MXPA00010252A - Method and device for linking surface to the seabed for a submarine pipeline installed at great depth - Google Patents

Abstract

The invention concerns a device for linking the surface to the seabed for a submarine pipeline installed at great depth comprising a tower consisting of at least a floater (5, 14) associated with an anchoring system (6, 8, 16) and bearing at least a vertical riser (9, 15) capable of reaching down to the sea floor (18);and at least a linking pipe (4, 3) from the floater (5, 14) towards some surface support (1). The invention is characterised in that the linking pipe is a riser whereof the wall is a rigid steel tube and the floater (5, 14) is installed at an immersion depth below the last thermocline (29).

Description

PROCEDURE AND DEVICE TO LINK THE SURFACE TO THE BED OF THE SEA FOR A PIPE SUBMARINA INSTALLED AT A GREAT DEPTH The present invention relates to a method and system for linking the bottom with the surface for a submarine pipeline installed at great depth. The technical sector of the invention is the field of manufacture and installation of high production columns for the underwater extraction of oil, gas, or other soluble or fusible materials or a suspension of minerals from an underwater well head for the purpose to develop production fields installed in the open sea along the coasts. The main application of the invention is in the field of oil production. The present invention relates to the known field of links of the type comprising a vertical tower anchored to the seabed and having a float located at the top of the tower, this float is connected to a floating support installed on the surface by means of a conduit whose own weight causes it to take the form of a catenary. In the present description, the production fields are considered as oil fields. As soon as the underwater depth of these fields becomes large, generally work from the floating supports. The heads of the wells are often distributed over the whole field and the production lines and also the water injection lines and the control command cables are placed in the seabed going to a fixed place that has a floating support placed vertically on it on the surface. In general, the flotation support has anchoring means in a manner that allows it to remain in position despite the effects of current, wind, and swell. It generally includes means to store and process oil and means to discharge it into dump tanks, which arrive at regular intervals to be taken to production. These flotation supports are known as "floating storage, production and discharge media" supports (FPSO) and the initials "FPSO" are used throughout the description to designate this support. These FPSOs are anchored either by a series of anchor lines running from each of the corners of the flotation support, in which case the FPSOs maintain a constant orientation substantially independent of the surrounding conditions, or even an FPSO has a secured turret to its structure and anchored by a series of anchor lines. Under these circumstances, the FPSO is free to rotate in relation to the tower, and it is this tower that maintains constant orientation; in these circumstances the FPSO takes an orientation that corresponds to the resultant forces due to wind, current, and waves on the ship's hull. In the following description, the links from the bottom to the surface are mostly described as being connected to the side of an FPSO that is anchored and that therefore has a substantially constant orientation (as shown in Figure 2), While the FPSO has a turret, then these links must be connected to the same turret (as shown in Figure 6). The connecting conduit of the bottom of the surface is known as an "elevator", this term is used in the present description, and it can be implemented in the form of a conduit that rises continuously from the conduits placed on the bed of the sea and that go directly to the FPSO, giving rise to a catenary configuration with an angle relative to the vertical in the FPSO, which is generally in the range of 3 ° to 15 ° (a catenary elevator). When the water depth is less than several hundred meters these links must necessarily be made using conduits that are flexible, however, as soon as the depth reaches or exceeds 800 meters to 1000 meters, the flexible conduits can be replaced by conduits which are strong and rigid, being constituted by tubular elements that are welded or screwed together and They make rigid material, such as composite material or thick steel. These rigid heavy material risers that take a catenary configuration are commonly referred to as "steel catenary elevators" (SCR) and the initials SCR are used in the present description regardless of whether the elevator in question is made of steel or of some another material such as a compound. A flexible conduit and a rigid riser type SCR when subjected to the gravity forces only, and when they are of the same height, present the same angle in relation to the vertical when they are connected to the FPSO, and have the same curvature on their entire suspended length. Mathematically, this curve is precisely defined and is known as a "catenary". However, SCRs are much simpler than technically speaking flexible conduits and are much less expensive. Flexible conduits are structures that are complex and expensive and that are made of multiple spiral wound sheaths and composite materials. The depth of certain oil fields is greater than 1500 meters and can be as great as from 2000 meters to 3000 meters. The voltage induced to the FPSO by each SCR can be as great as 250 metric tons up to 300 tons and the large number of elevators needed to develop certain fields leads to reinforcing the structure of the FPSOs considerably, and can lead to imbalance if the platform and the loading port It is not the same. In addition, during the circular movements of the FPSO with respect to its average position, the catenary formed by an SCR changes from the point of contact on the sea bed moving forward and backward and also from left to right at the same speed with the which moves the FPSO, basing or picking up a portion of the conduit. These movements are repeated for long periods of time and dig a groove in the badly consolidated beds of the class commonly found at great depth, thereby modifying the curvature of the catenary and leading, if the phenomenon is amplified, to risks that the conduits damaged, that is to say the submarine conduits can be damaged and / or the SCR can be damaged. Due to the multiplicity of lines that exist in installations of this type, it is preferred to use a solution of the tower type in which the conduits and cables converge at the foot of a tower and rise to the tower, either all the way to the surface, or also to a depth that is close to the surface, with flexible conduits that then extend from that depth to provide the links between the top of the tower and the FPSO. The tower is provided with flotation means to maintain it in vertical position and the elevators are connected to the foot of the tower with the submarine conduits via flexible coupling sleeves that adapt to the angular movements of the tower. tower. The resulting link is commonly known as a "hybrid lift tower" because it makes use of two technologies: first a vertical portion, the tower, in which the elevator is constituted by rigid vertical ducts, and secondly a portion The top of the elevator is made up of flexible conduits in a catenary configuration that connects the upper part of the tower with the FPSO. The French Patent FR 2 507 672 published on December 17, 1982 and entitled [in translation] "lifting column for large depths of water" describes a hybrid tower comprising a surface float connected to the FPSO or via flexible conduits and carrying suspended guides through which passes only the upper portions of the vertical fluid transfer conduits. The hybrid tower is anchored to the seabed by a tensioned cable that gives the link a certain amount of flexibility in vertical movement, the lower portions of the conduits are free and form bends in the seabed, against which they rest . The advantage of this hybrid tower is in the freedom that allows the FPSO to move away from its normal position at the same time as it results in a minimum amount of tension in the tower and in those portions of the conduits that are in the form of suspended catenaries, either on the seabed or on the surface. The FPSO is usually anchored by means of a multitude of lines connected to a system of anchors resting on the seabed. This anchor system gives rise to return forces that keep the FPSO in a neutral position. The bonds from the bottom to the surface give rise to additional vertical and horizontal forces that have the effect of displacing the axis of the FPSO in relation to the neutral position. In the absence of current, wind or swell, and when the tide is at its average level, the position of the FPSO corresponds to a "reference position" P0. Under the combined effects of the environmental conditions, both on the case of the FPSO and on the different elements that constitute the elevators, the FPSO will move away from the reference position in proportion to the resultant of all the forces applied to the system. In this way, for the forces in the FPSO hull that tend to move it away from the axis of the tower, the following effects are observed: first the catenary is stretched and its relative angle to the vertical and its point of attachment with the FPSO increases, increasing by this the vertical and horizontal forces on the FPSO; and secondly the angle of inclination of the tower due to said horizontal force also increases. In order to minimize the consequences of FPSO field trips, it is a general practice to increase the rigidity of the anchor system and provide flexibility in the links from the bottom to the surface. To this end, the configuration of the tower associated with the catenary has a great capacity to absorb the excursions of the FPSO, at the same time as it minimizes the movements of the tower and the deformation of the catenaries. To dampen the movements of the FPSO, it is desirable to increase the curvature of the conduit that connects it to the surface of the tower. It is believed that flexible conduits are better suited for making links between an FPSO and the top of the tower. In previous embodiments of "hybrid towers" as described in FR 2 507 672 or in other types of structures such as those described in U.S. Patent No. 4,391,332 and EP 0 802 302, use is made of welding flexible ducts, ie pipes that go down to a lower depth of the float before rising again later. This is possible because a flexible conduit is able to withstand fatigue even when its curvature has a radius of curvature of only a few meters. However, the internal structure of the flexible tubes is very complex and its cost very high, this is why the previous modalities of the hybrid towers have sought to raise the tower as much as possible to the surface while at the same time avoiding , the turbulent areas on the surface, ie the upper part of the tower will be at a depth which is generally not more than 200 meters, and preferably is approximately 50 meters. This makes it possible to use short lengths of flexible conduit which are therefore less expensive, and above this makes it possible to ensure that the connections between the flexible conduits and the upper part of the tower are made more accessible to the divers. All the elements of these hybrid towers or these catenary elevators must be made of dimensions so that they are able to withstand the swell, the current, and the movements of the surface vessel under extreme conditions at sea, which leads to submerged structures of considerable size able to withstand high levels of tension and to endure the phenomenon of fatigue throughout its useful life, which commonly reaches or exceeds 20 years. The problem is thus to be able to make and install these bottom links to the surface for submarine ducts at great depth, for example, deeper than 1000 meters, and of the type comprising a vertical tower anchored to the seabed and whose float The upper one is connected to a flotation support installed on the surface via a tube in the form of a catenary, at the same time, however, limiting forces in the floats and in the conduits connect it to the flotation support, the internal system is capable of endure tensions and fatigue, but nevertheless, adapts large displacements of the surface support without requiring structures that are large and too expensive, and which should be able to be easily and reversibly put in place so that they can easily be maintained and replaced. One solution to the proposed problem is a bottom-to-surface connection system for a subsea conduit installed at a great depth, the system comprising first a vertical tower consisting of at least one float associated with an anchoring system and carrying at least one a vertical elevator that connects the float to the sea bed and can be connected to submarine ducts resting on the seabed, and secondly at least one connecting duct that extends from the float to the surface support, According to the present invention, the connecting conduit is an elevator whose wall is a strong rigid pipe, in particular made of steel or composite material. For a rigid tube, the minimum acceptable radius of curvature is 10 to 100 times greater than that of a flexible conduit. To limit fatigue, it is accepted that the radius of curvature of a rigid conduit made of steel should generally be greater than about 100 meters. To provide flexibility and achieve identical capacity to absorb the movements of the flotation support and the movements of the tower, the bed of which the catenary is less curved when using a rigid conduit is compensated for by increasing the distance between the flotation support and the float in the upper part of the tower, and thereby increasing the length of the tower. rigid conduit. However, the apparent weight in the water of the rigid conduit is greater than that of the flexible conduit, so that the load on the float and the forces on the float at the top of the tower therefore increase. This could lead to the float oversizing, leading to high cost levels. This is the reason why it is preferable, in accordance with the present invention, to install the upper part of the tower float at a greater distance from the surface of the water, and in particular at a distance which is below the last thermocline (wherein "thermocline" is defined below), and preferably not less than 100 meters below the last thermocline. In particular, the float on the top of the tower is installed at least 300 meters below the surface of the water, and preferably at least 500 meters below the surface of the water, and more preferably at a depth that is greater than half the depth of the water. Basing the upper float of the tower in this way, the following advantages are obtained simultaneously: - the length of the rigid conduit provided by the link between the FPSO and the top of the tower increases, thereby providing greater damping of tower and FPSO movements; - the minimum acceptable radii of curvature for a rigid conduit in a catenary are satisfied, regardless of how much the system moves as a whole; and - the costs are minimized since for a shorter tower the underwater structure is less massive and therefore less expensive and the float required to put it under tension is smaller and therefore less expensive, and this is true despite the increase in the apparent weight of the duct water associated with its increased length. This is because the catenary does not rise or rises very little towards the float, so that the weight of the rigid conduit constituting the catenary is essentially supported directly by the FPSO. However, maintaining a tower of a certain height, in particular not less than 50 meters and preferably not less than 100 meters, is advantageous since being able to move the tower helps to cushion the system under the effect of movements of the FPSO. In a preferred embodiment, the anchoring system has at least one vertical tendon, one standing unit at the bottom to which the lower end of the tendon is fixed, and at least one guide through which the end of the bottom of the vertical elevator passes. More particularly, the guide can be in the standing unit. Advantageously, the tendon has a guide element distributed along its entire length, through which at least the vertical elevator passes. The standing unit can be placed only on the seabed and remain in place under its own weight, or it can also be anchored by means of piles or any other convenient device to keep it in place; The float is connected to the standing unit via a flexible connection located at the foot and via an axial link constituted either by a cable or by a metal bar or undoubtedly by a conduit. The axial link is known in the present description as a "tendon". In a preferred embodiment, the upper end of the vertical riser is suspended through at least one guide secured to the float, placed inside the float, or at the periphery thereof, the upper end of the vertical riser is connected via the top of the float with the bend at the end of the link tube, and the lower end of the vertical riser is convenient to be connected with the end of a connecting sleeve which is also bent, and this is movable between a high position and a low position in relation with the standing unit, the sleeve being suspended from the standing unit and being associated with return elements that force it towards its high position in the absence of the elevator, this return element possibly consists of a counterweight. By having a connection sleeve that is mobile in this way, variations in the length of the elevator under the effects of temperature and pressure can be adapted. In the upper part of the vertical riser, an embedding device secured to the lift rests against the support guide installed on the upper part of the float and thus supports the entire elevator: the lift is suspended then with this apparent weight in the water being supported by part of the flotation of the float. In a particular embodiment, each of the guide elements distributed along the entire length of the tendon and through which the vertical riser passes comprises a cylindrical cavity, preferably overlapped by a conical funnel, with an inside diameter of the cylindrical cavity being larger than the diameter of the vertical riser, and each of the guiding elements has a flexible membrane secured to the inner wall of its cylindrical cavity, thereby creating a spill-proof bag between the membrane and the inner wall, this bag being it can fill with a fluid, preferably of very high viscosity, so that it rests against the elevator. The friction shoes are preferably associated with the membrane so that it rests against the elevator when the bag is filled with fluid. The shoes allow the vertical lift to slide when its length varies under the effects of temperature and pressure. The objects of the present invention are also obtained by a linking method which makes use, as explained above, firstly of a vertical tower constituted by at least one float associated with an anchoring system and carrying at least one vertical lifter convenient to go down to the seabed, and secondly at least one connecting conduit from the float to a surface support, by which, in the present invention, the float is submerged to a depth below the last thermocline (where "thermocline" is defined and explained below), and the float is connected to the surface support via at least one strong rigid elevator that constitutes one of the link conduits. In a preferred implementation of the linking method of the invention: a standing unit is put in place on the seabed and secured to said bed; the lower end of a tendon is secured thereto with the opposite upper end of the tendon secured to the float, the link constituting the anchoring system of the vertical tower; - the vertical elevator is progressively lowered by example, from a flotation support located vertically above the float, through one of the guide assemblies thereof until its upper end comes to rest against the float, its lower end then being connected to the upper end of the float. coupling sleeve previously installed in the standing unit. As it moves downward, the vertical riser preferably passes in succession through a series of guides secured to the axial link, known as a "tendon," whereby it is ensured that it is maintained in a position that is substantially parallel to the tendon and the other vertical lifts, if they are already installed in adjacent guides, or that will be installed at a later date. In a particular implementation, the float is installed to be submerged to a depth that is greater than half the depth of the water in which the tower of the invention is anchored, thus making it possible to assemble the entire vertical riser before install it and transport it to a position vertically above the guide corresponding to the float so that it goes down through it. The result is a method of bonding the bottom to the novel surface for an underwater tube installed at great depth that satisfies the proposed problem. Studies of sea currents in several Oceans on the world show that there are several layers that start from the surface and go down towards the seabed. Thus, at depths exceeding 500 to 1000 meters, in the Atlantic Ocean configuration, the following is observed, as shown in Figure 1: - a surface layer 18! which can go down approximately 50 meters below the surface 19 and in which the currents are local and mainly due to the wind and the phenomenon of the tide. In this zone, the currents are large and substantially uniform over the depth of the layer. They can have speeds of as much as 2.5 meters per second (m / s) in East Africa; a transition zone 29j known as "thermocline" can be of various thicknesses but which is always of small thickness (3 meters to 10 meters). In this transition zone 29j, the current falls rapidly to coincide with the speed of the intermediate layer; - an intermediate layer I82 in which the currents are in the range of 0.5 meters / second to 1 meter / second. This intermediate layer extends from approximately -55 meters to approximately -150 meters in the currents, mainly thermal currents due to the climatic phenomenon; - a second transition zone 292 or "thermocline" which also has several thicknesses but always of small thickness (approximately 10 meters). In this transition zone, the current falls rapidly to coincide with the current in the bottom layer; and - a bottom 183 layer in which the currents are small, generally do not exceed 0.5 meter / second. These currents are due to the intercontinental movements of water. This layer starts at approximately -150 meters to approximately -170 meters and continues all the way down to the sea bed 12, that is down to the depths that can be as great as 1000 meters to 3000 meters, depending on the location. In certain seas, three thermoclines 29 can be observed in the upper portion, but as a general rule the lower layer I83 starts at around -170 meters to -200 meters. In this way, since the tower and its float according to the invention and as described below is located below the lower thermocline 292, it must be found in a water layer I83 that gives rise to the smaller stresses due to the current. In addition, the float is protected from the effects of the waves, these effects fall quickly with depth, and it is a common practice to ignore them as soon as the depth exceeds 120 meters to 150 meters. The forces to which the tower is subjected they then reduce considerably and are substantially uniform over their entire height since they are due to deep intercontinental currents. The system of the invention constituted by a tower associated with an SCR thus provides a much better performance in response to environmental conditions, both ordinary conditions and extreme conditions such as once-a-year conditions, 10-year conditions, and conditions 100 years old The forces and stresses are considerably reduced and the fatigue behavior of the various critical components increases considerably, making it possible to give a better service over the entire life of the field. The float is thus in considerable depth, and can be connected to the FPSO via at least one SCR instead of being connected via a flexible link as in the present practice. The SCR links are simple and also, the internal structure of the SCRs, the vertical lifts, and the ducts resting on the seabed can then be identical, simplifying in this way, the passage of the cleaning scrapers. It is essential for these cleaning scrapers to be passed frequently when solid deposits such as paraffin or hydrates are present, and it must be possible to act repeatedly and very vigorously without damaging the internal surfaces of the elevators and the conduits. In general, the float is installed at about half the total depth of the water, but could be installed higher or lower in order to take advantage of certain situations as described below. In any case, the float is never placed near the last thermocline as described above but always at a greater depth, for example, 100 meters below it, to ensure that it does not run the risk of being subjected to the disturbances generated by the thermocline, nor to the currents that exist in the upper layer in the case of disturbances in the environment of the planet in marine currents that significantly alter ocean movements. The SCR is connected to the vertical riser at the top of the float via a flexible joint that allows the angle between the axis of the tower and the axis of the catenary in the flexible joint to vary widely without imparting significant stress to the SCR or top of float The flexible joint can be either a ball-and-socket joint with sealing gaskets, or it can also be a layered ball made of a sandwich of elastomer sheets and metal sheets bonded together and capable of absorbing large amounts of angular movement by deforming the elastomers at the same time that it remains spill-proof complete due to the absence of rubbed surfaces, or you could definitely have a short length of flexible conduit capable of providing the same service. The system of the invention is advantageously adapted to an automatic connector located in the flexible connection, either between the tower and the flexible connection or between the flexible connection and the FPSO. In this way, this SCR can be installed in a way that is completely automatic without requiring the use of divers. The installation sequence then consists in installing the tower, then transporting the future SCR in a vertical position, and fixing it next to the FP? O in its final position. A cable connected to the lower end of the future SCR is then manipulated by a remotely operated vehicle (ROV) so that it is carried to the top of the tower and thus connected to a towing element secured to the float and controlled by example, by means of a remotely operated vehicle which then supplies the necessary energy at the same time as it supervises the operations by means of video cameras whose signals are taken to the surface for the use of the operators located in the service vessel. The cable is drawn in and the end of the SCR fitted with the male end piece of an automatic connector (for example) is brought up towards the female end part of the same automatic connector. At the end of the approach stage, the assembly is locked to each other and the towing element is released so that it is capable of to be used to install the next line. The principle of automatic connectors is well known to persons with experience in the hydraulic and pneumatic technique, therefore it is not described in more detail herein. This method of installation has the advantage of being entirely reversible, while the automatic connector is designed to be able to be disconnected. This is thus possible, in operation, acting on a single SCR for the purpose of disconnecting and replacing it without disturbing the rest of the production, and thus, without any need to stop production on adjacent elevators and SCRs.

Similarly, the tower and the vertical elevators are advantageously installed using the following sequences: the standing unit is put in place and secured to the seabed; - a tight tendon with guides and with the upper float installed; - the assembled vertical lift is transported in the vertical position so that it is vertically above its guide located on the float; - the vertical elevator is lowered progressively through its guides with the operations of lowering supervised from the surface; - at the end of the descent, the head of the elevator rests on the upper part of the float and includes bending and also, for example, the flexible connection having the female portion of the automatic connector described above secured thereto; and - the lower end of the vertical lifter is also advantageously adjusted with an automatic connector, preferably with the male portion thereof because it is smaller, and the assembly can be connected to the end of the submarine conduit that connects the foot of the tower with a of the well heads, the end being fitted with the female portion of the automatic connector. The installation of the vertical risers in this way has the advantage of being completely reversible, while the automatic connector on the foot of the elevator is also designed to be able to be disconnected. It is thus possible in operation to act on a single elevator to remove and replace it without disturbing the rest of the production, and thus, without any need to stop production on adjacent elevators and SCRs. To the extent that the float is installed at a depth of more than half the total water depth, the fully assembled lift can be transported in the vertical position and lowered through the float. If the float is higher than half the water depth, the container used to install the riser should be placed vertically above the float and the elevator elements shall be assembled with each other as the lower end thereof is lowered through the float and the different guides are installed along the tendon, the assembly being implemented, for example, by welding, by adhesive, or undoubtedly by mechanical assembly such as bolting, with bolts and flanges together, or with edging. In a preferred version of the system, a previously assembled length of the elevator is transported in the vertical position from an assembly site that is remote from the tower, the length being shorter than the depth of the water remaining between the surface and the top of the tower. In this way, the service vessel can take the position vertically above the float with a good length of the previously assembled elevator and adjusted at its lower end with the male portion of the automatic connector, ready to be lowered into and through the float and through of several guides installed along the tendon. As it moves down, the missing upper portion of the elevator is assembled as described above. The above described method of operation makes it possible to minimize the length of time in which the service vessel is present in the vicinity of the tower, whereby the risk of accidents is minimized. In this way, in order to be able to act at a later date and remove the sjSple elevator, it is preferable to use assembly methods that are suitable for rapid and non-destructive disassembly, such as bolting, whereby the lifter is enabled to be removed from its support, allowing it to be disassembled from the successive segments of the bolt. upper portion, but only in sufficient quantity to release the lower portion of the riser from the upper part of the float, after which the service vessel may change the position along with the rest of the suspended elevator thereof, orienting towards a location that is away from sensitive installations before finishing maintenance operations. In order to minimize the presence of the service vessel vertically above the tower, it is advantageous to install the float to a depth that is greater than half the total depth of the water, making it possible for the service vessel to install or remove a whole elevator without the need to assemble or disassemble any of its components, thereby reducing the risk of accidents in the vicinity of the tower and sensitive installations. Other features and advantages of the present invention will be more apparent upon reading the following description given in an illustrative and non-limiting manner with reference to the accompanying drawings, in which: - Figure 1 is a diagram of the entire depth of the water in an Atlantic Ocean type configuration as previously described, with values of indicator currents in meters per second (m / s) given along the abscissa and at the approximate depths of the different layers and the corresponding thermal times given in the ordinate; - Figure 2 is a perspective view of an oil field development at a depth of 1500 meters (m), showing the FPSO on the surface, a central tower to recover the oil effluent, and two lateral towers to inject water, - - Figure 3 is a sectional view through the float associated with a side view of the central tendon and the two elevators; - Figure 4 is a side view of the foot units of the tower including two elevators, the central tendon, and two sleeves for coupling with the subsea conduits; - Figure 5 is a side view of the standing unit of a tower having a single elevator; - Figure 6 is a diagram showing the results of static calculations for an FPSO anchored in the turret in water having a depth of 2000 meters, and connected to a tower of the invention located at a depth of 1000 meters; - Figure 7 is a graph of two curves that they represent variations in the horizontal tension and in the horizontal distance between the anchor foot unit and the FPSO float as a function of the depth of the float in water having a depth of 2000 meters, and for an excursion of 8 percent; - Figure 8 is a graph of two curves showing variations in the FPSO excursion and horizontal stress as a function of the depth of the float for a water depth of 2000 meters and for a distance between the FPSO and the float 950 meters; - Figure 9 is a side sectional view of one of the lifting tracks shown in Figure 3; and - Figure 10 is a sectional plan view on AA of Figure 9. In the drawings, elements that are identical or similar have the same references from one Figure to another, unless otherwise stated. Figure 2 shows an FPSO 1 anchored on an oil field at a depth of 1500 meters under water 18, by means of an anchoring system (not shown) and including, for example, at port, at port level, an support system 2 to support SCR conduits for oil effluents 3 and water injection conduits 4. SCR oil effluents are connected to a tower, for example, located less than 800 meters from surface 19, via the part upper float 5 having four positions, only two of which are occupied. The float is connected to the standing unit 8 on the seabed by means of a tendon 6 having a multitude of guides 7 fixed thereto, with the elevators 9 installed therethrough, the elevators being connected to the unit. foot with connection sleeves 11] connected to the subsea conduits 10 via an intermediate connection block 13; other connecting sleeves 112 are ready for the corresponding vertical risers to be installed. Two identical water injection towers are constituted by a float 14 installed at -1000 meters from the surface and connected to a foot unit 16 by means of an elevator 15 that also performs the tendon function. A connecting sleeve 17 provides the link between the bottom of the elevator and the intermediate connection block 13. The float of the oil effluent tower which is at -800 meters from the surface, for example, is located at the lateral distance of approximately 500 meters from a point vertically below the FPSO side for an SCR link in the form of a catenary that reaches the horizontality of the float, thereby greatly facilitating installation and maintenance operations by a surface vessel, without interfering with the operations of ordinary execution of the FPSO. In addition, the surface vessel can carry out the station vertically above the tower and can maneuver and risk damaging the permanent anchor lines of the FPSO. Since the float 14 of the water injection tower is -1000 meters below the surface, ie at a depth greater than the previous tower, it is located 550 meters from the FPSO side. Figure 3 is a sectional view of the float 5 of a tower of multiple elevators associated with a side view of the various associated components. The float 5 is constituted, for example, by a drawer filled with synthetic foam and is connected to the central tendon 6 via a linking device 14 having a variable inertia piece 21 at its lower end to transmit tensions between the tendon and the float. The float has hollow vertical guides 22 in alignment with the guiding elements 23 of the guide 7 installed in (optionally regular) intervals along the tendon 6 and secured thereto by a fastening device 24. The guides 22 may be either integrated inside the float, or they may be installed in its periphery, or certainly in its central portion. The guides receive the vertical risers 9 shown on the left of the Figure being fully installed and connected to the SCR 3, and to the right of the Figure at the beginning of the insertion of the more than 25 end of an automatic connector for an elevator 9 .

The end of the automatic connector 25 is connected to the front cable 26 which passes through each of the guides 22, 23 downwards to the foot unit 8 of the tower where a return pulley 27 is installed. The standing unit 8 and pulley 27 shown in Figure 4 are shown in Figure 3 by a dotted cable return line 28. Cable 26 raises the surface towards the service vessel where it is kept under tension by a tension cable winch constant. In this way, the service vessel is located vertically above the tower with the elevator 9 completely assembled since the -800 meters depth of the float 5 in this example is greater than 700 meters of the length of the elevator 9. A ROV secures the front cable 26 at the end of the automatic connector 25, the front cable having been pre-installed before the assembly comprises the foot unit 8, the tendon 6, and the float 5 being put in place. The other end is taken at the surface for connection with a constant voltage cable winch (not shown). The operation of lowering the elevator 9i is carried out by maintaining the tension in the cable 26, that tension then causes the end of the automatic connector 25 to pass through each of the guides 23l in succession. The tension required in the cable 26 to perform this operation increases by increasing the angle of inclination of the tower. During the installation of the first elevator in the tower, the tower will be in a substantially vertical position. After the corresponding SCR has been connected to the FPSO, the SCR will exert a horizontal force on the tower, thereby causing the tower to tilt relative to the vertical toward the FPSO. As the successive elevators are installed, the angle increases and the tension required in the cable 26 increases proportionally. The left side of Figure 3 shows the riser 92 installed in its guide 22. Its end 30 rests on the upper portion of the guide 22 and constitutes the female portion of an automatic connector in which the male portion 31 of the connector is received, the male portion is connected to a fold 32 secured the latter to the flexible joint 33 connected to the end of the SCR 3. Due to the height of the tower in this mode, the length of the SCR is shorter than the depth of the water and the SCR is assembled away from the field by the service vessel and then transported by hanging it to the FPSO from where it is transferred and has its upper end connected. Its lower end is fitted with the flexible joint 33, the fold 32, and the male portion 31 of the automatic connector is connected to a cable whose other end is transferred by the remotely operated vehicle with towing means (not shown) secured to the float and driven by energy supplied by or through the remotely operated vehicle, for example. When the cable is towed of the float, the conduit takes on a catenary shape, and when the male end piece 31 is near the corresponding female portion 30, the two portions are joined by means (not shown) known to the person skilled in the art of the connectors hydraulic and pneumatic After the SCR 3 has been put in place, an embedment 34 is installed on the float to lean against a collar 35 on the fold 32 so as to take the horizontal forces generated by the SCR and prevent the assembly and particularly the fold turn with respect to the axis 36 of the elevators 9. Figure 4 is a side view of the foot unit 8 of a tower of multiple elevators and is constituted by a ballasted base plate 40 resting on the bed of the sea 12 and which supports a metal structure having guides 31, and a central flexible junction 42 suitable for receiving the lower end of the tendon 6. Two elevators 9 are shown: to the right of the Figure the elevator 9j is connected via the male portion 25; from its automatic connector to the female portion 44j of said connector which is secured to the coupling sleeve 11j leading to the submarine underpasses (not shown). If subjected to temperature variations, the elevator 9 can be extended, sliding through several guides 7 distributed along the tower. In the lower part, the movement of the lower end can reach several meters several extreme variations: in this way, the Elevator 9j associated with its sleeve 11j is free to move vertically in guides 41j and 49l secured to the structure of standing unit 8. A counterweight system consisting of a weight 48¡ and a cable 46j passing over a pulley 45¡ secured to the structure of the standing unit 8 is connected to the reinforcement 501 on the sleeve 11j via a connection point 47i. The counterweight is dimensioned so that in the absence of the lifter 9 the sleeve is held in the high position with the reinforcement 50, becoming embedded in the structure of the foot unit 8 via the guide 49j. This high position is shown in detail to the right of the Figure where there is an elevator 92 in the process of being lowered, after the male portion 252 of the automatic connector has passed through the last guide 412. The cable 26 which it is kept under tension from the surface and that it was used to tow the end of the elevator through several guides has been disconnected by the remote operation vehicle. The lifter 92 is made to move downwardly until the male portion 252 is received in the female portion 442. During this engagement step, the sleeve 112 remains in its high position since the counterweight 482 is sized to support at least the own weight of the sleeve plus the vertical force required for the coupling stage. After the hooking has occurred, the lifter 9 can moving downward until its upper portion rests against the float, the sleeve 11 being in its low position and the counterweight being lifted correspondingly. Thus, in the case of future work requiring the elevator 92 to be removed, the remote operation vehicle will unlock the automatic connector 252-442 and during the removal of the elevator, the sleeve will return to its high position due to the action of the counterweight 482. Elevator 92 will be reinstalled after having been repaired in the same manner as it was initially installed since the apparatus of the system of the invention is completely reversible. Figures 9 and 10 show details of the guide element 7 for an elevator 9, this guide element being secured via a fastener part 24 to a tendon 6 (not shown). The guide element 7 is constituted by a cylindrical tube 7a surmounted by a conical tunnel 7b for guiding the male portion of an automatic connector (not shown) while the elevator is being put in place. Since the diameter of the connector is greater than that of the elevator 9, the guide must have a diameter that is considerably greater than that of the elevator 9. In order to limit and damp the lateral movements of the elevator in operation, the guide element 7 advantageously is provided with an adjustable diameter device that allows the internal diameter of the cylindrical tube 7a to be adjustment. During the operation of installing or removing an elevator, the device is completely retracted so that the cylindrical tube 7a has a maximum diameter, and the device is fully extended when the elevator is in an operating configuration. The adjustable device is constituted by a flexible membrane 60 secured to the cylindrical guide member 7a via upper and lower corrugating rings 61, whereby a sealed pouch 62 capable of receiving a fluid is established via an orifice 63 provided with an isolation valve 64. A plurality of shoes 65a-65b, for example, six or eight shoes, are secured to the membrane 60 and rest against the elevator 9 when the bag 62 is completely full. In both Figures 9 and 10, the left side of the Figure shows the membrane 60 associated with the shoe 65b in its retracted position, while the right side of the Figure shows the shoe associated with the shoe 65a in the active position, i.e. contact with the elevator. The bag 62 is in communication with an external chamber defined by a membrane 66 that is sealed by two rings 67, a hole 68 that places the two chambers in communication with each other. In this way, when the sac 62 is emptied of its contents by sucking out the fluid through the valve 64, both membranes 60 and 66 are pressed against the cylindrical guide 7a and the multitude of shoes 65 are completely retracted, thereby they leave a passage of maximum dimensions. When the elevator is in place, the filler fluid is pumped through the valve 64 until the outer membrane is inflated by the pressure. This valve is then closed and a centering effect is obtained, it being possible to adjust the force only by injecting an additional volume of fluid so as to inflate the outer membrane more, this membrane acts as a pressure vessel, ie it provides a supply of Pressure. By using a fluid with very high viscosity, such as an optionally filled viscose staple, the assembly can act as a shock absorber by absorbing energy, whereby the occurrence of vibratory phenomena in the elevator when subjected to the effects of the current is prevented. The stages of inflation, deflation or adjustment of the pressure are performed using the manipulator arms and pumps on board the remote operation vehicle service. The outer membrane 66 acts as a visual indicator, making this possible without additional elements to observe the guide status of the shock absorber, only by inspecting it using the cameras available in the remote operation vehicles. Figure 5 is a side view of the lower portion of a single elevator tower constituted by a foot unit 16 resting on the sea bed 12 and supporting a fold that engages with the sleeve 17 having a flexible joint 37 installed at its end, the union in turn it is connected to the female portion 38 of an automatic connector. The base of the elevator 15 is adjusted with the male portion 39 of the same automatic connector. In this embodiment of a system of the invention, the lifter 15 also acts as a tendon, and the automatic connector 38-39 together with the flexible joint 37 are sized to be able to take the tension generated by the fluid under pressure plus the tension created by the float 14 and the conditions surrounding the assembly comprising the SCR 4 and the tower. Figure 6 is a diagram showing two positions of a turret anchored to the FPSO, which is obtained using the results of static calculations, ie ignoring the dynamic effects, for an oil field at a depth of 2000 meters and with a float 5 of a tower of the invention placed at a depth of 1000 meters. The apparent linear weight in water of the SCR 3 and the single vertical elevator 9 acting as a tendon, and assuming that both are filled with oil, was taken as 97.96 kilograms / meter, and the net flotation in the float 5 was taken as 180 metric tons (the flotation of the float minus the apparent weight in water of float 5, the tendon, and the vertical elevator (s) 9). The SCR 3 and the vertical elevator 9 are made of the same material and with the same type of configuration, for example, a diameter of 10.25 inches and a thickness of 1 inch, with longitudinal rigidity assuming infinite and with given isolation. Sea water was considered as having a density of 1033 kilograms / cubic meter. The average position of the FPSO 1 is P0, and the results of the calculations give the characteristics of a remote position Pj and a close position P, corresponding to the maximum excursion of 8 percent water depth of 2000 meters, the float being 5 placed at a depth equal to approximately half of the total water depth and being connected to the bottom 12 by the riser 9 having a length of 1014 meters. In the far position Pj the minimum radius of curvature of SCR 3 is 506 meters with an angle greater than ?? of 19 ° for the tension of 157 tons, and a lower angle ß? of 15 ° for the horizontal tension of 51 tons; the developed length of SCR 3 is 1322 meters for float 5 submerged at 1019 meters; the upper angle 7i of the elevator 9 under the tension is 15 ° and the horizontal distance of the FPSO 1 to the foot unit 8 of the elevator is 1027 meters. For the near position P2, the minimum radius of curvature of the SCR 3 is 300 meters with an upper angle a2 of 13 ° for a tension of 133 tons, and a lower angle 02 of -10 ° for a horizontal tension of 30 tons, the developed length of the SCR 3 is naturally the same as in the previous position, ie 1322 meters, and the float 5 is submerge to a depth of 1000 meters; the top angle? 2 of the elevator 9 under tension is 9.6 ° and the horizontal distance of the FPSO 1 to the foot unit 8 is 868 meters, while the distance to the position Pg is L = 947 meters. Based on the assumptions described in detail with reference to Figure 6, Figure 7 shows how the horizontal tension and the distance L between the foot unit 8 and the FPSO 1 vary as a function of the depth of the float 5. In this way, it can be seen that for an increase in the depth of the float 5, the horizontal tension decreases, presenting a minimum at -1400 meters. In addition, for a depth that falls in the range of -1000 meters to -1800 meters, the tension is in the range of 52 tons to 53 tons, and in this way is substantially constant. Similarly, the distance L to the FPSO 1 has a maximum value at -1400 meters and remains substantially constant around 950 meters to 960 meters for a depth that is in the range of -1000 meters to -1800 meters. Thus, if two towers are installed at substantially the same distance from the FPSO with floats that are located at depths that are very different, their performance will be similar, but very different SCRs will not run any risk of interfering with one another. Based on the assumptions described with reference to Figure 6, Figure 8 shows variations in the excursion of the FPSO and in the horizontal tension as a function of the depth of the float S and for the distance of the FPSO l and the standing unit 8 being 950 meters (position P0). The calculations were made based on an 8 percent excursion corresponding to a float depth of 1000 meters. When designing oil fields, it is common practice to consider that the maximum excursion really corresponds to 8 percent of the water depth, which corresponds to 160 meters for water that has a depth of 2000 meters. Thus, it can be seen that for a reduction in the depth of the float 5, the maximum excursion and the horizontal tension tend to increase while for an increase in said depth, the excursion remains stable at around 8 percent and the tension remains stable to around 50 tons. Thus, it seems that for surplus depths of 1000 meters, the maximum excursion and tension remain stable and static. In this way, this constitutes an invariant for the system, this invariant had a stabilizing effect for the system that is subjected to dynamic effects. Thus, in the invention, locating the float 5 at a depth of more than half the water depth presents a great advantage for the stability of the system and thus, for its fatigue behavior during the lifetime of the field .

Thus, it seems that in order to develop fields that require a multitude of towers, a large amount of latitude can be made available to place the floats by placing the floats in the lower half of the water depth, thereby giving place to small variations in the horizontal forces and in the distance of the tower to the FPSO. Proceeding in this manner, it is possible to place a multitude of tower and SCR assemblies in three dimensions while avoiding interference between the floats and interference between the SCRs, thereby increasing the safety of the performance of the installations during the service life of the field. In all the descriptions of the systems according to the invention, the male and female portions of the automatic connectors have been described in a given position, but could be reversed without changing the character of the invention. Similarly, the position of the automatic connector and the adjacent flexible joint can be exchanged without changing the character of the invention. In general, a tower increases the capacity of the FPSO for the excursion around its average position while a SCR of large dimensions improves the damping of the system. The mathematical curve represented by the catenary taken by a line of linear mass and constant bending stiffness shows constant variation in its curvature Starting from the FPSO and going on and on the float, this curvature has a minimum value (minimum radius of curvature) in the FPSO and then increases to a maximum value (minimum radius of curvature) in the float. The FPSO that is subjected to environmental conditions will transmit its movements to the assembly constituted by the SCR and the tower. The excitation of the SCR will lead to global movements of the SCR, giving rise to local variations in the radius of curvature, which in turn will generate transverse movements that have the effect of absorbing a portion of energy. In this way, large-sized SCRs absorb a maximum amount of energy over their total length and the amount of excitation energy transferred to the float is reduced to a minimum. In this way, viewed from the tower, the SCR acts as a filter to filter the excitation movements generated by the FPSO. The tower that is favorable for improving the excursion capacity for small angular variations, however, is a poor buffer, and is also subjected to vibrations generated by turbulent phenomena (vortices), which is the reason why the system of the invention consists of in installing the tower and its float at a great depth in an area where the currents are stable and where the effects of vortices are small. In this way, for an oil field, for example, installed in 1500 meters of water, and with a tower that is short, for example, located 100 meters above the bottom, an SCR 41 which has a length of approximately 1400 meters will behave in relation to the FPSO as a conventional SCR while at the same time avoiding the disadvantages that exist in the prior art and which are associated with the formation of dirt at the point of contact and with the risk of damaging the SCR in this region. The presence of unions in articulation of the FPSO and in the float of the tower facilitates the excitation of the catenary, leading by this to the absorption of the energy and in this way, to the global damping, at the same time that the transmission of forces is minimized in the extremes, that is to say both in the FPSO and in the float of the tower, because no end is integrated. A tall tower is preferred when it is desired to have a high performance insulation system such as the duct system in the duct. The context of conduit in conduit is constituted by two concentric conduits with an insulating system installed between them. The insulating system can be polyurethane foam, synthetic foam, or a gas at an absolute pressure that can be in the lower pressure range, for example, in absolute vacuum, where absolute vacuum provides the best performance in terms of insulation .

On this subject, it is noted that the synthetic foam consists of microspheres, generally made of glass, immersed in a matrix of durable material of the epoxy or polyurethane type. This conduit conduit system is expensive and quite complex to increase since it is generally made of elements that have a length of 12 meters or 24 meters and that are assembled together by welding or by screwing. Although it is particularly convenient for tower elevators, it is more difficult to use in SCR at medium depths, it is preferred to use insulator systems that are stronger but less efficient and less expensive, such as synthetic foam protections. Thus, with a high tower, conduit technology is implemented in high performance conduit but expensive, but only within the tower, by which maximum guarantees are obtained in terms of the useful life of the tower is located in the calmest region of water depth. In the upper portion, the SCRs are used that are associated with insulation systems of lower performance in thermal terms, but more convenient to withstand the environmental conditions during the useful life of the installation, and this is obtained at a considerably lower cost. In this way, the fluid reaches the foot of the tower at a temperature of 55 ° C, for example, and will lose some degrees, for example, from 4 ° C to 5 ° C when traveling up the tower, this must be essentially that the effluent loses pressure as it travels over 45 percent, for example, of the depth of the water, while traveling over the rest of the water depth, ie 55 percent, in the SCR will lose a few more degrees, for example , from 7 to 9 degrees due in part to lower performance insulation and partly to effluent that loses pressure. In the example cited, the fluid will thus have a total loss of 11 ° C to 14 ° C while using two insulating systems that have very different levels of performance, since the aim is to optimize the global isolation based on criteria related to useful life and cost. A tall tower is also preferred when there is a tendency for gas plugs to form in the lift column. These plugs are followed by a liquid front that can move at a very high speed, erratically giving rise to internal phenomena of the water hammer type. These phenomena hit the SCR and rise to the FPSO, resulting in internal pressure fronts within the fluid. This hammer inside the vertical risers can give rise to forces of several tons at the ends. These forces will come to manifest in the float, but since its total mass can be from 100 tons to 200 tons, the consequences of these phenomena in the elevator system are insignificant. So it is considered that the effects of this hammer are second-order effects when they occur in the vertical tower, while they are first-order effects when they occur in an SCR of the same height. In this way, and in general, in effluent production configurations and particularly those that require isolation, it is advantageous to use tall towers. When water is injected, which is done with a fluid stream that is very stable and which consequently does not give rise to. hammer phenomena, it is preferable to install a short tower so that it is closer to the configuration of a simple SCR resting on the seabed, while, however, avoids the disadvantages described above in the prior art. Under these circumstances, it is advantageous for the central tendon to be replaced by a tube through which the injection water travels. The injection water elevators are generally provided in very small numbers and are connected to the seabed via multiple branches from which the subsea conduits extend to the water injection wells. These tendon ducts perform two functions, and although this option is certainly possible when oil effluents are produced, it is undesirable since maintenance operations then require that the complete float-duct-tendon assembly be dismantled. Oilfields are often developed in sequence for several years as wells are drilled and well heads are installed. The system of the invention advantageously makes it possible to install around the FPSO a multiplicity of mutually independent towers at various depths, which have the advantage of locate the foot of each tower at horizontal distances from the FPSO which may be greater with increasing depth of the float. This arrangement makes it possible to cause a large number of subsea conduits to converge on each foot of the tower without interfering with the feet of the adjacent towers or are the subsea conduits associated therewith.

Claims (14)

1. CLAIMS 1.
2. A bottom-to-surface link system for a submarine conduit installed at a great depth, the system comprises first of all a vertical tower constituted by at least one float (5, 14) associated with an anchoring system (6, 8, 16) and that it has at least one vertical lift (9, 15) connecting the float to the sea bed (18) and able to connect with one of the submarine channels that rest on the seabed, and secondly , at least one connecting conduit (4,3) from the float (5, 14) to a surface support (1), the system is characterized in that the connecting conduit (4,3) is an elevator whose wall is a Strong rigid conduit.
3. A link system according to claim 1, characterized in that the float (5,14) is installed at a depth below the last thermocline, preferably at a depth of more than 300 meters, and more preferably still more than 500 meters. 3. a linking system according to claim 2, characterized in that the first float is installed at a depth that is greater than half the depth of the water in which the tower is anchored.
4. A link system according to any of claims 1 to 3, characterized in that the anchoring system comprises at least one vertical tendon (6), one *? lower foot unit (8) where the end of the tendon is fixed, and at least one guide (41) through which passes the lower end (25) of the vertical elevator (9).
5. A link system according to claim 5, characterized in that the lower end (25) of the vertical lifter (9) is convenient for connecting to the end (41) of a connecting sleeve bend that moves between a position high and a low position in relation to the standing unit (8), the sleeve being suspended from the standing unit 0 and being associated with return means that force it towards a high position in the absence of an elevator (9).
6. 6. A system according to claim 4 or 5, characterized in that the tendon (6) has the guiding element (7) distributed along its entire length and through which at least the vertical lifter (9) passes.
7. A system according to any of claims 1 to 6, characterized in that the upper end (30) of the vertical lifter (9, 15) is suspended through at least one guide (22) secured to the float (5, 0). 14), and is connected via the upper part thereof to the bent end (32) of the connecting conduit (4,3).
8. A system according to claim 6 or 7, characterized in that the guide element (7) comprises a cylindrical cavity (7a), preferably overlapped by a conical funnel (7b), the internal diameter of the cavity being cylindrical (7a) greater than the diameter of the vertical lifter (9), and the guide element including a flexible membrane (60) secured to the inner wall of the cylindrical cavity (7a), thereby creating a spill-proof bag (62) between the membrane (60) and the inner wall, this bag can be filled with a fluid, preferably a fluid of very high viscosity, to press against the riser.
9. A system according to claim 8, characterized in that friction shoes (65) are associated with the membrane (60) and rest against the lifter (9) when the bag (62) is filled with fluid.
10. 10. A bottom-to-surface bonding method for a submarine conduit installed at a great depth, the method first of all makes use of a vertical tower constituted by at least one float (5, 14) associated with an anchor system (6). , 8, 16) and carrying at least one vertical lifter (9, 15) suitable for lowering to the seabed (18), and secondly at least one connecting conduit (4, 3) extending from the float (5, 14) to a surface support (1), the method being characterized in that the float (5, 14) is installed at a depth below the last thermocline (29).
11. 11. A linking method according to claim 10, characterized in that the float (5, 14) is connected to the surface support (1) via at least onestrong rigid elevator that constitutes the connecting tube (4, 3).
12. 12. A linking method according to claim 10 or 11, characterized in that: a standing unit (8) is installed in the seabed (12) and secured to the seabed (12), the lower end of a tendon (6) is attached to it, this tendon has its other, upper end, secured to the float (5), the assembly constituting the anchor system of the vertical tower; - the elevator (9) is progressively lowered from the surface (19) and through a guide assembly (22) of the float (5) until its upper end (30) comes to rest against the float (5), its lower end (25) is put in connection with the upper end of a connection sleeve (11) previously installed on the foot unit (8).
13. 13. A linking method according to any of claims 10 to 12, characterized in that the float (5, 14) is installed at a depth that is greater than half the depth of the water in which the tower is anchored . A linking method according to claims 12 and 13, characterized in that the complete vertical lifter (9) is assembled previously and that the lifter is transported in the vertical position up vertically above the corresponding guide (22) of the float ( 5) .