EP0247112A1

EP0247112A1 - Deep submarine anchoring method

Info

Publication number: EP0247112A1
Application number: EP19860906863
Authority: EP
Inventors: Pierre Le Mat Noune Chemin du Riou Merlet GUEVEL; Philippe Bardey; Jean-Luc Viaud
Original assignee: Commissariat a lEnergie Atomique CEA; Principia Recherche Developpement SA; Principia Recherche Developpement
Current assignee: Principia Recherche Developpement SA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA; Principia Recherche Developpement
Priority date: 1985-12-02
Filing date: 1986-12-01
Publication date: 1987-12-02
Also published as: FR2590862A2; WO1987003260A1

Abstract

Procédé pour l'ancrage sous-marin profond de structures flottantes, caractérisé en ce que l'on utilise à cet effet un ensemble comportant un engin de pénétration à vitesse limite élevée, des moyens d'accrochage et des moyens de repérage permanent de cet engin et des moyens de liaison entre ledit engin et lesdits moyens d'accrochage et de repérage, ledit ensemble étant conçu de manière que, étant largué depuis ladite structure, l'engin de pénétration s'enfouisse dans le fond marin à la profondeur calculée voulue pour assurer l'ancrage de ladite structure tandis que lesdits moyens de repérage demeurent au-dessus du fond, et en ce qu'on largue ledit ensemble depuis la surface, on en assure le repérage et on fixe enfin la ligne d'ancrage sur lesdits moyens d'accrochage.Method for deep underwater anchoring of floating structures, characterized in that an assembly is used for this purpose comprising a penetration device at high limit speed, hooking means and means for permanent location of this device and means of connection between said machine and said hooking and locating means, said assembly being designed so that, being released from said structure, the penetration machine buries itself in the seabed at the calculated depth desired for anchoring said structure while said locating means remain above the bottom, and in that said assembly is released from the surface, locating is ensured and finally the anchoring line is fixed on said means hanging.

Description

'' Process for deep underwater anchoring.

The depositors have written to the French register No. 85. 09355 the pr inc ip of a machine intended to move within an unlimited fluid, of the type whose front and rear forms are fixed by known technological considerations, this machine being characterized in that, for the purpose of lower the drag coefficient, avoid the separation of the boundary layer and eliminate cavitation and instability phenomena, the profile of the portion connecting the front and the rear is determined in such a way that the coefficient of pressure remains constant at all points of this connection portion.

As the first applications of such devices, this French patent cited, among other things, the recognition of the seabed, in particular their nature and their resistance to penetration, the device then having a vertical displacement.

The present invention relates to another application of these vertical displacement machines in the marine environment and of similar performance machines, namely the deep underwater anchoring of large structures.

Indeed, the terrains encountered at great depths are generally soft, which represents a serious difficulty for the immobilization of structures such as oil drilling platforms, which exert on their anchors very high vertical and horizontal traction forces, and therefore difficult to find suitable anchor points.

The invention consists in associating, with an anchoring member proper, which may be of a conventional nature or be designed in a new way, adapted to a particular structure to be immobilized, a machine as defined in the aforementioned patent or similar machine, the assembly thus formed, released from a surface support, that is to say from the structure to be immobilized, reaching the bottom at a high speed in particular thanks to its profile, then penetrating into the submarine soil over a significant depth, ensuring the anchoring of said body.

By "analogous device" is meant any device whose The whole is determined to obtain a high speed. According to the invention is also meant a machine comprising three parts: the penetration machine itself, means for connecting or hooking the anchor line or mooring to. this t machine, which will also be designated in the remainder of this description by anchor head, fixed to the tail of this machine and a connecting member between the first two parts; in this case, the unwinding reel of the guide wire connecting the machine to the surface support during the dropping can be arranged in the anchoring head; moreover, the connection member mentioned above may be a resistant cable or a concrete injection tube; in this case again, the masses and the profile of the assembly of the three parts are determined, on the one hand for obtaining a desired depth of penetration into the ground of the underwater soil, on the other hand, for that, during penetration into this terrain, the kinetic energy acquired and the Archimedes' thrust on the anchor head are made up to keep the connecting cable in tension or to prevent the pruning of the connecting tube.

According to a variant, to reduce the scour produced by the connecting cable, it is possible to use another type of known anchoring member not requiring burial, which it suffices to deposit on the seabed along a guide wire connecting the machine to the surface support, before anchoring; this will be for example the member, operating by suction cup effect, described in French patent 74/10700 of March 28, 1974.

According to a second embodiment of the invention, the machine itself constitutes the anchoring member, its profile being smooth and remaining so throughout the descent, and comprising side panels deploying under the effect of any effort of traction exerted after the arrival and positioning of the anchor, for example using explosive bolts or equivalent means, so as to constitute a sort of grapple opposing the tearing, which contributes to the solidity of anchoring.

To complete this solidity, several machines of the latter type can be combined in bundles or in clusters. It is thus possible to provide the anchorage with a resistance ranging from several hundred to several thousand tonnes of vertical traction.

However, due to the possible cyclic horizontal pulls which can be exerted on the machine, causing a scour of the ground and therefore reducing the effective thickness in which the machine is buried, it is provided, according to the invention, to connect this gear to a mooring system intended to reduce these horizontal pulls. Such a system can for example be a dead body resting on the surface of the bottom, further improving the holding. In this case, deep burial of the machine with a large penetration depth, associated with the suction cup effect member, may suffice for anchoring. The mooring of the line itself is allowed by a guide wire connecting the surface support to a hooking ring of the machine.

Mooring of the anchor line on the anchor head can be done by any appropriate means -, depending on how the latter is connected to the machine at great depth of penetration, either by a resistant connection cable, either by a tube allowing the injection of concrete.

According to a preferred embodiment of the invention, provision is made to associate with all the locating means, such as an ultrasonic transmitter, ensuring the control of the anchoring line with a view to its "clamping".

The invention therefore relates, firstly, to a method for deep underwater anchoring of floating structures, characterized in that an assembly is used for this purpose comprising a penetration device at high speed for fastening the fastening means and means for permanently locating this machine and means for connecting between said machine and said hooking and locating means, said assembly being designed so that, being dropped from said structure, the penetrating machine is buried in the seabed at the calculated depth desired to ensure the anchoring of said structure while said locating means remain above the bottom, and in that said assembly is released from the surface, or locating is ensured and fixed finally the anchor line on said attachment means.

We will now describe the invention with reference in the attached drawing in which:

- Figure 1 shows a first embodiment of an anchoring device according to the invention;

- Figure 2 shows a second embodiment of this machine;

- Figure 3 illustrates a means for reducing the cyclic horizontal displacements of the anchor point;

- Figure 4 schematically illustrates the application of the invention to the immobilization of an oil drilling platform.

The machine shown in Figure 1 is in the form of an axisymmetric machine with vertical movement 1, optionally equipped with pilot vanes 2, and intended to be connected by an anchor line (not shown) to a support structure of surface to be immobilized, as shown in Figure 4.

According to this embodiment, the machine 1 comprises four housings in the form of radial slots 3, in which the panels 4 are enclosed, pivotally mounted around horizontal axes 5 situated towards the head of the machine 5.

The machine, dropped from its support, arrives on the bottom with a high speed, of the order of 40 to 60 m / sec. thanks to its profile, as defined in the aforementioned patent, and sinks into the ground to a significant depth, of the order of 20 to 50 meters. As soon as the machine is immobilized after this burial, the panels 4 tilt outwards, as shown in 4 ′, and in addition pivoting by 90 ° around their axis under the effect of off-center friction which occurs from that the machine is under traction, so as to flourish flat in soft underwater terrain. In fact, the result of the friction forces is applied to the barycenter of the panel 4 which is laterally offset with respect to its axis of rotation. The anchoring is then provided in an extremely solid manner and can withstand significant pulls.

The machine shown in Figure 2 differs from the previous one in that it has no slots, panels 6 being curved so as to be pressed against the outer surface of the machine 1. The deployment "umbrella" of these panels 6 is primed, for example by explosive bolts arranged at their upper part 7 and triggering their rocker which continues until said panels lie flat in the soft underwater terrain as before.

Referring now to Figure 3, there is shown a surface support S, floating on the sea M, and connected by an anchor line 10 to a machine according to the invention, 11, buried in the ground and whose panels are deployed. According to the invention, to avoid scouring of the ground 12, which could result from cyclic horizontal displacements of the line, a mooring system such as a dead body 13 remains on the ground surface 14 threaded on the cable or on the connecting tube 10 '. The anchoring line 10 is attached to the whole of the machine and the dead body by an anchoring head 15 and can be ensured by an automatic connector system.

The guidance of the dead body for its incorporation into the machine with a large depth of penetration-anchor head, as well as the "clamping" of the anchor line, can be carried out by any appropriate means, depending on the type of connection. between anchor head and penetration device, for example by means of a guide line unwound from the anchor head during firing, or by petroleum-type equipment, based on hydrojets, guided by transmitters ultrasound (pingers) and video camera for the final phase.

Finally, FIG. 4 represents an oil drilling platform P resting on floating load-bearing structures F, connected by anchor lines 10 to dead bodies 13, resting on the bottom 14, and joined to machines according to l 'invention, 11, by resistant cables 10', hooked to rings 15. This system ensures an anchoring of the platform capable of withstanding tensile forces of the order of 5000 tonnes.

Within the framework of the same application, the present invention also relates to a certain number of measures, relating to the consolidation of such an anchoring, and to the installation and immobilization of pipelines.

Firstly, it is possible, according to the invention to inject from the surface into the anchoring device a load of concrete by means of a pipe terminating in a device with porous walls or opened by explosion after burial. Although the principle of this technique is known, its application in accordance with the invention has the advantage of being implemented much faster than with current means.

It can replace the mechanical anchoring means such as the panels 4 and 6 of FIGS. 1 and 2.

Secondly, in the technique of laying pipelines, it may prove useful to immobilize a section of pipe, especially in the case where this section is subjected to strong currents, or even when the ground on which it rest is of poor quality. In this case, it is possible, within the framework of the invention, to anchor said section by means of one or two buried machines as described above.

Finally, also in said technique, in the case where the pipe must be ripped from a laying point to a final point, by means of cables wrapping around pulleys fixed to solid fixed points, it is possible to use the means of the invention to create such fixed "hard" points.

It will be noted that, even without a piloting system, the machines according to the invention can be placed with a precision of the order of 20 meters relative to a target, but with appropriate piloting, this precision can be refined unless of one meter, which allows in particular the last aforementioned applications.

One of the essential advantages of the invention is that the machine at high limit speed is separated, when it is dropped, from the anchor line, the drag of which would considerably limit its speed if it were attached to the rear of this machine. The speed limit reached is that of the vehicle and of the attachment and connection means associated therewith with background tracking means such as ultrasonic emitters; in the case where the locating means consist of a guide wire unwound from the machine or the associated anchoring head, this wire, of small section, is immobile in water and only induces a very slight increase drag, which hardly penalizes the speed limit.

Claims

CLAIMS.

1. A method for deep underwater anchoring of floating structures, characterized in that an assembly is used for this purpose comprising a penetration device at high limit speed, attachment means and permanent location means of this machine and connecting means between said machine and said hooking and locating means, said assembly being designed so that, being released from said structure, the penetration machine buries itself in the seabed at depth calculated desired to ensure the anchoring of said structure while said locating means remain above the bottom, and in that said assembly is released from the surface, it is located and finally fixed the anchoring line on said attachment means.

2. Method according to claim 1, characterized in that the machine itself constitutes the anchoring member, its profile being smooth and remaining so throughout the descent, and comprising side panels deploying after burial, thanks to example with explosive bolts, so as to constitute a grapple opposing the tearing, and contributing to the solidity of the anchoring.

3. Method according to claim 2, characterized in that the panels are housed in slots distributed in radial planes of the body of the machine and, after burial, tilt outwards around axes located at their lower part, then rotate 90 ° to flourish as a corolla flat on the ground, under the effect of off-center friction resulting from tensile forces.

4. Method according to claim 2, characterized in that the panels are pressed against the outside of the body of the machine, their tilting towards the outside around axes located at their lower part being initiated after buried wise by example by explosive bolts located at their upper part, and ending spontaneously under the effect of off-center friction resulting from tensile forces.

5. Method according to any one of claims 1 to 4, characterized in that the machine is connected to the surface by a pipe intended for injecting concrete into and around said machine, with a view to creating or strengthening the anchor.

6. Method according to claim 2, characterized in that the anchoring member is of the suction cup type.

7. Method according to any one of the claims

1 to 6, characterized in that the locating means consist eir a guide wire unwound from said machine.

8. Method according to any one of claims

I to 6, characterized in that the means for permanent location of said machine consist of an ultrasonic transmitter.

9. Application of the method according to any one of claims 1 to 8, to the immobilization of pipelines in areas with strong currents and on poor quality soils.

10. Application of the method according to any one of claims 1 to 8 to the creation of fixed points for the installation of pipelines by shifting.