EP0699803B1 - Offshore drilling or production platform with anchoring means - Google Patents

Description

The present invention relates to platforms for oil drilling and relates more particularly but not exclusively to self-elevating platforms drilling, and / or production at sea.

Platforms for drilling in sea have legs that are placed directly on the seabed to depths of around 100 m. However for a long stay corresponding to the duration normal of a production campaign, the legs of a platform must be securely anchored in the bottom marine and it is necessary in order to consolidate them foundations, to fix each of the feet of the platform to the by means of piles deeply sunk into the ground which, considering the dimension of such piles, is an operation long and expensive because it requires intervention heavy equipment and whose operating cost is extremely high (see eg EP-A-0 056 635).

The invention aims to remedy the drawbacks known techniques, creating an oil platform drilling or exploitation at sea whose cost installation on a marine site is considerably reduced and not sensitive to scour risks and sagging.

Its object is therefore an oil platform drilling or exploitation at sea including a shell carried by legs provided with feet intended for lean on the seabed, characterized in that the walls of each of the legs define a space leading to the corresponding foot and in which are retracted from the leg anchoring posts carried by the foot, each leg being additionally provided at its part upper support means in line with said piles inside the space provided by the walls of the leg, of a device for driving said piles into the sea floor.

According to a characteristic of the invention, the anchor piles are carried by a support forming part of the foot and separable from it.

According to another characteristic of the invention, each leg is provided with means for guiding the piles at during their sinking.

According to another characteristic of the invention, each leg also carries peripheral anchor piles intended to withstand the tilting forces undergone by the platform especially under the effect of the swell.

La fig.1 est une vue schématique en perspective d'une plate-forme pétrolière suivant l'invention ;

La fig.2 est une vue schématique à plus grande échelle, en coupe suivant la ligne 2-2 de la figure 3, montrant plus en détail les pieux d'ancrage équipant chaque jambe de la plate-forme suivant l'invention ;

La fig.3 est une vue en plan du pied de la jambe de plate-forme de la fig.2 ; et,

La fig.4 est une vue partielle en perspective d'un dispositif d'enfoncement de pieux équipant tour à tour les jambes d'une plate-forme afin d'assurer l'ancrage de celles-ci dans le sol marin.

The invention will be better understood on reading the description which follows, made with reference to the appended drawings given solely by way of example and in which:

Fig.1 is a schematic perspective view of an oil platform according to the invention;

Fig.2 is a schematic view on a larger scale, in section along line 2-2 of Figure 3, showing in more detail the anchor piles fitted to each leg of the platform according to the invention;

Fig.3 is a plan view of the foot of the platform leg of Fig.2; and,

Fig.4 is a partial perspective view of a pile driving device in turn equipping the legs of a platform to ensure the anchoring thereof in the sea floor.

There is shown in fig.1 a platform of oil drilling can be either fixed or self-elevating and comprising a shell 1 carried on three legs 2 produced in the form of a truss of metal beams and each having a triangular section.

Each of the legs 2 is provided at its end bottom of a solid foot, 3 disc-shaped or triangle supporting leg 2 in its central part and provided with a separable support 4 constituted by a disc central of smaller diameter and carrying anchor piles 5 housed in the space delimited by the walls of the leg 2. The anchor piles 5 are section piles important and are intended to bear the effects of the load exerted on the legs by the mass of the platform. For this purpose, piles 5 must be deeply anchored in the sea floor.

To ensure this operation each leg 2 has at its upper end opposite the foot 3 a cage 7 also made of metal beams and intended to support the anchor piles 5 un hydraulic type hammer 8 suspended from cage 7 at by means of a cable 9 in a manner which will be described more in detail with reference to fig. 4. In order to absorb tilting efforts which are materialized by moments, each foot 3 in the form of a disc or triangle has at its periphery radial projections 10 arranged at 120 ° and carrying 12 more anchor piles smaller cross section than main anchor piles 5, these peripheral piles that can be driven in either lighter mobile equipment than conventional equipment used for the placement of anchor piles either using the hammer 8 carried by means which will also described with reference to FIG. 4.

Each of the legs 2 is equipped with means 14 for guiding the anchor piles located in space formed by the walls of the leg 2. These guide means may consist of a plate occupying a cross section of each leg and provided with holes axial in number equal to the number of anchor piles 5 that features each leg. In the present embodiment, each leg has three main anchor stakes 5 and six peripheral anchor piles.

One of the legs of the next platform the invention is shown partially, in more detail and on a larger scale in fig. 2.

We see in this figure that the foot in the form of disc has in its central part a housing 16 provided with a shoulder 17 intended to cooperate with a shoulder complementary 18 provided on support 4 for anchor piles 5 with interpositions of hydraulic cylinders 20 regularly distributed around the periphery of the support 4 and intended to be kept under pressure at the start set-up operations and in particular during driving the main anchor piles 5 and to be released so that the load of each of the legs is transmitted by the disc 3 to the support 4 after placing the peripheral anchor piles 12.

At its end intended to cooperate with the hammer 8, each anchor stake 5 which is shaped tubular comprises an end piece 22 for receiving shocks from the mass of the hammer 8.

The anchor piles pass through the plate guide 14 by axial passages provided with sleeves 24 provided therein directly above the pile locations 5 in their support 4. The guide plate 14 is fixed to the uprights 26 of the leg 2.

The main anchor piles 5 are mounted in axial bores 28 of the support 4 with interposition of devices 30 for axially immobilizing the piles or batteries 5 with respect to the support 4, constituted by example by sleeves made integral with the foot and internally provided with suitable means not (shown) blocking of the anchor piles relative to the sleeves.

The main anchor piles 5 are designed to support each 3 to 4,000 tonnes while the peripheral anchor piles 12 each support 1000 tonnes about. We therefore understand that the latter may have more modest dimensions than those of the central stacks and therefore they are easier to install without require the use of heavy equipment.

Peripheral anchor piles 12 are arranged in orifices of the disc 3 forming a foot each provided with a radially fixed clamp 10 to disc 3 by destructible fixing means such that for example explosive bolts not shown and intended to allow when removing the platform from separate foot 3 from it relative to its stakes peripheral anchor 12.

We see in fig. 3 that each leg of the platform according to the invention has in cross section an equilateral triangle shape. Anchor piles main 5 are also arranged in an equilateral triangle inside the space defined by the side walls of the leg 2. The peripheral anchor posts 12 are arranged at 120 ° opposite the vertices of the triangle equilateral defined by the cross section of the leg 2. Of course, the invention also applies to platform legs which would have different sections, in particular tubular legs of circular section.

Returning to fig. 1 we see that each leg 2 of the platform according to the invention comprises at its end, opposite the foot, a cage 7 for receiving and support for a hammer 8 for driving the anchor piles main 5.

This cage is generally prismatic in shape. It is carried out using a truss of beams metallic and at least one of its faces facing the interior of the shell 1 has a passage 40 of sufficient dimensions to let the hammer pass 8 in order to ensure the positioning in relation to the leg 2 of which he must drive the anchor piles 5 and removal using lifting and handling equipment equipping the platform (not shown) to transfer it to another leg of it. Each of the cages 7 has, at its free upper part, a circular rail 42 fixed to the ends of the vertical uprights 43 of the leg corresponding and on which, as best seen at the fig.4, is mounted angularly displaceable first beam or jib 44 by means of two carriages 45 diametrically opposite rolling on the circular rail.

Below beam 44 is mounted by means a spacer 46 a second beam 47 in length falling within the inside diameter of the circular rail 42 and on which is movably mounted a carriage 48 to which the hammer suspension cable 9 is hung hydraulic 8 which comprises a conduit 50 for supplying hydraulic fluid connected to a fluid source under pressure carried hull 1 (not shown).

We therefore see that thanks to the arrangement described in reference to fig. 4, under the effect of combined movements beam 44 and carriage 48, hammer 8 can be placed successively above the three piles or piles main anchor 5 to ensure their penetration.

The beam 44 angularly movable on the circular rail 42 has at one of its ends a extension 52 engaged telescopically in the beam 44 and carrying at its free end a cable 54 provided with a hook 56 for hanging the hydraulic hammer 8 in order to allow the use of said hammer also to insure the peripheral anchor piles 12.

The beam 44 carries in its middle a mast 58 whose the upper end is connected to the ends of the beam 44 by guy lines 60.

The angular displacement of the beam 44 on its rail 42 allows its extension 52 to reach all point of the periphery of the corresponding foot 3 and in particular to be successively at the base of peripheral anchor piles 12. To reach the piles, located below the shell 1, it comprises associated with each leg a passage 62 through which can lower the hammer 8 (Fig. 1).

The hammer 8 and its mounting means and of suspension constituted by the beam 44 and the carriages 45 are removable and transferable after the end of a ramming operation for anchor piles of a leg 2 towards the cage 7 of another leg.

The mass of such a set including the hammer can reach a hundred tonnes and we can therefore consider handling it using lifting existing on an oil platform by means of possibly a slight increase in its power.

We can also use for the transfer of the whole hammer a cable transfer device that we stretch between two cages.

The arrangement which has just been described can be used for both a fixed leg platform and for a self-elevating platform. In this last case, when the platform is in the towing position, the hull 1 then floating and the legs 2 being in mostly out of the water, the peripheral piles 12 which are normally found below the surface of the hull are engaged in the passages 62 provided in this one.

The other peripheral anchor piles 12 are are located outside the dimensions of the shell 1.

We can see that thanks to the arrangement of the invention, it is possible to set up an oil platform operating at sea using mainly or even only to equipment on board of the platform, and in any case using materials relatively unimportant exteriors for installation peripheral anchor piles 12.

It is therefore conceivable that it follows for the platform user a significant saving and that it is no longer dependent on the intervention of a third party to ensure the establishment of its platform.

For removing the platform, at the end of a drilling or exploitation operation, we proceed to the separation of the feet 3 in the form of discs relative to to the peripheral piles 12 by destroying the means of fixing which ensure the connection of the collars 10 to discs 3. Furthermore, the central shoulder 17 of the foot 3 disc-shaped 3 being turned inward and located above the complementary shoulder 18 of the support of the anchor piles 5 facing outwards, nothing stands in the way of raising the legs 2 either by mechanical means carried by the hull if it is a self-elevating platform, or by any other means of lifting in the case of a platform with fixed legs.

Main anchor piles 5 and piles peripheral anchor 12 remain stuck in the ground after removal of the platform.

Claims (13)

1. Offshore drilling or production platform comprising a shell (1) carried by legs (2) provided with feet (3) intended to rest on the sea bed, characterised in that the walls of each of the legs (2) define a space opening at the corresponding foot (3) and in which there are retracted anchoring piles (5) of the leg carried by the foot, each leg (2) also being equipped at its upper portion with supporting means (7) perpendicular to said piles within the space created by the walls of the leg (2) of a device for driving said piles into the sea bed.
2. Platform according to claim 1, characterised in that the anchoring piles (5) are carried by a support (4) forming part of the foot (3) and separable therefrom.
3. Platform according to one of claims 1 and 2, characterised in that each leg (2) is provided with means (14) for guiding the piles (5) during the driving process.
4. Platform according to one of claims 1 and 3, characterised in that each foot (3) also carries peripheral anchoring piles (12) intended to withstand the rocking imposed on the platform, in particular due to the swell.
5. Platform according to one of claims 2 to 4, characterised in that each foot (3) is disc-shaped and the support (4) for the anchoring piles (5) comprises a disc having a smaller diameter than the foot (3) and comprises an externally directed shoulder (18) whereas the foot (3) comprises a recess (16) for the support (4) provided with an inwardly directed shoulder (17) located above the shoulder (18) of the support (4).
6. Platform according to claim 5, characterised in that hydraulic jacks (20) intended to be released after the positioning of the anchoring piles (5) accommodated in the legs (2) are interposed between the respective shoulders (17, 18) of the foot (3) and of the support (4) and are distributed uniformly at the periphery of said support.
7. Platform according to one of claims 1 to 6, characterised in that each anchoring pile (5) accommodated in a leg (2) is associated with a device (30) for axial immobilisation of the pile relative to the support (4) after the pile has been driven into the ground.
8. Platform according to one of claims 3 to 7, characterised in that the guide means of the anchoring piles (5) inside the legs (2) comprise a guide plate (14) provided with axial passages equipped with sleeves (24) provided therein perpendicularly to the locations of the piles (5) in their support (4).
9. Platform according to one of claims 1 to 8, characterised in that the supporting means for the device for driving said piles into the ground comprise a cage (7) provided at the end of each leg (2) remote from its foot (3), said cage comprising, at its free end, a circular rail (42) fixed to the vertical columns (43) of the leg (2) on which there is angularly displaceably mounted a first girder (44) to which there is fixed a second girder (47) having a length inscribed in the internal diameter of the circular rail (42) and on which there is displaceably mounted a carriage (48), a suspension cable (9) of a driving device (8) being supported by said carriage.
10. Platform according to claim 9, characterised in that the cage (7) comprises, on at least one of its faces turned toward the interior of the shell (1), a passage (40) having adequate dimensions to allow the passage of the device (8) for driving the piles (5) so as to ensure that they are positioned relative to the leg of which it must drive the anchoring piles and to allow withdrawal in order to transfer it to another leg of the platform.
11. Platform according to one of claims 9, 10, characterised in that the first girder (44) comprises, at one end, an extension (52) engaged telescopically in the girder (44) and carrying, at its free end, means (54, 56) for suspension of the driving device (8) to enable this device to be used in order also to ensure the driving of the peripheral anchoring piles (12).
12. Platform according to claim 11, characterised in that the shell (1) comprises passages (62) for the driving device (8) to allow the driving of the peripheral anchoring piles (12) located below the bulk of the shell (1), said passages (52) also serving to receive the corresponding peripheral anchoring piles (12) in the raised position of the legs (2) during transportation of the platform to its site of erection.
13. Platform according to one of claims 9 to 12, characterised in that the first girder (44) is connected to the circular guide rail (42) by diametrically opposed carriages (45).

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