EP2286056B1 - Bed-to-surface connector installation of a rigide tube with a flexible duct having positive flotation - Google Patents

Abstract

The invention relates to a bed-to-surface connector installation (fig 1) comprising: - a rigid "riser" pipe (9), fixed at the lower end thereof to an anchoring device (4,5,6) on the sea bed, a flexible connector pipe (10) providing the connection between a floating support (12) and the upper end of said vertical riser (9), one end of said flexible pipe (10) being directly attached, preferably by a system of flanges (11), at the upper end of said riser (11), a terminal pipe element (8) at the lower end of the riser (9) forming an inertia transition part of said riser, a terminal part of the flexible pipe (10), on the side of the junction thereof at the upper end of said riser with a positive flotation, said terminal part of the flexible pipe (10) with a positive flotation extending over a part of the total length of the flexible pipe such that the flexible pipe has an S shape.

Description

The present invention relates to a bottom-to-surface connection installation between a submarine pipe resting at the bottom of the sea and a floating support surface, comprising a hybrid tower consisting of a flexible pipe connected to a rising rigid pipe, or riser vertical , whose lower end comprises an inertial transition piece allowing it to be embedded in an anchoring device comprising a base resting at the bottom of the sea.

The technical field of the invention is more particularly the field of the manufacture and installation of production risers for the underwater extraction of oil, gas or other soluble or fusible material or a suspension of mineral material from wellhead immersed to a floating support, 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.

The floating support generally comprises anchoring means to remain in position despite the effects of currents, winds and waves. It also generally comprises oil storage and processing means as well as means of unloading to removal tankers, the latter being present at regular intervals to carry out the removal of the production. The common name of these floating supports is the Anglo-Saxon term "Floating Production Storage Offloading" (meaning "floating medium of storage, production and unloading") which one uses the abbreviated term "FPSO" in the whole of the following description.

• un riser vertical dont l'extrémité inférieure est ancrée au fond de la mer par le biais d'une articulation flexible, et relié à une dite conduite reposant au fond de la mer, et l'extrémité supérieure est tendue par un flotteur immergé en sub-surface auquel elle est reliée, et
• une conduite de liaison, en général une conduite de liaison flexible, entre l'extrémité supérieure dudit riser et un support flottant en surface, ladite conduite de liaison flexible prenant, le cas échéant, de par son propre poids la forme d'une courbe en chaînette plongeante, c'est-à-dire descendant largement en dessous du flotteur pour remonter ensuite jusqu'audit support flottant.

Background-to-surface bonds of an underwater pipe resting at the bottom of the sea are known, a tour-hybrid link comprising:

• a vertical riser whose lower end is anchored to the bottom of the sea through a flexible joint, and connected to a said pipe resting at the bottom of the sea, and the upper end is stretched by a submerged submerged float to which it is connected, and
• a connecting pipe, generally a flexible connecting pipe, between the upper end of said riser and a floating support surface, said flexible connecting pipe taking, if appropriate, by its own weight in the form of a curve in plunging chain, that is to say, descending widely below the float and then up to said floating support.

Background-to-surface bonds are also known which are carried out continuously up to the sub-surface of the strong and rigid ducts constituted by tubular elements of thick steel welded or screwed together, in a chain configuration with a continuously variable curvature. throughout their length in suspension, commonly referred to as "Steel Catenary Riser" (SCRs) meaning "chain-shaped steel riser" and also commonly referred to as "catenary type rigid pipe" or "SCR type riser".

Such a catenary duct can go up to the floating support surface or only to a sub-surface float that tensions its upper end, which upper end is then connected to a floating support by a plunging flexible connecting pipe.

Reinforced catenary risers are described in WO 03/102350 of the plaintiff.

In WO 00/49267 (which is considered the closest the state of the art), it was proposed as connecting pipe between the riser whose top is tensioned by a float immersed on the surface and the floating support, rigid pipes of SCR type and one installs the float at the top of the riser at a greater distance from the surface, in particular at least 300 m from the surface, preferably at least 500 m.

In WO 00/49267 of the applicant, there is described a multiple hybrid tower comprising an anchoring system with a vertical tendon consisting of either a cable or a metal bar, or a pipe stretched at its upper end by a float. The lower end of the tendon is attached to a base resting at the bottom. Said tendon comprises guiding means distributed over its entire length through which passes a plurality of said risers vertical. Said base can be placed simply on the seabed and stay in place by its own weight, or remain anchored by means of batteries or any other device to keep it in place. In WO 00/49267 , the lower end of the riser vertical is adapted to be connected to the end of a bend, movable cuff, between a high position and a low position, relative to said base, to which this cuff is suspended and associated with a means of return bringing it back up in the absence of the riser. This mobility of the bent sleeve makes it possible to absorb the length variations of the riser under the effects of temperature and pressure. At the top of the vertical riser, a stop device, integral with it, comes to rest on the support guide installed at the head of the float and thus maintains the entire riser in suspension.

The connection with the submarine pipe resting on the seabed is generally effected by a pig-shaped or S-shaped pipe portion, said S being then made in a vertical or horizontal plane, the connection with said underwater pipe being generally carried out via an automatic connector.

This embodiment comprising a plurality of risers held by a central structure comprising guide means is relatively expensive and complex to install. On the other hand, the installation must be prefabricated on the ground before being towed at sea, then once on site, cabane to be put in place. In addition, its maintenance also requires relatively high operating costs.

In addition, since crude oil travels a great distance over several kilometers, it must be provided with an extremely costly level of insulation to, on the one hand, minimize the increase in viscosity which would lead to a reduction in the hourly production of the wells. and on the other hand to avoid the blockage of the flow by paraffin deposit, or formation of hydrates when the temperature drops to around 30-40 ° C. These last phenomena are all the more critical, especially in West Africa, that the temperature of the seabed is of the order of 4 ° C and that the crude oils are of the paraffinic type.

It is therefore desirable for the bottom-surface links to be of short lengths and thus for the bulk of the different links connected to the same floating support to be limited.

This is why it is sought to provide facilities capable of operating from the same floating support a plurality of bottom-surface links tower-hybrid compact size and simpler to install and can be manufactured at sea from a laying ship driving.

In WO 02/066786 and WO 2003/095788 Hybrid tower installations requiring the use of flexible joints between the vertical riser and the base have been described because the angular variations generated by the movements of the FPSO and by the action of the swell and the current on the pipes and the float tensioning the vertical portion of pipe, are important, reaching 5 to 10 ° and these variations prevent the use of rigid connection embedded in said base. Such flexible joints are very delicate and expensive to manufacture because they consist of stacks of elastomer layers and steel reinforcements and must withstand fatigue throughout the life of the facilities that exceeds 20-25 years or more. In addition, the presence of the float creates a voltage discontinuity at the gooseneck piece at the interface between the substantially vertical rigid pipe and the flexible pipe. chain configuration, which adversely affects overall stability at said interface and affects the mechanical strength of the installation.

In WO 02/103153 it has been sought to provide an installation which can be manufactured entirely on land, in particular as regards the assembly of the rigid pipes resting at the bottom of the sea and the vertical risers ensuring the bottom-surface connection. On the other hand, in WO 02/103153 , it was sought to implement an installation whose establishment at the bottom of the sea requires no flexible joint ball joint in the lower part of the tower. To do this, the underwater pipe resting at the bottom of the sea is connected to said vertical riser by a flexible pipe element held by a base resting at the bottom of the sea. The assembly of the lower end of the vertical riser and the the end of the pipe resting at the bottom of the sea, via said element of flexible pipe secured and held by said base, is pre-assembled on the ground before being towed at sea and deposited at the bottom of the sea where said base is , then, anchored. However, this embodiment has certain drawbacks because this anchoring system requires, for the towing and cabanage phase, considerable buoyancy elements to balance the weight of said base structure, and the flexible connecting elements are subjected to significant fatigue throughout the life of the facilities that reaches and exceeds 25-30 years.

Furthermore, in all the installations described in the prior art mentioned above, the vertical riser is tensioned by a sub-surface float and the connection between the vertical riser and the floating support is made by a flexible pipe in a chain configuration. plunger, whose end is connected to the upper end of said vertical riser by a gooseneck device. This mode of connection of the upper end of the vertical riser with the floating support has certain disadvantages in terms of mechanical strength, at the level of the voltage discontinuity created by the gooseneck connecting piece, and because of the tensioning of the riser vertical by a very large float volume, the latter is subjected to the action of currents and swell, which generates, for this type of connection angular variations of the top of the riser, very important, the latter reverberating in the foot of riser, at the level of flexible joint thus strongly solicited.

In GB-2,024,766 a vertical riser connected to a flexible pipe in a plunging chain configuration is described, the end of the flexible pipe connected to said riser has a curvature imposed by a vertical section gutter of circular shape resting at the top of a float of form toric, said gutter serving gooseneck and avoiding too small radii of curvature can lead to crushing of said flexible pipe. This embodiment does not prevent wear of the flexible pipe at its interaction with said channel, which affects the intrinsic reliability of the connection between the vertical riser and the flexible pipe in terms of mechanical strength over time .

An object of the present invention is therefore to provide a bottom-surface link installation with hybrid towers, compact, simple to install and can be manufactured at sea from a pipe laying ship, but the system of anchoring is of great strength and low cost, and whose manufacturing processes and implementation of the various constituent elements are simplified and also low cost, and can be carried out at sea, also, from a ship deposit.

Another purpose is to provide an installation that does not require the implementation of flexible joints, especially at the base of the vertical riser.

Another object of the present invention is to provide a bottom-surface connection installation as described above, which requires the implementation of a single connecting element, in particular a single automatic connector, between the end bottom of the vertical riser and the end of the pipe resting at the bottom of the sea.

• a- au moins une conduite rigide montante, sensiblement verticale, dénommée riser vertical, fixée à son extrémité inférieure à un dispositif d'ancrage au fond de mer, et
• b- au moins une conduite de liaison flexible assurant la liaison entre un support flottant et l'extrémité supérieure dudit riser vertical,
• c- une extrémité de ladite conduite flexible est directement raccordée, de préférence par un système de brides, à l'extrémité supérieure dudit riser vertical, et
• d- l'extrémité inférieure dudit riser vertical comprend un élément de conduite terminal formant une pièce de transition d'inertie dont la variation de l'inertie est telle que l'inertie dudit élément de conduite terminal, à son extrémité supérieure, soit sensiblement identique à celle de l'élément de conduite de la partie courante du riser vertical auquel elle est reliée, ladite inertie de l'élément de conduite terminal augmentant progressivement jusqu'à l'extrémité inférieure de ladite pièce de transition d'inertie, comprenant une première bride de fixation permettant l'encastrement de l'extrémité inférieure dudit riser vertical au niveau dudit dispositif d'ancrage au fond de la mer, caractérisée en ce que :
  • une partie terminale de la conduite flexible, du coté de sa jonction à l'extrémité supérieure dudit riser, présente une flottabilité positive, et au moins la partie supérieure dudit riser vertical présente également une flottabilité positive, de sorte que les flottabilités positives de ladite partie terminale de la conduite flexible et de ladite partie supérieure dudit riser vertical permettent le tensionnement dudit riser en position sensiblement verticale et l'alignement ou la continuité de courbure entre l'extrémité de ladite partie terminale de la conduite flexible et la partie supérieure dudit riser vertical au niveau de leur raccordement, ladite flottabilité positive étant apportée par une pluralité de flotteurs périphériques coaxiaux, régulièrement espacés et/ou un revêtement continu en matériau de flottabilité positive, et
  • ladite partie terminale de conduite flexible présentant une flottabilité positive, s'étend sur une partie de la longueur totale de la conduite flexible, telle que la conduite flexible présente une configuration en S, avec une première portion de conduite flexible du coté dudit support flottant présentant une courbure concave en forme de chaînette à configuration de chaînette plongeante et ladite partie terminale restante de ladite conduite flexible présentant une courbure convexe en forme de chaînette inversée de par sa flottabilité positive, l'extrémité de ladite partie terminale de conduite flexible, au niveau de l'extrémité supérieure dudit riser, étant située de préférence au dessus et sensiblement dans l'alignement de l'axe Z₁Z'₁ dudit riser à son extrémité supérieure.

To do this, the present invention provides a bottom-surface connection installation, particularly at a great depth of more than 1000 m, comprising:

• a- at least one upright rigid pipe, substantially vertical, called vertical riser, fixed at its lower end to an anchor device at the seabed, and
• b- at least one flexible connection line providing the connection between a floating support and the upper end of said vertical riser,
• c- one end of said flexible pipe is directly connected, preferably by a system of flanges, to the upper end of said vertical riser, and
• d- the lower end of said vertical riser comprises a terminal pipe element forming an inertial transition piece whose variation of inertia is such that the inertia of said terminal pipe element, at its upper end, is substantially identical to that of the driving element of the running part of the vertical riser to which it is connected, said inertia of the terminal pipe element gradually increasing to the lower end of said inertial transition piece, comprising a first fixing flange for embedding the lower end of said vertical riser at said anchoring device at the seabed, characterized in that:
  • an end portion of the flexible pipe, on the side of its junction at the upper end of said riser, has a positive buoyancy, and at least the upper portion of said vertical riser also has a positive buoyancy, so that the positive buoyancy of said portion terminal of the flexible pipe and said upper portion of said vertical riser allow the tensioning of said riser in substantially vertical position and the alignment or continuity of curvature between the end of said end portion of the pipe flexible and the upper portion of said vertical riser at their connection, said positive buoyancy being provided by a plurality of regularly spaced coaxial peripheral floats and / or a continuous coating of positive buoyancy material, and
  • said flexible hose end portion having a positive buoyancy, extends over a portion of the total length of the flexible pipe, such that the flexible pipe has an S-shaped configuration, with a first flexible pipe portion on the side of said floating support having a plunger-shaped concave chain-shaped curvature and said remaining terminal portion of said flexible pipe having a convex curvature in the form of a chain reversed by its positive buoyancy, the end of said flexible pipe end portion, at the level of the upper end of said riser being preferably located above and substantially in alignment with the axis Z ₁ Z ' _{1 of} said riser at its upper end.

The term "vertical riser" is used here to account for the theoretical position of the riser when the riser is at rest, provided that the riser axis can know angular movements with respect to the vertical and move in a cone. angle α whose apex corresponds to the point of attachment of the lower end of the riser on said base. The upper end of said vertical riser may be slightly curved. Therefore, the term "flexible pipe end portion substantially in alignment with the axis Z ₁ Z ' _{1 of} said upper riser" that the end of the inverted chain curve of said flexible pipe is substantially tangential to the end of said vertical riser. In any case, in continuity of variation of curvature, that is to say without singular point, in the mathematical sense.

By "inertia" is meant here the moment of inertia of said inertial transition line element with respect to an axis perpendicular to the axis of said inertial transition conductor element, which reflects the bending stiffness in each planes perpendicular to the XX 'axis of symmetry of said driving element, this moment of inertia being proportional to the product of the section of material by the square of its distance from said axis of the driving element.

The term "continuity of curvature" between the upper end of the vertical riser and the portion of the hose having a positive buoyancy, that said variation of curvature does not present any singular point, such as a sudden variation of the angle of inclination of its tangent or a point of inflection.

Preferably, the slope of the curve formed by the flexible pipe is such that the inclination of its tangent relative to the axis Z ₁ Z ' ₁ of the upper part of said vertical riser increases continuously and progressively from the connection point between the upper end of the vertical riser and the end of said end portion of flexible pipe of positive buoyancy, without point of inflection and without point of inversion of curvature.

The installation according to the present invention thus makes it possible to prevent the tensioning of the vertical riser by a float on the surface or sub-surface, at which its upper end would be suspended, on the one hand, and, on the other hand, to avoid the connection to said plunging flexible pipe via a gooseneck device, as used in the prior art. This not only results in greater intrinsic reliability in terms of mechanical strength over time of the connection between the vertical riser and the flexible pipe, because the gooseneck devices are fragile. But above all, this type of installation confers increased stability in terms of angular variation (y) of the angle of excursion of the upper end of the vertical riser relative to a theoretical position of vertical rest, because this angular variation is reduced in practice to a maximum angle not exceeding 5 °, in practice of the order of 1 to 4 ° with the installation according to the invention, whereas, in the embodiments of the prior art, the angular excursion could reach 5 to 10 ° or more.

Another advantage of the present invention is that, because of this small angular variation of the upper end of the vertical riser, it is possible to implement, at its lower end, a rigid recess on a base resting at the bottom of the sea, without having recourse to a part of transition of inertia of dimension too important and thus too expensive. It is therefore possible to avoid the implementation of a flexible hinge, in particular of the spherical flexible ball type, as long as the junction between the lower end of the riser and said recess comprises an inertia transition piece.

The positive buoyancy of the riser and the flexible pipe can be made in known manner by coaxial peripheral floats surrounding said pipes, or, preferably, as regards the rigid pipe of the vertical riser, a positive buoyancy material coating. , preferably also constituting an insulating material, such as syntactic foam, in the form of a shell enclosing said pipe. Such buoyancy elements resistant to very high pressures, that is to say at pressures of about 10 MPa per 1000 m of water, are known to those skilled in the art and are available from the BALMORAL company (UK).

More particularly, the positive buoyancy will be distributed regularly and uniformly over the entire length of said end portion 10a of the flexible pipe and at least said upper portion 9b of said rigid pipe.

Preferably, to give maximum flexibility to the entire bottom-surface connection, said end portion of the flexible pipe having a positive buoyancy extends over a length of 30 to 60% of the total length of the flexible pipe. preferably about half of the total length of said flexible pipe.

More particularly, said flexible pipe has a positive buoyancy over a length corresponding to 30 to 60%, of its total length, preferably about half of its total length.

The portion of plunging flexible pipe, that is to say, negative buoyancy may be even shorter than the anchoring of the floating support surface is steep.

More particularly, to give the entire bottom-surface connection the appropriate flexibility, said positive buoyancy exerted on the end portion of the flexible pipe and at least the upper portion of said riser, must exert a vertical tension on the foundation to the lower end of said rigid pipe as a function of the water depth according to the following formulation: F = kH, F being said vertical tension expressed in tonnes, H being said depth expressed in meters, and k being a factor of between 0.15 and 0.05, preferably about 0.1.

If the overall positive buoyancy is distributed evenly and regularly over the entire length of the rigid pipe and on a said flexible pipe end portion, said positive buoyancy must allow to obtain a vertical resultant thrust of 50 to 150 kg / m, that is, said required buoyancy should correspond to the apparent weight of said rigid pipe and said flexible pipe end portion plus additional buoyancy of 50 to 150 kg / m.

• ledit riser vertical est relié à son extrémité inférieure à au moins une conduite reposant au fond de la mer, et
• ledit dispositif d'ancrage comprend un dispositif de support et de raccordement fixé sur une embase posée et ancrée au fond de la mer, et
• ladite conduite reposant au fond de la mer comprend un premier élément de conduite rigide terminal solidaire de ladite embase reposant au fond de la mer et ledit premier élément de conduite terminal est maintenu fixement par rapport à ladite embase, avec, à son extrémité, une première partie d'élément de raccordement, de préférence un élément mâle ou femelle d'un connecteur automatique, et
• ladite première bride de fixation à l'extrémité inférieure de ladite pièce de transition d'inertie est fixée à une deuxième bride de fixation à l'extrémité d'un deuxième élément de conduite rigide coudé, solidaire dudit dispositif de support et de raccordement fixé sur ladite embase et supportant, de façon fixe et rigide, ledit deuxième élément de conduite rigide coudé, dont l'autre extrémité comprend une deuxième partie d'élément de raccordement complémentaire de ladite première partie d'élément de raccordement et raccordée à celle-ci lorsque ledit élément de support et de raccordement est fixé à ladite embase.

In a preferred embodiment of a bottom-surface connection plant, the latter comprises the following features, according to which:

• said vertical riser is connected at its lower end to at least one pipe resting at the bottom of the sea, and
• said anchoring device comprises a support and connection device fixed on a base stationed and anchored to the bottom of the sea, and
• said pipe lying at the bottom of the sea comprises a first terminal rigid pipe element integral with said base resting at the bottom of the sea and said first terminal pipe element is held fixed relative to said base, with at its end a first connecting element part, preferably a male or female element of an automatic connector, and
• said first fastening flange at the lower end of said inertial transition piece is attached to a second fastening flange at the end of a second bent rigid pipe member secured to said support and connecting device attached to said base and rigidly and rigidly supporting said second bent rigid pipe element, the other end of which comprises a second connecting element part complementary to and connected to said first connecting element part when said support and connection member is attached to said base.

It will be understood that the static geometry of said first rigid pipe element terminating said pipe lying at the bottom of the sea, with respect to said base, and the static geometry of said second rigid pipe element bent, with respect to said support and connection device. fixed to said base, allow to position the respective ends of said first and second rigid pipe members, so as to facilitate the connection of the complementary parts of automatic connectors once the support device is connected is fixed to said base.

• ladite embase est ancrée au fond de la mer par un premier pieu tubulaire passant à travers un orifice traversant de ladite embase, ledit premier pieu étant enfoncé dans le sol au fond de la mer, et sa partie supérieure coopérant avec l'embase de manière à permettre l'ancrage de ladite embase, et
• ledit dispositif de support et raccordement supportant ledit deuxième d'élément de conduite rigide coudé comporte un deuxième pieu tubulaire, dénommé insert tubulaire d'ancrage, inséré à l'intérieur dudit premier pieu tubulaire d'ancrage de ladite embase, ladite embase comprenant un dispositif de blocage retenant ledit insert-tubulaire d'ancrage à l'intérieur dudit premier pieu tubulaire en cas de traction dudit deuxième pieu tubulaire vers le haut.

More preferably, the bottom-surface bonding plant has the characteristics that:

• said base is anchored to the bottom of the sea by a first tubular pile passing through a through orifice of said base, said first pile being driven into the ground at the bottom of the sea, and its upper part cooperating with the base so as to allow the anchoring of said base, and
• said support and connection device supporting said second bent rigid pipe element comprises a second tubular pile, called tubular anchoring insert, inserted inside said first tubular anchoring pile of said base, said base comprising a device locking member retaining said tubular anchoring insert within said first tubular pile in case of pulling said second tubular pile upwards.

Preferably, said first and second piles are assemblies of standard unitary elements of rigid pipes or unitary unit portions of rigid pipes, said second pile being shorter than said first pile.

This anchoring system of the base and fixing said support device and connection, at the lower end of said inertial transition piece on said base, is particularly advantageous for the following reasons.

Firstly, the combination of the first pile and the tubular anchoring insert constitutes a guide system, which makes it possible to make said first connecting element parts and the second end connecting element part coincide with each other. on the one hand, the terminal pipe element of the sea-bottom pipe which is fixedly positioned with respect to said base, and, on the other hand, the end of said rigid pipe element fixedly positioned relative to said support device.

The transverse forces or shear forces resulting from the bending moment occurring at the seabed, at the level of the recess of the lower end of the vertical riser at said base, resulting from the angular variations of the riser at its end higher, are not transmitted to said base but said first anchor pile, which extends deep to the bottom of the sea over a length of 30 to 70 m. Thus it is possible to implement a said base of relatively small volume and weight, which allows to be able to descend relatively easily from the surface, integral with said first end pipe element of the pipe resting at the bottom of the sea.

More particularly, said tubular anchoring insert is positioned in the axis of said inertia transition piece and said second rigid pipe member supported by said support and connecting device is curved or bent so that said first automatic connector-type connection member portion is laterally disengaged from the remainder of said support and connection device, and said second connector-type connector element automatically at the end of said first rigid terminal conduit element of said pipe resting at the bottom of the sea, integral with said base, is also disengaged with respect to the orifice of said base and with respect to said support device and connection of which said anchoring insert is inserted inside said first anchor pile.

In this embodiment, said first end pipe member of said bottom-lying pipe may preferably also be bent to coincide with the end of said second bent rigid pipe member and allow easy connection by a underwater automaton type ROV at the bottom of the sea.

• l'extrémité supérieure la plus mince de la pièce de transition présente un diamètre intérieur et une épaisseur sensiblement égaux aux diamètre intérieur et épaisseur de l'extrémité inférieure dudit riser vertical, auquel elle est fixée, et
• l'extrémité inférieure de la pièce de transition, du coté de ladite première bride de fixation, présente un diamètre intérieur sensiblement égal à celui de l'extrémité inférieure dudit riser vertical, mais une épaisseur supérieure à, de préférence égale à 3 à 10 fois, celle de l'extrémité inférieure dudit riser vertical.

More particularly, said inertia transition conductor element has a cylindro-conical shape of which:

• the thinner upper end of the transition piece has an inner diameter and a thickness substantially equal to the inner diameter and thickness of the lower end of said vertical riser, to which it is attached, and
• the lower end of the transition piece, on the side of said first fastening flange, has an inside diameter substantially equal to that of the lower end of said vertical riser, but a thickness greater than, preferably equal to 3 to 10 times, that of the lower end of said vertical riser.

Such inertial transition pipe members may be 15 to 50 m in length. More particularly, the cylindrical portion extending over a length of 3 to 5 m and the conical portion over a length of 10 to 47 m. These parts are very expensive to manufacture because they must be made using very thick pipes, but of varying thickness, assembled together, and then machined on a very large lathe to obtain the conical shape. Such parts are very expensive to achieve, because to obtain a good result, it is necessary that the pipe assembled by welding before machining is perfectly rectilinear, and moreover the turns capable of precisely machining parts of 20 to 30m in length are difficult to find and at a very high operational cost.

In some extreme cases, the cylindroconic transition pieces can not be made of steel, and require the use of titanium, which further increases the cost and complexity.

According to another original feature of the present invention, said inertial transition terminal pipe element comprises a main rigid pipe element and at least one, preferably a plurality, of coaxial reinforcing pipe elements disposed coaxially with said element. main pipe, each said reinforcing pipe element having an internal diameter greater than the outer diameter of the main pipe element and, if appropriate, the other reinforcing pipe element (s) it contains , the different main pipe elements and reinforcing pipe element (s) being positioned with one of their ends situated at the same level in the direction of the axis of symmetry Z ₁ Z ' _{1 of} said pipe elements, and each said reinforcing pipe element having a length (h _i , with i = 2 to n) smaller than that of h ₁ of the main pipe element and the case the other reinforcing pipe elements (h _i-1 contained therein, the annular space (D _i -d _{i + 1} ) between the various pipe elements being filled with a solid filler material, and the various elements of coaxial main pipe and reinforcing pipe (8b-8d) are fixed to the same lower plate consisting of a said first fastening flange.

Advantageously, according to the invention, said annular space is completely filled with the same solid filler material, preferably comprising an elastomer material, more preferably based on polyurethane, having a Shore hardness greater than or equal to A50, more preferably A50. at D70, and said inertial transition element is covered with a corrosion-resistant elastomeric cover material, preferably of polyurethane type, said inertia transition end-conductor element having a substantially cylindrical-conical shape through its coating by said covering material.

According to the present invention, because the annular space is completely filled with the same filling material and the covering material imparts a cylindro-conical shape to the transition piece, a continuous variation of the cross-sectional diameter of the same is obtained. the piece and with the same filling material over the entire height of the transition piece, which results in a gradual and continuous variation of inertia, that is to say without discontinuity of inertia. In addition, the implementation of an elastomeric cover material provides a corrosion protection guaranteeing greater longevity to said transition piece, which is subjected to a high mechanical stress and without this protection would have reduced longevity.

It is understood that said solid filler material must have a compressive strength so as to transfer the shear forces to the higher order reinforcing pipe member "i + 1" in a manner proportional to the deformation of a said element. coaxial it contains order "i" under the effect of a bending effort. In practice the solid filler must have a Poisson's ratio of 0.3 to 0.49, preferably 0.4 to 0.45.

This filler material may be an elastomer such as rubber or polyurethane alone or in combination with sand.

It is understood that this type of inertial transition pipe element is advantageous in its simplicity of manufacture and therefore much less expensive than the pipe elements having a cylindrical-conical transition piece with a wall of variable thickness of the technique. earlier.

• pour des raisons pratiques de fabrication et de coût et aussi pour augmenter la flexibilité et donc la longévité de la pièce de transition, ledit matériau de couverture et ledit matériau de remplissage comprennent un même matériau élastomère, de préférence à base de polyuréthanne.
• ledit matériau solide de remplissage comprend un polyuréthanne de dureté shore A90 ou A95.
• le matériau solide de remplissage comprend un élastomère chargé en matériau particulaire, de préférence du sable.

According to other particular features of said inertial transition terminal pipe element of the present invention:

• for practical reasons of manufacture and cost and also to increase the flexibility and thus the longevity of the transition piece, said cover material and said filler material comprise the same elastomeric material, preferably based on polyurethane.
• said solid filler material comprises a polyurethane of shore hardness A90 or A95.
• the solid filler material comprises an elastomer loaded with particulate material, preferably sand.

In an alternative embodiment, the solid filler material is in the form of a hydraulic binder such as cement, optionally filled with particulate material, preferably sand.

• la différence entre le diamètre interne dudit élément de conduite principal et le diamètre externe dudit élément de conduite de renfort de plus grand diamètre est égale à 3 à 10 fois, l'épaisseur dudit élément de conduite principale, et le nombre desdits éléments de renfort coaxiaux est n = 2 à 4,
• la différence de longueur entre les différents éléments de conduite de renfort coaxiaux (h_i - h_i+1) est sensiblement constante et égale à $\left(h_i\times \frac{1}{n}\right),$
  
• l'espace annulaire entre deux desdits éléments de conduite est supérieur ou égal à l'épaisseur dudit élément de conduite de plus petite épaisseur et inférieur ou égal à deux fois l'épaisseur dudit élément de conduite de plus grande épaisseur délimitant ledit espace annulaire,
• la longueur dudit élément de conduite principale est de 10 à 50 m de préférence de 20 à 30 m et il comprend 2 ou 3 desdits éléments de renfort coaxiaux,
• lesdits élément de conduite principale et éléments de conduite de renforts coaxiaux sont constitués chacun de tout ou partie d'un élément unitaire de conduite standard, notamment conduite sous-marine standard en acier, ou constitué chacun de plusieurs éléments unitaires de conduite standard assemblés bout à bout et de préférence maintenus coaxialement par, des cales de centrage réparties régulièrement le long de leur direction longitudinale et sur la section circulaire dans leurs espaces annulaires.

In another embodiment, said solid filler material is in the form of a particulate material, preferably sand and / or a hydraulic binder such as cement:

• the difference between the inner diameter of said main pipe element and the outer diameter of said reinforcing pipe element of larger diameter is 3 to 10 times, the thickness of said pipe element main pipe, and the number of said coaxial reinforcing elements is n = 2 to 4,
• the difference in length between the various coaxial reinforcing pipe elements (h _i - h _{i + 1} ) is substantially constant and equal to $\left(h_i\times \frac{1}{\mathrm{not}}\right),$
  
• the annular space between two of said pipe elements is greater than or equal to the thickness of said pipe element of smaller thickness and less than or equal to twice the thickness of said pipe member of greater thickness defining said annular space,
• the length of said main pipe element is 10 to 50 m preferably 20 to 30 m and it comprises 2 or 3 of said coaxial reinforcing elements,
• said main pipe element and coaxial reinforcing pipe elements each consist of all or part of a standard unitary pipe element, in particular a standard underwater steel pipe, or each consisting of a plurality of standard pipe elements assembled end-to-end. end and preferably held coaxially by, centering wedges evenly distributed along their longitudinal direction and on the circular section in their annular spaces.

An important advantage of the bottom-surface connection plant of the present invention also lies in the simplicity of its installation at the bottom of the sea.

1. 1/ on descend, au fond de la mer, un dit dispositif d'ancrage, et
2. 2/- on descend une conduite rigide formant un riser vertical, directement fixée, à son extrémité supérieure, à une extrémité de ladite conduite flexible présentant une portion terminale de flottabilité positive, l'autre extrémité de ladite conduite flexible étant suspendue à un flotteur en sub-surface, et
3. 3/- on fixe l'extrémité inférieure de ladite pièce de transition par encastrement au niveau dudit dispositif d'ancrage, et
4. 4/- on déplace l'extrémité de ladite conduite flexible suspendue audit flotteur et on la fixe ou relie à un dit support flottant.

The present invention therefore also provides a process for placing at the bottom of the sea a bottom-surface connection installation according to the invention, comprising the following successive steps in which:

1. 1 / we descend, at the bottom of the sea, a said anchoring device, and
2. 2 / - down a rigid pipe forming a vertical riser, directly fixed at its upper end, at one end of said flexible pipe having a terminal portion of positive buoyancy, the other end of said flexible pipe being suspended from a sub-surface float, and
3. 3 / - the lower end of said transition piece is fixed by embedding at said anchoring device, and
4. 4 / - the end of said flexible pipe suspended from said float is moved and fixed or connected to a said floating support.

1. 1/- on descend, au fond de la mer, une dite embase solidaire d'un dit premier élément de conduite rigide, ladite embase comprenant un orifice traversant, et
2. 2/- on descend au fond de la mer un dit premier pieu tubulaire d'ancrage que l'on enfonce au fond de la mer à travers ledit orifice de l'embase, pour ancrer ladite embase au fond de la mer, et
3. 3/- on descend au fond de la mer, depuis un navire de surface, ladite conduite rigide constituant ledit riser vertical, directement fixée à son extrémité supérieure à une dite conduite flexible, ladite pièce de transition à l'extrémité inférieure dudit riser étant fixée à un dit dispositif de support et de raccordement, supportant un dit deuxième élément de conduite rigide coudé ainsi qu'un dit insert d'ancrage, et
4. 4/- on fixe ledit dispositif de support et de raccordement sur ladite embase en insérant ledit insert d'ancrage à l'intérieur dudit premier pieu tubulaire, et
5. 5/- de préférence, on verrouille ledit insert d'ancrage à l'intérieur dudit premier pieu tubulaire à l'aide d'un dispositif de blocage, et
6. 6/- on réalise le raccordement desdits premier élément de conduite rigide coudé et deuxième élément de conduite rigide coudé, et
7. 7/- on finit de descendre ladite conduite flexible présentant une portion terminale de flottabilité positive, avec l'autre extrémité de ladite conduite flexible suspendue à un flotteur en sub-surface, et
8. 8/- on déplace puis on fixe ou relie l'autre extrémité de ladite conduite flexible à un dit support flottant.

Preferably, a method of setting up a bottom-surface connection installation according to the invention comprises the following successive steps in which:

1. 1 / - descends, at the bottom of the sea, a said base integral with a said first rigid pipe element, said base comprising a through orifice, and
2. 2 / - it descends to the bottom of the sea said first tubular anchoring stake that is pressed to the bottom of the sea through said orifice of the base, to anchor said base to the bottom of the sea, and
3. 3 / - it descends to the bottom of the sea, from a surface vessel, said rigid pipe constituting said vertical riser, directly fixed at its upper end to a said flexible pipe, said transition piece at the lower end of said riser being fixed a said support and connection device, supporting a said second bent rigid pipe element and a said anchoring insert, and
4. 4 / - fixing said support device and connection to said base by inserting said anchoring insert inside said first tubular pile, and
5. 5 / - preferably, said anchoring insert is locked inside said first tubular pile with the aid of a locking device, and
6. 6 / - the connection of said first rigid elbow pipe element and second rigid elbow pipe element, and
7. 7 / - it ends up down said flexible pipe having a terminal portion of positive buoyancy, with the other end of said flexible pipe suspended from a sub-surface float, and
8. 8 / - it moves and then fixes or connects the other end of said flexible pipe to a said floating support.

This process according to the invention is particularly simple and therefore advantageous to set up. This simplicity results from the fact that the anchoring function on said base is filled by said anchoring insert, on the underside of said support and connection device, and that the bending moments experienced by the inertia transition piece are taken by the first anchoring pile driven to the bottom of the sea and not by said base, so that it is possible to implement a relatively low weight and low volume base.

• la figure 1 est une vue de côté d'une installation de liaison fond-surface 1 selon l'invention comportant une conduite rigide 9 de type Riser encastrée en partie basse dans un premier pieu 6 traversant une embase 4 et reliée à son extrémité supérieure 9b à une conduite flexible 10 flottante sur une partie terminale 10a de sa longueur, l'autre extrémité de la conduite étant reliée à un FPSO ("Floating Production Storage Offloading") 12,
• la figure 2A est une vue de côté de l'installation de la liaison fond-surface dans son embase en cours de mise en place à partir d'un navire de travail 20,
  la figure 2B est une vue de côté de la mise en place d'un dit premier pieu d'ancrage 6 dans une embase supportant l'extrémité d'un conduite sous-marine reposant sur le fond de la mer,
• la figure 2C est une vue de côté de l'extrémité inférieure du riser 9 avec une pièce de transition d'inertie 8 au niveau de son raccordement avec un dispositif de support et de raccordement 5 comprenant un insert tubulaire d'ancrage 5e à l'intérieur dudit pieu d'ancrage 6,
• la figure 3 est une vue de côté de l'installation de la liaison fond-surface, en cours de mise en place, après engagement de l'insert d'ancrage 5e dans le pieu d'ancrage 6,
• les figures 3A et 3B représentent en vue de côté et en coupe deux variantes d'embase du raccordement à une conduite reposant au fond de la mer d'une installation de liaison fond-surface selon l'invention,
• la figure 4 est une vue en coupe et en vue de côté d'une pièce de transition 8 massive en acier, de forme conique, installée à l'extrémité inférieure du riser 9,
• les figures 5A-5B-5C sont des vues en coupe et en vue de côté, d'une version préférée de réalisation d'une pièce de transition constituée d'empilements de conduites acier coaxiales, les interstices étant remplis de matériaux plastiques sur les figures 5B et 5C,
• la figure 6 est un diagramme illustrant la variation de l'inertie des pièces de transition selon la figure 5C.

Other features and advantages of the present invention will become more apparent in the light of the detailed description which follows, given in an illustrative and nonlimiting manner, with reference to the drawings in which:

• the figure 1 is a side view of a bottom-surface connection installation 1 according to the invention comprising a rigid pipe 9 of Riser type recessed in the lower part in a first pile 6 passing through a base 4 and connected at its upper end 9b to a pipe floating hose 10a on an end portion 10a of its length, the other end of the pipe being connected to a FPSO (Floating Production Storage Offloading) 12,
• the Figure 2A is a side view of the installation of the bottom-surface connection in its base being set up from a work vessel 20,
  the Figure 2B is a side view of the establishment of a said first anchoring pile 6 in a base supporting the end of an underwater pipe resting on the seabed,
• the Figure 2C is a side view of the lower end of the riser 9 with an inertia transition piece 8 at its connection with a support and connection device 5 comprising a tubular anchoring insert 5e inside said pile anchor 6,
• the figure 3 is a side view of the installation of the bottom-surface connection, in the course of being put in place, after engagement of the anchoring insert 5e in the anchoring pile 6,
• the Figures 3A and 3B show in side view and in section two base variants of the connection to a pipe resting at the bottom of the sea of a bottom-surface connection installation according to the invention,
• the figure 4 is a sectional and side view of a solid conical steel transition piece 8 installed at the lower end of the riser 9,
• the Figures 5A-5B-5C are views in section and in side view, of a preferred embodiment of a transition piece consisting of stacks of coaxial steel pipes, the interstices being filled with plastic materials on the Figures 5B and 5C ,
• the figure 6 is a diagram illustrating the variation of the inertia of the transition pieces according to the Figure 5C .

In the figure 1 there is shown a bottom-surface connection facility 1 connecting an underwater line 2 resting on the seabed 3 to a floating support type FPSO 12 surface moored by anchor lines 12a.

1. a) une conduite flexible 10 comprenant une première partie 10b concave qui s'étend depuis l'extrémité 10e de la conduite flexible fixée au support flottant 12 jusqu'à environ la moitié de la conduite flexible sous forme d'une configuration en chaînette plongeante de par sa flottabilité négative jusqu'à un point d'inflexion en 10d sensiblement à la moitié de longueur de la conduite flexible, la partie terminale 10a s'étendant depuis le point central d'inflexion 10d jusqu'à l'extrémité 10c de la conduite flexible présentant une flottabilité positive de par une pluralité de flotteurs 10f de préférence régulièrement espacés le long et autour de ladite portion terminale 10a de conduite flexible, et
2. b) une conduite rigide montante en acier 9 ou « riser vertical » équipée de moyens de flottabilité, non représentés, tels des demi-coquilles de mousse syntactique réparties de préférence de manière uniforme sur tout ou partie de la longueur de ladite conduite rigide, et comprenant à son extrémité inférieure une pièce de transition d'inertie 8 équipé d'une première bride de fixation 9a à son extrémité inférieure. La première bride de fixation 9a est fixée sur une deuxième bride de fixation 5a constituant la partie supérieure d'un dispositif de support et de raccordement 5, lui-même ancré sur le premier pieu 6 solidaire de l'embase 4 reposant au fond de la mer, ledit dispositif de support et raccordement 5 permettant le raccordement de l'extrémité inférieure du riser 9 à une conduite 2 reposant au fond de la mer, comme explicité ci-après.

An installation according to the invention comprises from the support 12 on the surface to a base 4 at the bottom of the sea, the following elements:

1. a) a flexible pipe 10 comprising a first concave part 10b which extends from the end 10e of the flexible pipe fixed to the floating support 12 up to about half of the flexible pipe in the form of a plunging chain configuration by its negative buoyancy to a point of inflection at 10d substantially half the length of the flexible pipe, the end portion 10a extending from the central point of inflection 10d to the end 10c of the flexible pipe having positive buoyancy by a plurality of floats 10f preferably evenly spaced along and around said end portion 10a of flexible pipe, and
2. b) a rigid steel riser pipe 9 or "riser vertical" equipped with buoyancy means, not shown, such half-shells of syntactic foam preferably distributed uniformly over all or part of the length of said rigid pipe, and comprising at its lower end an inertia transition piece 8 equipped with a first fastening flange 9a at its lower end. The first fastening flange 9a is fixed on a second fastening flange 5a constituting the upper part of a support and connection device 5, itself anchored on the first pile 6 integral with the base 4 resting at the bottom of the sea, said support device and connection 5 for connecting the lower end of the riser 9 to a pipe 2 resting at the bottom of the sea, as explained below.

The flexible pipe has a variation of continuous curvature, first concave in the plunger chain configuration part 10b, then convex in the positive buoyancy end portion 10a with an inflection point 10d between the two, thus forming an S disposed in a substantially vertical plane.

$$\mathrm{R}\mathrm{=}\mathrm{Ro}\mathrm{.}{\left(\mathrm{Y}\mathrm{/}\mathrm{Ro}\mathrm{+}\mathrm{1}\right)}^{\mathrm{2}}$$

dans lesquelles :

• x représente la distance dans la direction horizontale entre le point de tangence horizontale et un point M de la courbe,
• y représente l'altitude du point M (x et y sont donc les abscisses et ordonnées d'un point M de la courbe par rapport à un repère orthonormé dont l'origine est audit point de tangence)
• R₀ représente le rayon de courbure au dit point de tangence horizontale.
• R représente le rayon de courbure au point M (x, y)

The geometric curve formed by a conduct of uniform gravity weight suspended under gravity, called "chain" is a mathematical function of hyperbolic cosine type (Coshx = (e ^x + e ^-x ) / 2, connecting the abscissa and the ordinate of any point of the curve according to the following formulas: $$\mathrm{there}\mathrm{=}{\mathrm{R}}_{\mathrm{0}}\left(\cosh \left(\mathrm{x}\mathrm{/}{\mathrm{R}}_{\mathrm{0}}\right)\mathrm{-}\mathrm{1}\right)$$

$$\mathrm{R}\mathrm{=}\mathrm{ro}\mathrm{.}{\left(\mathrm{Y}\mathrm{/}\mathrm{ro}\mathrm{+}\mathrm{1}\right)}^{\mathrm{2}}$$

in which :

• x represents the distance in the horizontal direction between the point of horizontal tangency 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 tangency)
• R ₀ represents the radius of curvature at said point of horizontal tangency.
• R represents the radius of curvature at the point M (x, y)

Thus, the curvature varies along the chain from the surface (for a plunging chain) or from its end portion to the upper end of the riser (for an inverted chain) where its radius has a maximum value R _max , up to point of horizontal tangency (which is the low point of the plunging chain 10b and the high point of the inverted chain 10a), where its radius has a minimum value R _min (or R ₀ in the formula above).

In operation, as shown on the figure 1 when the upper part of the rigid pipe 9 is inclined at an inclination γ relative to the vertical ZZ ', the end 10c of the end portion of the positive buoyancy 10a of the flexible pipe remains substantially in the axial alignment Z' ₁ Z 'of the upper end 9b of the rigid pipe 9, and in any case in continuity of curvature variation with the upper end 9b of the rigid pipe, which can also be slightly curved. Here we mean by "continuous variation of curvature" that there is no singular point in the mathematical sense in this variation of curvature. This confers a better mechanical strength to the sealed fastener 11 between the two pipes and avoids the implementation of a gooseneck device as implemented in the prior art.

The advantage of this flexible pipe is to allow its initial portion 10b plunging to dampen the excursions of the floating supports 12 so as to stabilize the end 10c of the flexible pipe connected to a rigid riser pipe of the vertical riser 1.

The end of the portion of the floating end portion 10c of the flexible pipe carries a first fastening flange member 11 with the upper end of a rigid pipe extending from the seabed recessed at a base 4 resting at the bottom of the sea.

The vertical riser 9 is "tensioned" on the one hand by the buoyancy of the end portion 10a of the flexible pipe, but on the other hand and above all by floats regularly distributed at least on the upper part 9b, preferably all along the rigid pipe, especially in the form of syntactic foam advantageously acting as both an insulation and buoyancy system. These floats and this syntactic foam can be distributed along and around the rigid pipe over its entire length or, preferably, only on a portion of its upper part.

Thus, if the base 4 is at a depth of 2500 meters, it can be limited to coating the rigid pipe 1 of syntactic foam over a length of 1000 m from its upper end, which allows to implement a syntactic foam that must withstand less pressure than if it had to withstand pressures up to 2500 m, and therefore a radically reduced cost compared to a syntactic foam to withstand said depth of 2500 m.

The rigid pipe 1 according to the invention is therefore "tensioned" without implementation of a float surface or sub-surface as in the prior art, which limits the effects of the current and the swell, and thus drastically reduces the excursion of the upper part of the vertical riser and therefore the efforts in the foot of riser at the level of the embedding.

To give the whole of the bottom-surface connection a great flexibility, a vertical tension is advantageously exerted on the foundation according to the height of water according to the following formulation: F = kH, F being expressed in tonnes, H being expressed in meters, k being such that 0.15>k> 0.05, preferably k ≈ 0.1.

If the positive buoyancy is distributed over the entire length of the rigid pipe, it represents from 50 to 150 kg of resulting thrust per meter of pipe.

It is distributed, preferably continuously, along the rigid pipe, as well as along the end portion 10a of the flexible pipe. On the latter, the distribution is generally done by means of buoys 10f spaced from each other and regularly distributed on the portion 10a, each representing the equivalent of a few meters of the required thrust, for example for a spacing of 5 to 10 m the resulting thrust required for each float will be 250 to 1500 kg per float.

It is understood that the overall buoyancy corresponds to what is commonly called the "Archimedes thrust" or "Apparent Weight" on each of the parts of the bottom-surface connection: corresponding on the one hand to the buoyancy required for counterbalance the respective apparent weight of the rigid pipe and the flexible pipe, and secondly to the additional buoyancy necessary for tensioning which thus provides a resultant vertical thrust of 50 to 150 kg / m as previously described.

By doing so, the overall buoyancy at the transition between rigid pipe and flexible pipe being substantially constant, this results in a continuity of curvature variation between the upper end of said rigid pipe and the end of said flexible pipe which is connected, without singular point, to the mathematical meaning of the term.

The fastening flange system 11 between the upper end of the vertical riser 9 and the flexible pipe 10, and the connection of the fastening flanges 9a, 5a between the lower end to the inertia transition piece 8 and the device of FIG. connection support 5, provide sealed connections between the relevant conduits.

The base 4 resting at the bottom of the sea supports a first curved or curved terminal pipe element 2a of said pipe resting at the bottom of the sea 2. This first curved or curved end pipe element 2a comprises at its end a first male or female part of an automatic connector 7b, which is released laterally. relative to a through hole 4a of said base, but positioned fixedly and determined with respect to the axis ZZ 'of said orifice.

The support and connection device 5 supports a second rigid elbow pipe element 5b having at its upper end said second attachment flange 5a and at its lower end a second female or male part of an automatic connector 7a, complementary to Part 7b.

A first tubular anchoring pile 6 is lowered from an installation vessel 20 on the surface, then depressed, preferably beaten in known manner, through an orifice 4a vertically traversing from one end to the base 4 until a peripheral protuberance 6a at the upper end of said first pile 6 comes to cooperate with a complementary shape 4c in the upper part of said orifice 4a of the base. The orifice 4a is slightly larger than the first pile 6 to let it slide freely. And when the threshing of said first pile is completed, the base 4 is thus nailed to the ground without being able to move laterally or pivot around any horizontal axis.

Optionally, a plurality of orifices and said first piles 6 are provided.

In the method of setting up a bottom-surface connection installation according to the invention, the first step consists in descending to the bottom of the sea from the surface, said base equipped with said first terminal pipe element 2a of the resting pipe. at the bottom of the sea. After anchoring said base by a said first pile 6, anchoring of the transition piece 8 is carried out at the lower end of the vertical riser by fixing on the support and connection device 5, itself anchored on said base, thus forming a rigid recess of the lower end of the vertical riser.

The support and connection device 5 consists of elements of rigid structure and stiffener 5c supporting said second fastening flange 5a and said second curved rigid pipe element 5b, said rigid structure elements 5c also ensuring the connection between said second flange fixing 5a and a lower plate 5d supporting on the underside a second tubular pile 5e called tubular anchoring insert.

When the base 4 is anchored to the bottom of the sea 3 as shown on the Figure 2A the various surface-to-surface connection elements are manufactured on board the surface vessel 20, in particular assembling the rakes consisting of a plurality of standard pipe elements, which are progressively lowered. First of all, said device 5 is connected in a sealed manner to the lower end of the vertical riser 9 via the conical transition piece 8, then the entire vertical riser equipped with its buoyancy elements, and finally the flexible connecting pipe equipped with its buoyancy elements fixed in direct continuity with the upper end of the vertical riser 9.

The assembly and the laying of the rigid pipe 9 are conventionally made from the ship 20 by assembling unit pipe elements or reams of unitary elements stored on the surface vessel 20, and descended as and when a technique known to those skilled in the art and described in particular in previous patent applications in the name of the applicant, from a laying ship in J.

When all of the rigid pipe 9 has been manufactured and lowered to the seabed, is connected in known manner, for example by means of flanges 11 the upper end of the pipe 9 at the end of a flexible pipe 10, which as and when it deviates from the laying ship 20 is first of all under vertical form as depicted on the Figure 2A in that it is made floating at least in its end portion 10a by the buoyancy elements 10f evenly distributed over the end portion 10a.

It will also be noted that the rigid steel pipe 9 may be in known manner a Pipe-in-Pipe type pipe comprising an insulation system in the annular space between the two coaxial pipes constituting the riser 9 and furthermore a pipe system. insulation such as syntactic foam acting as a buoyancy system as described above.

When the lower end of the tubular anchoring insert 5e, preferably having a slightly conical shape 5f is positioned close to and in line with the orifice 4a of the base 4, it is advantageous to direct said tubular insert anchoring 5th, more precisely thanks to an automatic submarine or "ROV" 20a piloted from the surface. Said tubular insert 5e of length 10 to 15 m then returns naturally by its own weight in said first tubular anchoring pile driven to the bottom of the sea to a depth of 30 to 70 m.

The external diameter of the tubular anchoring insert 5e may be slightly smaller than the internal diameter of the first pile 6, for example less than 5 cm, which facilitates guiding the tubular insert 5 inside said first pile 6 , while preventing transverse movements in a horizontal plane once the tubular insert 5 is fully inserted as shown in FIG. figure 3 .

At this moment, a latch 4b shown in the retracted position on the Figure 2A is moved to the engaged position as on the figures 1 and 3 so as to block the upper plate 5d of the tubular insert 5e, inside said first pile 6, thus preventing any upward movement of the bottom-surface connection assembly 1 which is recessed via of the connecting support device 5 in the first pile 6 integral with said base 4.

After engaging the latch 4b, the turning of the flexible pipe is terminated as shown in FIG. figure 3 and connecting the upper end of the flexible pipe to a sub-surface temporary buoy 21, itself connected to a dead body 21b resting at the bottom of the sea by a cable 21a.

By doing so, it is advantageous to pre-install the entire bottom-surface connection 1 before the introduction of the FPSO 12, which greatly facilitates operations.

Once the floating support 12 is positioned on the surface, the end 10e of the flexible pipe 10 is recovered which is then connected to said floating support FPSO 12 as shown in FIG. figure 1 , and the provisional buoy 21 is recovered as well as its dead body 21b and its anchoring cable 21a.

The tubular insert 5e transmits to said first tubular pile 6, the bending moments due to the cutting and transverse forces experienced at the recess of the part 8 on the device 5.

The fixing system of the upper end of the rigid pipe 9 with the flexible pipe 10 and the tensioning of said pipes gives greater stability to the upper end of the rigid pipe 9 with an angular variation y not exceeding in operation the 5 ° C.

Thus, it has been possible according to the present invention to achieve a rigid embedding of the lower end of the rigid steel pipe 9 on the base 4 with the connecting support device 5. To do this, the lower end pipe element of the rigid pipe 9 comprises a conical transition piece 8 whose inertia in cross section increases progressively from a value substantially identical to the inertia of the pipe element of the riser 9 to which it is connected, in the tapered upper part of the transition piece 8, to a value 3 to 10 times greater than the level of its lower part connected to said first attachment flange 9a. The coefficient of variation of inertia essentially depends on the bending moment that the vertical riser must bear at said transition piece, said moment being a function of the maximum excursion of the upper part of the rigid steel pipe 9, therefore of the angle there. To achieve this transition piece 8 is used high yield strength steels and in extreme cases of stress, it may be necessary to manufacture titanium transition parts 8.

On the figure 4 , there is shown a cylindro-conical transition piece 8 having a variable thickness gradually increasing from the tapered upper part 81 to the thicker lower part 82 with a constant internal diameter corresponding to the internal diameter of a standard rigid pipe and In any event, at the internal diameter of the second rigid pipe element 6.

In a preferred version of the invention, shown in section and in side view on the Figures 5A-5B-5C , the transition piece 8 consists of a main steel pipe element 8a, preferably of internal diameter d ₁ identical to that of the current portion of the pipe 9, and preferably of thickness equal to or slightly greater than that of the of said current portion of said duct 9, and preferably of thickness equal to that of said second elbow pipe element 5b. To obtain an increase in inertia as one approaches the flange 9a, one has a succession of coaxial pipe elements (8b-8d) of heights (h ₂ , h ₃ , h ₄ ) each of said coaxial pipe elements having an internal diameter (d ₂ -d ₄ ) greater than the external diameter D ₁ -D ₃ of the preceding coaxial pipe element and a length or height less than the length of the previous pipe element, that is to say the pipe element that it contains or that it covers, and a thickness depending on the desired increase in stiffness.

So, on the Figure 5A , there is shown a transition piece 8 having a first inner pipe element 8a and three element 8b-8c-8d coaxial reinforcement pipe of increasing diameter d ₂ -d ₃ -d ₄ and lengths h ₂ -h ₃ -h ₄ decreasing, each of said coaxial pipe elements being integral with its lower end of the same said first flange 9a. To ensure a substantially continuous variation of the inertia between the high part of low inertia of the transition piece 8, and the low part of high inertia located at the connection with the flange 9a, is advantageously injected in the annular spaces between said elements of coaxial pipes, an elastomeric material 8e, preferably such as a polyurethane, whose shore hardness is adjusted to obtain the desired stiffness variation, in particular a shore hardness of A50 to D70.

It is sufficient to inject said rigid material 8e only in the annular gaps between the coaxial pipe elements, as shown in FIG. Figure 5C . However, according to the invention, a mold is installed in such a way as to obtain a cylindro-conical piece as shown in FIG. Figure 5B , which makes it possible to perform in a single operation the reinforcement of the transition piece and its protection vis-à-vis the aggression of the external environment by an outer coating thus conferring a cylindro-conical shape with a transition of steady and continuous inertia. Care should be taken not to cover the upper part of the transition piece with thermosetting resin over a length of 20 to 50 cm so as to be able to assemble it on board the installation vessel 20, by welding at the lower end of the the rigid pipe 9.

• on soude l'extrémité inférieure du premier élément de conduite principale 8a de plus grande longueur sur la bride 9a, et
• on insère autour dudit premier élément de conduite principal 8a un premier élément de conduite de renfort 8b coaxial dont on soude l'extrémité inférieure sur la même bride 9a, et
• on insère la deuxième conduite de renfort 8c autour du premier élément de conduite de renfort 8b, et on soude son extrémité inférieure sur la bride 9a, et

• on insère un troisième élément de conduite de renfort 8d de plus petite hauteur autour du deuxième élément de conduite de renfort 8c, et on soude son extrémité inférieure sur la bride 9a, et
• on injecte un matériau thermoplastique ou thermodurcissable entre les divers éléments de conduites, et le cas échéant on revêt leur surface externe à l'aide d'un un moule cylindro-conique pour obtenir la rigidité et variation d'inertie et protection contre la corrosion recherchées.

It will be understood that in order to manufacture the transition piece 8 according to the invention, the procedure is as follows:

• the lower end of the first main pipe element 8a of greater length is welded to the flange 9a, and
• a coaxial first reinforcing pipe element 8b is inserted around said first main pipe element 8a, the lower end of which is welded to the same flange 9a, and
• inserting the second reinforcing pipe 8c around the first reinforcing pipe element 8b, and weld its lower end to the flange 9a, and

• inserting a third reinforcing conduit member 8d of smaller height around the second reinforcing conduit member 8c, and welding its lower end to the flange 9a, and
• a thermoplastic or thermosetting material is injected between the various pipe elements, and, if necessary, their external surface is coated with a cylindro-conical mold in order to obtain the desired rigidity and variation in inertia and protection against corrosion. .

On the figure 6 , the variation diagram of the inertia I is plotted on the ordinate between the flange 9 and the upper end of the transition piece 8 of the Figures 5B and 5C . The dashed staircase 30 represents the variation of the steel section in the absence of roofing and filling material at each of the reinforcing pipe members. The curves 31-32-33 represent the variation of the inertia (ΣEI) of the transition piece 8 of the figures 4 and 5C depending on its length, depending on the type of filler material. Curve 33, of parabolic shape is obtained with a polyurethane filling material of shore hardness A90 or A95, and is a preferred version of the invention. The curve 31 is obtained with a much stiffer material, such as a cement with very high performance, alone or in combination with a powdery load, such as sand.

The intermediate curve 32 corresponds to the steel transition piece of the figure 4 .

The implementation of the same filling material and roofing material according to the cylindro-conical profile of the Figure 5B Polyurethane type, as described above, preferably hardness A90 or A95 is closer to the curve 32 than curves 31 and 33 and is therefore the preferred version of the invention in terms of inertia variation.

For example, a transition piece of 18m in length h ₁ is produced using a flange 9a of 200 mm thick on which is welded a main pipe element 8a of external diameter d ₁ = 323.85 mm, of thickness 20.6mm and length h ₁ = 18m, of a first coaxial reinforcement 8b of external diameter d ₂ = 457.20mm, thickness 12.7mm and length h ₂ = 12m, of a second coaxial reinforcement 8c of external diameter d ₃ = 609.6mm, thickness 6mm and length h ₃ = 6m. Then it overmould all, either in vertical position, or in an oblique position with a slope of 5 to 30% to facilitate filling and avoid voids, using a polyurethane resin 8th hardness shore A90 or A95. The space between the first pipe 8a and the first reinforcement 8b is 53.98mm, and the space between the second reinforcement and the first reinforcement is 70.2mm. The increase of the inertia is substantially of a factor k = 3 at the level of the first reinforcement 8b, and of a factor k = ₅ at the level of the second reinforcement 8c. During casting, vacuum cycles are advantageously carried out in the mold during filling so as to eliminate as much unwanted air bubbles as possible. Indeed, because the purpose of the transition piece is to be installed at a very great depth, the hydrostatic pressure can have detrimental effects on the overall mechanical operation following a collapse on itself of said bubbles due to said pressure which is substantially 10MPa per 1000m of water.

On the figure 3A , the invention has been described with a base 4 placed at the same time as the submarine pipe resting on the bottom, said base being stabilized by a first pile 6 therethrough. But we remain in the spirit of the invention considering as on the figure 3B a base 4 constituted by a suction anchor, having an orifice, preferably circular integrated with said suction anchor and acting as a pile 6 and capable of receiving the anchoring insert 5e. Thus, the support and connecting device 5 at the lower end of the bottom-surface connection is directly embedded in the suction anchor whose weight reaches 25 to 50 tons for a diameter of 3 to 5 m and a height of 20-25m. In this configuration, underwater driving 2 is laid independently and therefore requires a connecting pipe 7 manufactured on demand after installation of the bottom-surface connection and the underwater pipe 2. Said connecting pipe 7 then requires two automatic connectors 7a-7a ₁ , 7b ₁ -7b, one at each of its ends, whereas the version described with reference to the figure 3A only requires one 7a-7b automatic connector.

The invention has been described in a preferred version manufactured and simultaneously installed on site from a laying ship 20, but it remains in the spirit of the invention with a prefabrication of the complete set on a shipyard on land , the assembly then being towed substantially horizontally to the site, then finally cabane for the insertion of the anchoring insert 5e in the first tubular pile 6.

Claims (15)

1. A bottom-to-surface connection installation, in particular at great depth of more than 1000 m, the installation comprising:

   a) at least one substantially vertical rigid rising pipe, referred to as a vertical riser (9), fastened at its bottom end to an anchor device (4, 5, 6) at the sea bottom (3) ; and

   b) at least one flexible connection pipe (10) providing the connection between a floating support (12) and the top end of said vertical riser (9); and

   c) one end of said flexible pipe is directly connected, preferably via a flange system (11), to the top end of said vertical riser (9); and

   the installation being characterized in that:

   • the bottom end of said vertical riser comprises a terminal pipe element forming an inertia transition piece (8) in which inertia varies in such a manner that the inertia of said terminal pipe element at its top end is substantially equal to that of the pipe element of the main portion of the vertical riser to which it is connected, said inertia of the terminal pipe element (8) increasing progressively down to the bottom end of said inertia transition piece, and including a first fastening flange (9a) enabling the bottom end of said vertical riser to be restrained (5a-5e) at said anchor device (4, 5, 6) at the sea bottom,

   • a terminal portion (10a) of the flexible pipe adjacent to its junction with the top end of said riser presents positive buoyancy, and at least the top portion (9b) of said vertical riser also presents positive buoyancy, such that the positive buoyancies of said terminal portion (10a) of the flexible pipe and of said top portion (9a) of said vertical riser (9) enable said riser to be tensioned in a substantially vertical position and enable alignment or continuity of curvature to be achieved between the end of said terminal portion (10a) of the flexible pipe and the top portion (9b) of said vertical riser where they are connected together, said positive buoyancy being provided by a regularly spaced apart plurality of coaxial peripheral floats (10f) and/or a continuous coating of positive buoyancy material; and

   • said terminal portion (10a) of the flexible pipe (10) presenting positive buoyancy extends over a fraction of the total length of the flexible pipe, such that the flexible pipe presents an S-shaped configuration, with a first portion (10b) of flexible pipe beside said floating support (12) presenting concave curvature in the form of a catenary in a diving catenary configuration and said remaining terminal portion of said flexible pipe (10a) presenting convex curvature in an inverted catenary shape as a result of its positive buoyancy, the end (10c) of said terminal portion of the flexible pipe (10a) at the top end of said riser being situated above and preferably substantially in alignment with the axis Z₁Z'₁ of said riser at its top end (9b).
2. A bottom-to-surface connection installation according to claim 1, characterized in that:

   • said positive buoyancy is regularly and uniformly distributed over the entire length of said terminal portion (10a) of flexible pipe and over at least the top portion (9b) of rigid pipe, preferably over the entire length of said rigid pipe, so as to obtain a resultant vertical thrust of 50 kg/m to 150 kg/m over the entire length of said rigid pipe and the length of said terminal portion of flexible pipe; and

   • said flexible pipe (10) presents positive buoyancy (10a) over a length corresponding to 30% to 60% of its total length, preferably about half of its total length.
3. A bottom-to-surface connection installation according to claim 1 or claim 2, characterized in that:

   • said vertical riser (9) is connected at its bottom end to at least one pipe (2) resting on the sea bottom; and

   • said anchor device (4, 5, 6) comprises a support and coupling device (5) fastened to a base (4) placed on and anchored to (6) the sea bottom; and

   • said pipe (2) resting on the sea bottom includes a terminal first rigid pipe element (2a) secured to said base (4) resting on the sea bottom (3) and said terminal first pipe element is held stationary relative to said base with a first portion of a coupling element (7b) at its end, preferably a male or female element of an automatic connector; and

   • said first fastening flange (9a) at the bottom end of said inertia transition piece (8) is fastened to a second fastening flange (5a) at the end of a bent second rigid pipe element (5b) secured to said support and coupling device (5a-5e) fastened to said base (4) and supporting in stationary and rigid manner said bent second rigid pipe element (5b), with the other end thereof including a second coupling element portion (7a) complementary to said first coupling element portion (7b) and connected thereto when said support and coupling element (5a-5e) is fastened to said base.
4. A bottom-to-surface connection installation according to claim 3, characterized in that:

   • said base (4) is anchored to the sea bottom by a first tubular pile (6) passing through a through orifice (4a) in said base, said first pile (6) being driven into the ground at the sea bottom, and its top portion (6a) co-operating with the base in such a manner as to enable said base to be anchored; and

   • said support and coupling device (5a-5e) supporting said bent second rigid pipe element (5b) includes a second tubular pile, referred to as a tubular anchor insert (5e), that is inserted inside said first tubular anchor pile of said base, said base including a locking device (4a) retaining said tubular anchor insert (5e) inside said first tubular pile (2b) in the event of upward traction being applied to said second tubular pile (5e).
5. A bottom-to-surface connection installation according to claim 4, characterized in that said first and second piles are assemblies of standard rigid unit pipe elements or of portions of rigid unit pipe elements, said second pile being shorter than said first pile.
6. A bottom-to-surface connection installation according to claim 4 or claim 5, characterized in that said tubular anchor insert (5e) is positioned on the axis of said inertia transition piece (8) and said second rigid pipe element (5b) supported by said support and coupling device (5a-5e) is curved or bent so that said first coupling element portion (7a) of the automatic connector type is also offset laterally relative to the remainder of said support and coupling device (5), and said second coupling element portion (7b) of the automatic connector type at the end of said terminal first rigid pipe element (2a) of said pipe (2) resting on the sea bottom that is secured to said base (4) is also offset relative to the orifice (4a) in said base and relative to said support and coupling device (5) in which said anchor insert is inserted inside said first anchor pile (6).
7. A bottom-to-surface connection installation according to any one of claims 1 to 6, characterized in that said inertia transition terminal pipe element (8) is of cylindrical and conical shape, in which:

   • the thinnest top end of the transition piece presents an inside diameter d₁ and a thickness that are substantially equal to the inside diameter and the thickness of the bottom end of said vertical riser, to which it is fastened; and

   • the bottom end of the transition piece beside said first fastening flange (9a) presents an inside diameter d₁ substantially equal to the inside diameter of the bottom end of said vertical riser, but a thickness D₄-d₁ that is greater, preferably three to ten times greater than the thickness of the bottom end of said vertical riser.
8. A bottom-to-surface connection installation according to claim 6 or claim 7, characterized in that said inertia transition terminal pipe element (8) comprises a main rigid pipe element (8a) and at least one and preferably a plurality n of coaxial reinforcing pipe elements (8b-8d) placed coaxially around said main pipe element (8a), each said reinforcing pipe element (8b-8d) presenting an inside diameter d_i+1 greater than the outside diameter D₁, D_i of the main pipe element and where appropriate of the other reinforcing pipe element(s) it contains, the various main and reinforcing pipe elements (8a-8d) each being positioned with one end situated at the same level along the axis of symmetry Z₁Z'₁ of said pipe elements, and each said reinforcing pipe element (8b-8d) presenting a length h_i-1 with I = 2 to n, that is less than the height h₁ of the main pipe element, and where appropriate the heights h_i+1 of the other reinforcing pipe elements that it contains, the annular gap D₁ - d_i+1 between the various pipe elements being filled with a solid filler material (8e) and the various main and coaxial reinforcing pipe elements (8a-8d) are fastened to a common bottom plate (9a) constituted by a said first fastening flange (9a).
9. A bottom-to-surface connection installation according to claim 8, characterized in that:

   • said annular gap is completely filled with a common solid filler material preferably comprising an elastomer material, more preferably a material based on polyurethane, presenting hardness that is greater than or equal to A50 on the Shore scale, and more preferably that lies in the range A50 to D70 on the Shore scale; and

   • said inertia transition element is covered in a corrosion-resistant elastomer covering material, preferably of the polyurethane type, said inertia transition terminal pipe element presenting a substantially cylindrical-and-conical shape as a result of it being covered in said covering material.
10. A bottom-to-surface connection installation according to claim 8 or claim 9, characterized in that said covering material and said filler material comprise the same elastomer material, preferably based on polyurethane, said solid filler material preferably comprising polyurethane having hardness of A90 or A95 on the Shore scale.
11. A bottom-to-surface connection installation according to claim 8 or claim 10, characterized in that said filler material comprises an elastomer filled with a particulate material, preferably sand.
12. A bottom-to-surface connection installation according to any one of claims 8 to 11, characterized in that the length of said main pipe element (8a) lies in the range 10 m to 50 m, preferably in the range 20 m to 30 m, and comprises two or three of said coaxial reinforcing elements (8b-8d).
13. A bottom-to-surface connection installation according to any one of claims 8 to 12, characterized in that each of said main and coaxial reinforcing pipe elements (8a-8d) is constituted in full or in part by a standard unit pipe element, in particular a standard steel underwater pipe element, or each is constituted by a plurality of standard unit pipe elements assembled end to end and preferably held coaxially by centering spacers regularly distributed in their longitudinal direction and around the circular section in the annular gaps.
14. A method of putting a bottom-to-surface connection installation according to any one of claims 1 to 13 into place at the sea bottom (3), the method being characterized in that it comprises the following successive steps:

    1) lowering a said anchor device (5) to the sea bottom; and

    2) lowering a rigid pipe (9) forming a vertical riser that is fastened directly at its top end to one (10c) of said flexible pipe (10) and that presents a terminal portion (10a) of positive buoyancy, the other end (10e) of said flexible pipe (10) being suspended from a sub-surface float (21); and

    3) fastening the bottom end of said transition piece (8) so that it is restrained at said anchor device (5); and

    4) moving the end (10e) of said flexible pipe suspended from said float and fastening or connecting it to a said floating support (12).
15. A method according to claim 14, for putting a bottom-to-surface connection installation according to any one of claims 3 to 14 into place, the method being characterized in that the following successive steps are performed:

    1) lowering a said base (4) secured to a said rigid first pipe element (2a) to the sea bottom, said base (4) including a through orifice (4a); and

    2) lowering a said first tubular anchor pile (6) to the sea bottom and driving it into the bottom of the sea through said orifice (4a) in the base in order to anchor said base to the sea bottom; and

    3) from a surface ship (20), lowering said rigid pipe (9) constituting said vertical riser that is directly fastened at its top end to a said flexible pipe down to the sea bottom, said transition piece (8) at the bottom end of said riser being fastened to a said support and coupling device (5) that supports a bent second rigid pipe element (5b) and a said anchor insert (5e); and

    4) fastening said support and coupling device (5) to said base by inserting said anchor insert (5e) inside said first tubular pile (6); and

    5) preferably locking said anchor insert (5e) inside said first tubular pile (6) using a locking device (4b); and

    6) connecting together said first rigid pipe element (2a) and said bent second rigid pipe element (5b); and

    7) finishing lowering of said flexible pipe having a terminal portion of positive buoyancy, with the other end (10e) of said flexible pipe being suspended from a sub-surface float (21); and

    8) moving and then fastening or connecting the other end (10e) of said flexible pipe to a said floating support (12).

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