GB2401887A

GB2401887A - ROV deployed pressure containing closure for a subsea assembly

Info

Publication number: GB2401887A
Application number: GB0402832A
Authority: GB
Inventors: Glen Batten; David George Knowles
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-05-19
Filing date: 2004-02-09
Publication date: 2004-11-24
Also published as: GB0402832D0; GB0311380D0

Abstract

A pressure containing closure for a subsea assembly (e.g. a xmas tree cap) for sealing a flow bore of the subsea assembly is deployed by a remotely operated vehicle (ROV). The pressure containing closure comprises a plug (figure 3) to contain pressure within each individual bore, a locking mechanism 9 for locking the plug (figure 3) onto a profile of the bore, a plurality of sealing members 14, and an actuator 11 for coupling the locking mechanism 9 to an actuator frame 13. An ROV interface (1, figure 1) is provided for setting the sealing members 14 and expanding the locking mechanism 9 via the actuator frame 13.

Description

1 2401 887

ROV DEPLOYED PRESSURE CONTAINING CLOSURE FOR A SUBSEA

ASSEMBLY

The invention relates to the design, and method of installation, of a remotely installed pressure containing closure for a subsea assembly having at least one flow bore and more preferably a production bore and an annulus bore and alternatively a multi bore configuration.

Traditionally, pressure containing closures for subsea assemblies have been large heavy items which have, through necessity, been installed and retrieved by running down from surface on drill pipe. This method of installation and retrieval is costly to operators since each installation and retrieval requires a specific run of drill pipe. As Subsea Well depths become increasingly greater these costs increase significantly. Prior designs have tended to lock down the assembly to the outer hub of the assembly, which makes for a large and heavy closure design.

Therefore an object of the invention is to provide a small, lightweight closure which can be parked on a subsea assembly, prior to running, before subsequently being picked up subsea and installed by ROV. Alternatively, the closure may be run, by ROV, from surface.

Accordingly, to achieve the necessary reduction in weight and size, for deployment by ROV, this invention incorporates the lock down mechanism and the seals within the confines of the flow bore or bores.

A preferred embodiment of the invention relates to a closure for a subsea assembly with one flow bore, such as a Flowline Hub Cap Another preferred embodiment of the invention relates to a closure for a subsea assembly with production and annulus flow bores, such as a Tree Cap. This document henceforth describes said embodiment.

SUMMARY

The closure assembly comprises plugs for each flow bore which are attached to an ROV interface assembly. The closure is lifted from its park position by the ROV and lowered onto the hub of the subsea assembly. The Production bore plug is longer to assist with alignment during installation and to ensure that the closure cannot be installed incorrectly.

Each plug incorporates lockdown dogs and seals, which are biased to a retracted position to eliminate friction during installation of the plugs into the flow bores. The ROV hot stab interface is utilised to inject corrosion inhibitor into the flow bores and under the Tree Cap.

The ROV actuation interface is utilised, and each plug will lock into its flow bore and the seals will set. Forces generated by subsequent pressure in the closure flow bores will be resisted by the lock dogdown mechanism. The ROV hot stab interface is again utilised to pressure test below the plugs. Finally the ROV operated isolation valve is closed and installation is complete.

A preferred embodiment of the invention will now be described in more detail with reference to the accompanying drawings in which: FIG I shows a plan view of the closure assembly FIG 2 shows a section on A-A FIG 3 shows an enlarged detail of an individual Plug assembly with Dog type lockdown mechanism.

FIG 4 shows an enlarged detail of an individual Plug assembly with the preferred embodiment of a Snap Ring type lockdown mechanism.

FIG 5 shows a 3D visualization of a closure assembly in a preferred embodiment as a Tree Cap. I FIG 6 shows a 3D visualization of a closure assembly in a preferred embodiment as a Flowline Hub Cap.

Fig 1 highlights the positions of the ROV interfaces. The central interface 1 is the actuator for setting of the closure. This may be rotary or hydraulic. Interface 2 is the Hot Stab which is utilised for injection of corrosion inhibitor and pressure testing of the flow bores after setting of the closure. It may also be used for actuation of the setting mechanism should said mechanism be hydraulic in nature. Interface 3 is the ROV operated isolation valve which is used to isolate the flow bores after pressure testing. The grab handle 4 is used for lifting of the assembly and also for mechanically retrieving the assembly from surface should the primary actuator fail. The dummy stab 5 is usually located within the Hot Stab receptacle to keep out debris. Interface 6 is a park position for the dummy stab when the Hot Stab is in use.

Figure 2 shows a section through the centre line of the assembly. In the installed position, baseplate 7 rests upon the lower face of the hub of the subsea assembly. Two plug assemblies, typically as shown in figure 3 and figure 4, enter the production and annulus bores of the subsea assembly hub.

With reference to figure 3 (Dog type lockdown mechanism) each plug assembly comprises the following. A dog housing 8 which is suspended from baseplate 7. Located within windows in the dog housing 8 are a plurality of dogs 9 which are bias to the retracted position by a plurality of springs at each dog position. The body 10 of the plug is attached I to an actuator 1 I by shear pins 12 (figure 2). Positioned on the body 10 are dual seals 14 separated by spacer 15. The seals 14 are positioned on smaller die recesses on the body 10 so that they will not seal in the flow bore until they have been expanded by the mechanism of the ROV actuator. Suspended from the body 10 of the production bore plug is an alignment pin 16 which serves to ease installation and ensure that the assembly can only be installed in the correct position. Attached to the top of the body I O is the flow conduit 17 which serves as access into each bore for injection, test and vent purposes. Said flow conduit is sealed into the plug with a proprietary metal sealing connection and feeds through the centre ofthe actuator 11 from where it can be hard piped to the Hot Stab Receptacle 2 and ROV operated needle valve 3. The actuator 11 is suspended from the actuator frame 13 (figure 2) such that upward movement of the actuator frame 13 will expand the dogs 9 and set the seals 14. The dogs 9 expand into a specially machined profile within each flow bore which in turn resists the forces generated by pressure contained below the plug 9.

With reference to figure 4 (Snap Ring type lockdown mechanism) each plug assembly comprises the following. An upper housing 27 which is suspended from baseplate.7. A lower housing 29 is attached to the upper housing by means of a plurality of guide rods 30.

A snap ring 28 is held captive between the upper and lower housings and is supported internally by an actuator 11. The body 10 of the plug is attached to the actuator 11 by shear pins 12 (figure 2). Positioned on the body -10 are Hal seals 14 separated by spacer 15. The seals 14 are positioned on smaller die recesses on the body 10 so that they will not seal in the flow bore until they have been expanded by the mechanism of the ROV actuator.

Suspended from the body 10 ofthe production bore plug is an alignment pin 16 which serves to ease installation and ensure that the assembly can only be installed in the correct position. Attached to the top of the body 10 is the flow conduit 17 which serves as access into each bore for injection, test and vent purposes. Said flow conduit is sealed into the I plug with a proprietary metal sealing connection and feeds through the centre of the actuator 11 from where it can be hard piped to the Hot Stab Receptacle 2 and ROV operated needle valve 3. The actuator 11 is suspended from the actuator frame 13 (figure 2) such that upward movement of the actuator frame 13 will expand the snap ring 28 and set the seals 14. The snap ring 28 expands into a specially machined profile within each flow bore which in turn resists the forces generated by pressure contained below the plug.

With reference to figure 2, an ROV actuator assembly is attached to baseplate 7. The ROV actuator assembly comprises the following. A lower housing 20 and upper housing 21 are attached by a plurality of shear pins 22. A shaft 23 is held captive by a flange 24 and a split bearing ring 25. The shaft 23 is attached to the actuator frame 13 by a right hand coarse thread 26. Accordingly, right hand rotation will move the actuator frame 13 upward which will lock the closure assembly. Conversely left hand rotation will unlock the closure assembly.

A light cap 18 attaches to baseplate 7 to protect the hub from debris and this is sealed at the periphery of the subsea hub with flat elastomeric material 19.

In the event that the actuating mechanism fails to unlock the closure assembly, application of increased torque over and above nominal operating torque will shear pins 12 and allow the dogs to retract for retrieval.

In the event that the actuating mechanism becomes inoperable, a tugger line from surface may be attached to grab handle 4 and, on application of overfull, pins 22 and 12 will shear and allow the dogs to retract for retrieval. I It is to be understood that the aforementioned descriptions are illustrative only and that other means and techniques can be used without departing from the full scope of the invention as described in the claims of the invention.

Claims

1. Pressure containing closure for a subsea assembly where the lock down mechanism and seals are incorporated within the confines of the flow bore.

2. Closure as claim I where dual flow bores exist, preferably production and annulus bores in a configuration such as a Xmas Tree Cap

3. Closure as claim 1 where multi flow bores exist.

4. Closure as claimed in any preceding claim where the seals may be elastomeric or metal to metal or a combination of both.

5. Closure as claimed in any preceding claim where the seals are unset until the closure is locked down.

6. Closure as claimed in any preceding claim where facility for injection, test, vent and isolation for the flow bore is included.

7. Closure as claimed in any preceding claim where installation and retrieval of the cap may be achieved by ROV.

8. Closure as claimed in any preceding claim where retrieval from surface can be achieved.

9. Closure as claimed in any preceding claim where lock or unlock of the cap by ROV may be by mechanical or hydraulic means.