GB2226352A

GB2226352A - A modular protective structure for underwater installations

Info

Publication number: GB2226352A
Application number: GB8925792A
Authority: GB
Inventors: Jon Flidh; Per Andersen
Original assignee: Aker Engineering AS
Current assignee: Aker Engineering AS
Priority date: 1988-11-16
Filing date: 1989-11-15
Publication date: 1990-06-27
Anticipated expiration: 2009-11-15
Also published as: GB2226352B; GB8925792D0; NO167098C; NO885110D0; NO885110L; NO167098B

Abstract

A protective structure for underwater installations, such as oil wells on the sea bed, comprises a number of generally identical rigid, hollow basic elements (1) which are built together to the required form and size in accordance with the number of wells to be protected. The basic elements (1) have cavities which are closed so as to provide sufficient buoyancy for the protective structure to be towed to the place of installation. Furthermore, the basic elements (1) are provided with removable covers over openings (12) (Fig 2C not shown) through which concrete may be filled once the protective structure has been set in place on the sea bed, thus providing strength, weight and stability. The lower corners of the structure may be provided with downwardly extending plate extensions (10) (Fig 2C not shown) penetrating the sea bed to prevent trawl wires or the like from getting caught under the structure. <IMAGE>

Description

PROTECTIVE STRUCTURE The present invention relates to a protective structure for underwater installations.

Such protective structures are used e.g. for oil installations on the sea bed to protect against outside influence e.g. from fishing gear, anchors and objects dumped from vessels on the surface. The protective structure must therefore be able to resist relatively high loads in all directions without being shifted out of position or being deformed to such an extent that this will affect the installation to be protected. Furthermore, it is normally desireable that trawlers should be able to pass without their fishing gear being damaged.

The protective structures most commonly used so far have either consisted of a concrete structure held in position on the sea bed by its own weight, or a pipe structure built according to the truss principle and held in position by means of piles arranged in the sea bed. Thus, from US-PS No. 4 220 421 a structure is known consisting of an annular, rigid protective structure having a hollow annular internal chamber and a plurality of bag-like containers which are arranged around the chamber and communicating with the chamber through holes in its outer wall. The bags are filled with concrete which is pumped into them through the chamber and are arranged so that if an anchor or other object should get tangled in one or more of them, they will be torn loose so that the anchor may pass over the protective structure.During the installation of such a protective structure it will be difficult to ascertain that the bags all are filled with concrete in the desired manner and, besides, the structure will be difficult to move once it has been installed. Furthermore, the structure is intended for use with a single well-head and is difficult to adapt to clusters of wells.

Embodiments of the present invention may provide a protective structure which is easy to install and use as compared to prior art structures.

According to one aspect of the invention there is provided a structure for the protection of underwater installations, having a lower side for resting on the sea bed and an upper side having at least one sloping face for deflecting foreign objects towed along the sea bed, and further comprising at least three substantially identical rigid basic elements connected together and extending between the lower and upper sides of the structure, wherein the basic elements are adapted to be filled with concrete in order to ballast and strengthen the structure.

Since this protective structure comprises a number of identical basic elements built together, it is easily adapted to different needs as regards the number and layout of wells in the cluster and its extent.

According to a second aspect of the invention there is provided a rigid hollow element for incorporation into a protective structure for underwater installations containing a number of such elements, the element having a lower face which, in use, rests on the sea bed and a sloping face adapted to deflect foreign objects towed along the sea bed, wherein the element also comprises means for allowing it to be at least partially filled with concrete in order to ballast and strengthen the structure.

The basic elements preferably have cavities which are watertight or can be made so, and are shaped so that they may be fabricated, handled and shipped in a simple manner, e.g. by floating, to the place of installation. Through ballasting the protective structure may be placed in a controlled manner on the sea bed, whereupon the elements are filled with concrete by means of a pumping technique so that the structure obtains sufficient weight to retain its position without the use of piles. After curing the concrete will contribute to the strength and stability of the protective structure.

Further advantageous features of the invention are recited in the dependent claims and will appear from the following description of exemplifying embodiments of the invention shown in the appended drawings.

Fig. 1 is an isometric view of a protective structure according to the invention for a single well.

Figs. 2A - C shown a basic element for a protective structure according to the invention in side view, end view and plan view, respectively.

Figs. 3A - E show plan views of protective structures for one, two, four, six and eight wells, respectively.

In Fig. 1 a protective structure is shown comprising four generally triangular basic elements 1.

The basic elements are arranged radially around a central space 7, which provides room for drilling and production equipment. On the outside the basic elements 1 are attached to each other by means of steel sections 2, which are dimensioned so as to withstand the load from e.g. an anchor getting tangled. One or more of the steel sections 2 may be provided with sheet metal in order to make room for equipment associated with the pulling in and fixation of pipelines. At the top the inner parts of the basic elements are connected by means of steel sections 3, which define an opening into the central space 7. At the bottom the inner parts of the basic elements 1 are connected by means of a frame member 8, which also is made of steel sections.

The frame 8 also contains a central hole 9 used as a guide during drilling operations.

The protective structure may be fitted with a detachable cover 6 for further protection of the installations. Moreover, one or more sides of the protective structure may likewise be covered with permanent or detachable covers in applications where this is desirable. These covers may be made as a grating of steel sections or as closed plate covers.

Since the strength and stability of the protective structure is high due to the basic elements 1 filled with concrete and the connecting sections 2, 3 and 8, there will be no need for further stiffening arrangements. The protective structure will therefore provide free access to the central space 7 from four sides and also vertically, which provides good access for divers and any remotely controlled underwater equipment.

The basic element 1 will now be described with reference to the exemplifying embodiment shown in Figs.

2A - C. Each basic element has a vertical section of generally triangular form as shown in Fig. 2A and is constructed as a hollow box of flat, relatively thin plates, which are internally braced by means of webs and stiffeners 13 in accordance with conventional shipbuilding methods. In cross-section the elements broaden downwardly and radially outwardly, as shown in Figures 2B and 2C. After location of the protective structure on the sea bed concrete is pumped into the element and provides it with weight and further strength.

At the outer corners of the basic element a projecting plate 10 is placed for penetrating into the sea bed. In addition to helping keep the structure in position, the plate projection 10 prevents e.g. trawl wires from lodging under the corners of the protective structure. The plate projections may be shaped in accordance with the sea bed conditions on the place of installation and may, if necessary, be supplemented by additional elements which penetrate into the sea bed.

Furthermore, the basic element contains a throughgoing welded tube 11 which serves as a hoisting point.

Consequently, the protective structure may be hoisted even though it is not fitted with lifting lugs; this is advantageous since such lugs would project so that fishing gear etc. could get caught.

The basic element shown also contains openings 12 which may be closed with covers fastened with bolts.

The openings 12 provide access for filling the basic elements with water when the protective structure is to be lowered to the sea bed. The openings also provide access for pumping the concrete into the basic elements once the structure has been placed on the sea bed, while concurrently permitting the water displaced by the concrete to escape.

Figs. 3A - 3E demonstrate how identical elements 1 in accordance with the invention can be assembled to suit the well layout. In these figures the arrangement is essentially rectangular with basic elements at the corners and intermediate elements as required.

It will be understood that protective structures in accordance with the invention, particularly the smaller embodiments, will have a sufficiently low weight prior to installation that they may often be capable of being freighted to the place of installation on an anchor handling vessel, a supply ship or the like. Alternatively, the protective structure may be towed to the installation place since the basic elements 1 will provide sufficient buoyancy for the structure to float.

Although the embodiments shown are all of rectangular configuration and have one basic element at each corner, other arrangements of a similar modular or regular pattern are envisaged, such as triangular or hexagonal structures. Also although the regular symmetric layout leads to simplification in assembly it is not absolutely necessary.

It will therefore be seen that the invention envisages a protective structure for underwater installations, such as oil wells on the sea bed, which, when it surrounds the installation, is filled with concrete, said protective structure being provided with sloping sides for repelling foreign objects towed along the sea bed, characterised by a modular construction comprising a number of generally identical basic elements which are built together to meet the requirements at hand as regards shape, size and number of wells.

Claims

CLAIMS:

1. A structure for the protection of underwater installations, having a lower side for resting on the sea bed and an upper side having at least one sloping face for deflecting foreign objects towed along the sea bed, and further comprising at least three substantially identical rigid basic elements connected together and extending between the lower and upper sides of the structure, wherein the basic elements are adapted to be filled with concrete in order to ballast and strengthen the structure.

2. A protective structure according to claim 1, wherein at least one of the basic elements has a closed or closable cavity providing sufficient buoyancy for the protective structure to be towed during transportation to the place of installation.

3. A structure according to claim 1 or 2, wherein the basic elements each have two or more openings for the injection of concrete, the openings being provided with removable covers.

4. A structure according to any preceding claim, wherein each basic element comprises a box of plate material having internal bracing in the form of webs or the like.

5. A structure according to any preceding claim, wherein each basic element is, in vertical crosssection, generally triangular in form so as to provide a sloping face for the structure as aforesaid.

6. A structure according to any preceding claim, wherein at least one of the basic elements has at its lower outer corner a downwardly extending plate for penetration into the sea bed.

7. A structure according to any preceding claim, wherein at least one of the basic elements has an aperture near its uppermost part for engagement by hoisting equipment.

8. A structure according to any preceding claim, wherein the basic elements are arranged around a central opening providing space for drilling and production equipment and possibly being closable by means of at least one cover.

9. A structure according to any preceding claim, wherein the basic elements are connected to each other by means of steel sections and a central frame member near the lower side of the structure.

10. A structure according to claim 8 or 9, wherein the basic elements are arranged generally in the form of a star with access between them to the central space.

11. A structure according to any preceding claim and in the form of a rectangle, one basic element being arranged at each corner of the rectangle.

12. A structure substantially as described herein with reference to Figures 1 and 3A, or any of Figures 3B - 3E of the accompanying drawings.

13. A rigid hollow element for incorporation into a protective structure for underwater installations containing a number of such elements, the element having a lower face which, in use, rests on the sea bed and a sloping face adapted to deflect foreign objects towed along the sea bed, wherein the element also comprises means for allowing it to be at least partially filled with concrete in order to ballast and strengthen the structure.

14. An element according to claim 14 and further comprising plates extending from the lower face in order, in use, to anchor the element to the sea bed.

15. An element substantially as described in Figures 2A - 2C of the accompanying drawings.

16. A protective structure for underwater installations, such as oil wells on the sea bed, which, when it surrounds the installation, is filled with concrete, said protective structure being provided with sloping sides for repelling foreign objects towed along the sea bed, characterised by a modular construction comprising a number of generally identical basic elements which are built together to meet the requirements at hand as regards shape, size and number of wells.