NO341933B1 - An apparatus for protecting subsea well structures - Google Patents

Abstract

The present invention relates to an apparatus for protecting subsea well structures located on a seabed, where the apparatus for protecting subsea well structures com prises a frame structure comprised of structural members, where the frame structure is adapted to encompass the subsea well structures it is to protect, and deflector means connected to the frame structure, where the deflector means is / are adapted to extend away from the frame structure when the protection structure is located on the seabed, the deflector means contacting the seabed at a distance from the frame structure , thereby defining a sloping deflector surface extending upwardly from the seabed and to the frame structure.

Description

FIELD OF THE INVENTION

The present invention relates to an apparatus for protecting subsea well structures, and more particularly to apparatus for preventing damage to the subsea well structures by fishing trawler nets and boards, anchors and other towed objects that could be brought into contact with said structures. The apparatus comprises a frame structure and deflector means being connected to the frame structure and arranged to extend away from the frame structure and slantingly down to the sea bed when the apparatus is mounted to the subsea well structures.

BACKGROUND

The production of oil and gas from offshore wells has developed into a major endeavour of the petroleum industry. Such wells are now being drilled throughout the world at many locations, some of which are in commercial fishing areas, such as the North Sea, where nets, trawling board equipment, anchors and other equipment being towed underwater may come into contact with the subsea well structures.

Such nets and/or trawling board equipment can be highly damaging to a well head or a Christmas tree when they become entangled. Further, they are capable of severely bending, or at least inflicting minor damage to well head and/or Christmas tree parts. The well heads and/or Christmas trees, although built for strength, are nonetheless vulnerable to being distorted when subjected to a severe pulling force.

Another source of possible danger to subsea well structures stems from the use of anchors and anchor chains. It can be appreciated that in the instance of a heavy chain, the chain could become snagged or at least partly wrapped around a part of the subsea well structure. Thus, when the chain is retrieved, it could distort or even break parts of the subsea well structure.

The undesirable consequence of such an underwater emergency would be an uncontrolled flow of crude oil or gas. There have been instances for example when well heads and/or Christmas trees have been damaged by anchor chains to the point where the well has become unusable.

It has therefore become desirable, if not mandatory, to provide some form of protective coverage for exposed subsea well structures.

Preferably, such protective units are designed to deflect or deter damaging contact between the subsea well structure and heavy moving objects or lines. Thus, a protective unit’s primary function is to permit the subsea well structure to operate in a safe manner and yet be readily accessible for work-over purposes and/or for diver inspection.

Unfortunately, as the Christmas trees are typically provided on the seabed and often far offshore, their operational location renders them highly susceptible to accidental damage. As mentioned above, a principal cause of significant damage is bottom gear towed by trawlers which can impact with and snag on the trees.

Previously proposed protective structures include a freestanding frame which can be placed over, but not in contact with a Christmas tree and anchored and mounted on its own dedicated anchoring points and foundations. Such a protective structure is unduly expensive and awkward to install as it is of such a size that it cannot conventionally be installed from a drilling rig and thus, the service of a separate specialist installation vessel must be acquired. Furthermore, the manner by which the protection structure is secured to the seabed is such that the installation is complex and usually requires a piling spread, the services of a number of divers and remotely operated vehicles (ROV). This significantly increases the cost of the installation.

It has also been proposed to use steel or concrete domes that may be as tall as 10 meters with bases as large as 20 meters in diameter. As the total weight of these constructions may approach or exceed 90.000 kg, this weight is relied upon to retain them in position.

In all cases the physical size and/or weight of these prior art structures make their handling and installation difficult.

WO 98/04805 A1 discloses an overtrawlable protection envelope for a subsea structure, where the envelope is anchored by connecting it to the subsea structure. The envelope may be defined by four legs pivotally deployable from folded positions to deployed positions during installation. Each leg may include separate upper and lower portions when used to protect a two-part structure such as one comprising a flowbase and a tree. The legs may also have telescopic parts.

US 4.519.727 A discloses a well head protector for a well which is located at the floor of an offshore body of water. The protector includes a plurality of discrete sub-assemblies which, for installation purposes, are initially transported to a drilling vessel and positioned above the well head. The sub-assemblies are sequentially lowered from the vessel deck and assembled above the water surface into a composite unit. The completed unit is guidably lowered by the vessel’s drilling derrick to its position surrounding the well head. The deflecting elements are then lowered into place.

WO 03/071092 A1 discloses a protection structure and method for subsea oil recovery operations, where at least one leg is pivotally mounted to a frame for movement between a first position in which it is folded back over the frame, and a second position in which it extends out from the frame. The frame is lowered to the seabed with the leg in its first position, then the leg is pivoted to the second position at the seabed to support the frame over the installation.

US 5.810.515 A discloses a protective device for an installation mounted on the seabed, where means for protecting the device comprises a central portion which is arranged to be attached to the upper section of the device and legs which are linked to the central section and arranged to extend away from it and slantingly down to the seabed. The legs can be pivoted into a position wherein their longitudinal direction is substantially coincident.

An object of the present invention is to alleviate some or all of the above problems.

It is a further object of the present invention to provide a compact and lightweight apparatus for protecting subsea well structures where the apparatus can be readily installed at a seabed location.

The objects are achieved with an apparatus for protecting subsea well structures according to the present invention as defined in the enclosed independent claim, where embodiments of the invention are given in independent claims.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an apparatus for protecting subsea well structures, where the apparatus comprises a frame structure, the frame structure comprising a plurality of structural members encompassing the subsea well structures and deflector means connected to the frame structure, where the deflector means are being adapted to extend away from the frame structure to be brought to contact the seabed at a distance from the frame structure to define a sloping deflector surface extending upwardly from the seabed to the frame structure, where each deflector means comprises a first leg element and a second leg element that are pivotally connected to each other through a first pivot connection, where the second leg element further is pivotally connected to the frame structure through a second pivot connection, the second pivot connection allowing the deflector means to rotate about a vertical axis extending through a deflector means in the frame structure.

However, it should be understood that the deflector means may also comprise more leg elements, whereby two subsequent leg elements would be connected to each other through a pivot connection.

In one embodiment a deflector means receiving element may be connected to the frame structure, where this deflector means receiving element is adapted to receive an end of the second leg element. A person skilled in the art would know that the end of the second leg element could be adapted to receive the deflector means receiving element.

The apparatus for protecting subsea well structures may comprise a plurality of deflector means, for instance four deflector means, but it should be understood the apparatus also could comprise fewer or more deflector means. The deflector means may, for instance, be connected to the corners of the frame structure, or an extension of the corner, but it may also be envisaged that the deflector means could be connected to the sides of the frame structure.

It could also be envisaged that the deflector means can comprise a different number of leg elements, such that some deflector means may comprise two leg elements, while other deflector means may comprise three or more leg elements.

The deflector means may furthermore be arranged symmetrically about each other, or they may be arranged in an uneven way.

The deflector means may be either fixedly or releasably connected to the f rame structure. When the deflector means are fixedly connected to the frame structure, it should be understood that the deflector means can pivot about the pivot connections, but that the deflector means cannot be removed from the frame structure. When the deflector means are releasably connected to the frame structure, it should be understood that the deflector means can be removed from the frame structure, but that the deflector means can, when connected to the frame structure, pivot about the pivot connections.

The frame structure may have a rectangular or quadratic form, but it should be understood that the frame structure may also have other forms, for instance a polygonal or a circular form. The frame structure is manufactured from a plurality of structural members, such as beams, girders or the like, where the structural members are connected to form the frame structure. The frame structure may be provided with a centrally arranged ring-shaped or annular element, such that the apparatus for protecting the subsea well structures may be connected to the subsea well structure which it is to protect. However, one could also envisage that the apparatus for protecting the subsea well structures may be manufactured in such a way that it would not need to be connected to the subsea well structure it is to protect, whereby the apparatus could be positioned on the seabed and encompassing the subsea well structure which it is to protect.

As the leg elements of the deflector means are connected to each other through a first pivot connection, the leg elements can be adjusted relative each other in order to, for example, compensate for an uneven seabed, thereby levelling the apparatus for protecting subsea well structures relative the seabed.

In one embodiment at least one leg element of the deflector means may comprise a locking arrangement, such that the leg elements may be locked relative each other in a desired position. A person skilled in the art would know how this can be done, whereby this is not described further herein.

The arrangement of the second leg element of the deflector means being pivotally connected to the frame structure through a second connection will allow each deflector means to be moved from a folded and retracted position, where the deflector means are located adjacent or even on the top of the frame structure, and to a deployed position where the deflector means are spread out from the frame structure.

The above arrangement will result in that the apparatus for protecting subsea wel l structures according to the present invention will have a reduced footprint in the folded and retracted position and an enlarged footprint in the deployed position which defines an overtrawlable profile. The ability to reduce the footprint of the protective structure can allow the protective structure to be deployed through, for example, a moon pool of a drilling rig.

The deflector means may be designed with a smooth surface, such that trawler nets, boards and other towed objects that could be brought into contact with the deflector means would “glide” over the deflector means, not becoming entangled in the deflector means. A person skilled in the art would know how this is done, whereby this is not described further herein.

The first pivot connection between the first and second leg elements may be obtained by providing one of the leg elements with two ears, where each of the ears has a throughgoing hole, and the other leg element with a throughgoing hole, whereby the throughgoing holes of the two leg elements can be aligned and a bolt and nut can be used to connect the first and second leg elements. A person skilled in the art would know that such a pivot connection also can be obtained in other ways.

The second pivot connection between the second leg element and the frame structure or deflector means receiving element may be obtained by providing an end of the second leg element as a male part, for instance in the form of a pin or pivot, and the frame structure or deflector means receiving element as a female part, for instance in the form of a sleeve or bushing, whereby the female part will receive the male part when the deflector means are connected to the frame structure or deflector means receiving element. Furthermore, each of the male and female part may comprise a plurality of cams or the like, where the deflector means can be rotated relative the frame structure when the cams of the male and female parts are brought out of abutment with each other. It could furthermore be envisaged that the male part is provided with one or more pins and the female part with one or more guiding grooves in its inside, thereby allowing the deflector means to be rotated relative the frame structure. The pivot connection may also comprise a locking arrangement, such that the deflector means can be locked in a position relative the frame structure. A person skilled in the art would know that such a pivot connection also can be obtained in other ways.

When the apparatus for protecting subsea well structures is to be brought from a folded and retracted position and to the deployed position (or vice versa), a wire or the like can be used. The wire can then be connected to the first leg element of the deflector means in order to lift the first leg element and thereafter to rotate the deflector means around an axis A extending through the deflector means receiving element to its deployed position. This procedure is repeated for each of the deflector means. However, it should be understood that a remotely operated vehicle (ROV) can be used instead of the wire.

DETAILED DESCRIPTION

In the following, preferred embodiments of the invention will be described in detail , by way of example only, with reference to the accompanying figures, where:

Figure 1 is a perspective view, from above, of a first embodiment of an apparatus for protecting subsea well structure according to the present invention,

Figure 2 is a perspective view, from side, of the apparatus for protecting subsea well structures illustrated in figure 1, where the protection structure is installed on sea bed,

Figures 3-5 show details of the apparatus for protecting subsea well structures illustrated in figure 1,

Figure 6 is a perspective view of the apparatus for protecting subsea well structures illustrated in figure 1, where the apparatus for protecting subsea well structures are shown in a folded and retracted position,

Figure 7 is a perspective view of an alternative way to arrange the apparatus for protecting subsea well structure in a folded and retracted position, and

Figures 8A-8C is a perspective view of further embodiments of an apparatus for protecting subsea well structure according to the present invention.

Figure 1 shows an apparatus 1 for protecting subsea well structures according to the present invention from above, where it can be seen that the protection structure comprises a plurality of structural members 3, 4, 5, 6 that are connected to form a frame structure 2 in the apparatus 1 for protecting subsea well structures.

At each end of the structural members 6 is connected a deflector means receiving element 7 (see also figure 3), where the deflector means receiving element 7 is configured to receive a deflector means 8.

Each deflector means receiving element 7 and deflector means 8 is arranged in such a way that the deflector means 8 can be rotated about an axis A (see figure 4) extending vertically through the deflector means receiving element 7.

As shown in figures 3 and 4, the deflector means 8 comprises a first leg element 81 and a second leg element 82, where the first and second leg elements 81, 82 are connected to each other through a first pivot connection P (see also figure 3). The first leg element 81 comprises two plate elements 85 arranged at a distance from each other, where a protruding part 86 of the plate elements 85 is provided with a throughgoing hole. The second leg element 82 is provided with a throughgoing hole. The throughgoing holes of the first and second leg elements 81, 82 are aligned and a bolt or the like is used to connect the elements 81, 82.

The deflector means 8 can be adjusted independently of each other such that the apparatus 1 for protecting subsea well structures can be levelled in relation to an uneven seabed B, as shown in figure 2. Here the left deflector means 8 is in contact with the seabed B at a larger distance from the frame structure 2 than the right deflector means 8.

When apparatus 1 for protecting subsea well structures is to be brought from a folded and retracted position, as shown in figure 6, and to a deployed position, as shown in figure 1, a wire W or the like will in appropriate ways be connected to the first leg element 81, whereby the wire W is used to lift the first leg element 81 up from the frame structure 2, and further to rotate the deflector means 8 around the axis (A) extending vertically through the deflector means receiving element 7, in order to place the deflector means 8 in contact with the seabed B at a desired location.

In figure 2 the apparatus 1 for protecting subsea well structures is lowered to the seabed B and connected to a subsea well structure S, for instance a well head, and the deflector means 8 are spread out to be in the deployed position. The first pivot connection P will allow the first and second leg elements 81, 82 to be adjusted relative each other, whereby this arrangement is used to level the apparatus 1 for protecting subsea well structures with the seabed B.

The deflector means 8 are designed with a smooth surface 83, such that trawler nets, boards and other towed objects (not shown) that could be brought into contact with the deflector means 8 will “glide” over the deflector means 8, thus avoiding becoming entangled in the deflector means.

The deflector means 8 may be designed with a smooth surface, such that trawler nets, boards and other towed objects that could be brought into contact with the deflector means 8 will “glide” over the deflector means 8, thus avoiding becoming entangled in the deflector means 8.

A second pivot connection 9 between the second leg element 82 and the deflector means receiving element 7 is shown in greater detail in figures 3 and 4, where it can be seen that an end of the second leg element 82 comprises a pin or pivot 87, while the deflector means receiving element 7 have a form of a sleeve or a bushing, such that the pin or pivot 87 can be received in the sleeve or bushing when the deflector means 8 and deflector means receiving element 7 are connected to each other. Each of the second leg element 82 and deflector means receiving element 7 are provided with a plurality of cam members 88, 89.

When the deflector means 8 are to be brought from the folded and retracted position and to the deployed position, the deflector means 8 must be lifted upwards a given distance, such that the cam members 88, 89 of the second leg element 82 and deflector means receiving element 7 are brought out of abutment with each other. Once the deflector means 8 are rotated to a desired position, for instance to the deployed position as shown in figure 1, the deflector means 8 are allowed to move downwardly in order to bring the cam members 88, 89 of the second leg element 82 and deflector means receiving element 7 into abutment with each other again, whereby the deflector means 8 are locked in this position.

In an alternative embodiment of the second pivot connection 9, when the deflector means 8 are located in the folded and retracted position, the cam members 88, 89 of the second leg element 82 and deflector means receiving element 7 are held out of abutment with each other through a supporting device (not shown) that supports the deflector means 8 in this position, whereby the deflector means 8 must not be lifted upwards a given distance in order to be rotated. The rotation of the deflector means 8 to the desired position, for instance to the deployed position as shown in figure 1, will result in that the supporting device will not support the deflector means 8 any more, whereby the deflector means 8 are allowed to move downwardly in order to bring the cam members 88, 89 of the second leg element 82 and deflector means receiving element 7 into abutment with each other again, thereby locking the deflector means 8 in this position.

A skilled person in the art would understand that the above male and female pivotable connection can be obtained in other ways.

Figure 6 illustrates the apparatus 1 for protecting subsea well structure, where the apparatus 1 is prepared to be lowered from a vessel 100.

The vessel 100 utilized for installing the apparatus 1 is preferably a drilling vessel of the semi-submersible type which is capable of being anchored or otherwise held in place at the water’s surface. The vessel 100 includes primarily a deck 101 which supports working equipment necessary to accomplish a drilling operation. The deck 101 holds, for example, an upstanding derrick (not shown), as well as the rotary table and drive mechanism for the latter, which are operable to support a drill string for forming a well into the ocean floor.

The deck 101 is provided with a vertical opening 102 extending vertically therethrough providing direct access between the derrick (not shown) and the surface of water. Such an access or passageway 102 is generally referred to in the industry as a moon pool.

The apparatus 1 is conveniently lowered from the vessel 100 by the vessel’s drilling equipment to the subsea equipment the protection structure 1 is to protect by way of wires 103.

However, a person skilled in the art would understand that other types of vessel can be used when lowering the apparatus 1 for protecting subsea well structures to the seabed B.

In figure 7 is shown an alternative way to arrange the apparatus 1 for protecting subsea well structure in a folded and retracted position, where the first and second leg elements 81, 82 of the deflector means 8 are locked relative each other in a position where they form a straight line (i.e. with no angle between them).

Figures 8A-8C show further embodiments of an apparatus 1 for protecting subsea well structure according to the present invention, where it can be seen that the apparatus 1 can comprise a different number of deflector means 8, where the number of deflector means 8 can be selected in view of the specific terms the apparatus 1 for protecting subsea well structure according to the present invention is to be used with.

The present invention has now been explained with reference to exemplary embodiments, but a person of skill in the art will appreciate that changes and modifications may be made to these exemplary embodiments that are within the scope of the invention as defined in the following claims.

Claims (11)

1. An apparatus (1) for protecting subsea well structures located on a seabed (B), the apparatus (1) comprising:

- a frame structure (2) comprising a plurality of structural members (3, 4, 5, 6) adapted to encompass the subsea equipment,

- one or more deflector means (8) connected to the frame structure (2), where each deflector means (8) is adapted to extend away from the frame structure (2) to be brought into contact with the seabed (B) at a distance from the frame structure (2), characterized in that each deflector means (8) comprises a first leg element (81) and a second leg element (82) being pivotally connected through a first pivot connection (P), where the first pivot connection (P) allows the first and second leg elements (81, 82) to rotate about a horizontal axis extending through the first pivot connection (P), where the first leg element (81) defines a sloping deflector surface (83) extending upwardly from the seabed (B) to the frame structure (2), where the second leg element (82) further is pivotally connected to the frame structure (2) through a second pivot connection (9), the second pivot connection (9) allowing the deflector means (8) to rotate around an axis A extending vertically through a deflector means receiving element (7) in the frame structure (2).

2. Apparatus according to claim 1, characterized in that the frame structure (2) comprises at least one deflector means receiving element (7).

3. Apparatus according to claim 1, characterized in that the or each deflector means (8) comprises a leg having one end adjustably attached to the deflector means receiving element (7), and the other end in contact with the seabed (B).

4. Apparatus according to any one of claims 1 to 3, characterized in that the first leg element (81) is provided with a throughgoing hole and a protruding part (86) of plate elements (85) of the second leg element (82) is provided with a throughgoing hole, a bolt or the like being used to connect the first and second leg elements (81, 82).

5. Apparatus according to claim 1, characterized in that at least one of the structural members (3, 4, 5, 6) has an annular form.

6. Apparatus according to any of claims 1 to 5, characterized in that the deflector means (8) comprises locking means for locking the first leg element (81) to the second leg element (82) in a fixed position when the deflector means (8) are in its operative position.

7. Apparatus according to any of claims 1 to 6, characterized in that an end of the second leg element (82) comprises a pin or pivot (87) and the deflector means receiving element (7) comprises a sleeve or bushing, the sleeve or bushing being adapted to receive the pin or pivot (87), each of the second leg element (82) and the deflector means receiving element (7) further comprising a plurality of cam members (88, 89).

8. Apparatus according to any of claims 1 to 7, characterized in that an end of the second leg element (82) comprises a pin or pivot (87) and the deflector means receiving element (7) comprises a sleeve or bushing, the sleeve or bushing being adapted to receive the pin or pivot (87), the pin or pivot (87) further comprising at least one peg, and the sleeve or bushing being provided with at least one guiding groove on its inside.

9. Apparatus according to any of claims 1 to 8, characterized in that the pivot connection (9) comprises a releasably locking arrangement for releasably locking the second leg element (82) to the deflector means receiving element (7).

10. Apparatus according to any of claims 1 to 9, characterized in that the first leg element (81) is provided with a slot (84) adapted to receive a wire or the like.

11. Apparatus according to any of claims 1 to 10, characterized in that at least one “tooth” is connected to an end of the second leg element (82).