US3394553A - Underwater anchored pillar for supporting a platform - Google Patents

Description

July 30, 1968 H. VIDAL 3,394,553

UNDERWATER ANCHORED PILLAR FOR SUPPORTING A PLATFORM Filed llay 23, 1966 3 Sheets-Sheet 1 ATTORNEYS July 30,- 1968 VIDAL I 3,394,553

UNDERWATER ANCHORED PILLAR FORE SUPPORTING A PLATFORII Filed May 23, 1966 I 3 Sheets-Sheet 2 July 30, 1968 H. VIDAL. 3,394,553

UNDERWATER ANCHORED PILLAR FOR SUPPORTING A PLATFORM Filed May 23, 1966 3 Sheets-Sheet 3 mvmoa Hen/51 V 24/ ATTORNEYS United States Patent 3,394,553 UNDERWATER ANCHORED PILLAR FOR SUPPORTING A PLATFORM Henri Vidal, Saint-Cloud, France, assignor t0 LInstitut Francais du Petrole des Carburants et Lubrifiants, Rueil- Malmaison, Hauts-de-Seine, France Filed May 23, 1966, Ser. No. 552,239 Claims priority, applicatigrzi France, May 26, 1965, 18 5 6 Claims. 331. 61-465) ABSTRACT OF THE DISCLOSURE The invention relates to a pillar capable of being anchored at the bottom of the sea for supporting a platform or the like for carrying out work, such as supporting ocean drilling material or material associated with an underwater petroleum production well located at the base of the pillar.

An object of the invention is the construction of a pillar designed to be placed in a vertical position in the water whose base can be anchored upon the bottom by means of a massive anchoring easily put in place even when the depth of water is considerable.

Another object of the invention is to provide a pillar maintained in vertical position by a heavy removable anchorage which can be easily raised in order to permit the transport of the pillar to another position, the same heavy movable structure then being reused for anchoring the pillar at a newly chosen place.

A further object of the invention is to provide means for removably anchoring the pillar to secure a great stability thereof, even when the portative force at the bottom of the water is slight.

A further object of the invention is the construction of a pillar having at its upper portion a structure capable of sustaining a platform, such structure being capable, as desired, of being spread out or retracted according to whether the pillar occupies the chosen position or is to be transported to another position for anchoring.

A further object is to provide a pillar to be anchored with very great stability in a removable manner for the execution of under water petroleum drilling at different locations.

With the above and other objects in view which will become apparent from the detailed description below some non-limitative examples are shown in the drawings, in which:

FIGURE 1 illustrates schematically a pillar according to the invention when being towed towards a chosen location for its anchoring.

FIGURE 1a is a schematic cross-sectional View taken upon section line aa of FIGURE 1 showing the footing of the pillar partially filled with water during its towing.

FIGURES 1b and 10 show schematically two consecutive phases for placing the pillar into vertical position at the place fixed for its anchoring.

FIGURE 2 illustrates schematically a method for providing a massive removable anchorage for maintaining the footing of the pillar upon the sea bottom.

Patented July 30, 1968 FIGURE 2a shows diagrammatically in chain of balls with one ball in section used for constructing the massive removable anchorage.

FIGURE 3 shows schematically a pillar located in place with a platform at its upper portion.

FIGURES 4, 4a and 4b illustrate diagrammatically a preferred method of constructing a platform.

FIGURES 5 and 5a illustrate schematically a method of hoisting a floating platform to the top of the pillar.

A pillar according to the invention is schematically shown in FIGURE 1 floating upon the water before being towed to position and put in place. It comprises essentially in the example shown a metallic tube 1 having a footing or base 2 fixed to an end thereof which is to be placed upon the sea bottom where it will be anchored.

The metallic tube 1 moreover can be replaced by any other type of elongated structure solid or latticed which can have any desired form of cross-section such as circular, polygonal, etc.

The footing 2 is preferably formed by a caisson interiorly partitioned. The partitions 3 shown in FIGURE 1a are perpendicular to the upper face 4 and the lower face 5 of the footing which they connect together playing the role of counterbraces. The partitions which extend radially in the example shown in FIGURE 1a form tight compartments such as 6 in the footing.

In the construction shown in FIGURES 1 to 10 the assembly formed by the tube 1 and the footing or caisson 2 can float as shown in FIGURE 1 and may then be towed away by a boat to the position chosen for the anchoring of the pillar.

One of the tight compartments of the footing is filled with water, as compartment 7 in FIGURE la, so as to prevent the assembly from rotating during towing.

Upon arrival at the chosen position, the compartments and the footing are all filled with water by the simple opening of a water gate.

The towing vessel is then removed a little and the tube 1 progressively rights itself first into the position shown in FIGURE lb then after the admission of a certain quantity of water to the interior of the tube 1 into the vertical position. The pillar continues to sink by the progressive admission of water into the tube until the footing 2 gently rests upon the bottom of the sea 8. See FIG. 10.

If the bottom is not substantially horizontal compressed air may be sent in a known manner through orifices, not shown, located in the lateral surface of the footing in the neighborhood of the lower face 5 thereof. In this way the sand is driven until the footing takes a substantially horizontal position. The footing 2 is then anchored in a removable way upon the bottom so as to secure a stability of the tube upon the foundation ground 8.

The method of anchoring utilizes anchoring chains formed by heavy masses connected to one another by a deformable connection and these masses can have any form whatsoever, for example, the form of a ball, as shown.

In what follows there will be used for greater simplicity the term chains of balls to designate such an anchoring chain. The deformable connection connecting adjacent balls of the chain of balls can be formed by one or several cables, a chain, or even by an assembly of a plurality of rigid elements articulated together.

According to the construction shOWn in FIGURE 2a the anchoring chain is formed by the balls 9, for example, of concrete fixed upon a steel cable 10 which may be of stainless steel and spaced from one another.

But it is understood that one may use any other material than concrete in order to form the balls. It may even be more advantageous in certain cases to form the balls from a material of heavy density such as castings, considering that the total quantity of the balls depend not upon its total real weight but upon its apparent weight in water. Balls of heavy density unalterable by sea water can be formed by masses of concrete having a core of high density, for example, a casting.

Such a chain where the balls can assume the most complicated positions without the cable deteriorating FIG. 2a) is extremely movable, of easy operation, and allows by winding about the tube 1 in the manner that will now be described to form a massive anchoring of the footing 2 and of the lower portion of the pillar with very interesting features.

The pillar being placed in the position shown in FIG- URE 1c is maintained near the ship 11 upon which is stacked a chain of balls 12 FIG. 2). At the top of the pillar there is installed a rotating crane of known type whose boom 13 rotates about the vertical axis of the tube 1 through the intermediary of a bearing 35. In reality the rotating crane can be of very slight dimensions from the fact that it only supports a minimum load corresponding to a length of chain equal to the height of the pillar. The rotation movement of the crane 13 about its axis allows winding the chain of balls 12 around the tube 1 and upon the footing 2 of the pillar.

From the vessel 11 upon which it is stacked and the rotating boom 13, the chain of balls 12 passes upon the sprocket wheels 14 and 15 carried by the vessel 11 and the sprocket wheels 16 and 17 and the hawser pipe 18 carried by the pillar. The sprocket wheels 15 and 16 are mechanically driven in synchronism in known manner. The sprocket wheels 14 and 17 which only have the function of guiding can be replaced by hawser pipes for securing the same function.

The sprocket wheels are winding drums wherein the drums have cavities corresponding to the form of the balls, regularly spaced upon their peripheries. Upon FIG- URE 2 these drums are shown schematically as having the cross-sectional form of gears.

In FIGURE 2, the sprocket wheel 17 has an axis substantially horizontal carried by the support 33 fixed to the boom 13 of the crane and thus rotating with it about the axis of the pillar. The axis of the sprocket wheel 16 is carried by a support 32 which rests upon the support 33 through the intermediary of rollers cooperating with a circular rail 34 which allows that it need not be driven by the rotation of the boom 13 of the crane.

The chain of balls 12 is unwound in a continuous way between the vessel 11 and the pillar and the portion 19 of the chain stretches and slackens according to the position of the vessel with respect to the pillar. This position has no need of being fixed rigorously and it is only necessary to operate the vessel so that it remains in the immediate vicinity of the vertical tube 1.

The winding of the chain of balls 12 is thus secured by the rotation of the boom 13 of the crane and is displaced laterally by the hawser pipe 18 with relation to the axis of the pillar. This can be realized very simply, for example, by using a highly inclined boom 13, comprising at its end an arm 36 articulated at 37 and whose inclination can be regulated by the hydraulic jack 38 connecting the arm to the boom 13. Such a type of crane is usual and need not be further described.

The chain of balls 12 wound about the lower portion of the tube 1 and upon the footing 2 (FIGURE 3) forms a massive anchorage which is easy to put in place under the water and it has the advantage of adapting itself to the final packing of the foundations.

The massive anchorage 20 acts by its own weight while loading the entire surface of the footing 2 with a heavy pressure because one can give to the lateral wall 21 a very strong slope, such wall being capable of having even a vertical slope in spite of a relatively great height of the massive anchorage 20.

In the case of bad terrain the massive anchorage 20 can project from the footing, see FIG. 3, while loading the bottom about such footing, which improves considerably the portative force of the ground and can avoid possible erosion due to movements of the sea. A pillar thus anchored by a chain of balls can be calculated so as to resist very strong swells due to a tempest while standing perfectly vertical.

When a pillar so constructed is used for work such as drilling or securing underwater petroleum production it must support a platform 22 substantially horizontal as shown in FIGURE 3.

FIGURES 4, 4a and 4b show a simple means for constructing such a platform. According to this form of construction the pillar comprises at its upper portion at the periphery of the tube 1, retractible members or arms 23 articulated to the axes 24 on the supports 24a fixed to the tube 1, such articulation permitting the arms 23 to pivot from one position where they are folded against the tube as shown in FIGURE 4 to a substantially horizontal position as shown in FIGURE 4a in which they can be locked by any appropriate known means. In the position of transport of the pillar as shown in FIGURE 1, the articulated arms 23 are folded against the tube 1, and they are deployed when the pillar has been placed vertically at the chosen place and anchored to the bottom.

The means used for pivoting the articulated arms 23 can result from the combination of cables such as 25 wherein one end is fixed to an articulated arm while the other end of each of these cables are connected to a container 26 capable of sliding at the interior of the tube 1. It is suflicient therefore to fill the container 26 progressively with water by pumping in order to cause it to descend into the tube 1 which deploys the articulated arms 23.

FIGURE 4b is a top view of a pillar showing such articulated arms deployed and these arms are able to sup port a substantially horizontal platform.

It would also be possible to unfold each articulated arm one after another by means of a winch located at the upper portion of tube 1 and upon which are wound the different cables 25 each corresponding to an articulated arm.

A further possiblity for constructing a substantially horizontal platform when the pillar is anchored in vertical position comprises using the method as illustrated by FIGURES 5 and 5a.

According to this method one uses one or several floating platform elements such as 27 and 28 associated with the upper portion of the tube 1. These are connected by cables such as 29 passing upon the pulleys 30 and fixed to the top of a floating container 31 capable of sliding at the interior of tube 1. Pumping means will allow filling the floating container 31 and the progressive emptying of the interior of tube 1 which brings about the descent of the floating container thereby causing the cables 29 to raise the platform 27 and 28.

However, the construction of the platform shown by FIGURES 4, 4a and 4b is preferable since it is simpler and allows the easy towing of the pillar when the articulated arms are folded back along the length of tube 1, these arms then presenting slight hydrodynamical resistance.

A pillar thus constructed and anchored as set forth presents a considerable advantage in being able to be displaced while carrying out operations in reverse to those described above for putting it in place, that is to say, by commencing by recovering the chain of balls 12 into a vessel and then floating the pillar by emptying therefrom the water which it contains. In view of allowing the recovery of such a chain of balls, the end of the chain of balls at the end of the winding may be connected by a cable to a surface buoy. It would thus be possible to lead the end of the chain upon the vessel by simple traction upon the cable which would permit unwinding the chain of balls according to an inverse process from that followed for the formation of the massive anchorage.

There will now be given purely in an illustrative way, the characteristic principles of a pillar constructed according to the invention, anchored upon the sea bottom, such pillar being 'capable of resisting extremely severe conditions of use.

These conditions are essentially the following:

Depth of water of 100 meters, tubular pillar of 120 meters in length and 5 meters in diameter,

A tempest swell having a total trough of meters and a wave length of 100 meters.

The platform at the top of the pillar capable of supporting a total load of 3,000 tons, of which 2,000 tons are exactly centered upon the vertical axis of the tube and 1,000 tons, of which the center of gravity can be eccentric meters with relation to such axis.

Upon the base with the above factors, the pillar is constructed with an annular envelope 5 meters in diameter having 2,200 cm. of steel per linear meter of circumference at the base and 650 cm. at the summit with a working stress of steel of 1800 kg./cm.

According to one form of construction given by way of example a cross section of steel of the envelope varies linearly between the two values throughout the length of the immersed portion of the tube.

The footing has been chosen of a diameter of 31 meters and the height of the chain of balls mounted thereon of 16.50 meters (for an apparent density of a chain of balls immersed of 1.1).

Under these conditions the strongest load per unit area exercised by the footing upon the terrain of the foundation has a value of 3.6 kg./cm. (in normal times the pressure upon the ground is almost constant and equal to half of such value).

The portative force of an average sand (having a friction angle of 32 to 33 and a density in water 1.1) is about three times the value indicated above of the maximum load per unit area exerted upon the ground by the footing.

It results therefrom that in the case of average sand the stability of the pillar according to the invention is perfectly assured with a coefficient of security of the order of 3 in spite of the very pessimistic conditions of use which were assumed.

:Moreover, as has already been indicated above in the case of very bad terrain, the chain of balls may be put in place so as to exhibit the additional advantage of improving the stability of the pillar by loading the terrain about such footing, which permits increasing the portative force of the terrain.

Numerous modifications or additions can be made in the constructional forms of the invention set forth above without departing from the spirit of the invention such as defined in the following claims.

I claim:

1. An underwater pillar comprising a vertically elongated structure, a footing located at the lower portion of said elongated structure, said footing being designed to rest upon the underwater bottom and having a cross-section greater than that of said elongated structure, a removable heavy anchoring means comprising a plurality of heavy masses, a deformable connection interconnecting adjacent masses to form an anchoring chain wound about the lower portion of said elongated structure with a portion of said anchoring chain resting upon said footing and constituting a massive anchorage loading said footing and being supported by said underwater bottom in the neighborhood of said footing.

2. An underwater pillar as set forth in claim 1, comprising means for supporting a platform at the upper part of said elongated structure, said supporting means comprising arms pivotally mounted on the upper portion of said pillar and means for unfolding said arms from a position folded against said elongated structure to a position substantially transversal thereto.

3. An underwater pillar as set forth in claim 2, Wherein said means for unfolding said pivotable arms comprises a reservoir connected to said arms and adapted to slide vertically inside said elongated structure upon filling with water, to secure the unfolding of said pivotable arms.

4. An underwater pillar as set forth in claim 1, Wherein said footing has radial partitions dividing said footing into a plurality of water tight compartments.

5. A method for placing in a body of water a removable pillar having an elongated structure with a footing at one of its ends of greater cross-section than that of said elongated structure, with great stability in place, the assembly of said elongated structure and said footing having a positive buoyancy, comprising the steps of transporting by floating said pillar to the place at which it is to be anchored, placing said pillar in vertical position by pumping water into the interior thereof until said footing rests upon the underwater bottom, thereafter forming a removable anchoring of said pillar by winding about said pillar an anchoring chain formed of heavy masses interconnected by deformable connections, said anchoring chain being wound at the base of said pillar with at least a portion of said chain being disposed upon the footing of said pillar.

6. A method as set forth in claim 5, wherein a portion of said chain is also disposed upon the underwater bottom adjacent said footing.

References Cited UNITED STATES PATENTS 2,496,532 2/1950 Gross 6146.5

2,622,404 12/ 1952 Rice 61-465 3,111,926 11/1963 Shatto 114-206 FOREIGN PATENTS 1,381,245 11/1964 France.

JACOB SHAPIRO, Primary Examiner.

Images