GB2611083A

GB2611083A - Gas shield

Info

Publication number: GB2611083A
Application number: GB2113761.7A
Authority: GB
Inventors: Olav Myking John; Magne Hisdal Pal; Andrew Foshaug Kristen
Original assignee: Connector Subsea Solutions AS
Current assignee: Connector Subsea Solutions AS
Priority date: 2021-09-27
Filing date: 2021-09-27
Publication date: 2023-03-29
Anticipated expiration: 2041-09-27
Also published as: GB202113761D0; GB2611083B

Abstract

Gas shield 204 is secured to a wellhead on pipe 102 in between the subsea structure (such as a Christmas tree) 101 and the seabed. The main parts of the gas shield 204 are substantially frustoconical and block or deflect the flow of gas 103 off the subsea structure 101. Any deposit formation that occurs due to hydrates, and/or other components, in the gas 103 remain on the gas shield 204. First and second parts of the shield 204, which may be two halves, are placed on the subsea structure by means installation structures comprising frame 201 with two parallel rails 203 and moveable support 202. Movement of each moveable support 202 along its rails 203 may be actioned by a ROV, or each frame 201 may comprise a motor and/or hydraulic drive system for moving its moveable support 202 along the rails 203.The sections of the shield 204 may then be secured by fasteners actuated by a ROV

Description

GAS SHIELD

Field

The field of the invention is the subsea industry. Embodiments provide a gas shield that may be attached to a subsea pipe. Advantageously, the gas shield may prevent a direct gas flow onto another subsea structure.

Background

In the subsea industry, a wellhead may be located on a seabed. The wellhead is an end of a pipe that protrudes from the seabed.

When used for the extraction of oil well products, the wellhead may receive oil well products, such as oil, gas and/or water, that flow into the pipe under the seabed. When a riser is connected to the wellhead, the oil well products may flow through the riser to the surface of the sea for collection in a tanker or onshore facility. The connection between the wellhead and the riser may be temporary. When the wellhead is not connected to a riser, the wellhead blocks the end of the pipe so that the oil well products do not flow into the sea.

Subsea wellheads may also be used for other purposes, such as for extracting other types of fluids and for injecting fluids into a seabed.

A number of subsea structures may be connected to a pipe at the wellhead. An example of a subsea structure that may be connected to the pipe is a Christmas Tree (XT), which typically comprises a valve arrangement. There is a general need to improve the provision of subsea structures at a wellhead.

Summary

Aspects of the invention are set out in the appended independent claims. Optional aspects are set out in the dependent claims. Any aspects, embodiments and examples of the present disclosure which do not fall under the scope of the appended claims do not form part of the invention and are merely provided for illustrative purposes.

List of figures Figure 1 shows a subsea wellhead, Figure 2 shows sections of a gas shield attached to subsea installation structures according 10 to an embodiment, Figure 3 shows sections of a gas shield attached to subsea installation structures according to an embodiment; Figure 4 shows sections of a gas shield when positioned by subsea installation structures so they may be attached to each other according to an embodiment; Figure 5 shows a gas shield attached to a pipe as well as subsea installation structures according to an embodiment; and Figure 6 shows a gas shield attached to pipe so as to block a direct gas flow onto a subsea structure according to an embodiment

Description of embodiments

Embodiments provide a subsea gas shield for protecting one or more other subsea structures from a direct gas flow. The subsea gas shield is shown in Figure 6. Embodiments also provide a method of installing a gas shield on a subsea pipe. Different stages of the method are shown in Figures 2 to 5. Embodiments are described in more detail below.

Figure 1 shows a subsea wellhead according to known techniques. A subsea pipe 102 protrudes from a seabed. Attached to the pipe 102 is a subsea structure 101. The subsea structure 101 may be a Christmas Tree (XT). A XT may comprise valves, casing spools, and/or fittings for regulating the flow of fluid through the pipe 102.

A problem experienced by the subsea structure 101 shown in Figure 1 is that gas 103 may flow out of the seabed around the pipe 102. The gas 103 may flow onto the subsea structure 101. The gas 103 may comprise hydrates and/or other components that may cause deposits. The flow of the gas 103 onto the subsea structure 101 may eventually result in deposits, such as hydrates and/or other deposits, forming on and/or in the subsea structure 101. The formation of deposits on and/or in the subsea structure 101 may be detrimental to the operation of the subsea structure 101. For example, deposits may make the actuation of valves difficult and may even cause complete failure of a valve, or other component, of the subsea structure 101.

Embodiments may solve the above problem by providing a gas shield 204 around the pipe 102 at a subsea wellhead. As shown in Figure 6, the gas shield 204 may be secured to the pipe 102 in between the subsea structure 101 and the seabed. The shape of the main part of the gas shield 204 for blocking the flow of gas 103 may comprise the substantial surface of a cone frustum. The gas shield 204 may also comprise a tubular part for surrounding the pipe 102. The gas shield 204 may also comprise other parts. The parts of the gas shield 204 may have any shape so long as the gas shield 204 may be secured to the pipe 102 and the gas shield 204 is a substantial block to a longitudinal flow of gas 103 along the outer surface of the pipe 102.

The gas shield 204 may be made from, for example, stainless steel and/or any other material that is typically used in the subsea industry.

The gas shield 204 according to embodiments may Nock a direct flow of gas 103 onto all, or the substantial part of, the subsea structure 101. The gas shield 204 may deflect the flow path of gas 103 so that there is substantially no flow of gas 103 onto the subsea structure 101. Any deposit formation that occurs due to hydrates, and/or other components, in the gas 103 may only be on the gas shield 204. Advantageously, the gas shield 204 may substantially prevent deposit formation occurring on the subsea structure 101.

Embodiments also provide a method of installing a gas shield 204 onto a subsea pipe 102. The method allows a subsea pipe 102 to be retrofitted with a gas shield 204. The method of installing the gas shield 204 onto the pipe 102 is explained below with reference to Figures 2 to 6.

A first step of the method may comprise assembling first and second sections of a gas shield 204 on respective first and second subsea installation structures The first and second subsea installation structures may be substantially the same as each other.

Each subsea installation structure may comprise a frame 201 with a moveable support 202. As shown in at least Figure 2, each frame 201 may be a substantially planar structure. The frame 201 may comprise two parallel rails 203 that the moveable support 202 may move along. At an end of each subsea installation structure, each of the rails 203 may extend from a main body of the frame 201 so that the end is substantially U-shaped. A section of a gas shield 204 may be attached to the moveable support 202. The section of the gas shield 204 may be attached to the moveable support 202 by, for example, a fastener, such as a bolt, or by another technique.

The moveable supports 202 of the first and second subsea installation structures may respectively hold the first and second sections of the gas shield 204. When secured to each other, the first and second sections of the gas shield 204 may provide a complete gas shield 204. As shown in at least Figure 2, each section of the gas shield 204 may be half of a gas shield 204. The first and second sections of the gas shield 204 may be substantially the same as each other.

The securing of first and second sections of the gas shield to the respective first and second subsea installation structures may be performed above the surface of the sea, such as onshore, on an offshore platform or on a vessel.

1 5 The first and second subsea installation structures may then be lowered to where the gas shield 204 is to be installed. When attaching a gas shield 204 to a subsea pipe 102, the first and second subsea installation structures may be lowered so that they sit on the seabed. As shown in Figure 2, the first and second subsea installation structures may be positioned close to, and on opposite sides of', the pipe 102. The gas shield 204 sections may both be below a subsea structure 101 that is already attached to the pipe 102.

As shown in Figure 3, the moveable support 202 of the first subsea installation structure may move along its rails 203 so that the first section of the gas shield 204 is positioned on the outer diameter of pipe 102. The movement of the moveable support 202 along the rails 203 may be due to the moveable support 202 being pushed, for example by a remotely operated vehicle (ROV). Alternatively, the frame 201 may comprise a motor and/or hydraulic drive system for moving the moveable support 202 along the rails 203.

As shown in Figure 4, the moveable support 202 of the second subsea installation structure may move along its rails 203 so that the second section of the gas shield 204 is positioned on the outer diameter of pipe 102. The movement of the moveable support 202 along the rails 203 may be due to the moveable support 202 being pushed, for example by a ROV.

Alternatively, the frame 201 may comprise a motor and/or hydraulic drive system for moving the moveable support 202 along the rails 203.

The first and second sections of the gas shield 204 may then be secured to each other. For example, the first and second sections of the gas shield 204 may be fastened to each other.

The fasteners may be actuated by a ROY. The fasteners may comprise bolts. The fasteners may have been attached to the first and/or second sections of the gas shield 204 prior to the subsea installation structures being lowered to the wellhead. The first and second sections of the gas shield 204 may thereby be secured both to each other and to the pipe 102. A complete gas shield 204 may thereby secured to the pipe 102 below the subsea structure 101.

The first and second sections of the gas shield 204 may be detached from their respective supports 202. The detachment of each section of the gas shield 204 may be performed by, 20 for example, a ROY turning a fastener such as a bolt.

As shown in Figure 5, the moveable supports 202 of the first and second subsea installation structures may both move along their rails 203 so that they are separated from the gas shield 204. The movement of each moveable support 202 along its rails 203 may be due to the moveable support 202 being pulled, for example by a ROV. Alternatively, each frame 201 may comprise a motor and/or hydraulic drive system for moving its moveable support 202 along the rails 203.

The first and second subsea installation structures may then be lifted so that they are returned to the surface of the sea. A gas shield 204 that is attached to a pipe 102, as shown in Figure 6, is thereby provided. The gas shield 204 may block a direct gas 103 flow onto a substantial part of a subsea structure 101 attached to the pipe 102.

In a preferred embodiment, the subsea structure 101 is a XT. The approximate dimensions of the XT may be: Width = about 4000mm to 6000mm, Length = about 4000mm to 6000mm, and Height = about 4000mm to 6000mm.

The pipe's 102 outer diameter may be about 400mm to 600mm, such as 464mm. The distance along the pipe 102 between the lower surface of the subsea structure 101 and the 15 seabed may be about 1500mm. The seabed may be located at a depth of about 1400m to 1800m.

Embodiments include a number of modifications and variations to the techniques described above.

In the above-described embodiments, the first and second sections of gas shield 204 are substantially the same as each other. Embodiments, also include the use of first and second sections of gas shield 204 that comprise substantial differences to each other. For example, one of the sections of gas shield 204 may provide more than half of the completely assembled gas shield 204.

In the above-described embodiments, the first and second sections of the gas shield 204 are fastened to each other. Embodiments also include the use of other techniques for securing gas shield 204 sections to each other, such as welding.

In the above-described embodiments, the support 202 of each subsea installation structure is moveable. Embodiments also include the use of subsea installation structures with fixed supports that are not moveable relative to their frame 201. The fixed supports may be located relative to their frames as shown in Figure 4. The subsea installation structures may be moved in an orthogonal direction to the longitudinal axis of the pipe 102 to position the sections of the gas shield 204 so that they may secured to each other and/or the pipe 102. After the gas shield 204 has been secured to the pipe 102, the subsea installation structures may be moved in an orthogonal direction to the longitudinal axis of the pipe 102 before being raised to the surface so as to avoid a collision between the supports and the gas shield 204.

Embodiments also include the use of more than two gas shield 204 sections, and more than two corresponding subsea installation structures, for installing a gas shield 204 that comprises more than two sections.

Embodiments also include installing the gas shield 204 on a subsea section of the pipe 102 that is away from the seabed, such that the subsea installation structures are unable to sit on the seabed when installing the gas shield 204. The first and second subsea installation structures may both be lowered to where the gas shield 204 is to be installed. The first and second subsea installation structures may then be secured to each other and the pipe 102.

The processes described above with reference to at least Figures 3 to 5 may then be repeated to secure the gas shield 204 to the section of the pipe 102.

Embodiments also include the gas shield 204 comprising first and second sections that are both made from lightweight materials. For example, each section of the gas shield 204 may comprise a glass fibre cover over a structural frame. Each section of the gas shield 204 may be designed so that an alternative method may be used to secure the gas shield 204 to a pipe 102 in a retrofitting process. In particular, each section of the gas shield 204 may comprise skis so that it can slide along a seabed. The process of securing the gas shield to the pipe 102 may comprise the following steps: 1) A first section of the gas shield may be lowered onto the seabed an positioned next to, but slightly spaced apart from, the pipe 102 2) A second section of the gas shield may then be lowered onto the seabed an positioned next to, but slightly spaced apart from, the pipe 102 on a diametrically opposite side to the first section.

3) One or more ROVs may push each section along the seabed to bring the sections into contact with each other around the pipe 102. Each section may comprise Ode funnels and pins to assist with alignment when they are brought together. The lightweight construction of each section may allow both sections to be pushed along the seabed by ROVs. In the event that the sections are too heavy to be pushed into position by one or more ROVs, embodiments also include a ROV attaching one or more winch wires between each section. For example, two winch wires may be attached between the sections, with the winch wires on either side of the pipe 102. A hydraulic stab, or other mechanism, may then be operated so that the sections are pulled together by the winches. The sections may be only pulled together by the winch, or both pulled by the winch and pushed by ROVs.

4) One or more ROVs may then operate one or more fasteners on one, or both, sections so that the sections are secured to each other and/or to the pipe 102.

Advantageously, the above attachment method does not require the use of first arid second subsea installation structures. In the above method, each section may be a substantially cuboid structure so that its shape is more suitable for pushing along a seabed In all embodiments, each section may comprise a sealing mechanism so that there is substantially no gas flow through the gas shield 204 when the sections of the gas shield 204 are secured together. For example, the contacting surfaces of the sections may be covered by rubber seals, or any other type of seal, so that the connection between them is gas tight Embodiments also include a gas shield 204 that comprises only a single section. The single section may be a substantially complete gas shield 204 that can have any design that allows it to be positioned on, and secured to, a pipe 102. For example, the single section may comprise a slot so that it can be slid onto a pipe 102. Alternatively, the single section may comprise two sub-sections, with each sub-section corresponding to a section according to any of the above-described embodiments. The two sub-sections may, for example, joined together by a hinge. The two sub-sections may, for example, be pushed together around a pipe by ROVs The accompanying drawings are provided for purposes of illustration only, and the dimensions, positions, order, and relative sizes reflected in the drawings attached hereto may vary. The detailed description will be better understood in conjunction with the accompanying drawings, with reference made in detail to embodiments of the present subject matter, examples of which are illustrated in the drawings. Each example is provided by way of explanation of the present subject matter, not limitation of the present subject matter. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the present subject matter. Thus, it is intended that the present subject matter covers such modifications and variations as come within the scope of the appended claims and their equivalents.

In the foregoing description, it will be appreciated that the phrases "at least one", -one or more', and "and/or", as used herein, are open-ended expressions that are both conjunctive and disjunctive in operation. The term "a" or "an" entity, as used herein, refers to one or more of that entity. As such, the terms "a" (or "an'), "one or more" and "at least one" can be used interchangeably herein. Ml directional references (e.g., proximal, distal, upper, lower, upward, downward, left, right, lateral, longitudinal, front, back, top, bottom, above, below, vertical, horizontal, radial, axial, clockwise, counterclockwise, and/or the like) are used for identification purposes to aid the reader's understanding of the present disclosure, and/or serve to distinguish regions of the associated elements from one another, and do not limit the associated element, particularly as to the position, orientation, or use of this disclosure.

Claims

Claims: 1. A gas shield arrangement comprising: a first gas shield section; and a second gas shield section; wherein the first and second gas shield sections are arranged to be secured to each other and/or a subsea pipe in a subsea assembly operation to provide a gas shield on the subsea pipe.
2 The gas shield arrangement according to claim 1, wherein, when the first and second gas shield sections are secured to each other to provide a gas shield on a pipe, the gas shield comprises a part for blocking a longitudinal flow path of gas along the outer surface of the pipe
3 The gas shield arrangement according to claim 2, wherein the part for blocking a longitudinal flow path of gas along the outer surface of the pipe comprises a surface that is substantially the surface of the frustum of a cone.
4 The gas shield arrangement according to any preceding claim, wherein, when the first and second gas shield sections are secured to each other to provide a gas shield on a pipe, the gas shield comprises a part for securing the gas shield to the pipe.
5. The gas shield arrangement according to any preceding claim, wherein the gas shield arrangement further comprises one or more fasteners for securing the first and second gas shield sections to each other and/or the pipe
6. The gas shield arrangement according to claim 5, wherein the fasteners are operable by a remotely operated vehicle.
7. A gas shield that is the gas shield arrangement according to any of claims Ito 6 when on a subsea pipe.
8 A method of installing a gas shield on a subsea pipe, the method comprising: assembling a first subsea installation structure arrangement that comprises a frame and a support with a first section of a gas shield attached to the support; assembling a second subsea installation structure arrangement that comprises a frame and a support with a second section of the gas shield attached to the support; positioning the first subsea installation structure arrangement and the second subsea installation structure arrangement on opposite sides of a subsea pipe; and securing the first and second sections of the gas shield to each other and/or the pipe.
9 The method according to claim 8, wherein, after the first subsea installation structure arrangement and the second subsea installation structure arrangement have been positioned on opposite sides of a subsea pipe, the method further comprises: moving the first support relative to the frame of the first subsea installation structure to position the first section of the gas shield next to the pipe, and moving the second support relative to the frame of the second subsea installation structure to position the second section of the gas shield next to the pipe
10. The method according to claim 8 or 9, wherein securing the first and second sections of the gas shield to each other and/or the pipe comprises using remotely operated vehicles to operate one or more fasteners
11. The method according to any of claims 8 to 10, wherein the first and second sections of the gas shield are comprised by a gas shield arrangement according to any of claims 1 to 6.
12. A method of installing a gas shield on a subsea pipe, the method comprising: positioning a first section of a gas shield on a seabed and next to a subsea pipe; positioning a second section of a gas shield on the seabed and next to the subsea pipe, wherein the first and second sections are positioned on opposite sides of the subsea pipe; bringing the first and second sections together around the subsea pipe; and securing the first and second sections to each other and/or the subsea pipe.
13. The method according to claim 12, wherein bringing the first and second sections together around the subsea pipe comprises pushing the first and second sections together by one or more ROVs.
14. The method according to claim 12 or 13, wherein bringing the first and second sections together around the subsea pipe comprises: attaching one or more winch wires between the first and second sections and operating a winch that pulls the first and second sections together.
15. A gas shield arrangement comprising: a first gas shield section; and one or more further gas shield sections; wherein the first and one or more further gas shield sections are arranged to be secured to each other and/or a subsea pipe in a subsea assembly operation to provide a gas shield on the subsea pipe.
16. A gas shield arrangement comprising: a single gas shield section; wherein the gas shield section is arranged to be secured to a subsea pipe in a subsea assembly operation to provide a gas shield on the subsea pipe.