NO344543B1

NO344543B1 - A subsea protection structure

Info

Publication number: NO344543B1
Application number: NO20181096A
Authority: NO
Inventors: Jon Inge Brattekås; Christian Suhrke Brattekås; Mathias V Berg
Original assignee: Csub As
Priority date: 2018-08-20
Filing date: 2018-08-20
Publication date: 2020-01-27

Description

A<SUBSEA PROTECTION STRUCTURE>

Technical Field

[0001] The present invention relates to the field of subsea protection structures of the type used in the oil and gas industry in connection with subsea hydrocarbon wells and associated subsea equipment.

Background Art

[0002] It is common to protect subsea equipment, such as wellheads of subsea hydrocarbon wells, from damage such as from fishing equipment or falling equipment. Subsea wells are typically protected with well protection structures.

Where only one subsea well shall be protected, such as a satellite well, the protection structure is often referred to as a SWPS (single well protection structure). Although protecting only one single subsea wellhead, SWPS’s are large and heavy.

[0003] While the most common well protection structures are made of steel framework, there are known some examples of well protection structures that are made of glass-reinforced polymers (GRP).

[0004] One such example is disclosed on www.compositesworld.com, under the headline “Subsea Wellhead And Pipeline Protection Covers”, from 2002. This protection structure comprises a dome-like cap structure that covers the wellhead, wherein the entire cap structure can be pivoted away about a hinge section at one bottom edge.

[0005] A similar structural solution is disclosed in GB2426266, wherein the entire cap structure can be pivoted away for access to the equipment inside.

[0006] WO03044316 discloses a structure for protection of a subsea well. The structure has a base structure lying on the seabed and a top structure that covers a well area. The base structure is made of a composite material.

[0007] NO952933 shows another well protection structure, being a framework structure having pivotable hatches on its top portion.

[0008] EP2628892 presents another protection structure, having a plurality of joined bars.

[0009] Finally, GB2468040 presents a subsea protection structure having two arcuated beams onto which top covers are attached. The structure is made of composite materials.

[0010] To support well protection structures on the seabed, it is common to use suction anchors that are distributed about the position of the well. Other methods may include piling into the seabed.

[0011] An object of the present invention may be to provide a well protection assembly that is cost-effective and reliable.

[0012] Another object of the present invention may be to provide a well protection assembly that is easy and cost-effective to install and to use.

[0013] Yet another object of the present invention may be to provide a well protection assembly that is durable, and which needs less maintenance.

[0014] A further object of the present invention may be to provide a well protection assembly that provides easy access to the wellhead.

Summary of invention

[0015] According to the present invention, there is provided a subsea protection structure of a composite material, comprising a top portion and at least four legs extending down from the top portion. It further has side openings between adjacent legs. The legs and the top portion are moulded as one single piece. The legs comprise an inwardly open channel. The channel has a vertical extension of at least half the vertical extension of the entire subsea protection structure.

[0016] The said composite material can advantageously be glass-fiber reinforced polymer, commonly referred to as GRP.

[0017] With the term inwardly open channel, is meant that the legs have a channel shape, where the channel substantially has two side walls that extend from a bottom wall. In some embodiments, the channel-shape may have a cross section formed like a capitol U letter, having a smooth, curved bottom. In other embodiments, the cross section of the channel may be more like the cross section of the letter V, or a cup, having somewhat sharper edges in the interface between the side walls and the bottom wall.

[0018] When moulding the legs and top portion in one single piece, one does not need an attachment step. I.e. one will not need to attach a separately moulded top portion and legs before the protection structure is ready for use.

[0019] In some embodiments of the invention, at least two of the legs comprise a free, lower end.

[0020] With the term free lower end is meant that the lower end of the leg is not attached to other legs with a connection located at this lower end. In other words, the legs extend freely downwards from the top portion and are self-supported.

[0021] The legs can comprise a foot portion that rests directly on the seabed when the subsea protection structure is landed on the seabed.

[0022] The foot portion of the legs can comprise a substantially horizontal or inclined support wall and a downwardly extending anchoring wall that is configured to extend into the seabed.

[0023] The legs can comprise a foot portion configured to land on the seabed or on a separate support structure, and the size of the channel can be larger at a horizontal cross section at a first position than at a horizontal cross section at a second position that is above the first position. In such embodiments, the legs can thus be wider or larger at their lower section than at their upper section or mid-section.

[0024] Advantageously, in some embodiments of the invention, the side openings can comprise a downwardly extending skirt at their upper part of their perimeter. Such a skirt will prevent equipment, such as fishing equipment, to get fastened. A typical example of such equipment is a trawl door.

Brief description of drawings

[0025] While various features of the invention have been discussed in general terms above, a more detailed and non-limiting example of embodiment will be presented in the following with reference to the drawings, in which

Fig. 1 is a perspective view of a well protection assembly according to the invention;

Fig. 2 is a perspective view of another embodiment of a well protection assembly according to the invention;

Fig. 3 is a top view of the well protection assembly shown in Fig.1;

Fig. 4 is a perspective view of a base structure shown in Fig.1;

Fig. 5 is an enlarged cross section side view of a corner portion of the base structure shown in Fig.4;

Fig. 6 is an enlarged cross section view of a locking arrangement configured to releasably attach the protective top structure to the base structure;

Fig. 7 is a perspective view of the protective top structure shown in Fig.1 in a separate state;

Fig. 8 is a perspective view of a subsea protection structure according to the invention; and

Fig. 9 is an enlarged cross section side view of the lower end of one of the legs shown in Fig.8.

Detailed description of the invention

[0026] Fig. 1 depicts a single well protection assembly 1 according to the present invention. The assembly 1 comprises two main parts, namely a top structure 100 and a base structure 200.

[0027] As will be discussed in detail further below, the base structure 200 rests on the seabed and supports the top structure 100 when in the installed mode as shown in Fig.1.

[0028] The top structure 100 has a horizontal upper face, which comprises two pivoting hatches 101. In Fig.1, the hatches 101 are shown in an open position, exposing an open top aperture 103. When in this open position, substantially the entire upper horizontal face of the top structure 100 is open. When installed over a subsea well (not shown), the operator may access the well from above through the top aperture 103, for instance during well workover operations. The assembly 1 comprises a wellhead space 4, which is configured to accommodate a wellhead of a subsea well.

[0029] The top structure 100 comprises four legs 105 that extend downwards from the upper face with an inclined orientation.

[0030] On each of the four legs 105 there is provided a lifting interface 107, for use during lifting.

[0031] Encircling the top aperture 103 and located at the upper portion of the four legs 105, there is a top ring section 109. The hatches 101 are connected to the top ring section 109 with hinges.

[0032] The top ring section 109 has a substantially rectangular or square shape, however with rounded outer corners.

[0033] In addition to the top aperture 103, which may be closed with the hatches 101, the top structure 100 comprises four side openings 111. The side openings 111 are arranged between two adjacent legs 105. Upwardly, the side openings are confined by the top ring section 109. Downwardly, the side openings are confined by a lower beam 113. The lower beams 113 extend between the lower portion of the adjacent legs 105.

[0034] While three of the four side openings 111 are partly confined downwardly with such a lower beam 113, one of the four side openings 111 is not. Rather, as appears from Fig.1 and Fig.7, one of the side openings 111 are open in the downward direction. This is advantageous if the operator wants to remove the top structure 100 from or land the top structure 100 onto the base structure 200 shown in Fig. 4. This is because absence of the lower beam 113 makes the top structure 100 able not to interfere with the flowline 9 (cf. Fig.4).

[0035] Fig. 2 depicts a perspective view of a single well protection assembly resembling the embodiment shown in Fig.1. However, in the embodiment shown in Fig. 2, the top ring section 109 is not continuous about the top aperture 103. Instead, there is a ring interruption 115. The ring interruption facilitates connection of a pipeline to the wellhead equipment (such as a subsea tree).

[0036] Moreover, contrary to the embodiment shown in Fig.1, in the embodiment shown in Fig.2 the base structure 200 and the top structure 100 is one single unit.

[0037] Fig. 3 depicts the single well protection assembly 1 shown in Fig.1 with a top view. As appears from Fig.3, the top aperture 103, which in the shown state is closed with two hatches 101, has a substantially square shape.

[0038] The outer perimeter of the base structure 200 also has a generally square shape. Notably, however, the four corners of the base structure 200 have a rounded shape.

[0039] Fig. 4 depicts the base structure 200 installed on the seabed and surrounding the wellhead 3 of a subsea hydrocarbon well. The base structure 200 comprises a base structure ring 202. The base structure ring 202 exhibits a generally squared shape in the shown embodiment.

[0040] At each of the four corners, there is an upwardly extending landing guide element 201. The landing guide elements 201 are configured to engage with the top structure 100 when the top structure 100 is landed on the base structure 200. This engagement will align the top structure 100 to the position of the base structure 200, ensuring that these two main parts are correctly assembled.

[0041] In the shown embodiment, the landing guide elements 201 have a curved overall shape that somewhat follows the curved shape of the corner of the base structure 200. Furthermore, the landing guide elements 201 have an upper portion that has a smaller horizontal extension than their lower portion.

[0042] In the shown situation in Fig.4, a remotely operated vehicle (ROV) 5 is operating a schematically shown subsea Xmas tree 7 arranged on the wellhead 3. A flowline 9 is connected the Xmas tree 7.

[0043] Fig. 5 shows an enlarged side view of a portion of the base structure 200. From this view, some aspects of the shape of the landing guide element 201 can be appreciated. The landing guide element 201 has an outer guiding face 203.

Furthermore, it has an upper guiding face 205, and a rear guiding face 207.

[0044] The upper guiding face 205 constitutes the vertically upper part of the landing guide element 201.

[0045] The generally curved shape of the landing guide element 201 comprises two end faces 209, where the curved shape ends.

[0046] As can be seen from Fig.5, the outer guiding face 203, the rear guiding face 207, and the end face 209 all exhibit an inclination with respect to the vertical. The upper guiding face 205 is in the shown embodiment substantially horizontal.

[0047] The lower ends of the legs 105 (cf. Fig.1) comprise an inner guide wall 106, which is configured to engage with and slide against the outer guiding face 203 of the landing guide element 201 when the top structure 100 is landed on the base structure 200. As now will be appreciated by the skilled reader, the four inner guide walls 106, of which one is located at the lower portion of the respective four legs 105, together form a landing capturing area. When the top structure 100 lands on the base structure 200, the four landing guide elements 201 must be positioned within this capturing area, so that the outer guiding faces 203 will engage the inner guide walls 106.

[0048] Advantageously, since the landing guide elements 201 constitute the upper part of the base structure 200, they are the first part of the base structure 200 with which the top structure 100 engages when landing.

[0049] As discussed above, the base structure 200 has a generally rectangular shape or a square shape. Between each of the four base corners 211 there extends a base beam 213.

[0050] Advantageously, the rectangular shape of the base structure 200 is continuous. This contributes to the stability of the base structure.

[0051] As is perhaps shown best in Fig.5, the base beams 213 has the shape of a channel 204 with two substantially vertically extending channel walls 215. The channel 204 is formed by the two channel walls 215 and an upper, substantially horizontal channel top face 217. The cross section through the channel thus has the general shape of the letter “U”, being oriented upside-down.

[0052] The vertical extension of the channel 204 can typically be between 0,5 and 3 meters, advantageously about 1 meter. It may however also be smaller or larger, depending on application and seabed condition.

[0053] As appears from Fig.4, the channel walls 215 of the base beams 213 can advantageously have corrugations 219.

[0054] In the shown embodiment, the corners of the rectangular shape of the base structure 200 also has channel walls 215 and the horizontal channel top face 217. In other words, the channel 204 extends along the entire rectangular shape of the base structure.

[0055] The landing guide elements 201 advantageously protrudes upwards from the horizontal top face 217.

[0056] In the enlarged side view of Fig.5, the seabed 300 is schematically indicated with a generally horizontal line. When landing the base structure 200 on the seabed 300, the channel walls 215 will extend into the seabed 300. In this manner, the base structure 200 will be anchored to the seabed 300 and will provide support to the top structure 100.

[0057] In some embodiments, the base structure 200 can comprise means for establishing a negative pressure within the channel 204, i.e. in the space between the seabed 300, the two channel walls 215, and the channel top face 217. Such means can for instance comprise a fluid communication interface through the channel top face 217 equipped with a suction interface 218. The suction interface 218 can typically connect to an ROV-operated suction device, by means of which the operator can pump fluid out from the channel 204, thereby forcing the base structure 200 into the seabed 300.

[0058] In scenarios where the operator is not using suction for forcing the base structure into the seabed, an opening in the channel 204 may still be advantageous. If the operator lowers the base structure 200 into the seabed by gravity or by application of another downwardly directed force, it may be advantageous to let fluid out of the channel through an opening. Hence, the suction interface 218 will still be advantageous even if not used for the provision of a negative pressure in the channel.

[0059] Reference is now made to Fig.1, Fig.4 and Fig.6, for discussion of locking the top structure 100 to the base structure 200 after landing. As an be seen in Fig.4, the base structure 200 comprises a base locking part 221. In the shown embodiment, the base locking part 221 is arranged on the channel top face 217 and in contact with the outer guiding face 203 of the landing guide element 201.

[0060] When the top structure 100 is in a landed position, a top structure locking part 121 is aligned with the base locking part 221. In the shown embodiment, one top structure locking part 121 is provided at the lower portion of each leg 105.

[0061] Fig. 6 depicts an enlarged cross section side view of the base locking part 221 and the top structure locking part 121, in a locked state. The base locking part 221 and the top structure locking part 121 are part of a locking arrangement 20.

[0062] The base locking part 221 protrudes up from the channel top wall 217.

Furthermore, the base locking part 221 has at least one aperture 223, through which a locking bolt 122 extends, when in the locked mode. A shown in Fig.6, the top structure locking part 121 has two top apertures 123, through which the locking bolt 122 extends.

[0063] The locking arrangement 20 further comprises a bolt housing 125, in which the locking bolt 122 is supported. The bolt housing 125 is configured to let the locking bolt 122 slide axially between a locked and unlocked position. In Fig.6, the locking bolt 122 is shown in the locked position. By sliding it leftwards in the situation shown in Fig.6, it will be moved into the unlocked position, i.e. out of engagement with the top aperture 121 and the base aperture 221. Such movement of the locking bolt 122 can advantageously be performed with an ROV.

[0064] The well protection assembly 1 according to the present invention is produced in a composite material, such as GRP (glass-fiber reinforced polymers). In preferred embodiments, both the top structure 100 and the base structure 200 are produced in GRP.

[0065] Furthermore, the top structure 100 and/or the base structure 200 are preferably produced with vacuum infusion.

[0066] Fig. 7 depicts the top protection structure 100 in a separate state, i.e. not installed on the base structure 200. Due to the relatively low weight of the top structure 100, it is provided with top structure ballast elements 127. The top structure ballast elements 127 increase the weight of the top structure 100 and facilitate landing on the base structure. In the embodiment shown herein, the top structure ballast elements 127 are integrated in two oppositely arranged lower beams 113 of the top structure 100.

[0067] In Fig.7 the location of the inner guide wall 106 is indicated. As discussed above, the inner guide walls 106 will engage with the landing guide elements 201 on the base structure 200 during landing.

[0068] The base structure 200 is correspondingly provided with base ballast elements (not shown). In this embodiment, the base ballast elements are integrated in the base beams 213. The base ballast elements contribute in anchoring the base structure 200 to the seabed 300. They also contribute in forcing the channel walls 215 into the seabed 300 during installation. Advantageously, the base ballast elements 227 comprise metal, such as steel. Moreover, the base ballast elements 227 are advantageously fully encapsulated within the GRP material of the base structure 200, such as with a lamination sheet.

[0069] Still referring to Fig.7, the side openings 111 are at their upper part of their perimeter provided with a skirt 129. While the general shape of the top structure 100 has an inclined outer face, the skirts 129 are substantially vertical. Advantageously, the skirts 129 extend along an edge portion at the lower part of the top ring section 109, in the position above the side openings 111, and some distance down on the legs 105. The legs 105 constitute a lateral boundary of the side openings 111, and the skirts 129 advantageously extend some distance down along this boundary or edge.

[0070] The skirts 129 will contribute in preventing foreign objects, such as trawl equipment, to get stuck in the well protection assembly 1.

[0071] Provision of the skirts 129 makes the relatively large size of the side openings 111 possible.

[0072] In embodiments where the well protection assembly 1 comprises the protective top structure 100 and the base structure 200 in two separate parts, one may choose to land the base structure 200 on the seabed before landing the protective top structure 100 onto the base structure. One may also however choose to land both the protective top structure 100 and the base structure 200 simultaneously, while being attached together.

[0073] While the example of embodiment presented above relates to a single well protection structure, it shall be appreciated that at least some of the claims may relate to a well protection structure configured to protect a plurality of adjacently arranged wellheads.

[0074] Fig. 8 depicts a subsea protection structure 500 made of a composite material, such as GRP. It has a top portion 501, which in the shown embodiment comprises a substantially flat and horizontal upper face 503.

[0075] Down from the top portion 501 there extend six legs 505. The legs 505 comprise a free, lower end 507. The free lower ends 507 are supported only by the legs themselves, i.e. they are not attached to adjacent legs by a horizontal beam or the like. This facilitates placement of the protection structure 500 over subsea equipment that is connected to pipeline, an umbilical or the like extending from the equipment.

[0076] At the lower ends 507 of the legs 505 there is a foot portion 509. In this embodiment, the foot portion 509 is configured to land on the seabed.

[0077] Between the adjacent legs 505 there are side openings 511. The side openings provide access to equipment that is protected by the subsea protection structure 500.

[0078] At the upper perimeter of the side openings, there are provided downwardly extending skirts 529. The downwardly extending skirts 529 prevents fishing equipment or other possible equipment to get stuck at the upper edge of the side openings 511.

[0079] As can be seen from Fig.8, the legs 505 comprises an inwardly open channel 513. In the shown embodiment, the channel has the general shape of the letter “U”. This shape of the legs 505 provides stiffness. Moreover, this shape makes it possible to remove the legs from the mould after a moulding process.

[0080] The legs 505 are thus made of a sheet material, that is shaped like a channel, having an inwardly facing inner face and an outwardly directed outer face.

[0081] The subsea protection structure 500 can be moulded in one piece, i.e. the top portion 501 and the legs 505 are moulded with the same mould in one run.

[0082] As also appears from the view of Fig.8, the legs 505 are larger at their lower portion than they are at a position between their lower portion and the top portion 501. In other words, the U-shape of their horizontal cross section through the channel exhibits a larger “U” close to the foot portion than at the location closer to the top portion 501.

[0083] While the subsea protection structure 500 shown herein has six legs 505, it shall be appreciated that it may in other embodiments have a larger or smaller number of legs, for instance four legs 505.

[0084] Fig. 9 depicts a cross section side view of a lower end 507 of one leg 505, comprising the foot portion 509. The foot portion 509 comprises a substantially downwardly extending anchoring wall 515. The anchoring wall 515 is configured to extend down into the seabed when the protection structure 500 has landed.

[0085] Furthermore, the foot portion 509 comprises a substantially horizontal support wall 517.

[0086] The channel 513 is also indicated in the view shown in Fig.9.

Claims

1. A subsea protection structure (500) of a composite material, comprising a top portion (501) and at least four legs (505) extending down from the top portion, and side openings (511) between adjacent legs

characterized in that

- the legs (505) and the top portion (501) are moulded as one single piece;

- the legs (505) comprise an inwardly open channel (513), the channel having a vertical extension of at least half the vertical extension of the entire subsea protection structure (500).

2. A subsea protection structure (500) according to claim 1, characterized in that at least two of the legs (505) comprise a free, lower end (507).

3. A subsea protection structure (500) according to claim 1 or claim 2, characterized in that the legs (505) comprises a foot portion (509) that rest directly on the seabed.

4. A subsea protection structure (500) according to claim 3, characterized in that the foot portion (509) of the legs (505) comprises a substantially horizontal or inclined support wall (517) and a downwardly extending anchoring wall (515) configured to extend into the seabed.

5. A subsea protection structure (500) according to one of claims 1 to 4, characterized in that the legs (505) comprise a foot portion configured to land on the seabed or on a separate support structure, and that the size of the channel (513) is larger at a horizontal cross section at a first position than at a horizontal cross section at a second position that is above the first position.

6. A subsea protection structure (500) according to one of the claims 1 to 5, characterized in that the side openings (511) comprise a downwardly extending skirt (529) at their upper part of their perimeter.