Cover for use with a subsea structure

Abstract

A cover 100 for a connection mechanism (4) of a subsea structure (2) is provided. The cover includes a plurality of hydraulic couplers 102 configured to connect with respective connectors of the conne

Description

TECHNICAL FIELD The present disclosure relates to a cover for use with a subsea structure and to a method of using such a cover. BACKGROUND In various subsea applications including the field of subsea oil and gas production, and the field of subsea SCO2 re-injection, there is a need to provide connections between different structures. These connections include connections for at least power delivery, control signals and product delivery. In various examples, hydraulic fluids and I or other chemicals are required to be sent from a first subsea structure to either a second subsea structure or to a structure located above the surface. Typically, service line connections (including hydraulic connections) between such first and second structures are implemented using a connector at each end of a relatively flexible bundle of service lines, including hydraulic cables, each connector being configured to connect with a connection mechanism provided on a respective one of the structures. One example of such a connector is a Multi Quick Connection flying plate, in which the service lines may be joined to tubes within the flying plate. It will be appreciated that the connection mechanism on a subsea structure is vulnerable to damage both during installation of the structure subsea and when installed subsea and prior to be connected with a connector (for example a Multi Quick Connection flying plate). It is therefore desirable to provide a cover to protect the connection mechanism on such a structure. It is also desirable to provide hydraulic compensation to a hydraulic system within a subsea structure during deployment thereof (and before a service line or flying lead is connected to the subsea structure). The present disclosure provides a cover, which is configured to be connected to a subsea structure so as to protect the connection mechanism of the subsea structure prior to connection with a bundle of service lines and also to provide hydraulic compensation to the subsea structure. SUMMARY From a first aspect, the disclosure provides a cover for a connection mechanism of a subsea structure, the cover comprising: a plurality of hydraulic couplers configured to connect with respective connectors of the connection mechanism; a hydraulic compensation mechanism fluidly connected with one or more of the plurality of hydraulic couplers; and a valve configured to be moved between a closed state in which the hydraulic compensation mechanism is fluidly isolated from the one or more of the plurality of hydraulic couplers and an open state in which the hydraulic compensation mechanism is fluidly connected to the one or more of the plurality of hydraulic couplers, wherein the hydraulic compensation mechanism is configured to compensate hydraulic pressure in the subsea structure when the plurality of hydraulic couplers are fluidly connected with the respective connectors of the connection mechanism and the valve is open. It will be understood that a cover according to the disclosure may be used both to provide hydraulic compensation to a subsea structure. The cover may also cover the connection mechanism of a subsea structure when installed subsea, thus sealing against fluid ingress to or egress from the subsea structure, relative to the subsea environment. This may be achieved by the hydraulic compensation mechanism and the valve which can be closed to isolate the hydraulic compensation mechanism from the subsea structure when desired. In any example of the disclosure, the hydraulic compensation mechanism may comprise a manifold block fluidly connected with one or more of the plurality of hydraulic couplers. In any example of the disclosure, the hydraulic compensation mechanism may comprise an accumulator bladder fluidly connected with the manifold block. In any example of the disclosure, the valve may be configured such that the accumulator bladder is fluidly isolated from the manifold block when the valve is closed and the accumulator bladder is fluidly connected to the manifold block when the valve is open. In any example of the disclosure, the cover may comprise a further valve, and the hydraulic compensation mechanism may be fluidly isolated from the connection mechanism when at least one of the valve and the further valve are closed. In any example of the disclosure, the cover may comprise a housing surrounding at least part of the hydraulic compensation mechanism and I or the conduits. In any example of the disclosure, the cover may comprise an injection port for injecting hydraulic fluid into the hydraulic compensation system. In some examples, the cover may further comprise an injection line connecting the injection port to the hydraulic compensation system. In some examples, the cover may further comprise an injection line isolation valve in the injection line. In any example of the disclosure, the cover may comprise an air purge port. In any example of the disclosure, the cover may comprise a sealed conduit external of the cover and connected with the hydraulic compensation system. In any example, the sealed conduit can be cut so as to balance the internal pressure of the hydraulic compensation system with an external pressure. From a further aspect, the disclosure provides a method of installing a subsea structure, the method comprising: connecting the plurality of hydraulic couplers of a cover according to any preceding claim with the respective connectors of the connection mechanism of a subsea structure; and installing the subsea structure at a subsea location. In any example of the disclosure, the method may comprise either before or after installing the subsea structure at a subsea location, opening the valve to compensate hydraulic pressure in the subsea structure. In any example of the disclosure, the method may comprise subsequently closing the valve so as to isolate the hydraulic compensation mechanism from the one or more of the plurality of hydraulic couplers. In any example of the disclosure, the method may comprise keeping the plurality of hydraulic couplers of the cover connected to the respective connectors of the connection mechanism of the subsea structure so as to protect the connection mechanism. In any example of the disclosure, the method may comprise subsequently removing the cover from the subsea structure; and connecting a hydraulic connector to the connection mechanism. Although certain advantages are discussed below in relation to the features detailed above, other advantages of these features may become apparent to the skilled person following the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS One or more non-limiting examples will now be described, by way of example only, and with reference to the accompanying figures in which: Figure 1 is a front view of a subsea structure and a cover according to an example of the disclosure; Figure 2 is a side view of a cover according to an example of the disclosure; Figure 3 is a front view of the cover of Figure 2; Figure 4 is an exploded view of the cover of Figure 2; Figure 5 is a schematic diagram showing the hydraulic compensation system in a cover according to an example of the disclosure; and Figure 6 is a schematic diagram showing a method of using a cover according to an example of the disclosure. DETAILED DESCRIPTION Figure 1 shows a subsea structure 2, which is a subsea distribution unit (SDU) in the example shown but could be any other suitable subsea structure such as a subsea host structure for CO2 injection into a subsea storage site or for oil and gas production, also including but not limited to a Christmas tree (XT), a manifold or an umbilical termination assembly (UTA). The subsea structure 2 comprises a connection mechanism 4 formed on a plate 6 which is fixed to the subsea structure 2 and which includes a plurality of receptors which are not visible in Figure 1 and which are configured to form a hydraulic connection with respective connectors of a flying plate of a hydraulic flying lead. Once installed subsea, the subsea structure 2 may be connected to the surface (not shown) or to a further subsea installation (not shown) by service lines (not shown) including hydraulic cables and optionally, electrical and / or optical cables. Prior to installation and during deployment however, it may be desirable to provide hydraulic compensation to the subsea structure. It is further desirable to protect the connection mechanism 4 from potential damage during installation of the subsea structure 2 and also after the subsea structure 2 has been installed on the seabed (not shown) and before the connection mechanism 4 has been connected to a hydraulic flying lead (not shown). In any example of the disclosure, a cover 100 is provided which is configured to provide hydraulic compensation when mounted to the subsea structure 2 and to protect the connection mechanism 4 from damage as will be described further below. The cover 100 may take any suitable form. In any example of the disclosure however, and as seen for example in Figures 2 to 5, the cover 100 includes a plurality of hydraulic couplers 102 configured to connect with respective connectors of the connection mechanism 4. The cover 100 also includes a hydraulic compensation system including a manifold block 104 fluidly connected with one or more of the plurality of hydraulic couplers 102. In any example, the manifold block 104 may be fluidly connected with one or more of the plurality of hydraulic couplers 102 via respective conduits 106. A compensation or accumulator bladder 108 (which is also part of the hydraulic compensation system) is fluidly connected with the manifold block 104. In any example, the accumulator bladder 108 is fluidly connected with the manifold block 104 via a tube 110. The cover 100 also includes a valve 112 configured to be moved between a closed state in which it isolates the accumulator bladder 108 from the manifold block 104 and an open state in which the accumulator bladder is fluidly connected to the manifold block. When the plurality of hydraulic couplers 102 are fluidly connected with the respective connectors of the connection mechanism 4 and the valve 112 is open, the accumulator bladder 108 is fluidly connected with the connection mechanism so as to compensate hydraulic pressure in the subsea structure 2. In any example of the disclosure, the hydraulic couplers 102 may extend approximately parallel to one another in a first direction D1 and may be spaced from each other, for example being arranged circumferentially and being positioned so as to engage with respective connectors of the connection mechanism 4. In any example, the hydraulic couplers 102 may be mounted in any suitable arrangement and may for example form part of a flying plate or a Multi Quick connection flying plate, for example being similar to the arrangement provided on a flying lead. It will be understood that the hydraulic couplers 102 may be configured such that each connector of the connection mechanism 4 is connected with and / or locked to a respective one of the hydraulic couplers 102. In any example of the disclosure, the hydraulic couplers 102 may engage with respective connectors of the connection mechanism 4 such that the cover 100 may function to retain and I or maintain the hydraulic pressure of the subsea structure 2 to which it is connected. The retention of this pressure may be achieved at least in part by a sealed connection which may be formed between each respective connected hydraulic coupler 102 and connector. As described above, a respective conduit 106 extends from each hydraulic coupler 102 to a respective port 114 in the manifold block 104 so as to provide a fluid connection between the manifold block 104 and a respective hydraulic coupler 102. In some examples and as seen in Figure 4, the conduits 106 may extend away from the hydraulic couplers 102 in the first direction D1 and then extend around a bend to extend towards the manifold block 104 in a second direction D2 which may be approximately perpendicular to the first direction D1. In such examples, the manifold block 104 may be spaced from the hydraulic couplers 102 in the second direction D2. The manifold block 104 may be approximately cuboid in form and may be configured to extend between the conduits 106 and the accumulator bladder 108. A first face 116 of the manifold block 104 faces toward the conduits 106 and includes a plurality of the ports 114 for receiving respective conduits 106. A second, opposite face (not shown) of the manifold block 104 includes a further port (not shown) which is connected to the tube 110 such that a first end 110A of the tube 110 is connected to the manifold block 104 and a second, opposite end 110B of the tube 110 is connected to the accumulator bladder 108. In any example, the valve 112 may be positioned so as to block flow through the tube 110 when closed, thus fluidly isolating the accumulator bladder 108 from the manifold block 104. In any example, a further valve 118 may also be provided which is also configured to be moved between a closed state in which it isolates the accumulator bladder 108 from the manifold block 104 and an open state in which the accumulator bladder is fluidly connected to the manifold block. The further valve 118 can also be positioned so as to block flow through the tube 110 when closed and can be spaced from the valve 112 along the tube 110 in the direction of flow therethrough. It will be understood that the further valve 118 may act as a failsafe or redundant valve which is only needed in the event of the failure of the valve 112. In any example, the valve 112 and / or the further valve 118 may be ball valves. In any example, the valve 112 and / or the further valve 118 may be individually or jointly openable to allow fluid to flow through the tube 110 such that the accumulator bladder 108 is in fluid communication with the manifold block 104. In any example, the valve 112 and I or the further valve 118 may be individually or jointly closable to reduce or stop fluid flow through the tube 110 such that the accumulator bladder 108 is not in fluid communication with the manifold block 104 (in other words is isolated from the manifold block). In any example, the valve 112 and I or the further valve 118 may be openable and I or closable by a remotely operated vehicle (ROV) and / or may be manually openable and / or closable and / or may be openable and / or closable by automatic means, for example by a signal sent from a ship above the water’s surface. In any example, the valve 112 and / or the further valve 118 may limit or reduce the potential of damage due to possible back pressure, for example pressure from the subsea structure acting on the valve 112 and / or the further valve 118 which could damage the accumulator bladder 108 if able to pass through the valve 112 and / or the further valve 118. In the example shown, the tube 110 extends from the accumulator bladder 108 and then extends around the bladder 108 in such a way that the valve 112 is located on a first side of the bladder 108 and the further valve 118 is located on a second, opposite side of the bladder 108. In any example of the disclosure and as shown in Figures 2 to 4, the cover 100 may include a housing 120 which may include openings (not shown) to allow for water ingress so as to balance the internal pressure with that of the external environment when in a subsea environment. The housing 120 may surround at least part of the hydraulic compensation mechanism, for example the accumulator bladder 108, and I or the conduits 106 and I or the manifold block 104. The housing 120 may include a first part 122 (shown in dotted lines in Figure 2) which surrounds the accumulator bladder 108 and a second part 124 which surrounds the conduits 106. As seen in the exploded view of Figure 4, the second housing part 124 in some examples is configured to be attached to and extend from the manifold block 104 so as to extend around the accumulator bladder 108. The second housing part 124 includes a front half 126 and a back half 128, which are configured to be joined together and to be fixed to the manifold block 104 at a first end thereof. The second housing part 124 also includes a plate 130 which is attached to the front half 126 and the back half 128 so as to close the end of the second housing part 124 removed from the manifold block 104. In any example of the disclosure, an aperture 132 may be formed in the housing 120, through which a mechanism 136 for opening and I or closing the valve 112 may extend such that a diver or ROV may engage with the mechanism to change the valve between the open and closed positions. In any example of the disclosure, a further aperture 134 may be formed in the housing 120, through which a mechanism 138 for opening and I or closing the further valve 118 may extend such that a diver or ROV may engage with the mechanism to change the valve between the open and closed positions. In any example of the disclosure, the mechanism 136 may include a groove or other shape into which a tool or protrusion of an ROV arm may be inserted to be turn and thus open the valve. The aperture 132 and I or the further aperture 134 may be formed in the first housing part 122, for example in the front half 126. In any example of the disclosure, the second housing part 124 may include a frame 140 configured to be connected to the manifold block 104 and to extend around the conduits 106 and to abut against an annular plate 142 which forms part of a multi quick connector on which the hydraulic couplers 102 are mounted. In any example of the disclosure, the cover 100 may include an injection port 150 which allows hydraulic fluid to be injected into the hydraulic compensation system if required. In any example, the injection port 150 may be mounted to and external of the housing 120 and may be connected to an injection line 152 which extends through the housing 120 and is fluidly connected with the tube 110, in the example shown at a location adjacent the join with the manifold block 104. An injection line isolation valve 154 may be provided in the injection line 152 which acts to isolate the injection line 152 from the rest of the hydraulic compensation system when closed. It will be understood that the injection line isolation valve 154 can be manually or automatically opened and closed as required. In some examples, the injection line isolation valve 154 may be a hand operated needle valve. Figure 5 is a schematic representation of the hydraulic connections of a cover 100 according to an example of the disclosure. The boundary of the cover is represented by the dashed line 500. As seen more clearly in Figure 5, in some examples, the tube 110 fluidly connects the accumulator bladder 108 with the manifold block 104. As described above, the valve 112 and the further valve 118 are arranged in series in the tube 110 in the example shown. As seen in Figure 5 for example, an adapter 502 may be provided on each conduit 106 for attaching the respective conduit to a coupler 102. Each respective coupler 102 may include either a vented or non-vented poppet. In any example of the disclosure, the cover 100 may include an air purge port 160. This may be used to remove air from the hydraulic compensation system during topside installation, for example when hydraulic fluid is being added to the hydraulic compensation system or to a subsea structure to which the cover is connected. The air purge port 160 thus enables any air present in the hydraulic compensation system to be removed so as to improve the efficacy of the hydraulic compensation system. It will be understood that in any example of the disclosure the air purge port 160 may include a closure 162 (as shown schematically in Figure 5) such that the air purge port may be sealed or capped by the closure 162 such that air cannot enter via the air purge port 160 when the closure is closed. As also seen in Figure 5, the air purge port 160 may be fluidly connected with the manifold block 104 so as to allow air to escape from the hydraulic compensation system. In any example of the disclosure, the cover 100 may include a further conduit 170 which is connected with the hydraulic compensation system and which extends through the housing 120 to provide a sealed external conduit which can be cut (for example, manually or by an ROV, for example by ROV scissors) in the case of a hydraulic lock so as to balance the internal pressure of the hydraulic compensation system with the external pressure and so avoid a vacuum being generated. As seen in Figure 5, the further conduit 170 may be fluidly connected with the manifold block 104 although it could also be connected to a different part of the hydraulic compensation system if preferred. A method of installing a subsea structure using a cover according to the disclosure will now be described with reference to Figure 6. At a first step 200, prior to installing the subsea structure 2 on the seabed, a cover 100 according to the disclosure is mated with the subsea structure 2 by connecting the respective connectors of the connection mechanism 4 of the subsea structure 2 with respective hydraulic couplers 102 of the cover 100. At a second (optional) step 202, if desired or necessary, the valve 112 (and the further valve 118 if present) is opened to bring the accumulator bladder 108 into fluid communication with the subsea structure and to provide hydraulic compensation thereto. It will be understood that the step of opening the valve 112 and I or the further valve 118 may be carried out either before or after installing the subsea structure on the seabed as required. In some examples, the step of opening the valve 112 and / or the further valve 118 is carried out before installing the subsea structure on the seabed and the valve 112 and / or the further valve 118 are kept open during the installation such that hydraulic pressure in the subsea structure may be compensated gradually during installation of the subsea structure on the seabed. In any example of the disclosure, one or both of steps 200 and 202 may be carried out at a location remote from the subsea installation, including for example on land or at a surface location. Once the valve(s) have been opened, at step 204 the subsea structure 2 is moved to its desired subsea location and installed subsea. It will be understood that this installation step may include forming connections between the subsea structure 2 and other structures or control centres which may be either subsea, on land or at the surface. At step 206, once hydraulic compensation is no longer required, the valve(s) are closed so as to isolate the accumulator bladder 108 from the subsea structure 2. By isolating the accumulator bladder 108 from the subsea structure 2 in this way, the risk of damage to the bladder due to back pressure from the hydraulic system of the subsea structure can be reduced or even removed. The subsea structure 2 with the cover 100 attached thereto can then remain insitu, the cover acting to protect the connection mechanism 4 from potential damage or water ingress. When or if it is desired to form a hydraulic connection with the subsea structure 2, the cover 100 may be removed and a flying lead or other hydraulic connector may be connected to the connection mechanism 4. Further, should it be necessary to remove the hydraulic connection at any time, the cover 100 may be reconnected with the connection mechanism as required. It will be understood that the provision of a hydraulic compensation mechanism and one or more valves in the cover allows a single cover to be used and left in situ on a subsea structure until the cover needs to be removed to allow hydraulic cables to be connected to the subsea structure. Thus, the cover according to the disclosure can function as both a long term protective cover subsea and also as a hydraulic compensation provider to be used before the hydraulic system of a subsea structure is fully compensated, for example during deployment of the structure. The use of a single cover to achieve both of these functions reduces the number of subsea interventions or procedures required to install, remove or maintain a subsea structure, thus providing a significant saving in both time and costs for such processes both in oil and gas and in subsea SCO2 re-injection applications. In any example of the disclosure, approximately parallel to may mean within + or-10 degrees to parallel to or within + or - 15 degrees to parallel to or within + or - 20 degrees to parallel to. In any example of the disclosure, approximately perpendicular to may mean within + or - 10 degrees to perpendicular to or within + or - 15 degrees to perpendicular to or within + or - 20 degrees to perpendicular to. While the disclosure has been described in detail in connection with only a limited number of examples, it should be readily understood that the disclosure is not limited to such disclosed examples. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of disclosure. Additionally, while various examples of the disclosure have been described, it is to be understood that aspects of the disclosure may include only some of the described examples. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A cover for a connection mechanism of a subsea structure, the cover comprising:a plurality of hydraulic couplers configured to connect with respective connectors of the connection mechanism;a hydraulic compensation mechanism fluidly connected with one or more of the plurality of hydraulic couplers; anda valve configured to be moved between a closed state in which the hydraulic compensation mechanism is fluidly isolated from the one or more of the plurality of hydraulic couplers and an open state in which the hydraulic compensation mechanism is fluidly connected to the one or more of the plurality of hydraulic couplers,wherein the hydraulic compensation mechanism is configured to compensate hydraulic pressure in the subsea structure when the plurality of hydraulic couplers are fluidly connected with the respective connectors of the connection mechanism and the valve is open.

2. A cover as claimed in claim 1, the hydraulic compensation mechanism comprising:a manifold block fluidly connected with one or more of the plurality of hydraulic couplers.

3. A cover as claimed in claim 2, the hydraulic compensation mechanism comprising:an accumulator bladder fluidly connected with the manifold block.

4. A cover as claimed in claim 3, wherein the valve is configured such that the accumulator bladder is fluidly isolated from the manifold block when the valve is closed and the accumulator bladder is fluidly connected to the manifold block when the valve is open.

5. A cover as claimed in any preceding claim, the cover comprising a further valve, wherein the hydraulic compensation mechanism is fluidly isolatedfrom the connection mechanism when at least one of the valve and the further valve are closed.

6. A cover as claimed in any preceding claim, the cover comprising a housing surrounding at least part of the hydraulic compensation mechanism and I or the conduits.

7. A cover as claimed in any preceding claim, the cover comprising an injection port for injecting hydraulic fluid into the hydraulic compensation system.

8. A cover as claimed in claim 7, further comprising an injection line connecting the injection port to the hydraulic compensation system.

9. A cover as claimed in claim 8, further comprising an injection line isolation valve in the injection line.

10. A cover as claimed in any preceding claim, the cover comprising an air purge port.

11. A cover as claimed in any preceding claim, the cover comprising a sealed conduit external of the cover and connected with the hydraulic compensation system, wherein the sealed conduit can be cut so as to balance the internal pressure of the hydraulic compensation system with an external pressure.

12. A method of installing a subsea structure, the method comprising: connecting the plurality of hydraulic couplers of a cover according to any preceding claim with the respective connectors of the connection mechanism of a subsea structure; andinstalling the subsea structure at a subsea location.

13. A method as claimed in claim 12, the method comprising:either before or after installing the subsea structure at a subsea location, opening the valve to compensate hydraulic pressure in the subsea structure.5 14. A method as claimed in claim 13, the method comprising:subsequently closing the valve so as to isolate the hydraulic compensation mechanism from the one or more of the plurality of hydraulic couplers; and / orkeeping the plurality of hydraulic couplers of the cover connected to 10 the respective connectors of the connection mechanism of thesubsea structure so as to protect the connection mechanism.

15. A method as claimed in any of claims 12 to 14, the method comprising: subsequently removing the cover from the subsea structure; and15 connecting a hydraulic connector to the connection mechanism.17

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