EP1395731B1 - Underwater pipeline connection joined to a riser - Google Patents

Abstract

The present invention relates to an installation providing a bottom-to-surface connection for an undersea pipe resting on the sea bottom, in particular at great depth, the installation being of the hybrid tower type having a static base placed on the sea bottom. In the installation of the present invention, said pipe resting on the sea bottom is connected by a flexible pipe element constituting a bend to a vertical riser whose bottom end is held in fixed position relative to said base.

Description

The present invention relates to a bottom-surface connection installation at least one underwater pipe installed at great depth of the tour-hybrid type.

The technical field of the invention is the field of manufacturing and the installation of risers or "risers" of production for extraction underwater oil, gas or other soluble or fuse material or a suspension of mineral material from wellhead immersed for the development of production fields in the open sea off the coast of ribs, still called "riser". The main and immediate application of the invention is in the field of oil production.

A floating support generally comprises anchoring means for remaining in position despite the effects of currents, winds and swell. It comprises also in general means of storage and processing of oil as well as means of unloading to oil tankers, the latter presenting at regular intervals to carry out the removal of production. The name of these floating supports is the Anglo-Saxon term "Floating Production Storage Offloading "(meaning" floating storage medium, production and unloading "), the abbreviated term" FPSO "will be used in the whole of the following description.

Due to the multiplicity of lines existing on this type of installation, we have been made to implement round-hybrid-type bottom-surface which substantially vertical rigid pipes referred to herein as "riser vertical ", provide the link between the subsea pipes lying at the bottom of the sea and ascend along a tower to a depth close to the surface, depth from which flexible pipes provide the connection between the top of the tower, namely the vertical risers, and the floating support. The tower is then provided with buoyancy means to remain in a vertical position and the risers are connected, in turn, to the submarine pipes by rigid cuffs, absorbing the vertical movements of the tower. The set is commonly called "Hybrid Tour" because it involves two technologies, on the one hand a vertical part, the tower, in which the riser is consisting of rigid pipes, on the other hand the upper part of the riser consisting of Chainset hoses which provide the connection to the floating support.

French Patent FR 2,507,672, published on December 17, 1982, is known from entitled "Rising Column for Deep Waters", which describes a such a hybrid tower.

The present invention relates more particularly to the known domain of type links having a vertical hybrid tower anchored to the bottom and composed of a float located at the top of a vertical riser, the latter being connected by a pipe, in particular a flexible pipe taking by its own weight the Shape of a chain from the top of the riser to a floating support installed on the surface.

The interest of such a hybrid tower lies in the possibility for the support floating to be able to deviate from its normal position by inducing a minimum of constraints in the tower as well as in portions of pipe-shaped chaines in suspension, both at the bottom and on the surface.

We know the patent on behalf of the present applicant, WO 00/49267 which describes a tower whose float is at a depth greater than half-height of water and whose catenary link to the surface vessel is made using rigid pipes of great thickness. The tower thus described, requires at the level of its base, flexible connecting cuffs allowing connecting the lower end of the vertical risers of said tower to the pipe underwater resting on the bottom, so as to absorb the movements resulting from the expansions due to the temperature of the transported fluid.

More particularly, in WO 00/49267, the anchoring system comprises a vertical tendon consisting of either a cable or a metal bar, or still a conduct 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 has guiding means distributed along its entire length through which pass said vertical risers. Said base can be placed simply on the bottom of the sea and stay in place by its own weight, or remain anchored by means of batteries or any other device suitable for maintaining it square. In WO 00/49267, the lower end of the vertical riser is adapted to be connected to the end of an angled sleeve, movable, between a high position and a low position, relative to said base, to which this cuff is suspended and associated with a return means bringing it back to a high position the absence of the riser. This mobility of the bent sleeve makes it possible to absorb the variations in the length of the riser under the effects of temperature and pressure. At the top of the vertical riser, a stop device, integral with it, comes lean on the support guide installed at the head of the float and thus maintain the all the riser in suspension.

In addition, crude oil traveling over very long distances, several kilometers, we try to provide them with an extreme level of insulation for, on the one minimize the increase in viscosity that would lead to a reduction in the hourly production of the wells, and on the other hand to avoid blocking the flow by depositing paraffin, 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 the crude oils are paraffinic type.

Many thermal insulation systems are known that allow to achieve the required level of performance and resist the pressure of the bottom from the sea which is of the order of 150 bars at 1500m depth. We quote between other concepts of the "pipe-in-pipe" type, including a pipe carrying the hot fluid installed in an external protective line, the space between two pipes being either simply filled with insulation, confined or not confined empty, or simply empty. Many other materials have been developed to provide high performance insulation, some of they being pressure resistant, simply surround the hot and are generally confined within a flexible or rigid outer casing, in equipressure and whose main function is to maintain over time a substantially constant geometry.

All these devices carrying a hot fluid within an isolated pipe present, to varying degrees, differential expansion phenomena. In effect the inner pipe, usually made of steel, is at a temperature which is seeks to maintain the highest possible, for example 60 or 80 ° C, while the outer shell, often also steel, is at the temperature sea water, ie around 4 ° C. The efforts made on the connecting elements between inner pipe and outer shell are considerable and can reach several tens or even hundreds of tonnes and the resulting overall elongation is of the order of 1 to 2 m in the case of insulated pipes from 1000 to 1200m long.

The problem posed according to the present invention is to be able to realize and install such bottom-to-surface connections for large subsea depths, such as beyond 1000 meters for example, and of type comprising a vertical tower and whose transported fluid must be maintained above a minimum temperature until reaching the surface, minimizing components subject to heat loss, avoiding the disadvantages created by the clean thermal expansion, or differential, of the various components of said tower so as to withstand the extreme stresses and phenomena of accumulated fatigue over the lifetime of the structure, which is currently years.

Another problem of the present invention is to provide an installation of cross-hybrid type bottom-surface connection whose anchoring system is of a high resistance and low cost, including the method of setting up different constituent elements be simplified to the extreme and also a weak cost.

In particular, an object of the present invention is to provide an installation which can be prefabricated entirely on land, particularly as regards the assembly of the rigid pipes intended to constitute said pipes resting at the bottom of the sea and said risers vertical.

More particularly, another object of the present invention is to provide an installation whose installation at the bottom of the sea does not require the implementation automatic connector and preferably no flexible joints to ball joint in the lower part of the tower. The automatic connectors are connectors whose locking between the male part and the female part complementary is designed to be done very simply at the bottom of the sea at using a robot controlled from a ROV without the need for intervention direct manual staff. These automatic connectors as well as the joints Flexible ball joints are very expensive.

Another problem underlying the invention is to provide an installation which allows to intervene inside the underwater pipe resting at the bottom of sea, by a process of coiled-tubing type from the surface and from the upper end of the vertical riser.

1) au moins un riser vertical relié à son extrémité inférieure à au moins une conduite sous-marine reposant au fond de la mer, et à son extrémité supérieure à au moins un flotteur, et

2) de préférence au moins une conduite de liaison, de préférence encore une conduite flexible, assurant la liaison entre un support flottant et l'extrémité supérieure dudit riser vertical, et

3) la liaison entre l'extrémité inférieure dudit riser vertical et une dite conduite sous-marine reposant au fond de la mer se fait par l'intermédiaire d'un système d'ancrage comprenant une embase posée sur le fond, caractérisée en ce que :

a- l'extrémité inférieure du riser vertical est reliée à l'extrémité de la conduite reposant au fond de la mer par au moins un premier élément de conduite flexible qui présente une courbure en forme de coude, et

b- ladite embase comprend une plateforme reposant au sol et une structure supérieure solidaire de ladite plateforme qui maintient en position lesdites extrémités de ladite conduite sous-marine reposant au fond et dudit riser vertical raccordées audit premier élément de conduite flexible, de sorte que :

• l'extrémité dudit premier élément de conduite flexible raccordée à l'extrémité inférieure du riser vertical est maintenue en position fixe par rapport à ladite embase, et
• de préférence, les axes (XX', YY') desdites extrémités de ladite conduite sous-marine reposant au fond et dudit riser vertical sont maintenus dans un même plan perpendiculaire à ladite plateforme.

A solution to the problems posed is therefore a bottom-surface connection system for submarine pipe resting at the bottom of the sea, particularly at great depth, in which said underwater pipe resting at the bottom is connected to a vertical riser by at least a flexible pipe element held by a base, comprising more specifically:

1) at least one vertical riser connected at its lower end to at least one submarine pipe resting at the bottom of the sea, and at its upper end to at least one float, and

2) preferably at least one connecting pipe, more preferably a flexible pipe, providing the connection between a floating support and the upper end of said vertical riser, and

3) the connection between the lower end of said vertical riser and said underwater pipe resting at the bottom of the sea is via an anchoring system comprising a base placed on the bottom, characterized in that :

a- the lower end of the vertical riser is connected to the end of the pipe resting at the bottom of the sea by at least a first flexible pipe element which has a curvature-shaped elbow, and

b- said base comprises a platform resting on the ground and an upper structure integral with said platform which holds in position said ends of said underwater pipe resting at the bottom and said vertical riser connected to said first flexible pipe element, so that:

• the end of said first flexible pipe element connected to the lower end of the vertical riser is held in a fixed position with respect to said base, and
• preferably, the axes (XX ', YY') of said ends of said underwater pipe resting at the bottom and said vertical riser are held in the same plane perpendicular to said platform.

• les conduites flexibles connues de l'homme de l'art conformément au domaine technique de l'invention comme mentionné ci-dessus, notamment dans le domaine des technologies de l'extraction sous-marine de pétrole en particulier, les conduites flexibles utilisées pour la liaison entre le support flottant et l'extrémité supérieure des conduites rigides constituant ledit riser vertical. Ces conduites flexibles sont classiquement constituées d'un tube interne de matériau polymère flexible renforcé par des armatures de fils métalliques tressés formant des gaines spiralées. Ces conduites flexibles sont capables de résister à des pressions internes ou extemes considérables, pouvant atteindre et dépasser 100 Mpa, tout en acceptant des courbures en mode dynamique ou statique très importantes, c'est-à-dire représentant un rayon de courbure très faible, jusqu'à 10 fois, voire 5 fois leur diamètre. Ce type de flexible est fabriqué et commercialisé par la société Coflexip-France.
• Ainsi que, plus généralement, toute conduite de rigidité réduite par rapport à la rigidité des conduites en acier ou matériau composite rigide constituant lesdits risers, en particulier des conduites à rigidité réduite telles que décrites dans WO 97/25561 comportant une paroi externe métallique tubulaire rigide comportant des fentes ou rainures qui s'étendent selon un trajet hélicoïdal à la surface de ladite paroi externe, ladite paroi externe renfermant une conduite interne de métal ondulé assurant l'étanchéité tout en autorisant de par sa forme ondulée et sa faible épaisseur une courbure similaire à celle des conduites en matière plastique polymère. Les fentes ou rainures réalisées dans les conduites métalliques rigides de la paroi tubulaire externe permettent de conférer à ces parois externes une flexibilité similaire, mais cependant moins importante que celle d'un flexible. Par contre, sa fabrication est beaucoup plus simple à réaliser et son prix de revient n'est qu'une petite fraction de celui d'un flexible équivalent. En effet, un flexible de quelques mètres de longueur nécessite des embouts d'extrémité extrêmement coûteux, car délicats à fabriquer et à assembler, alors que la conduite à rigidité réduite selon le brevet WO 97/25561 peut être fabriqué dans une ébauche de tube d'acier similaire à celui des conduites rigides adjacentes, puis simplement soudées à ces derniers pour assurer la jonction.

The term "flexible driving element" means the following driving elements:

• the flexible pipes known to those skilled in the art in accordance with the technical field of the invention as mentioned above, especially in the field of underwater oil extraction technologies in particular, the flexible pipes used for the connection between the floating support and the upper end of the rigid pipes constituting said vertical riser. These flexible pipes are conventionally made of an inner tube of flexible polymer material reinforced by reinforcement braided metal son forming spiral ducts. These flexible pipes are capable of withstanding considerable internal or external pressures, capable of reaching and exceeding 100 MPa, while accepting very dynamic or static mode curvatures, that is to say representing a very small radius of curvature, up to 10 times, even 5 times their diameter. This type of hose is manufactured and marketed by Coflexip-France.
• As well as, more generally, any pipe of reduced rigidity with respect to the rigidity of steel pipes or rigid composite material constituting said risers, in particular pipes with reduced rigidity as described in WO 97/25561 having a rigid tubular metal outer wall. having slots or grooves which extend along a helical path on the surface of said outer wall, said outer wall enclosing a corrugated inner metal conduit providing sealing while permitting a similar curvature due to its undulating shape and low thickness; to that of polymer plastic pipes. The slots or grooves made in the rigid metal pipes of the outer tubular wall allow to give these external walls a similar flexibility, but less important than that of a flexible. On the other hand, its manufacture is much simpler to realize and its cost price is only a small fraction of that of an equivalent hose. Indeed, a hose of a few meters in length requires extremely expensive end caps, because delicate to manufacture and assemble, while the pipe with reduced rigidity according to the patent WO 97/25561 can be manufactured in a blank of tube d similar to that of adjacent rigid pipes, and then simply welded to the latter to join them.

Said first flexible or reduced-stiffness element, present so an elbow-shaped curvature turned upward and the curvature is maintained in a substantially vertical plane when said platform rests substantially horizontally on the bottom of the sea.

Here is meant by "elbow" two short straight sections of pipe exposed at 90 °, connected to each other by a curved section presenting at rest a shape of an arc of a circle, preferably with a radius of curvature, in particular a radius of curvature of less than 10 m, more particularly of the order of 5 to 10 m. To do this, it is possible to use a said first flexible driving element of length of 7.5 to 15m.

In WO 00/49267, the tower comprising several risers is stretched by a central tendon which suspends a plurality of vertical risers, and the vertex of the tendon stretched by a float constitutes a point of reference at a fixed altitude, with variation of the apparent overall weight of risers and their contents; and the whole movement was absorbed by the angled connection cuffs at the bottom, expensive parts and difficult to make and install. According to the present invention, the point substantially fixed at altitude is at the bottom of the tower at the lower end of the riser at connection level with said first flexible pipe element, which allows to remove the angled connecting sleeves, the movements differentials between the risers being absorbed by the float (s) which is (are) free (s) to move vertically at the top of each of the said (s) riser (s).

• une conduite flexible ou à rigidité réduite si le flotteur de tête se trouve proche de la surface, ou
• une conduite rigide si le flotteur de tête se trouve à grande profondeur.

Said connecting line between the floating support and the upper end of the vertical riser may be:

• a flexible or low rigidity pipe if the head float is close to the surface, or
• a rigid pipe if the head float is at a great depth.

a) Ledit riser vertical comprend à son extrémité inférieure une portion de conduite rigide terminale reliée à la partie supérieure dudit riser vertical par un deuxième élément de conduite flexible, lequel autorise des mouvements angulaires α de ladite partie supérieure par rapport à ladite portion de conduite rigide terminale, et

b) ladite embase comprend une structure supérieure qui maintient rigidement en position fixe par rapport à l'embase, ladite portion de conduite rigide terminale dudit riser vertical dont l'extrémité est reliée audit premier élément de conduite flexible.

According to a preferred embodiment of the invention, the installation according to the invention is characterized in that:

a) said vertical riser comprises at its lower end a terminal rigid pipe portion connected to the upper portion of said vertical riser by a second flexible pipe element, which allows angular movements α of said upper portion relative to said rigid pipe portion; terminal, and

b) said base comprises an upper structure which rigidly holds in fixed position relative to the base, said terminal rigid pipe portion of said vertical riser whose end is connected to said first flexible pipe element.

The axis of said rigid pipe portion is therefore substantially vertical and therefore fixed when held in position by said upper structure, said axis being preferably perpendicular to said platform.

This preferred embodiment with a said second driving element flexible avoids the use of a flexible joint type ball joint.

However, in one embodiment, it is possible to use such a flexible gasket to the place of said second flexible pipe element. A flexible seal allows a significant variation of the angle α between the axis of the tower and the axis of the riser part vertically attached to the base, without causing significant constraints in the pipe portions located on either side of said flexible seal. This seal flexible can be in a known manner is a spherical ball joint with joints seal, a laminated patella consisting of leaf sandwiches of elastomers and adhered sheets, able to absorb movements significant angular distortion of the elastomers, while maintaining a perfect seal due to the absence of friction seals.

In a particular embodiment, said base comprises mounting brackets adapted to maintain a fixed position relative to the base the end of said underwater pipe resting at the bottom.

In this embodiment, said first flexible pipe element, in the area of the elbow, presents a controlled geometry that is found perfectly stabilized, locking at the connection between the riser vertical and said first flexible element taking up all the tension vertically created by the float head of the riser, said voltage up to 100 T. The first flexible pipe element therefore no longer supports any movement or effort, both from the bottom-up conduct and from the part of the vertical riser.

However, in a preferred embodiment, said base comprises guiding elements that allow translational movement longitudinal along its axis XX 'of the end of said underwater pipe resting at the bottom.

Said guide means prevent displacement in translation in another direction, that is to say in a direction comprising a component vertical YY 'and / or a lateral component ZZ'.

In this second embodiment, the geometry of the elbow remains controlled even if it is not completely stabilized.

More particularly, said guiding elements comprise rollers or friction pads on which said driving end resting at the bottom can slide in longitudinal translation in the axis XX 'of said end, thus avoiding transferring the thrust forces on the base, forces due to the background effect (internal pressure in the pipe), as well as the thermal expansion of said pipe.

In this second embodiment according to which the end of the underwater pipe resting at the bottom can move longitudinally along its axis, we understand that this displacement induces a deformation of the curvature of said first flexible pipe element. However, the displacement of the end of the bottom-lying pipe occurs exceptionally and only under the effect of thrusts caused by the expansion of that pipe due to variations in temperature and / or internal pressure of the fluid it vehicle. It does not represent, in general, not more than 1 to 2 m.

In a particular embodiment, said base comprises a so-called upper structure secured to a said platform, said upper structure forming a console in elevation with respect to said platform, said platform preferably being secured to said guide means preferably consisting of still in rollers distributed on both sides of the base of said console resting on said platform, and said console comprises in its part in elevation relative to said platform a particular lock type flange or clamp for locking said lower end of said riser.

Preferably, said guide means also comprise anti-rotation devices that prevent rotation of the end of the pipe around its longitudinal axis XX '. These anti-rotation devices therefore allow to avoid that the torsion phenomena generated at the level of the underwater pipe during the expansion or retraction movements of the underwater pipe under the effect of pressure or temperature, are transmitted to the flexible structure of said first elbow-shaped flexible pipe element.

Thus, the anti-rotation device prevents torsional damage to the flexible portion in the form of an elbow during said movements of expansion or retractation of the underwater pipe.

In a preferred embodiment, said base comprises a so-called upper structure secured to a said platform, said upper structure forming a console in elevation with respect to said platform, said platform preferably being integral with said guide means preferably consisting of still in rollers distributed on both sides of the base of said console resting on said platform, and said console comprises in its part in elevation relative to said platform a particular lock type flange or clamp for locking said lower end of said riser.

Preferably, said base comprises a platform, which cooperates with stabilizing elements including dead bodies on top said platform and / or suction anchors passing through said platform to be buried in the ground.

The installation according to the present invention is advantageous because the quasi entire hybrid tower can be prefabricated ashore, then towed on site, and, once the base is stabilized by dead bodies or suction anchors, the portion of riser is placed in a substantially vertical position by simple deballasting of the head float, or simply by pulling from the surface, avoiding the use of automatic connectors and Flexible ball joints, the latter being indispensable in the prior art.

Another advantage of the present invention is also the reduction the overall cost, resulting from the removal of any flexible joint and any automatic connector between the different portions of pipes as well as the removal of the angled sleeves used in the prior art to connect the vertical riser and the resting pipe at the bottom of the sea, whose costs may represent in the prior art more than 25% of the total cost of the installation. Indeed, such a bent sleeve, according to the technique previous, is complex to manufacture because, after depositing on the ground of the end of the pipe resting on the bottom of the sea and after installation of the base, which are deposited in a target area respectively each, in general, a circle of approximately 5 to 10 m in diameter, considerable uncertainty as to their relative position, a metrology of the relative position and orientation of the ends of the lines shall be carried out at using an ROV (abbreviated name of the English term "Remote Operated Vehicle" meaning "automatic submarine, remotely controlled from the surface"); the cuff is then made, either on the ground or on board the installation vessel, then set up thanks to an ROV. Moreover, such a cuff requires means of connection, usually two automatic connectors, one at each end of the cuff, between the vertical riser and the pipe resting at the bottom of the sea. Finally, it must be pointed out that the effective thermal insulation of such angled cuff with its automatic connectors, used in the prior art, is extremely complicated to achieve, and therefore very costly, which greatly increases the cost and complexity of the installation in the case where one implements pipes which one seeks extreme insulation.

The installation according to the invention makes it possible to eliminate all these elements of the art previous, ie the connecting cuffs, the connectors automatic and flexible joints-joints and provide the best cost, a riser tower incorporating the most efficient insulation technologies.

Finally, in WO 00/49267, since the driving ends resting on the bottom are deposited in target areas and remote from the base of the turn, it is necessary to install prefabricated cuffs with a succession of straight parts and elbows of varying angles to connect the end of the pipe resting at the bottom at the base of the tower. These headlines are expensive and difficult to install and create cold spots detrimental to good thermal insulation.

The installation according to the invention thus makes it possible to eliminate all these disadvantages of the prior art and to provide at the best cost, a riser tower incorporating the the most efficient insulation technologies.

• au moins deux dits risers verticaux sensiblement parallèles et rapprochés, reliés à leur extrémité supérieure à au moins un flotteur et,
• au moins deux dites conduites sous-marines reposant au fond de la mer, et
• ladite embase maintenant en position fixe par rapport à l'embase les extrémités inférieures desdits risers verticaux, et
• ladite installation comprenant au moins deux dits éléments de conduite flexible reliant les extrémités des conduites sous-marines reposant au fond de la mer et lesdites extrémités inférieures desdits risers verticaux.

In one embodiment, the installation according to the invention comprises:

• at least two so-called vertical risers substantially parallel and close together, connected at their upper end to at least one float and,
• at least two underwater pipes resting at the bottom of the sea, and
• said base now in a fixed position relative to the base the lower ends of said vertical risers, and
• said installation comprising at least two said flexible pipe elements connecting the ends of subsea pipes lying at the bottom of the sea and said lower ends of said risers vertical.

More particularly, the two so-called underwater pipes resting on the bottom of the sea are assembled into a bundle within a single envelope of flexible protection for confining an insulating material, preferably paraffin or a gelled compound, surrounding said conduits.

• au moins deux dites conduites sous-marines reposant sur le fond de la mer sont assemblées en faisceau au sein d'une même enveloppe de protection souple permettant de confiner un matériau isolant, de préférence de la paraffine ou un composé gélifié, entourant lesdites conduites, et
• au moins deux dits risers verticaux sont assemblés en faisceau au sein d'une même enveloppe de protection souple permettant de confiner un matériau isolant, de préférence de la paraffine ou un composé gélifié, entourant lesdits risers,
• la liaison entre chacune des conduites élémentaires du faisceau, depuis la conduite du faisceau reposant sur le fond vers la conduite correspondante du faisceau vertical étant constitué par au moins un dit premier élément de conduite flexible, de préférence préinstallé à terre lors de la fabrication, en continuité des dites conduites élémentaires rigides.

More particularly still, the installation according to the invention comprises:

• at least two said submarine pipes resting on the seabed are assembled in a bundle within a single flexible protective envelope for confining an insulating material, preferably paraffin or a gelled compound, surrounding said pipes, and
• at least two said vertical risers are assembled in a bundle within a single flexible protective envelope for confining an insulating material, preferably paraffin or a gelled compound, surrounding said risers,
• the connection between each of the elementary ducts of the bundle, from the pipe of the beam resting on the bottom to the corresponding pipe of the vertical bundle being constituted by at least one said first flexible pipe element, preferably pre-installed on the ground during manufacture, in continuity of said rigid elementary conduits.

In another embodiment, the two so-called vertical risers are not not assembled in a bundle and to facilitate differential movements between risers, first and second vertical risers not assembled in bundles are maintained substantially parallel by means of a sliding connection system permitting the axial displacements of said first riser relative to said second riser, said connecting system comprising a tubular collar fixed around said first riser, said collar being rigidly connected to a sliding tubular ring freely around said second riser, preferably a plurality of said collars of the same sliding connection system being distributed along each of said risers alternately with said rings of another said linkage system on a even says riser. This sliding link system allows risers to move vertically but not transversely, ie they remain substantially equidistant in a plane perpendicular to their axis.

In a particular embodiment, said vertical riser comprises in its upper part above said second flexible pipe element, a insulated pipe system consisting of a set of two pipes coaxial pipes comprising an inner pipe and an outer pipe, a fluid or insulating material, preferably a phase change material of the type paraffin or a gelled compound being preferably placed between the two said conducted, or by maintaining a high vacuum between them.

The junctions between the different components of the float assembly, flexible pipe and riser vertical being located not far from the surface, are subject to the combined effects of swell and current. In addition, the support of surface being subjected not only to the swell and the current, but also to effects of the wind, the overall movements create at the level of the singular point the junction between riser and flexible pipe, considerable effort in the various mechanical constituents. Indeed, the float exerts traction vertical upwards, which may vary from a few tens of tons to several hundreds of tons or even more than 1000 tons, depending on the depth water that can reach 1500m, or even 3000m, and depending on the internal diameter of the conduct which can vary from 6 "to 14", even 16 ".Thus the efforts to be transmitted are and the overall movements are clocked up, inter alia, rhythm of the swell, ie with a period varying typically, in period agitated, between 8 and 20 seconds. Combined fatigue cycles over the lifetime of the field thus reach values exceeding several tens of millions of cycles. This is why an installation according to the present invention comprises advantageously at least one float, preferably a group comprising a plurality of floats installed at the top of each, at least two so-called risers vertically, arranged in such a way that said floats are held together with the means of a structure supporting them and allowing vertical displacements relative to each of said groups of floats relative to one another, in particular displacements generated by differential expansion. said floats are therefore free to move vertically but they are enough spaced so that, according to the deformations of their supporting structures, all physical contact of groups of floats between them is avoided.

Another problem according to the present invention is to allow a easy intervention inside said riser from the surface, in particular from allow the inspection or cleaning of the vertical riser, by introducing a rigid tube from the upper end of the float, passing through said connection device between float and vertical riser.

Indeed, these bottom-surface bonds convey a polyphasic fluid, it is at say a fluid composed of crude oil, water and gas. However, during the ascent of the fluid, the local pressure decreases and the gas bubbles then increase by volume, creating instability phenomena of the fluid vein that can lead to big jolts. During production shutdowns, the gas is found in the high part and the oil-water mixture is trapped in the low points, it is at say in the lower part of the hose area in chain, as well as in the lower part of the substantially vertical section of the riser.

The multiphase mixture, consisting of crude oil, water and gas, tendency, when the temperature falls below a value between 30 and 40 ° C, to create two types of caps that may block production. A first type of plug is due to the formation of hydrates from the phase gaseous in the presence of water, another type is due to the freezing of paraffin contained in varying proportions in the crude oil of certain fields oil companies, particularly in West Africa.

We know the method of intervention inside the pipes, so-called "coiled-tubing", consisting in pushing a rigid tube of small diameter, in general 20 to 50mm, through the pipe. Said rigid tube is stored wound by simple bending on a drum, then untwisted when unwrapped. Said tube can measure several thousand meters in one length. The end of the tube located at the barrel of the storage drum is connected via a joint with a pumping device capable of injecting a high-pressure liquid and at high temperature. Thus, by pushing the thin tube through the pipe, now the pumping and the back pressure, this pipe is cleaned thanks to the injection of a hot product capable of dissolving the caps. This method Intervention is commonly used in vertical shaft on pipes obstructed by paraffin or hydrate formations, common and feared phenomena in all the production facilities of crude oil. The "coiled-tubing" process is hereinafter referred to as "cleaning continuous casing "or NTC.

• un troisième élément de conduite souple dont les extrémités sont encastrées au niveau respectivement dudit flotteur et de l'extrémité supérieure du riser,
• la liaison de ladite troisième conduite souple à l'extrémité supérieure dudit riser se faisant par l'intermédiaire d'un dispositif en forme de col de cygne, lequel dispositif en forme de col de cygne assure aussi la liaison entre ledit riser et une dite conduite de liaison avec le support flottant, de préférence une dite conduite flexible,
• ladite troisième conduite souple étant, de préférence, prolongée à travers ledit flotteur par une conduite tubulaire rigide traversant le flotteur de part en part, de sorte que l'on peut intervenir à l'intérieur dudit riser vertical à partir de la partie supérieure du flotteur à travers ladite conduite tubulaire rigide, puis ledit dispositif de liaison constitué de ladite troisième conduite souple est à travers ledit dispositif en forme de col de cygne, de façon à accéder à l'intérieur dudit riser et le nettoyer par injection de liquide et /ou par raclage de la paroi interne dudit riser, puis de ladite conduite sous-marine reposant au fond de la mer.

The installation according to the invention comprises a connection device between said float and the upper end of said riser comprising:

• a third flexible pipe element whose ends are recessed at respectively said float and the upper end of the riser,
• the connection of said third flexible pipe to the upper end of said riser being via a device in the shape of a gooseneck, which device in the shape of a gooseneck also ensures the connection between said riser and said pipe connecting with the floating support, preferably a so-called flexible pipe,
• said third flexible pipe being preferably extended through said float by a rigid tubular pipe passing through the float from one side to the other, so that it is possible to intervene inside said vertical riser from the upper part of the float through said rigid tubular conduit, then said connecting device consisting of said third flexible conduit is through said gooseneck device, so as to access the interior of said riser and clean it by liquid injection and / or by scraping the inner wall of said riser, then said underwater pipe resting at the bottom of the sea.

The gooseneck device includes a straight portion upper which ensures the junction between said vertical riser and said third flexible pipe connected to said float. On this said right part of the device in gooseneck shape, a curved elbow-shaped derivation, allows the junction between the end of said vertical riser and the end of said flexible pipe itself connected to said floating support. The ends of said curve being substantially tangent to the curve of the chain constituted by the flexible pipe which provides the connection to the floating support, and substantially tangent with said right part of the gooseneck device.

The main advantage of the installation according to the invention is that all elements are prefabricated on the ground before being installed. They can be mounted to check that all elements cooperate properly, including including the locking means; thus, the assembly of the installation is greatly simplified and the operational time of installation vessels reduced to a minimum. In the prior art, underwater pipes were then, after installation of the risers, bent connection were manufactured on the basis of high precision metrology realized thanks to the ROVs. The sleeve, prefabricated on the ground or on site can measure several tens of meters and must then be installed by the same ROV, which represents a considerable operational time, so a very low cost high because of the sophistication of specialized installation vessels. Gain realized by the device and the method according to the invention, can be divided into several installing ship days as well as removing connectors indispensable automatic at each end of the cuff prefabricated, which represents a considerable cost reduction.

1) on pré-assemble bout à bout en alignement ladite conduite destinée à reposer au fond de la mer, ledit premier élément de conduite flexible, ladite conduite rigide destinée à constituer ledit riser vertical, et le cas échéant et de préférence, ledit deuxième élément de conduite flexible,

2) on met en place une dite embase coopérant avec l'assemblage obtenu à l'étape 1, de sorte que :

• ladite conduite destinée à reposer au fond de la mer et ladite conduite rigide destinée à constituer ledit riser vertical sont fixées sur ladite plateforme, de préférence à proximité des extrémités desdites conduites, reliées auxdits éléments de conduite flexibles et
• l'extrémité dudit premier élément de conduite flexible raccordée à l'extrémité inférieure dudit riser vertical, n'est pas maintenue par ladite structure supérieure de l'embase.

3) On remorque en mer l'assemblage obtenu après l'étape 2 jusqu'au site voulu et,

4) on dépose sur le fond de la mer ladite embase que l'on stabilise de préférence avec desdits éléments de stabilisation, et

5) on désolidarise de l'embase ledit riser, puis

6) on solidarise ladite extrémité inférieure dudit riser avec ladite structure supérieure de l'embase pour la maintenir dans ladite position fixe verticale par rapport à l'embase.

The objectives of the present invention are therefore also obtained by a method of setting up an installation which comprises the steps in which:

1) is pre-assembled end to end in alignment said pipe intended to rest at the bottom of the sea, said first flexible pipe element, said rigid pipe intended to constitute said vertical riser, and if appropriate and preferably, said second element flexible driving,

2) putting in place a said base cooperating with the assembly obtained in step 1, so that:

• said pipe intended to rest at the bottom of the sea and said rigid pipe intended to constitute said vertical riser are fixed on said platform, preferably close to the ends of said pipes, connected to said flexible pipe elements and
• the end of said first flexible pipe element connected to the lower end of said vertical riser, is not maintained by said upper structure of the base.

(3) The assembly obtained after Stage 2 is towed offshore to the desired site and,

4) depositing on the seabed said base which is preferably stabilized with said stabilizing elements, and

5) disengages the base said riser, then

6) secures said lower end of said riser with said upper structure of the base to maintain it in said vertical fixed position relative to the base.

La figure 1 est une vue en coupe de la partie supérieure d'une tour hybride reliée à un support flottant de type FPSO, un navire d'intervention effectuant une opération de maintenance à la verticale de ladite tour.

La figure 2 représente une vue de côté de la même tour selon la présente invention, en configuration définitive, après stabilisation de l'embase, cabanage du riser vertical et verrouillage de la partie intermédiaire.

La figure 3 est une vue de dessus relative à la figure 2.

La figure 4 est une vue de côté d'une tour selon la présente invention, dans laquelle la conduite horizontale reposant sur le fond est libre de se déplacer parallèlement à son axe par rapport à l'embase fixée au sol.

La figure 5 représente une vue de côté d'une tour hybride mono-tube en cours de remorquage, près du fond de la mer, vers son site d'installation.

La figure 6A est une vue en coupe représentant les sections d'une conduite interne et d'une conduite externe d'un riser vertical isolé par un ensemble du type "pipe-in-pipe".

La figure 6B représente une vue en coupe d'une section d'un faisceau de deux conduites sous-marines reposant au fond de la mer.

La figure 7 est une vue de côté de deux risers verticaux solidarisés par des moyens de liaison et de guidage coulissants.

La figure 8 est une vue de côté de l'extrémité supérieure des risers verticaux avec un dispositif du type col de cygne permettant de les relier d'une part, au support flottant par l'intermédiaire d'une conduite flexible, et d'autre part, aux flotteurs.

Les figures 9 et 10 sont respectivement des vues de dessus et de côté des flotteurs situés en continuité directe des deux risers verticaux.

La figure 11 représente des moyens de guidage de l'extrémité de la conduite sous-marine sur l'embase, lesdits moyens de guidage comprenant des dispositifs anti-rotation.

Other features and advantages of the present invention will become apparent in the detailed light of the embodiments which follow, with reference to FIGS. 1 to 11.

Figure 1 is a sectional view of the upper part of a hybrid tower connected to an FPSO floating support, an intervention vessel carrying out a maintenance operation vertically of said tower.

FIG. 2 represents a side view of the same tower according to the present invention, in final configuration, after stabilization of the base, racking of the vertical riser and locking of the intermediate part.

FIG. 3 is a view from above relating to FIG. 2.

Figure 4 is a side view of a tower according to the present invention, wherein the horizontal pipe resting on the bottom is free to move parallel to its axis relative to the base fixed to the ground.

Figure 5 shows a side view of a single-tube hybrid tower being towed near the seabed to its installation site.

Figure 6A is a sectional view showing the sections of an inner pipe and an outer pipe of a riser vertical isolated by a set of the type "pipe-in-pipe".

Figure 6B shows a sectional view of a section of a bundle of two subsea pipes lying at the bottom of the sea.

Figure 7 is a side view of two vertical risers secured by connecting means and sliding guide.

FIG. 8 is a side view of the upper end of the vertical risers with a gooseneck device for connecting them to the floating support via a flexible pipe and on the other hand, floats.

Figures 9 and 10 are respectively top and side views of the floats located in direct continuity of the two vertical risers.

Figure 11 shows guide means of the end of the underwater pipe on the base, said guide means comprising anti-rotation devices.

a) au moins un riser vertical 5 relié à son extrémité inférieure à au moins une conduite sous-marine 11 reposant au fond de la mer (non représentée), et à son extrémité supérieure à au moins un flotteur 6, et

b) au moins une conduite de liaison 3, de préférence une conduite flexible, assurant la liaison entre un support flottant 1 et l'extrémité supérieure dudit riser vertical 5.

FIG. 1 shows a bottom-surface connection installation for submarine pipe 11 resting at the bottom of the sea, particularly at great depth, comprising:

a) at least one vertical riser 5 connected at its lower end to at least one submarine pipe 11 resting at the bottom of the sea (not shown), and at its upper end to at least one float 6, and

b) at least one connecting pipe 3, preferably a flexible pipe, providing the connection between a floating support 1 and the upper end of said vertical riser 5.

Figure 2 shows an installation according to the invention with a tower in a vertical position relative to the base resting at the bottom. The base comprises a platform 15 ₁ constituted by a flat support placed at the bottom of the sea whose length, for illustrative purposes, can represent 30 to 50 m, and its width 5 to 10m. The base comprises an upper structure in the form of a console 15 ₂ in elevation with respect to the platform 15 ₁ whose height, for illustrative purposes, may exceed 10 m.

Said bracket 15 ₂ , integral with said platform, consists of a structure that straddles the end of the submarine pipe 11 resting at the bottom of the sea. The underwater pipe 11 resting at the bottom of the sea is made integral with the platform 15 ₁ by flange-type mounting brackets or conventional clamping collar 16 ₁ which hold it fixed relative to the base. These attachment supports 16 ₁ disposed on said platform are spaced from each other by several meters, so as to create a recess of said pipe in said platform. The lower end of the vertical riser 5 is composed of a rigid pipe portion 13, for example of the type used for the current portion of the vertical riser steel.

The lower end 5 ₁ of the vertical riser 5 formed as in the embodiment of Figure 2 with a rigid pipe portion 13, is held in a fixed position at the top of the bracket 15 _2. This terminal portion of rigid pipe 13 is made integral with the bracket ₂ at the top of the latter by means of a conventional clamping collar ₃ as shown in FIG. 3, said clamping collar being locked by bolts (not shown), inserted and locked by the installation ROV, automatic underwater intervention robot piloted from the surface.

This clamp is sized to take over all vertical stresses on the riser up to 100 tons.

The lower end of the terminal rigid vertical pipe portion 13 secured to the upper part of the bracket ₂ and the end of the underwater pipe 11 resting at the bottom of the sea which passes through the base of the console are arranged substantially perpendicularly and are connected to each other by a first flexible pipe member 12. Said first flexible pipe element is therefore suspended at the top of the console or elevation of the console and has a substantially elbow-shaped curvature at right angles.

This first flexible pipe element 12 is constituted by a length a unitary element of flexible pipe of the type used for the connection flexible pipe 3 between the floating support and the head 4 of the riser, or preferably of the type described in WO 97/25561.

In FIG. 2, the base is stabilized by suction anchors 17 which are well adapted to take up the thrust forces exerted on the base structure, generated by the variations of pressure and fluid temperature inside the underwater pipe 11 resting at the bottom of the sea. Said suction anchors 17 are dark through the orifices 16 ₃ of said platform 15 ₁ . These are in fact portions of pipes disposed perpendicularly to the base through these orifices 16 ₃ . These pipe portions have on the underside a free opening and on the upper face a sealed seal 20 ₁ so that it forms a bell of large diameter and generally elongated. Such anchors 17 may be several meters in diameter and 20 to 30 m high, or even larger. They can weigh from 15 to 50 tons each, or even more.

A second flexible pipe element 14 ensures the connection between the upper part or the current part ₂ of the vertical riser and the upper end of said rigid pipe end portion 13 fixedly held at the top of the bracket ₂ . This second flexible pipe element 14 allows angular movements of the upper part ₂ of the riser with respect to the axis YY 'of the rigid pipe end portion 13 constituting the lower part 5 ₁ of the riser in a fixed position relative to the console.

The two flexible pipe members 12 and 14 have a different function. The first flexible pipe element 12 must have great flexibility because configuration in a straight line during towing as will be explained later, it must be curved to form a substantially right angle when commissioning the facility. This curved configuration becomes definitive when the latches 15 ₃ at the top of the console are actuated to fix the lower end of the riser. Therefore, the geometry of the curvature of the first flexible pipe element remains substantially constant throughout the life of the installation. On the other hand, the second flexible pipe element, although it also in a straight line during towing, allows, after vertical positioning, movements of said vertical riser limited to a cone of angle α with respect to the axis YY ' of the rigid terminal pipe portion 13. The angle α is small, especially 5 to 10 °. But the angular movements are permanent throughout the operational life of the installation, so that the second flexible pipe element must be sized to withstand fatigue throughout the life of the facility, which can reach 20 years. Thus, the first flexible element 12 will be very flexible so that it can be bent over 90 ° without damage, but will be practically no longer solicited during the entire service life, whereas the second flexible element 14 will only be deformed by a few degrees, but throughout the life of the installation, and at the mercy of the swell and current movements on the entire hybrid tower and the floating support, which represents several million cycles.

Figure 4 shows a preferred version of a hybrid tower installation according to the invention, in which the submarine pipe 11 resting on the bottom is free to move in translation parallel to its axis XX ', in roller guides 19 integral with the base. Guiding the underwater pipe resting at the bottom allows longitudinal movements thereof along its axis, so that said pipe 11 exerts practically no effort on the base structure, since the expansion of said underwater pipe 11 due to variations in temperature and internal pressure of the fluid is absorbed by deforming the curvature of said first flexible pipe element. For allow said translational movements of the underwater pipe 11, which can represent 1 to 2 m, the radius of curvature of said first element of flexible pipe is more important in this embodiment of FIG. in the embodiment of Figure 2, as shown. In particular, in the embodiment of FIG. 2, the length of the first driving element flexible represents 7.5m to 15m while in Figure 4, it can represent 12.5 to 20 m. The first flexible driving element 12 is subject to movements, that in the event of a significant variation in temperature and operating pressure inside the pipes, which remains exceptional. Given the greater length of the first element of flexible pipe 12 in the embodiment of FIG. 4, the base an upper structure dimensioned accordingly. In the case of platforms of large dimensions, it increases advantageously the stability by dead bodies 18 resting on the platform. The rolls of guide 19 disposed below the end of the underwater pipe 11 resting at the bottom of the sea, have axes preferably parallel to the said platform and solidary of it, and arranged on both sides of the base of the console.

In FIG. 11, the guide means 19 for the underwater pipe have been described. 11 resting on the bottom, as friction pads allowing longitudinal displacements in the only direction XX ', corresponding to the axis of said pipe, displacements in a direction YY 'upwards being then impossible as well as the lateral displacements in a direction ZZ '. Of course, friction pads can also be used instead. other device to reduce friction.

The pads 19 are mounted around the pipe 11 by means of an assembly structure 19 ₃ surrounding said pipe.

• d'une part une barre 19₁ solidaire de l'extrémité de la conduite 11 et s'étendant verticalement en sous face de celle-ci, et
• d'autre part des patins de frottement ou des rouleaux 19₂ solidaires de ladite embase 15, lesquels sont disposés en contact glissant avec ladite barre 19₁ et de part et d'autre de ladite barre 19₁.

Anti-rotation devices include:

• on the one hand a bar 19 ₁ integral with the end of the pipe 11 and extending vertically in the underside of the latter, and
• on the other hand friction pads or rollers 19 ₂ secured to said base 15, which are arranged in sliding contact with said bar 19 ₁ and on either side of said bar 19 ₁ .

Thus, during displacements in longitudinal translation on the rollers or guide pads 19, any twisting rotation of the end of the pipe on itself about its longitudinal axis XX 'is prevented by the anti-rotation devices 19 ₁ , 19 ₂ . The anti-rotation devices 19 ₁ , 19 ₂ thus prevent the transmission to the said first elbow-shaped flexible pipe element of the twisting phenomena of the pipe around its axis which appear during the expansion or retraction movements of the pipe. under the effect of pressure or temperature.

1- On préfabrique à terre les éléments constitutifs de la tour riser hybride en assemblant bout à bout et successivement :

• la conduite sous-marine 11 destinée à reposer au fond de la mer,
• le premier élément de conduite flexible 12,
• la portion terminale de conduite rigide 13 destinée à constituer l'extrémité inférieure du riser vertical 5,
• le deuxième élément de conduite flexible 14, et
• la partie courante 5₂ du riser vertical 5.

2- On met en place l'embase comme représenté sur la figure 5 qui représente une tour hybride en cours de remorquage vers le site de l'installation. L'embase est rendue solidaire de l'extrémité de la conduite sous-marine 11 destinée à reposer au fond de la mer par des supports de fixation rigides 16₁ de type collier de serrage conventionnel, solidarisant ladite conduite à ladite plateforme 15₁ sur laquelle elle repose. Ces supports de fixation sont bloqués de manière définitive dans le cas d'une mise en service selon la figure 2 ou provisoire dans le cas d'une mise en service selon la figure 4. Ladite portion terminale de riser constituée par la conduite rigide intermédiaire 13, ainsi que la partie supérieure ou partie courante 5₂ du riser destiné à constituer le riser vertical 5, sont également rendues solidaires de la plateforme 15₁ au moyen de supports de fixation provisoires 16₂ du type bride ou collier de serrage conventionnel. L'extrémité supérieure du futur riser vertical 5 est équipée lors de la préfabrication à terre, d'un col de cygne 4, d'un flexible de raccordement 7 ainsi que d'un flotteur 6 dûment ballasté. Le câble de remorquage, non représenté est, par exemple, connecté à l'extrémité du flotteur de tête 6. La portion de conduite flexible 3 assurant la liaison entre le col de cygne 4 et le support flottant 1, tel que représenté sur la figure 1, et avantageusement rabattue le long de la conduite rigide destinée à constituer le riser vertical 5 et fixé fermement au moyen de sangles.

3- On tire l'assemblage obtenu à l'étape 2 vers le large au fur et à mesure de la progression de ladite fabrication de l'installation.

4- En fin de fabrication, on remorque l'ensemble des éléments de la tour hybride ainsi constituée en conduite continue vers le site d'installation.

5- En fin de remorquage, on dépose sur le fond de la mer la structure embase dans la zone cible à proximité du futur support flottant 1. Pour ce faire, on déballaste des flotteurs (non représentés) qui permettaient de maintenir l'installation à une certaine hauteur par rapport au niveau du fond de la mer pendant le remorquage.

6- On stabilise ladite embase au moyen d'ancre(s) à succion 17 foncée(s) à travers le(s) orifice(s) 16₃ de la plateforme ou en descendant des corps morts 18 sur la plateforme. L'ancre à succion 17 est descendue au moyen d'une oreille de levage 20₂ jusqu'à pénétrer le sol. Un ROV non représenté se connecte alors sur l'orifice 20₃ du couvercle 20₁ et à l'aide d'une pompe, met en dépression l'intérieur de la cloche. L'effort résultant est considérable et tend à faire pénétrer l'ancre à succion dans le sol jusqu'à ce que le talon 20₄ en face supérieure vienne en butée avec la plateforme, la stabilisant ainsi.

7- On relâche les supports de fixation provisoires 16₂ desdites portions de conduite rigide 13 et 5, et le cas échéant de l'extrémité de la conduite sous-marine 11 reposant au fond de la mer.

8- On cabane la portion de conduite constituant le futur riser vertical 5 par simple déballastage du flotteur de tête 6, par exemple par une purge à l'air comprimé, ou encore en tirant depuis le navire d'installation 10 installé en surface, l'extrémité supérieure du flotteur de tête 6. Dans ce cas, le flotteur est purgé à l'air en fin de relevage, lorsque le riser vertical 5 est en position sensiblement verticale.

9- On solidarise l'élément de conduite rigide terminale intermédiaire 13 au moyen d'un verrou 15₃ constitué d'une bride ou collier de serrage conventionnel qui la rend solidaire de la plateforme 15₁ de la structure embase. La libération des supports de fixation provisoires 16₂ et le verrouillage au sommet de la console 15₂ sont les seules interventions à réaliser au fond de la mer. Mais ces opérations peuvent être réalisées aisément et rapidement à l'aide d'un ROV.

10- On libère les sangles de maintien de ladite conduite flexible 3 (non représentée sur la figure 4) et l'extrémité de ladite conduite flexible 3 est alors simplement tirée depuis et vers le support flottant 1 avant d'être raccordée comme détaillé sur la figure 1. Dans le cas où la conduite de liaison flexible 3 est mise en place et connectée au col de cygne 4, son raccordement est réalisé au moyen de connecteur automatique de type mâle-femelle opéré par un ROV, soit au moyen de bride conventionnelle mise en place par des plongeurs, si la profondeur d'eau leur permet d'intervenir.

In the method of setting up an installation according to the invention, the following successive steps are carried out:

1- The components of the hybrid riser tower are prefabricated on the ground by assembling end to end and successively:

• the underwater pipe 11 intended to rest at the bottom of the sea,
• the first flexible pipe element 12,
• the end portion of rigid pipe 13 intended to constitute the lower end of vertical riser 5,
• the second flexible pipe element 14, and
• the current part 5 ₂ of the vertical riser 5.

2- We set up the base as shown in Figure 5 which shows a hybrid tower being towed to the site of the installation. The base is made integral with the end of the underwater pipe 11 intended to rest at the bottom of the sea by rigid mounting brackets 16 ₁ conventional clamp type, solidarisant said pipe to said platform _{1 1} on which she rests. These fixing brackets are permanently locked in the case of a commissioning according to FIG. 2 or provisional in the case of a commissioning according to FIG. 4. Said end portion of riser consisting of the intermediate rigid pipe 13 as well as the upper part or the common part 5 ₂ of the riser intended to constitute the vertical riser 5, are also made integral with the platform ₁ by means of temporary fixing supports 16 ₂ of the conventional flange or clamp type. The upper end of the future vertical riser 5 is equipped during prefabrication on the ground, a gooseneck 4, a connecting hose 7 and a float 6 duly ballasted. The towing cable, not shown is, for example, connected to the end of the head float 6. The flexible pipe portion 3 ensuring the connection between the gooseneck 4 and the floating support 1, as shown in FIG. 1, and advantageously folded along the rigid pipe intended to form the vertical riser 5 and fixed firmly by means of straps.

3- We draw the assembly obtained in step 2 offshore as the progress of said manufacture of the installation.

4- At the end of manufacture, all the elements of the hybrid tower thus formed are towed in continuous ducting to the installation site.

5- At the end of towing, the base structure is deposited on the seabed in the target zone near the future floating support 1. To this end, floats (not shown) are deballasted which made it possible to maintain the installation at a certain height from sea level during towing.

6- The said base is stabilized by means of anchor (s) suction 17 dark (s) through the (s) orifice (s) 16 ₃ of the platform or down dead bodies 18 on the platform. The suction anchor 17 is lowered by means of a lifting lug 20 ₂ to penetrate the ground. A not shown ROV then connects to the orifice 20 ₃ of the cover ₁ and ₁ with the aid of a pump, puts depression inside the bell. The resulting effort is considerable and tends to make the suction anchor penetrate into the ground until the heel 20 ₄ on the upper face comes into abutment with the platform, thus stabilizing it.

7- The temporary fixing supports 16 _{2 of} said rigid pipe portions 13 and 5, and where appropriate the end of the underwater pipe 11 resting at the bottom of the sea, are released.

8- The pipe portion constituting the future vertical riser 5 is shacked by simply deballasting the head float 6, for example by purging with compressed air, or by pulling from the installation vessel 10 installed on the surface, In this case, the float is air purged at the end of lifting, when the vertical riser 5 is in a substantially vertical position.

The intermediate rigid terminal pipe element 13 is secured by means of a latch ₃ constituted by a conventional flange or clamping collar which makes it integral with the platform ₁ of the base structure. The release of the temporary fixing brackets 16 ₂ and the locking at the top of the console 15 ₂ are the only interventions to be performed at the bottom of the sea. But these operations can be performed easily and quickly using a ROV.

10-One releases the holding straps of said flexible pipe 3 (not shown in Figure 4) and the end of said flexible pipe 3 is then simply pulled from and to the floating support 1 before being connected as detailed on the 1. In the case where the flexible connecting pipe 3 is put in place and connected to the gooseneck 4, its connection is made by means of a male-female automatic connector operated by an ROV, or by means of a conventional flange. put in place by divers, if the depth of water allows them to intervene.

In FIG. 6A, said vertical riser 5 comprises in its upper part above said second flexible pipe element 14 a pipe system consisting of a pipe-in-pipe type thermal insulation system comprising a set of two coaxial pipes comprising an inner pipe 5 ₂ and an outer pipe 5 _3, a fluid or insulating April ₅ consisting for example paraffin wax material or a gel, preferably being positioned between said two piping 5 _2, 5 _3. In a preferred version the space between the two said pipes consists of a high vacuum.

In FIG. 6B, the two so-called submarine ducts 11 ₁ , 11 ₂ resting on the bottom of the sea, or constituting the vertical riser portion, are assembled in a bundle within the same flexible protective envelope 11 ₃ flowing , for confining an insulating material 11 ₄ , preferably paraffin or a gel, surrounding said conduits.

In the latter case, one of the two pipes of the vertical beam is equipped at its end with the second flexible pipe element 14, then with the rigid pipe end portion 13 which will be secured to the top of the bracket 15 ₂ by means of the latch 15 ₃ , said latch ensuring the transmission of vertical forces exerted on said vertical riser, to the console, so to the base and its anchoring system. The second line of the vertical beam will be connected directly to the corresponding pipe of the beam resting on the bottom by means of a hose or a pipe with reduced rigidity, the latter being either free to move in space, or obliged to pass in guides which will then limit the deflections. Thus, the first conduct of the vertical beam will support the vertical forces of the tower, the second pipe then being free to move in space, or forced to pass in guides.

Figure 7 details a preferred way to allow movement axial axes of one of the risers 5a, 5b with respect to the other and when these are not assembled in a bundle, so that the differential expansions between risers can be released and do not induce unacceptable constraints, which could damage or ruin the tower. The device according to the invention consists of a tubular collar 25 firmly attached to the riser 5a and connected rigidly at 27 to a tubular ring 26 sliding freely on the riser 5b. The collars are distributed along the risers, at regular intervals or not, and installed preferably in opposition as represented on the same Fig. Thus, the two risers being integral with the base at the level of connections with said second flexible pipe element 14, if only the riser 5a is in temperature the sliding rings 26 allow the expansion of said riser 5a and almost all the expansion is at the top of the vertical riser, at the gooseneck as shown in Figure 8.

• une troisième conduite souple 7 dont les extrémités sont encastrées au niveau respectivement de la sous-face dudit flotteur 6 et de l'extrémité supérieure du riser 5,
• la liaison de ladite troisième conduite souple 7 à l'extrémité supérieure dudit riser 5 se faisant par l'intermédiaire d'un dispositif en forme de col de cygne 4, lequel dispositif en forme de col de cygne 4 assure aussi la liaison entre ledit riser 5 et une dite conduite flexible 3 avec le support flottant,
• ladite troisième conduite souple 7 étant prolongée à travers ledit flotteur 6 par une conduite tubulaire rigide 8 traversant le flotteur de part en part, de sorte que l'on peut intervenir à l'intérieur dudit riser vertical 5 à partir de la partie supérieure du flotteur 6 à travers ladite conduite tubulaire rigide 8, puis ledit dispositif de liaison constitué de ladite troisième conduite souple 7 et à travers ledit dispositif en forme de col de cygne 4, de façon à accéder à l'intérieur dudit riser 5 et le nettoyer par injection de liquide et /ou par raclage de la paroi interne dudit riser 5, puis de ladite conduite sous-marine 11 reposant au fond de la mer.

In FIG. 8, the installation comprises a connection device 4, 7 between said float 6 and the upper end of said riser 5, comprising:

• a third flexible pipe 7 whose ends are recessed at respectively the underside of said float 6 and the upper end of the riser 5,
• the connection of said third flexible pipe 7 to the upper end of said riser 5 being via a device in the shape of a gooseneck 4, which device in the shape of a gooseneck 4 also provides the connection between said riser 5 and a said flexible pipe 3 with the floating support,
• said third flexible pipe 7 being extended through said float 6 by a rigid tubular pipe 8 passing through the float from one side, so that it is possible to intervene inside said vertical riser 5 from the upper part of the float 6 through said rigid tubular pipe 8, then said connecting device consisting of said third flexible pipe 7 and through said gooseneck device 4, so as to access the interior of said riser 5 and clean it by injection liquid and / or by scraping the inner wall of said riser 5, then said underwater pipe 11 resting at the bottom of the sea.

Said third flexible pipe 7 has at its ends elements of gradual variation of inertia section 7 ₁ , 7 ₂ respectively at the underside of the float 6 and the upper end 4 ₁ of the gooseneck.

In FIG. 9, the installation according to the invention comprises two groups each comprising a plurality of floats 30a, 30b at the top of the at least two so-called vertical risers 5a, 5b. Said floats 30a, 30b of the same group are held together and fixed in relation to each other by means of a rigid structure in the form of a rectangular frame consisting of two bars vertical parallels 33 and two transverse parallel bars 36 enclosing them and supporting them. The two rectangular frames of the two groups of floats 30a, 30b are connected to each other by two articulated frames in the form of parallelogram on each side, each consisting of two parallel bars substantially vertical 33 and connected at their ends by joints 35 at the ends of transverse parallel bars upper 34a and lower 34b.

The assembly forms a deformable parallelepiped by vertical translation said rectangular frames relative to each other, allowing relative vertical displacements of each of said groups of floats, one for each relationship to the other, generated in particular by differential expansion.

As detailed in FIGS. 9 and 10, the structure supports a group of three floats 30a, whose central float is crossed by a pipe 8 in continuity of said third flexible 7 and opening to the upper part of said float on a sealed orifice 9, for example a plug valve spherical. Thus, all the operations of maintenance of the riser and a large portion of pipe resting on the bottom of the sea from a surface vessel 10 installed vertically of said valve access 32a; the operation of coiled tubing being possible in the driving part resting on the bottom of the sea, provided that the radius of curvature of the elbow located in the base is sufficiently large, for example 5m or 7m or more.

In FIG. 8, the riser 5b being cold, is shorter than the riser 5a at higher temperature. Similarly, in FIG. 10 the group of floats 30b is is offset downward substantially the same distance. Both groups floats 30a, 30b are maintained substantially equidistant by means of the Parallelogram structures forming deformable parallelepipeds vertically, allows the vertical displacements generated, for example by the differential expansion of the two risers 5a, 5b, one being hot, the other being temperature of the sea water, so cold.

The connecting means of the floats have been described by means of bars 33, 34, articulated at the axis 35, but can equally well be made by deformable elements, for example elastomers, it being understood that the purpose sought is to maintain substantially constant distance both groups floats 30a-30b, to prevent them from colliding under the effect of the swell and current, while allowing relative movements in one direction corresponding substantially to the axis of the vertical pipes.

In the same way, in FIG. 7, it remains within the scope of the invention if we replace the collars 25 and sliding rings 26 serving to guide the two vertical risers in the running part, by articulated bars similar to those previously described for the guidance of floats 30.

Claims (17)

1. A bottom-to-surface connection installation for an undersea pipe (11) resting on the sea bottom, in particular at great depth, the installation comprising:

   I) at least one vertical riser (5) connected at its bottom end to at least one undersea pipe (11) resting on the sea bottom, and at its top end to at least one float (6);

   II) preferably at least one connection pipe (3) also preferably a flexible pipe, providing a connection between a floating support (1) and the top end (4) of said vertical riser (5); and

   III) the connection between the bottom end (5₁) of said vertical riser (5) and a said undersea pipe (11) resting on the sea bottom being provided by means of an anchor system comprising a base (15₁, 15₂) resting on the bottom, and characterised in that:

   a- the bottom end (5₁) of the vertical riser (5) is connected to the end of the pipe (11) resting on the sea bottom via at least a first flexible pipe element (12) that is curved to form a bend; and

   b- said base comprises a platform (15₁) resting on the bottom and a superstructure (15₂) secured to said platform and holding in position said ends of said undersea pipe (11) resting on the sea bottom and of said vertical riser as connected to said first flexible pipe element, whereby:

   the end of said first flexible pipe element (12) connected to the bottom end (5₁) of the vertical riser (5) is held in a position (15₃) that is fixed relative to said base (15₁, 15₂); and

   the axes (XX', YY') of said ends of said undersea pipe (11) resting on the bottom and of said vertical riser (5) connected to said first flexible pipe element (12) are preferably held in a common plane perpendicular to said platform.
2. An installation according to claim 1, characterised in that:

   a) said vertical riser (5) comprises a terminal portion of rigid pipe (13) at its bottom end (5₁), which portion is connected to the top portion (5₂) of said vertical riser via a second flexible pipe element (14), thus allowing said top portion (5₂) to move through an angle α relative to said terminal portion of rigid pipe (13); and

   b) said base (15₁, 15₂) comprises a superstructure (15₂) which holds said terminal portion of rigid pipe (13) of said vertical riser (5) whose end is connected to said first flexible pipe element (12) rigidly in a fixed position (15₃) relative to the base.
3. An installation according to claim 1 or claim 2, characterised in that said base (15₁, 15₂) has fixing supports (16₁) suitable for holding the end of said first flexible pipe element (12) connected to the end of said undersea pipe (11) resting on the bottom in a position that is fixed relative to the base.
4. An installation according to claim 1 or claim 2, characterised in that said base (15₁, 15₂) has guide elements (19) which allow the end of said undersea pipe (11) resting on the bottom to move in longitudinal translation along its own axis XX'.
5. An installation according to claim 4, characterised in that said guide elements comprise rollers or sliding skids (19) over which said end of the undersea pipe (11) resting on the bottom can slide in longitudinal translation along the axis XX' of said end.
6. An installation according to claim 4 or claim 5, characterised in that said guide means comprise anti-rotation devices (19₁, 19₂) which prevent said end of said undersea pipe (11) from turning about its said longitudinal axis (XX').
7. An installation according to one of claims 1 to 6, said base comprising a said superstructure (15₂) secured to a said platform (15₁), said superstructure forming a bracket standing up on said platform, said platform preferably being secured to said guide means (19) preferably consisting in rollers distributed on either side of the bottom of said bracket resting on said platform, and said bracket having a latch (15₃) in its portion that is above said platform so as to enable said bottom end (5₁, 13) of said riser to be locked in position.
8. An installation according to one of claims 1 to 7, characterised in that said base comprises a platform (15₁) which cooperates with stabilizing elements (17, 18) comprising deadweights (18) placed on said platform (15₁) and/or suction anchors (17) passing through (16₃) said platform to be driven into the seabed.
9. An installation according to one of claims 1 to 8, characterised in that it comprises a connection device (4, 7) between said float (6) and the top end (5₂) of said riser (5), said device comprising:

   a third flexible pipe element (7) whose ends are connected in non-hinged manner respectively to the under-surface of said float (6) and to the top end of said vertical riser (5); and

   the connection of said third flexible pipe (7) to the top end of said riser (5) taking place via a swanneck-shaped device (4), which swanneck-shaped device (4) also provides the connection between said riser (5) and a said connection pipe (3) connected to the floating support, preferably a said flexible connection pipe (3);

   said third flexible pipe (7) preferably being extended through said float (6) by a rigid tubular pipe (8) passing right through the float so as to make it possible to take action on the inside of said vertical riser (5) from the top portion of the float (6) through said rigid tubular pipe (8), then through said connection device constituted by said third flexible pipe (7) and then through said swanneck-shaped device (4) so as to access the inside of said riser (5) and clean it by injecting liquid and/or by scraping the inside wall of said riser (5), and then said undersea pipe (11) resting on the sea bottom.
10. An installation according to one of claims 1 to 9, characterised in that it comprises:

    at least two of said vertical risers (5a, 5b) that are substantially parallel and close together, being connected at their top ends to at least one float;

    at least two of said pipes (11) resting on the sea bottom;

    said base (15₁, 15₂) holding the bottom ends (13) of said vertical risers (5) in fixed position relative to the base; and

    said installation including at least two of said flexible pipe elements (12) connecting the ends of the undersea pipes (11) resting on the sea bottom to said bottom ends (13) of said vertical risers.
11. An installation according to one of claims 1 to 10, characterised in that the at least two said undersea pipes (11₁, 11₂) resting on the sea bottom are assembled together as a bundle within a common flexible protective casing (11₃) enabling an insulating material (11₄), preferably paraffin or a gel compound, to be confined around said undersea pipes (11₁, 11₂).
12. An installation according to claim 10 or claim 11,
    characterised in that:

    at least two of said undersea pipes (11₁, 11₂) resting on the sea bottom are assembled together as a bundle in a common flexible protective casing (11₃) enabling an insulating material (11₄), preferably paraffin or a gel compound to be confined around said pipes; and

    at least two of said vertical risers (5a, 5b) are assembled together to constitute a bundle within a common flexible protective casing enabling an insulating material, preferably paraffin or a gel compound to be confined around said risers;

    the connection of each individual pipe in the bundle between a pipe of the bundle resting on the bottom and the corresponding pipe in the vertical bundle being constituted by at least one of said first flexible pipe elements.
13. An installation according to claim 10 or claim 11, characterised in that a first vertical riser (5a) and a second vertical riser (5b) are held substantially parallel to each other by means of a sliding connection system (25-27) allowing said first and second risers (5a, 5b) to move axially relative to each other, said connection system comprising a tubular collar (25) fixed around said first riser (5a), said collar (25) being rigidly connected (27) to a tubular ring (26) that is free to slide on said second riser (5b), and preferably a plurality of said collars (25) of a same sliding connection system (28₁) being distributed along each one of said risers (5a, 5b) in alternation with said rings (26) of another said connection system (28₂) on a same said riser (5a, 5b).
14. An installation according to one of claims 10 to 13, characterised in that it includes at least one float, preferably a group comprising a plurality of floats (30a, 30b) at the top of each of said at least two vertical risers (5a, 5b), said floats (30a, 30b) being held together by means of a structure (33, 34, 35, and 36) supporting them while allowing relative vertical displacements between said groups of floats relative to one other.
15. An installation according to claim 14, characterised in that said structure supporting said groups of floats comprises hinged structures forming parallelograms (33, 34a, 34b) that are deformable in vertical translation.
16. An installation according to one of claims 1 to 15, characterised in that in its top portion above said second flexible pipe element (14), said vertical riser (5) comprises a system of insulated pipes made up of a set of two coaxial pipes comprising an inner pipe (5₂) and an outer pipe (5₃), an insulating fluid or material (5₄) or a vacuum being preferably located between said two pipes (5₂, 5₃).
17. A method of installing an installation according to one of claims 1 to 16, the method being characterised in that it comprises the following steps:

    1) the following are preassembled in succession end to end: said pipe (11) for resting on the sea bottom; said first flexible pipe element (12); said rigid pipe for constituting said vertical riser (5); and, where appropriate and preferably, said second flexible pipe element;

    2) a said base (15₁, 15₂) is put into place co-operating with the assembly obtained in step 1), whereby:

    said pipe for resting on the sea bottom and said rigid pipe for constituting said vertical riser are fixed to said platform (15₁), preferably close to the ends of said pipes (11, 13) that are connected to said flexible pipe elements (12, 14); and

    the end of said first flexible pipe element (12) connected to the bottom end (5₁, 13) of said vertical riser is not held by said superstructure (15₂) of the base;

    3) the assembly obtained after step 2 is towed to the desired site;

    4) said base (15₁, 15₂) is put on the sea bottom and stabilized, preferably with said stabilizing elements (17, 18);

    5) said base is separated (16₂) from said riser (5, 13); and

    6) said bottom end (13) of said riser (5) is connected (15₃) with said superstructure (15₂) of the base so as to be held in said fixed vertical position relative to the base.

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