom-surface connection installation comprising an elastic damping device taking up the tension of the upper end of a rigid pipe in the 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.
• 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 reinjection 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 "), the abbreviated term” FPSO “throughout the following description, or” FDPU “or” Floating Drilling & Production Unit “(meaning” floating drilling and production means "), where the support Floating 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 “drilling riser” ensuring the connection between the floating support and a wellhead located at the bottom of the sea.
• the bottom-surface connection pipe 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 from 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 of which the value generally varies from 5 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.
• Step Catenary Riser meaning "chain-shaped steel riser” which will be used for the abbreviated term “SCR” or " catenary riser “in the present description, whether steel or other material such as a composite material.
• x represents the distance in the horizontal direction between said contact point 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 at the point of contact)
• - R 0 represents the radius of curvature at the point of contact is to say at the point of horizontal tangency.
• R represents the radius of curvature at the point M (x, y)
• the curvature varies continuously along the chain from the surface, or its radius has a maximum value R max , up to the point of contact, or its radius has a minimum value R min (or R 0 in the formula below). above).
• R max maximum value
• R min minimum value
• the pipe has a radius of curvature which is maximum at the top of the chain, generally at least 1500, in particular from 1500 to 5000m, ie at the point of suspension on the FPSO, and which decreases until at 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.
• the contact point moves back and forth and, in the raised area or rested on the bottom, the radius of curvature successively passes from a minimum value R m ⁇ n to a extremely high value, 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.
• the floating support is anchored in general by 8 or 16 lines of anchors usually equally distributed and located in Angles. Under the effect of wind and current, the floating support moves inside a surface called "circle excursion", substantially elliptical or circular and substantially centered relative 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.
• 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.
• a flexible flexible joint device On the surface, at the level of the connection of the riser head with the floating support, a flexible flexible joint device called “flexjoint” is generally installed, so as to absorb the angular variations of the top of the riser, during the movements of the support floating.
• These "flexjoints” consisting mainly of elastomers, in particular 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.
• 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 radically increasing the fatigue strength of said bottom-surface connection.
• 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, characterized in that said upper end of the rigid pipe is connected to said floating support by:
• a flexible link comprising at least one elastic damping device to ensure the connection between the upper end of the riser and a hooked point on said floating support, said elastic 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 manner.
• the elastic damping device 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 maintained taut, and this variation of distance is controlled within limits pre-established by the characteristics and elastic properties of the elastic damping device;
• 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 a increase in distance in case traction and a decrease in case of relaxation of the tension exerted on the elastic damping device.
• the device damping elastic 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 implementation of a flexible articulation device of the flexjoint type at the junction between the rigid pipe and the floating support.
• the elastic damping device makes it possible to limit the movements in the zone of the riser foot, and thus 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:
• the elastic damping device is:
• an elastic damping device according to the invention in line with the upper end of the rigid pipe as described above allows to further reduce the movements of the upper end of the rigid pipe induced by the heave motions of the floating support, and the short-term variations of the most damaging periods that result, that in the case where the elastic damping device is supported entirely by the floating support and cooperates with said cable by means of return pulleys on the floating support.
• connection between the upper end of the rigid pipe and the flexible pipe is via an angled device called gooseneck, so as to allow the flexible pipe to dip below the level of the pipe. upper end of the rigid pipe before going back 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 again the tensions exerted on the floating support or the head of riser following the movements of the head of yaw 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 lurches and pounding of the floating support.
• 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.
• 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.
• said elastic mechanical damping device comprises a spring combined with a return pulley and a counterweight, one end of said spring being rigidly fixed to a said point of attachment on said floating support and the other end said spring being fixed to said counterweight, said flexible link ensuring the connection between said counterweight and said upper end of rigid pipe passing through said first return pulley.
• This embodiment makes it possible to implement springs only taking up 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 .
• 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, making it possible to control the movement of the rod of the cylinder, said first cable or chain being attached to the upper end of said rigid pipe and cooperating with the ends of said rigid cylinder rod, so that a pull exerted by the upper end of the rigid pipe on said first cable or chain is taken up by a thrust exerted by the cylinder rod under the effect of the hydraulic pressure supplied by said hydraulic energy storage system, said thrust of the cylinder rod exerting an opposite traction on said first cable or chain taking up the tension exerted by the upper end of said rigid pipe.
• 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.
• the elastic hydro-pneumatic damping device is characterized in that: - said accumulator system consists of a plurality of tanks filled partly with liquid and partly with gas,
• control of the pressure losses by devices for varying 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 of displacement of the cylinder rod for corresponding variations hydraulic pressure in the accumulator system and the hydraulic cylinder.
• 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.
• said safety device comprises a bar articulated on said floating support, which articulated bar 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.
• 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. a security device. It is understood that this particular embodiment not including said first cable or chain implies that the link flexible according to the invention does not cooperate with any return pulley.
• 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.
• FIG. 1 is a side view of a rigid underwater 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 FIG. three different positions la, Ib, Ic, according to the prior art.
• FIG. 2 is a curve detailing the voltage variations in the riser in quasi-static motion and in dynamics.
• FIG. 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.
• FIG. 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-5C are cross-sectional views of a damping device according to the invention consisting of conical rings, respectively in assembly configuration, prestressing and operation.
• FIG. 6A represents a view of the rod head of the jack of FIG. 6.
• FIG. 1 there is shown in side view a bottom-surface connection 1 of the SCR type, suspended on a floating support 10 of FPSO type anchored at 11, and resting on the bottom of the sea 13 at the point of contact 14.
• the curvature varies along the chain from the surface, or its radius has a maximum value, up to the point of contact, or its radius has a minimum value R.
• 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 bottom of the sea.
• the support floating moves away from the normal position 10a, which has the effect of straightening the chain Ic 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 R 2 , 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.
• the displacement towards the right of the floating support has the effect of relaxing the chain Ib and of resting a part of the pipe on the bottom of the sea.
• the radius R 0 at the point contact 14a decreases to the value Ri in 14b, as well as the horizontal tension in the pipe at the same point 14b, and the tension in the pipe at said floating support.
• the radius of curvature of the pipe is minimal in the portion in suspension, 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 it generally remains a residual curvature.
• the contact point 14 moves from the right on the left and, in the raised or rested zone on the bottom, the radius of curvature successively passes from a minimum value Rmin to an extremely high value, even infinite in the case of a configuration substantially in a straight line.
• 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.
• the elastic damping device 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 the subsurface where its upper end Ii is connected to a floating support 1) in which said rigid pipe is a catenary type pipe (SCR) rising from the seabed 13 to said subsurface in a chain curve having a substantially continuously variable curvature up to its upper end, and said upper end Ii of the rigid pipe is connected to said floating support by:
• SCR catenary type pipe
• a flexible pipe 2 adapted 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 pipe device 6, and
• 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 hooked point 5 on said floating support located above the level of the surface of the sea, said elastic damping device 4 taking up the tension of said rigid pipe at its upper end, and adapted to allow the variation of the distance between the upper end of the rigid pipe and the floating support, so as to control while maintaining said flexible link stretched.
• said flexible pipe 2 has an end 2i connected to the upper end of the gooseneck 6 at the end. upper of the rigid pipe and the other end 2 2 connected to pipes 53b on board the floating support.
• 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 hanging point 5 of the floating support. and the other end of the resilient damping device 4, 20.
• the elastic damping device 4, 30 comprises a spring 30i associated with a counterweight 30 2 , said spring 30i being attached at one end to a hooking point 5 of the solid support, said first cable 3 ensuring the connection between the other end of the elastic damping device 4, 30 and the upper end of the rigid pipe li.
• the upper end of said rigid pipe is located in a 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 Ii of riser under the effects of quasi-static movements and dynamic movements of the floating support.
• Curve C2 represents the combination of quasi-static C2a and dynamic C2b variations over a quasi-static period of 200-300 seconds.
• 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-5D.
• the belleville washers 20b are arranged alternately axially reversed, thus forming a succession of pairs 20a of frustoconical washers 20b threaded by their axial perforation around a said first rod 22.
• each frustoconical washer 20b of the same pair 20a being turned toward each other 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 so as 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 compressed into a state of pre-stress as illustrated in Figure 5B.
• a washer or end stop 22b is then secured to said rod, so that if one pulls down on the fastener 22a, the compression of the spring and therefore the return force F is increased.
• 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 represented in FIG. 2.
• the device 20 according to the invention will always have its length of rod 22 output located between the two points 23b-23c of 5D diagram, and give the desired flexibility between the structure of the barge and the upper end of the riser.
• 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.
• 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, 25-10m.
• 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 30 2 connected to a first cable 3 rotated around a said first pulley. of return 7 secured to the barge.
• a counterweight 30 2 connected to a first cable 3 rotated around a said first pulley. of return 7 secured to the barge.
• the counterweight rises upwards or downwards thus giving flexibility to the connection between the barge and the riser, thus avoiding transmitting the movements at the foot of the said riser chain.
• an additional elastic device 30i for example a spring, is added, or a belleville washer device 20 with a capacity lower than that described with reference to FIGS. 5A-5D.
• the tension of the riser being counterbalanced by the counterweight 3O 2 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. 5D, and at a maximum value of 35 tons corresponding to point 23c of the same FIG. 5D.
• 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). reference), the first cable
• the hydraulic cylinder is connected by a pipe 46 of the cylinder body 41 to a first set of three hydraulic accumulator tanks 44a constituting a first system passive. Indeed, when the voltage at the riser increases, the pressure in the hydraulic circuit increases and the oil 44b compresses the upper gas 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.
• 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).
• 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 shunt 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.
• the 45 e -45f slave valve of the active device then opens and releases the oil from the second precharged accumulator to a pressure higher and thus restores the desired level of pressure.
• a hydraulic pump 45c recharges the second accumulator as needed to maintain the overpressure, by drawing the oil into the discharge tank 45b.
• 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 cover 45b in case increasing the voltage above a first fixed upper threshold, or by re-injecting the oil through the controlled valve 45e-45f in the event of a drop in voltage below a second lower threshold set to maintain the displacement of the cylinder rod within controlled limits.
• 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.
• FIGS. 7A-7C show a preferred version of the invention 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.
• 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.
• said device 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.
• 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 with each other as detailed in FIG. 7B, in the position Ic of the riser 1. Once the connection is completed, the cable 50a is deviated and the riser takes the position Id.
• the device is then installed.
• damping and softening for example the device 20 of Figure 3, or a hydraulic cylinder 40 associated with accumulators 44-45 as described with reference to Figure 6, integral with a hooking point 5 fixed on 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 to the rigid pipes 53 of the barge 10, said flexible pipe being guided at 54a-54b respectively at the bars 51a-51b.
• the first bar 51a is telescopic and comprises two elements.
• the elastic damping device induces no compression force within the telescopic bar 51a 1-51a2, 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.
• 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 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.
• 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.
• 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.
• 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.
• 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.
• hawser made of thermoplastic fibers of high capacity and of great length.
• 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 will advantageously be 100 to 200m to provide the necessary clearance 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.

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• 2007
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