GB2069955A

GB2069955A - Anchoring apparatus for a ship used in the production of hydrocarbons

Info

Publication number: GB2069955A
Application number: GB8101501A
Authority: GB
Original assignee: Societe National Elf Aquitaine
Current assignee: Societe National Elf Aquitaine
Priority date: 1980-01-17
Filing date: 1981-01-19
Publication date: 1981-09-03
Also published as: FR2473981B1; ES498569A0; FR2473981A1; ES8203749A1; NO810148L

Abstract

Anchoring apparatus for a ship used in the production of hydrocarbons. Such an apparatus is constituted by an upper body of positive buoyancy, a lower body of negative buoyancy, a connecting means of predetermined length between the upper and lower bodies, and anchoring means between one of these three elements and the sea bed, and characterised in that the buoyance of the upper body is inferior in absolute value to that of the other elements. Since the highest point of the upper body is arranged to be spaced from the lowest point of the lower body by a length less than the depth of the water in which the apparatus is to be used, by at least the maximum draught of ships, the apparatus represents only a minor hindrance to navigation. <IMAGE>

Description

SPECIFICATION Anchoring apparatus for a ship used in the production of hydrocarbons The present invention relates to an anchoring apparatus for a ship used in the production of hydrocarbons, and particularly for such a ship having a central well.

In production tests and thereafter for the working of underwater hydrocarbon wells, one of the major problems is posed by the number and complexity of the connections between the ship and the sea bed, by various connections with installations situated on the sea bed and by anchoring connections with the bed itself.

Anchoring by conventional means requires the positioning of several lines each of which comprises a portion placed on the sea bed and a portion connecting the sea bed to the ship. Then the wellhead is connected-up by means of a flexible or jointed conduit. Besides the fact that the use of this system leads to cluttering up the sea bed over a large area, it does not allow rapid disconnection of the ship from its various connections when the surface of the sea is too disturbed and, more especially, reconnection is very difficult if such disconnection has been carried out hastily.

Docking the ship on the head of a swingable column or on a buoy connected to the head of a swingable column by a jointed or flexible connection gives more latitude for rapid disconnection of the ship and the surface equipment, but this system presents many problems in the designing of the metal structure, more particularly so as to ensure satisfactory transmission of forces from the head of the swingable column to the ship and vice versa, since the means employed are heavy and situated in a cantilever manner with respect to the ship.

The present invention has as an object the obviation or reduction of these difficulties and proposes a column provided with flexibility since there is a connection such as a chain or cable between an upper body or buoy capable of being either situated in a central well of the ship or immersed to a depth allowing the passage of ships, and a lower body of negative buoyancy the lateral displacements of which are limited about a stable mean position. Moreover with the upper body supporting the means connecting with the bed installations, these connecting means do not have to be disassembled when the upper body is disconnected from the ship, and this greatly facilitates subsequent re-connection.

According to the present invention there is provided an anchoring apparatus constituted by a body having positive buoyancy and arranged to be uppermost in use in water and adapted to have attached thereto and suspended therefrom a connection means connecting with installations on the sea bed, a body with negative buoyancy arranged in use to be lower than the upper body, a connecting means of predetermined length between the upper body and the lower body, referred to as a vertical link, and anchoring means for connecting one of the three aforesaid elements to the sea bed, said anchoring means comprising a portion arranged to anchor the anchoring means to the sea bed, in which apparatus the upper body has a buoyancy lower than the apparent weight in water of the assembly constituted by the vertical link, the lower body, and the portion of the connecting means with the sea bed installations to be suspended on the upper body, and greater than the apparent weight of the vertical link and the portion of the connecting means with the bed installations to be suspended on the upper body, the upper body being provided with means for connecting with lifting means adapted to move the upper body from a submerged position, in which its highest point is spaced from the lowest point of the lower body by a length less than the maximum depth of the water at the anchorage point by at least the amount of the maximum draught of ships likely to pass directly over the apparatus, and in which the lower body rests on the sea bed, to an emergence position, the anchoring means being of sufficient dimensions to allow the vertical displacement of the upper body between the submerged and emergence positions.

With such an apparatus the lifting means may be either installed on the service vessel or, at least in part, included in the upper body in the form of dischargeable ballast or any other means.

According to a preferred constructional form, an anchoring apparatus according to the invention for a ship for the production of hydrocarbons, having a central well, is constituted by an upper body having positive buoyancy, a lower body with negative buoyancy, a connecting means of predetermined length between the upper body and the lower body, referred to as the vertical link, and anchoring means connecting one of the three aforesaid elements and the sea bed, these anchoring means comprising a portion immersed in the sea and another portion resting on the sea bed.In such an apparatus the upper body has a buoyancy lower than the apparent weight of the assembly constituted by the vertical link, the lower body and the portion of the means connecting with the bed installations which is suspended on the upper body, and greater than the apparent weight of the vertical link and the portion of the means connecting with the bed installations which is suspended on the upper body, the upper body having its highest point spaced from lowest point of the lower body by a length less than the maximum sea depth at the anchorage point by at least the amount of the maximum draught of ships likely to pass right overhead of the apparatus, the upper body being provided with means for connecting with lifting means of the ship which are capable of displacing the upper body from an immersed position wherein the lower body rests on the sea bed to an emergence position where the upper body is lodged in the central well of the ship, the upper body being provided with means for fixing to a frame resting on the ship by means for rotational movement relatively to the axis of the central well, the anchoring means being of sufficient dimensions to allow the vertical displacement of the upper body between the immersed and emergence positions.

The anchoring means are generally situated between the lower body and the sea bed, and they may be constituted by a plurality of anchoring lines, generally chains terminating either at anchors or at piles.

These anchoring means may comprise a plurality of lines whose ends are fixed to a flat frame, which frame may be fixed to the sea bed by a plurality of piles or the like.

This flat frame may be generally polygonal in plan, and in such a case the lines may be fixed to the apices of the polygonal frame.

For reasons of handiness, handling and balancing the mechanical forces transmitted, the polygonal plan of such a frame is preferably regular and concentric.

The lines may be fixed on vertical posts integral with the frame at the apices of the polygonal frame.

When the anchoring means are constituted by lines fixed to the upper body, which has the result of reducing the significance of the lower body to being a means for controlling the submerged and emergence positions of the upper body, it is preferred to use as one of these lines a connecting means between the upper body and the installations arranged on the sea bed.

In one particular form of embodiment the lower body is constituted by a polygonal frame and the anchoring means comprise a plurality of lines connecting various points distributed about the frame to the head of a vertical anchoring pile fixed in the sea bed. The polygonal frame may indeed have an annular or circular form.

According to other constructional forms the lower body is connected to an anchorage bed by a framework which is trapezoidal in form, rigid, and articulated on two horizontal pivotal axes, one end on the said bed, the other on the lower body.

The lower body may be slidably mounted on a vertical pile driven into the sea bed and acting as an anchoring means. The lower body may be annular in form and have a central aperture allowing sliding on the pile, or it may be provided with an offset sliding means.

The invention will be understood from the following description given, by way of nonlimitative example, of embodiments of the apparatus according to the invention, illustrated with the aid of the following drawings: Fig. 1 shows a basic diagram of the anchoring apparatus according to the invention associated with a production vessel.

Fig. 2 shows a similar diagrammatic view of an anchoring apparatus according to the invention not associated with a production vessel.

Fig. 3 shows anchoring lines terminating in anchors.

Fig. 4 shows anchoring lines terminating at piles.

Fig. 5 shows anchoring lines fixed to a polygonal frame.

Fig. 6 shows anchoring lines fixed to piles which themselves are fixed to the apices of a polygonal frame.

Fig. 7 shows a lower body sliding along a vertical pile with a central sliding passage.

Fig. 8 shows a lower body sliding along a vertical pile with a lateral sliding guide.

Fig. 9 shows the lower body connected to anchoring bedrock by a rigid frame with pivotal connection means (elevation).

Fig. 10 shows the arrangement of Fig. 9 in plan.

Fig. 11 shows an annular lower body attached to a pile.

Fig. 1 2 shows the apparatus with anchoring lines fixed to the upper body.

Fig. 13 shows lifting apparatus for the upper body.

Fig. 14 shows apparatus for installation of the upper body in the central well of the ship.

Referring now to Fig. 1 , this shows diagrammatically the basic elements of an anchoring apparatus for a ship 1 for the production of hydrocarbons, having a central well 2.

Such an apparatus is constituted by an upper body 3 with positive buoyancy, a lower body 4 with negative buoyancy, a link referred to as the vertical link and of predetermined length, between the upper body 5 and the lower body 4, and anchoring means such as 6 connecting in this case the lower body 4 to the sea bed 7.

The anchoring means such as 6 comprises a portion 8 held up in the water and a portion 9 resting on the sea bed. The anchoring means are of various per se known types such as the chains shown in Fig. 1, or cables.

The upper body 3 has a positive buoyancy lower than the apparent weight of the assembly constituted by the vertical link 5, the lower body 4 and the portion of the connecting means 14 connecting with the sea bed installations which is suspended on the upper body 3 and greater than the apparent weight of the vertical link 5 and the portion of the connecting means 14 connecting with the sea bed installations which is suspended on the upper body 3.

The upper body 3 is provided with means, not shown here, for connection to lifting means on the ship which are adapted to displace the upper body from a submerged position wherein the lower body rests on the sea bed to an emergence position for the upper body wherein this upper body is lodged in the central well of the ship. The upper body 3 is provided with means, not shown, for fixing to a frame resting on the ship by means of rotational means also not shown, rotatable relatively to the axis ZZ' of the central well 2.

The upper body 3 is connected to a production installation represented by a well head 10 situated on the sea bed 7, by a flexible connection 14 comprising at least one flexible duct and electrical cables for transmitting remote commands and telemetric signals. The flexible tube 14 extends through the upper body 3 through a duct 1 5 and is connected by way of a rotary joint 1 6 to a conduit 1 7 connecting the ship 1 to a ship for storing the product, this ship not being shown. Generally a treatment plant is interposed in this production line.

Referring now to Fig. 2, this shows diagrammatically an anchoring apparatus constituted by an upper body 3 having positive buoyancy, a lower body 4 having negative buoyancy, a link 5 referred to as the vertical link, and of predetermined length, between the upper body 3 and the lower body 4, and anchoring means such as 6 in this case connecting the lower body 4 to the sea bed 7.

The upper body 3 is provided with means, not shown, for connecting with lifting means dependent from a ship not shown here which are capable of displacing the upper body 3 from a submerged position wherein the lower body rests on the sea bed to a position where the upper body emerges and wherein the body 3 constitutes an actual buoy. These lifting means are constituted here by dischargeable ballast not shown.

The upper body 3 is connected ton the one hand to an underwater production installation represented by the well head 10, and is connected on the other hand by a conduit 17 by way of a rotary joint 1 6 to a storage ship not shown.

Preferably the anchoring means 6 connect the lower body 4 to the sea bed 7. This is the case in the arrangements shown in Figs. 3 to 10.

Fig. 3 shows an arrangement of anchoring means constituted by chains 6 ending at anchors 18.

Fig. 4 shows an arrangement wherein the chains 6 terminate in piles 1 9 driven into the sea bed by any known means such as piledriving or the use of an explosive anchor device. This arrangement makes it possible to reduce the length of chain immobilised since the anchoring results both from the weight of the chain and from the reaction forces of the pile on the chain.

Fig. 5 shows a system for fixing the lower end of anchoring lines to the apices of a flat frame 20 the shape of which is polygonal. This frame may be of the type having two planes of symmetry at right angles. It may constitute a regular polygon and, in this case, it is convenient to give the same length to the various anchoring lines. The frame is fixed to the sea bed by its weight alone, or by piles.

Fig. 6 shows a section through an apparatus wherein the anchoring lines are fixed to posts 21 fixed securely to a polygonal frame 20 at each of the polygon apices. These posts may advantageously be constituted, as indicated on the left in Fig. 5, by tubes wherein straight rods 22 can slide which penetrate into the sea bed and thus contribute to fixing the frame securely on the sea bed. In Fig. 6 on the right the rod 22 slides through an aperture of the frame.

Figs. 7 and 8 show two examples of arrangements wherein the lower body 8 slides along a vertical pile 23 put into place in the sea bed by percussion, by drilling, by driving or even by the use of an explosive anchor device, all these methods being known per se. In Fig. 7 the lower body 4 is annular and pierced with a central aperture 24 used for sliding along the pile 23. In Fig. 8 the lower body 4 is provided laterally with a guide means 25 with an aperture 26 for sliding along the pile 23.

Figs. 9 and 10, show in elevation and in plan, views of an arrangement for connecting the lower body 4 to the sea bed 7 by means of an articulated frame 27 comprising two pivotal connections, pivoting about two parallel rectilinear axes, the pivotal connection 28 being with a frame 29 fixed on the bed and the pivotal connection 30 being to the lower body 4.

Fig. 11 shows an annular lower body 4 attached to the head 31 of a pile 23 by means of several chains such as 6. The lengths of the chains 6 are determined, in accordance with the positions of their attachment points on the ring 4 and with the height of the head 31 of pile 23, so that the lower body or rings 4 can move freely between the position of rest on the ground corresponding to the submersion of the upper body, and the offset end positions corresponding to the emergence of the upper body.

In various arrangements which have now been described it will be noted that the lateral displacement of the upper body 4 is limited about a mean position when the upper body 3 is displaced between the submerged and emergent end positions.

In Fig. 12 the anchoring lines connect the upper body 3 to the sea bed 7. The function of the lower body 4 is limited to the control of the buoyancy of the general apparatus and in fact to the control of the displacement of the upper body 3 from the emergent position to the submerged position.

In an arrangement as shown in Fig. 1 2 the lines may be constituted by chains and this solution has no advantage relatively to the production ship anchored in conventional manner, apart from the advantages present by the detachable connection with the sea bed installations. On the other hand when one of the flexible connecting means 14 between the production ship and the sea bed installations is used as anchoring line means, a simplification is achieved and thus a considerable economy in the means employed. These flexible connecting means 1 4 comprise at least one conduit for the transfer of gaseous or liquid hydrocarbons, electrical conductors and possibly conduits for various service fluids such as oil or gas under pressure, and electrical conductors for the transmission of orders and data.Moreover these means comprise a reinforced sheath, reinforced with cables or fabrics of steel wires, giving them a considerable tensile strength, long life, and allowing them to be used as anchoring means.

Fig. 1 3 shows an apparatus for the lifting of the upper body. This apparatus comprises on a carriage 32, adapted to move on a manoeuvring bridge 33, a winch or windlass 34 on which is engaged an end of a manipulating chain 35 and a guide pulley 36 accompanied by a device 37 for tensioning and stopping the chain, where the other end of the manipulating chain 35 is engaged. This chain passes along the groove of a pulley 38 whose bracket is fast with the upper wall of the upper body 3. These various items of equipment are each known per se.

To lift the upper body 3 when submerged, the carriage 22 is positioned such that the axes of the winch 34 and of the guide pulley 36 are symmetrical relatively to the Axis ZZ' of the central well 2 of the ship 1. The manipulating chain 35 which up to then is stored at the guide pulley side is displaced by using its own weight.

Divers or remote-guided manipulators pass the chain into the groove of the pulley 38 and bring the end up again and secure it in the winch groove. Then the operation lifting the body 3 can be carried out.

Fig. 14 shows an apparatus for installing the upper body 3 in the central well 2 of the ship. On the upper region of the upper body there can be seen the chain pulley 38 over which the manipulating chain passes during positioning. This positioning is effected by means of an apparatus mounted on a carriage adapted to move on a control bridge 33 situated above the surface 39, the top face of a rotary skirt element 40. This rotary skirt element 40 rests by means of a roller bearing 41 on an annular element 42 fast with the hull of the ship, and it comprises means such as hydraulic bolts 43 for connecting it securely to the upper body 3.

A union 44 can be seen at the upper region of the body 3 for connection to the collecting conduit 1 6 indicated in Fig. 1. Situated at the lower region of the body 3 is the inlet for the vertical link 5 axially of the body 3. This vertical link 5, generally constituted by a chain, ends in a chain stopper 45 situated in the central portion of the body in a duct used for the positioning of the link 5 and its position adjustment when the anchoring apparatus is put in place. Also situated at the lower portion of the body 3 is the inlet for the conduit 14 which is used for connection with the underwater production station.

The invention is of course in now way limited to the constructional forms described and illustrated.

It can be modified in many ways within the ability of the person skilled in the art, depending on the uses envisaged, and without departing from the scope of the invention as defined by the appendent Claims.

Such apparatus, based on the invention, have in common the following advantages: As anchoring means they do not encumber the sea bed floor to any great extent and they allow easy disconnection and especially re-connection, with few underwater manipulations. When the apparatus is associated with a ship having a central well, the work can be carried out in a particularly protected zone.

As means for supporting the connection between the production ship and the installations situated on the underwater floor they allow connection and re-connection of these connections to be carried out in the open air and under good conditions, especially when the upper body is installed in the central well of the ship.

Claims

1. Anchoring apparatus constituted by a body having positive buoyancy and arranged to be uppermost in use in water and adapted to have attached thereto and suspended therefrom a connection means connecting with installations on the sea bed, a body with negative buoyancy arranged in use to be lower than the upper body, a connecting means of predetermined length between the upper body and the lower body, referred to as a vertical link, and anchoring means for connecting one of the three aforesaid elements to the sea bed, said anchoring means comprising a portion arranged to anchor the anchoring means to the sea bed, in which apparatus the upper body has a buoyancy lower then the apparent weight in water of the assembly constituted by the vertical link, the lower body, and the portion of the connecting means with the sea bed installations to be suspended on the upper body, and greater than the apparent weight of the vertical link and the portion of the means connecting with the bed installations to be suspended on the upper body, the upper body being provided with means for connecting with lifting means adapted to move the upper body from a submerged position, in which its highest point is spaced from the lowest point of the lower body by a length less than the maximum depth of the water at the anchorage point by at least the amount of the maximum draught of ships likely to pass directly over the apparatus, and in which the lower body rests on the sea bed, to an emergence position, the anchoring means being of sufficient dimensions to allow the vertical displacement of the upper body between the submerged and emergence positions.

2. Anchoring apparatus for a ship for the production of hydrocarbons, having a central well, constituted by an upper body with positive buoyancy, a lower body with negative buoyancy, a connecting means for predetermined length between the upper body and the lower body, referred to as a vertical link, and anchoring means for connecting one of the three aforesaid elements and the sea bed, these anchoring means comprising a portion to be submerged in the water and a portion for resting on the sea bed, wherein the upper body has a buoyancy lower than the apparent weight in water of the assembly constituted by the vertical link, the lower body and the portion of the means connecting with the sea bed installation which is suspended on the upper body, and greater than the apparent weight of the vertical link and the portion of the means connecting with the bed installations which is suspended on the upper body, the upper body having its highest point spaced from the lowest point of the lower body by a length less than the maximum sea depth at the anchorage point by at least the amount of the maximum draught of ships likely to pass directly above the apparatus, the upper body being provided with means for connecting with lifting means of the ship which are capable of displacing the upper body from an immersed position wherein the lower body rests on the sea bed to an emergence position wherein the upper body is lodged in the central well of the ship, the upper body being provided with means for fixing to a frame resting on the ship through the agency of means allowing rotation relatively to the axis of the central well, the anchoring means being of sufficient dimensions to allow the vertical displacement of the upper body between the immersed and emerged positions.

3. Apparatus according to Claim 2, wherein the anchoring means comprise a plurality of lines whose ends are fixed on a flat frame, this frame being fixed to the sea bed by a plurality of piles or the like.

4. Apparatus according to Claim 3, wherein the lines are fixed to the flat frame at the apices of a polygon.

5. Apparatus according to Claim 3, wherein the lines are fixed to the flat frame at the apices of a concentric regular polygon.

6. Apparatus according to Claim 3, wherein the lines are fixed to vertical posts fixed to the said frame at the apices of a polygon.

7. Apparatus according to Claim 2, wherein of the anchoring means connecting the upper body to the sea bed at least one is constituted by a connecting means between the said upper body and the installations arranged on the sea bed.

8. Apparatus according to Claim 2, wherein the lower body is constituted by a polygonal frame and the anchoring means comprise a plurality of lines connecting various points distributed about the frame to the head of a vertical anchoring pile planted in the sea bed.

9. Anchoring apparatus for a ship for the production of hydrocarbons, substantially as herein before described, with reference to the accompanying drawings.

10. The combination of an anchoring apparatus as claimed in any preceding Claim and a ship for the production of hydrocarbons having a well adapted to receive the said upper body of the anchoring apparatus and provided with lifting means for raising the upper body from a said immersed position to a said emergence position.

11. The features herein before disclosed, or their equivalents, in any novel selection.