WO2010065993A1

WO2010065993A1 - Removal/fitting of subsea sealing plug(s)

Info

Publication number: WO2010065993A1
Application number: PCT/AU2009/001592
Authority: WO
Inventors: Robert William Jones; Brett Mitchell Walker; Alexander Jeffrey Burns
Original assignee: Well Ops Sea Pty Ltd
Priority date: 2008-12-08
Filing date: 2009-12-08
Publication date: 2010-06-17

Abstract

A method, system and device (1) for releasing a plug (12a,12b) from a subsea wellhead (24) or subsea drill string (casing 25), the system including a tool support structure (2,3), a tool head member including a plug engaging member (11) to engage a complimentary mating feature (30a,30b) of the plug to be released, a drive mechanism (15,16) to rotate the plug engaging member in a required direction, and a plug lifting mechanism 4'arranged such that, in use, a lifting reaction force is directed downwards to the seabed to enable the released plug to be withdrawn upwardly from the respective wellhead or casing. The tool support structure can be operated or lowered from a sea going vessel, a platform or a rig.

Description

REMOVAL/FITTING OF SUBSEA SEALING PLUG(Sl TECHNICAL FIELD

The present invention relates to tightening and releasing of sealing plugs that are present in the wellheads and/or casing strings of oil and gas wells. BACKGROUND

To prevent oil and gas leaking from oil or gas wells, at least two plugs are fitted into a conductor casing or wellhead to form an oil/gas tight seal as the required barrier.

One type of sealing plug, amongst others, has an externally threaded feature on it which matches an internally threaded feature of the conductor casing.

From time-to-time, such plugs require removal to allow various types of maintenance and other work to be performed on the oil/gas well.

Presently, the industry standard method of removing the plugs is to use a drilling rig or vessel whereby a tool, which has an end adapted to fit into a mating feature included on the plug, is fastened to one end of a length of suitable tubing.

This tool assembly is then partially lowered into the water from the drilling rig or vessel and a further additional length of tubing is fastened to the uppermost end of the tube that still remains on board the drilling rig or vessel. The tool assembly continues being further lowered into the water and, at suitable intervals, additional lengths of tubing are fastened, one to another, until the lowermost end of a tool assembly is long enough for the end adapter to be able to engage with the threaded plug in the casing or wellhead.

The remaining tube on board the drilling rig or vessel is then rotated in the required direction to rotatively drive the sealing plug, thereby causing the relative screw threads of the plug and wellhead to be completely disengaged.

However, due to the necessary design of the seal of the plug and the fact that the plug may have been under water for a considerable time, removing the sealed portion of the plug from the casing or wellhead requires a considerable vertical separating force. This vertical force is provided on a drilling rig or vessel by using a crane line attached either directly to the uppermost tube of the tool assembly and then pulling upwards, or connecting the crane line directly to the plug and pulling upwards. Either operation is impractical on a vessel, especially where movement of the drilling rig or vessel can cause locating or lifting problems.

Furthermore, in certain applications there is a need to retrieve an internal tree cap (ITC) or tubing hanger (TH) from the 'Christmas tree' (XT) of a subsea wellhead. A device known as a tubing hanger retrieval tool (THRET) is presently used to retrieve the ITC and TH from the subsea tree. A THRET is designed to be connected to the end of Drill string via a 4.5' IF thread and has two degrees of freedom, up/down, and clockwise/anti-clockwise rotation. In operation, the drill string will lower the THRET subsea into the top of the XT from the surface until the THRET bottoms out on either the ITC or TH. The THRET has a key on it that aligns into the ITC or TH. The drill string will then rotate the THRET via the use of drive motor at the surface, commonly referred to as a top drive, such that the mechanics of the THRET force a split ring to expand and engage into the ITC or TH. It typically takes a number of complete revolutions (e.g. 4.5 complete turns) for the split ring to fully engage. The top drive will pull up on the drill sting and THRET to pull the ITC or TH out and recover it to the vessel at the surface. As may be appreciated by the reader, such procedures as described above are both time-consuming and expensive due to the necessity of requiring a sophisticated drilling rig or vessel and associated equipment. Also, there can be practical problems in trying to locate and connect to the plug or XT at the top of the casing and try to lift the plug or XT upwards from the drilling rig or vessel often several hundreds of metres on the surface above.

It has been found desirable to alleviate these problems. SUMMARY OF THE INVENTION With the aforementioned in mind, one form of the present invention provides a system for releasing a plug from a wellhead or drill string casing, the system including a tool support structure, a tool head member including a plug engaging member to engage a complimentary mating feature of the plug to be released, a drive mechanism to rotate the plug engaging member in a required direction, and a plug lifting mechanism arranged such that, in use, a lifting reaction force is directed downwards to the seabed to enable the released plug to be withdrawn upwardly from the respective wellhead or casing. Preferred features of the present invention include; A counting device to count the number of revolutions to release the plug, such as a counting device to count the number of revolutions of the plug once the engaging member is engaged in it.

The device or system may utilise a pneumatic or hydraulic drive arrangement to rotate the tool head and thereby rotate and release the plug. An electric drive mechanism may be employed as an alternative. A choice of interchangeable engaging members to suit different sizes and types of sealing plugs.

The tool support structure may locate and/or engage on at least one guide section of the wellhead or casing.

Another aspect of the present invention provides a device for releasing a plug from a wellhead or drill string casing, the device including a drive mechanism to releasably engage with and rotate the plug engaging member in a required direction, a plug lifting mechanism arranged such that, in use, a lifting reaction force of the lifting mechanism is directed downwards to the seabed to enable the released plug, which is releasably retained by a retaining means, and the plug withdrawn upwardly from the respective wellhead or casing.

The device or system may be remotely operated from a sea surface, avoiding the need for direct rotational drive from the surface. Drive connection can be by umbilical, such as hydraulic and/or pneumatic and/or electric operation. Thus, positioning of the device onto the wellhead or other equipment has less problems than trying to connect several lengths of sectional drive together as the device is lowered into the water and the vessel or rig is moving due to wave, tidal and/or current movements. Essentially, the device can include one or more rams or jacks, an end of which extend(s) upwards and the other end of which pushes down, thereby to effect a lifting force to a releasably retained plug.

Whilst the present specification refers to well plugs, other removable devices, such as valves are ensilaged to be removed and/or fitted falling within the scope of the present invention.

A further form of the present invention provides a method of releasing a plug from a wellhead or drill string casing, including; a) Lowering and locating a tool support structure to a subsea wellhead or drill string casing; b) Connecting a plug engaging member to a plug to be released c) Rotating the engaging member engaged with the plug until the plug is released; and d) Applying a lifting force to the released plug by extending one or more rams with the lift force reacted through the support structure.

The method may include rotating the plug engaging member mechanically, hydraulically, pneumatically or electrically. The method may include counting a number of revolutions of the engaging member or plug.

The device or system may be operated, and the plug may be released, by remote operation or control from the surface without the need for a drilling rig or drill ship. Lifting force for removing the plug may be applied by reacting a downward force, such as pushing on the seabed, wellhead and/or Christmas tree apparatus.

It will be appreciated that the system and/or method may be employed to insert/tighten a plug. For example, the support structure may be located on a subsea wellhead or drill string casing, a plug mated with the plug engaging member, and the engaging member rotated whilst at least one ram is retracted. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a cross-sectional diagram of an embodiment of the present invention shown deployed in the water above a wellhead ready to be lowered upon it. Figure 2 is a plan view of the embodiment in figure 1 .

Figure 3 shows the same embodiment located on the guide pillars of an oil well with the tool head member located and connected to a plug.

Figure 4 shows the end adapter connected to the sealing plug and the jacks have been operated to extract the sealing plug. PARTICULAR DESCRIPTION

According to one or more preferred embodiments of the present invention, assembly of the system 1 can be conducted as follows: Locating legs 2 are fastened to the frame 3. At least one hydraulic jack, ram or cylinder 4 is attached via a retaining nut 5a at one end thereof to the frame and the other end(s) 5 thereof attached to a top plate 6. Attached also to the top plate is a sleeve 7 held in place by bolts 8. Within the sleeve 7 is a shaft 9 with its lowermost end 10 connected to an end adapter (engaging member) 1 1 . Different end adapters 1 1 are required for different makes/types/styles of plug 12. The hydraulic jacks, rams or cylinders are driven by hydraulic pressure via a supply 21

Bearings 13 in the sleeve allow rotation of the shaft 9 and also a thrust nut 14 provides a thrust bearing face. The shaft 9 is connected to a gearbox 15 and the gearbox is connected to hydraulic motor 16. The gearbox is connected to the sleeve 7.

The sleeve 7 locates within the body and is able to slide vertically but is restricted from turning by means of keyways 17.

An incremental/decremental counter 18 is provided to count revolutions of the shaft once the end adapter has engaged the plug and the shaft is rotated to release the plug.

With the hydraulic jacks locked in place, the apparatus is lowered via an eyebolt 19 from the vessel to be just above the wellhead. A diver or ROV manoeuvres the assembly onto the guide pillars. The end adapter (engaging member) is engaged with the upper plug.

Additional hydraulic equipment may be incorporated into the system to allow specific makes of plug 12a to be engaged and/or rotated.

The end plug 12a is now rotated the required number of times by the hydraulic motor which is connected to the gearbox and shaft. The hydraulic motor is driven by hydraulic pressure through supply 20a and return 20b lines. The counter indicates the number of turns made and the operator then closes the hydraulic motor control valve when the required number of turns is reached.

The outer sleeve 22 may include a locating means 23 to aid locating the adaptor with the plug. The hydraulic jack(s) now operate to lift the plug 12a clear of the conductor casing by reacting the downwards force applied against the wellhead/seabed. Thus, removal of the plug(s) is achieved without requiring the need for direct rotational drive from the surface. The lower plug 12b is removed by repeating the above operation. However, it may not be necessary to lift the whole apparatus back onto the vessel, as a diver or ROV can remove the first plug from the end adapter with the apparatus lifted just clear of the guide pillars. The wellhead 24 includes a hydrocarbon conductor tube 25 housing the upper plug 12a and lower plug 12b. The locating legs 2 slide over the guide pillars 26. The locating legs 2 can include locating guides 2a such as flared lower ends as shown.

Figure 2 shows a plan view of the system. The lifting eyebolt 19 is shown in the centre. Four locating legs 2 are shown. The frame 3 connects the locating legs 2 to the outer sleeve 22 and jacks 4.

Figure 4 shows the upper plug 12a undone and lifted up by extension of the jacks, rams or cylinders. This is achieved by hydraulic pressure. Other drive sources may be used, such as pneumatic pressure via suitable rams or electrical drive.

Figure 3 shows the top drive device located onto the wellhead with the adaptor engaged with the upper plug. The locating legs are located over the guide pillars and the outer sleeve is located over the hydrocarbon conductor tube. The hydraulic motor rotates the adaptor a requisite number of turns until the plug is released. The hydraulic jacks, rams or cylinders can lift the plug during rotation or after rotation. Once undone, the plug can then be lifted away by the device. The lower plug can be undone in similar fashion.

Further embodiments of the present invention are herein described as a "subsea top drive" (SSTD) and are able to achieve all the abovementioned THRET functions without the need for or use of a drill string or surface top drive and can be deployed from a work class vessel. The SSTD is equipped with a variable release multi balanced connect (VR-MBC) which enables all of the hydraulic controls to be connected via an umbilical that will release under a preset tension such that in the event of the vessel at the surface moving away (drive off or drift off), the VR-MBC can released. In the event of other drive mechanisms, such as pneumatic, electric or mechanically operated remotely from the surface, a similar quick release mechanism is envisaged As shown in the accompanying figures, particular features of the SSTD include a telescopic pipe/sleeve which contains both the tubing hanger retrieval tool (THRET) and the hydraulic drive that rotates it.

Up and down moment is achieve via at least one hydraulic piston (multiple pistons are preferred - such as four pistons) that extend and contract the telescopic sleeve. The pistons have a combined upwards force of 160 tonnes at 5000psi. The bottom of the hydraulic pistons are flange mounted to a 50mm thick plate that lands directly onto the top of the XT such that the pushing force is transmitted directly into the XT body. The top of the hydraulic pistons are connected to 100mm thick plate that is attached (welded in the present example though other forms of attachment are envisaged) to the upper inner telescopic sleeve. The upper telescopic sleeve, which fits inside the internal diameter (ID) of the lower telescopic pipe contains the hydraulic drive that drives the THRET.

This hydraulic drive for the THRET is contained within the inner sleeve via a 120mm think flange that attaches (e.g. bolts) to the bottom of the inner sleeve. The drive flange has a large hole drilled through its centre allowing the drive shaft to pass through. Bronze plain bearings are press fitted into the flange to allow the heavily loaded drive shaft to rotate without galling. The Drive shaft has a thread on the end to mimic the connection of the drill string. The THRET is torqued onto the drive shaft (such as with 20,000ft/lbs (27,000Nm)), which is significantly more than what the drive can generate at 10,000Nm so the drive shaft to THRET connection will not come loose during operation. The drive shaft has a shoulder above the thread that lands on the bottom side of the drive flange. On the top side of the drive flange the drive shaft has a large stub 'ACME' thread machined around it that a large drive nut threads onto and axially restrains the drive shaft to the drive flange. The drive nut is fastened to the drive shaft via multiple bolts that act in shear to prevent the drive nut from undoing from the drive shaft. Above the drive nut the drive shaft is splined to suit a planetary gearbox which is driven by a hydraulic motor. The combination of the planetary gearbox and hydraulic motor is what was previously referred to as the "Drive". The Drive is not directly axially restrained to the drive shaft, but merely rests on the drive shaft and transmits torque through the spline. The Drive is axially and angularly restrained via a gearbox adaptor that bolts to the underside of the gearbox and loosely fits inside the inner sleave and is pinned into the Inner sleeve via multiple pins. The gearbox adaptor mating holes for the pins have a diametrical clearance such that the Drive is not fixed to the inner sleave but can move as one with the drive shaft and THRET within the telescopic pipes. This loose tolerance combined with other specified loose tolerances within the telescopic pipes and drive system allows the THRET to move both laterally and at an angle from the vertical to mimic the forgiveness of a long slender drill string. The pins provide both axial restraint for the gearbox and hydraulic motor but more importantly resist the torque generated and transfers the torque into the inner sleeve. The sleeve is keyed to the outer sleeve via two keys at the top of the outer sleeve. The torque is then transmitted from the outer sleeve to the guide post funnels and into the guide posts on the XT.

The SSTD has rotation indicator that is geared to the drive shaft such that the drive shaft rotates at a speed greater than that of the drive/THRET, such as four times faster, (though faster or slower speeds are possible and speeds can be varied) and can easily be seen by a remotely operated vehicle (ROV) on the top of the SSTD.

The SSTD of the present invention is relatively light in comparison to its pulling capacity, torque and versatility. For example, applications of the SSTD can weigh as little as 6.5 tonnes. It is versatile as it can be easily changed to adapt different tooling to it, such as it can also be fitted with a tubing hanger running tool and/or other tooling that would conventionally be fitting to the end of a drill string. Torque capacity can be easily increased by simply changing the planetary gearbox out for a larger one and the number and/or size of the hydraulic pistons can be increased to increase the lifting/pulling force.

Claims

CLAIMS:

1. A system for releasing a plug from a wellhead or drill string casing, the system including a tool support structure, a tool head member including a plug engaging member to engage a complimentary mating feature of the plug to be released, a drive mechanism to rotate the plug engaging member in a required direction, and a plug lifting mechanism arranged such that, in use, a lifting reaction force is directed downwards to the seabed to enable the released plug to be withdrawn upwardly from the respective wellhead or casing.

2. A system according to claim 1 , wherein the drive mechanism is hydraulically, pneumatically or electrically operated.

3. A system according to claim 1 or 2, including a counting device to count the number of revolutions to release the plug.

4. A system according to any one of the preceding claims, wherein the plug engaging member is interchangeable from a selection of interchangeable engaging members to suit different sizes and/or types of plugs.

5. A system according to any one of the preceding claims, wherein the tool support structure is arranged to locate and/or engage on at least one guide section of the wellhead or casing.

6. A system according to any one of the preceding claims, wherein the tool support structure includes at least one hydraulic or pneumatic ram for raising the plug engaging member.

7. A system according to any one of the preceding claims, wherein the tool head member includes a plug retaining device.

8. A system according to claim 7, wherein the plug engaging member releasably retains the plug during lifting.

9. A method of releasing a plug from a wellhead or drill string casing, including; a) Lowering and locating a tool support structure to a subsea wellhead or drill string casing; b) Connecting a plug engaging member to a plug to be released; c) Rotating the engaging member engaged with the plug until the plug is released; and d) Applying a lifting force to the released plug by extending one or more rams with the lift force reacted through the support structure.

10. A method according to claim 9, wherein rotation of the engaging member is effected hydraulically, pneumatically or electrically.

1 1 . A method according to claim 9 or 10, including counting a number of revolutions of the engaging member or plug.

12. A method according to any one of claims 9 to 1 1 , wherein the plug is released or applied by remote control from the surface.

13. A method according to any one of claims 9 to 12, wherein the plug is lifted by reacting a lifting force against the seabed, wellhead and/or Christmas tree apparatus.

14. A method according to claim 13 wherein the lifting force is applied by one or more jacks, rams or cylinders.

15. A method according to claim 14, wherein the one or more jacks, rams or cylinders is/are driven by hydraulic or pneumatic pressure.

16. A method according to any one of claims 9 to 15, wherein the tool support structure is lowered from a sea going vessel, a platform or a rig.

17. A device for releasing a plug from a wellhead or drill string casing, the device including a drive mechanism to releasably engage with and rotate the plug engaging member in a required direction, a plug lifting mechanism arranged such that, in use, a lifting reaction force of the lifting mechanism is directed downwards to the seabed to enable the released plug, which is releasably retained by a retaining means, and the plug withdrawn upwardly from the respective wellhead or casing.

18. A device according to claim 17 used in a system according to any one of claims 1 to 8 or in a method according to any one of claims 9 to 16.