GB2330160A

GB2330160A - Well cap

Info

Publication number: GB2330160A
Application number: GB9821739A
Authority: GB
Inventors: Bilderbeek B H Van; Mark Boyd; Michael Angus Robertson
Original assignee: Plexus Ocean Systems Ltd
Current assignee: Plexus Ocean Systems Ltd
Priority date: 1997-10-08
Filing date: 1998-10-07
Publication date: 1999-04-14
Also published as: GB9721242D0; GB9821739D0

Abstract

A temporary abandonment cap 26 for an oil well has a through bore 32 through which tools can be passed down the well while the cap is still in place, to protect the tieback components in the well. The bore also assists in centralising tie back tools when other casings are to be added to the well and/or when the cap is to be removed. The cap is in the form of a sleeve 30 with seals 60,62 either side of the opening of an annulus 20 between two concentric well casings 14,16, so that when the cap is in place, it seals of that annulus. The sleeve is also long enough to protect tieback threads and tieback seal areas on the casings. The sleeve makes a positive engagement with both the casings, so that it is retained in place.

Description

WELL CAP This invention relates to a cap for temporarily sealing a well, such as an oil or gas well, so as to leave the well in a sealed state and so that it can be re-entered at a later date. The cap can for example engage with a wellhead or a mudline fitting.

Usually, but not always, the cap will be fitted subsea.

The facility to re-enter the well at a later date is critical for wells such as, for example, pre-drilled platform wells and high cost/high production wells. To enable the well to be sealed in a way which will allow later re-entry, it is necessary to protect tieback threads, seal areas, and to contain any bore pressures which may occur during the period between drilling and tieback.

It is well known to provide a temporary abandonment cap for a well which simply caps the well casings to prevent foreign matter from obstructing or damaging the tie back seal areas or the tie back threads. Such caps in some cases are also able to seal any bore pressures arising within the hanger. However such caps require removal prior to any engagement of any tie back connector.

It is also known to provide a so called dual temporary abandonment cap where one part of the cap provides a seal against annulus pressure below the intermediate casing tie back profile, and a second cap protects the actual tie back connection areas. When the well is to be reentered, the first part of the cap is removed to allow the tie back connections to be made, prior to the removal of the first part of the cap.

According to the present invention, there is provided a method of temporarily sealing an annulus between casings of different diameters in a well, the method comprising the steps of installing in the well a cap comprising a hollow sleeve with a first external seal adapted to seal against the internal bore of the smaller diameter casing and a second external seal adapted to seal against the internal bore of the larger diameter casing and an open port through the sleeve wall, locking the sleeve to the casings to prevent relative axial movement between the sleeve and the casings, and closing the open port.

The invention also provides a cap for temporarily sealing an annulus between casings of different diameters in a well, the cap comprising a hollow sleeve with a first external seal adapted to seal against the internal bore of the smaller diameter casing and a second external seal adapted to seal against the internal bore of the larger diameter casing, means for locking the sleeve to the casings to prevent relative axial movement between the sleeve and the casings, a port extending through the sleeve wall between the seals, and means for opening and closing the port while the cap is in place in a well.

Through the use of a hollow sleeve, it is possible to protect the tie back seal areas and tie back threads, and to seal against annulus pressure, whilst leaving an axial passage through the centre of the production casing bore.

This axial passage facilitates subsequent tie back operations, as the tie back tool can be provided with a guidance string which projects in front of the tie back threads. The guidance string then extends through the hollow sleeve when tie back is being effected, to centralise the tie back tool and casing threads.

Furthermore, the weight of the guidance string can be effective in correcting any axial misalignment between the casing and the tie back tool, particularly as this weight acts directly in the area where the threads are to be engaged.

Preferably the sleeve is locked to both the smaller diameter and the larger diameter casings. This ensures that the sleeve stays in place and provides the necessary seal, even if there is some movement between the two casings, perhaps as a result of pressure below the cap, or as a result of ground movement.

The sleeve may include a pressure relief passage through the sleeve which passage is normally closed to provide an effective continuous sleeve wall, but which may be opened to relieve pressure built up in the annulus.

The means for locking the sleeve to the larger diameter casing may be provided on a cuff which has limited axial freedom of movement on the sleeve. The cuff may be initially latched to the sleeve in one end position, in which position the locking means is not actuated, and may be unlatched by the action of positioning the cap in the well, whereupon the cuff moves to a second position in which the locking means are automatically actuated.

The sleeve may be provided with a ratchet type threaded ring for engagement with threads in the wall of the smaller diameter casing, to lock the sleeve to the smaller diameter casing.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a cross section through part of an oil well in which is installed a temporary abandonment cap in accordance with the invention; Figure 2 shows the cap of Figure 1 prior to final installation in a drill string; and Figure 3 is a view similar to Figure 2, but showing a handling tool engaged in the cap.

Figure 1 shows a well comprising a conductor 10, a surface casing 12, an intermediate casing 14, and a production casing 16. The casings are supported on one another on hangers, in the conventional way.

It will be seen, particularly from Figure 2, that the production casing 16 stops at a point 18, and an annulus 20 exists between the intermediate casing 14 and the production casing 16, this annulus being open in the region of the top of the production casing, at 18.

The internal bore of the production casing 16 has two sets of threads. One set of threads 22 is used to tie back the production casing to a production rig, and the other set of threads 24 is used to secure a temporary abandonment cap generally designated 26 to the casing.

The intermediate casing inner surface has annular grooves 28 which, in use, will cooperate with locking dogs on the cap 26.

The cap 26 comprises a main body 30 which is in the form of a sleeve and has a through-bore 32. This bore is open at the top and the bottom of the cap and allows tools to be passed through the cap 26. The cap has a continuous cylindrical wall, apart from the presence of a pressure relief port 34 (of which there may be one, or there may be a number spaced around the circumference of the cap).

Within a counterbored section 36 of the cap there is an internal sleeve 38 which is rotatable within the main body 30, on threads 40 so that rotation of the internal sleeve 38 causes the sleeve to rise and fall in the counterbored section 36, between the position shown where the pressure relief opening 34 is open, and an opposite end position (shown in Figure 2) in which the sleeve 38 blocks the opening 34 and makes a seal on either side of the opening through O-ring seals 40. A retainer ring 52 closes the counterbored section 36 of the body and retains the internal sleeve 38.

A J-type connector 42 allows a running tool or handling tool to be connected to the sleeve 38, and when the running tool is thus connected and the sleeve 38 is in its lowermost position, the running tool connected to the connector 42 can be used to run the cap into the bore.

When the cap is ready for insertion into a bore, and before it has been so inserted, a cuff 44, which is axially movable on the body 30, is held in one end position by engagement between a lip 46 on the cuff and a corresponding lip 48 formed in a latch 50 which is fixed to the body (see Figure 2). The latch 50 is spring mounted so that under normal, unrestrained conditions, the latch ring 50 is biased radially outwardly and engages the lip 46.

When the cap is prepared and ready to be used, it takes up the position shown in Figure 2, with the cuff 44 latched in position on the body 30. When the cap is run into the well, it passes down the bore of the intermediate casing 14 without interruption. However, when the lower part 32 of body 30 enters the production casing 16, a number of things happen: The latch ring 50 is depressed radially inwardly by contact with the top tapering portion 18 of the production casing 16. The latch ring then releases the cuff 44.

The cuff 44 comes into contact with the top edge 18 of the production casing and is held against further downward axial movement by this abutment.

A ratchet thread ring 54 engages with the internal threads 24 in the production casing 16. The cuff 44 is provided with circumferentially spaced locking dogs 56. Initially these locking dogs are located in an inward position (Figures 2 and 3) where they do not extend beyond the cylindrical periphery of the cap 26.

However when the cuff is moved axially after having been released from the latch ring 50, a back face of the dogs 56 rides on a cam surface 58 onto a larger diameter external surface portion of the body 30, and this causes the dogs 56 to be urged outwards into a position where they come into engagement with and lock in the annular grooves 28 in the intermediate casing 14 (Figure 1). At the same time, a top edge of the cuff 44 traps a seal ring 60 between the body 30 and the internal wall of the intermediate casing 14, to provide a seal.

In order to run the cap 26 into the bore, a handling tool 70 extends into the cap and engages, through radially outwardly directed pins 72, with the connector 42. The lower end of the tool 70 has a guidance pin 74 which leads the tool into a central position within the cap.

By rotating the tool 70, the sleeve 38 is run down to a position where it closes the port 36.

As the cap is run in, the threaded ring 54 at the lower end of the cap contracts and rides over the threads 24 until a point is reached at which the running tool cannot drive the cap any further merely be axial pressure. At this point, the running tool begins to rotate the cap and the threads on the ring 54 mate with the threads 24 to draw the cap down into the bore, and this final tightening of the cap will result in a compression of the seal 60 between the cuff 44 and an outwardly directed lip at the top of the body 30.

Finally, when the lower part of the body 30 is received in the production casing 16, O-ring seals 62 make a seal with the internal surface of the casing 16. Thus the annulus 20 between the seals 60 and 62 (provided the pressure relief valve 34 is closed by the internal sleeve 38) . Any pressure which arises in the annulus 20 cannot therefore escape unless the sleeve 38 is raised to open the pressure relief port 34 or the cap is removed entirely.

Prior to fitting of the cap, the internal bore of the production casing is sealed by a conventional bore seal which may for example be a cemented seal or some other type of removable bore seal. If cement is used, the bore will be reopened by drilling out the cement block.

Removal of the temporary abandonment cap 26 is the reverse of the installation procedure. A handling tool 70 is engaged with the connector 42 and is initially rotated to raise the sleeve 38 and to allow any build up of pressure below the cap to escape under controlled conditions. Further rotation starts unscrewing the threads 54, 24. Once the body 30 has been lifted enough to allow the dogs 56 to fall below the cam surface 58, they will come out of engagement with the grooves 28 in the intermediate casing, and provided that the threads 24, 54 are also out of engagement, the cap can be lifted out of the bore, leaving the tie back thread 22 ready to accept a tie back connection.

When another casing is to be tied back to the intermediate casing 14, for example to the threads 76, the casing is introduced into the well on the end of a running tool which will have a guidance pin or guidance string similar to the pin 74 used on the handling tool which installs the cap. This string first of all centralises the new casing in the existing casing, and also the weight of the guidance string assists to correct any misalignment between the axis of the new casing and the axis of the existing casing, before the threads of the new casing and the existing casing are engaged. The cap described here allows not only effective capping of a well, but most importantly makes it easy to reopen the well at a later time.

Claims

Claims 1. A method of temporarily sealing an annulus between casings of different diameters in a well, the method comprising the steps of installing in the well a cap comprising a hollow sleeve with a first external seal adapted to seal against the internal bore of the smaller diameter casing and a second external seal adapted to seal against the internal bore of the larger diameter casing and an open port through the sleeve wall, locking the sleeve to the casings to prevent relative axial movement between the sleeve and the casings, and closing the open port.
2. A cap for temporarily sealing an annulus between casings of different diameters in a well, the cap comprising a hollow sleeve with a first external seal adapted to seal against the internal bore of the smaller diameter casing and a second external seal adapted to seal against the internal bore of the larger diameter casing, means for locking the sleeve to the casings to prevent relative axial movement between the sleeve and the casings, a port extending through the sleeve wall between the seals, and means for opening and closing the port while the cap is in place in a well.
3. A cap as claimed in Claim 2, wherein the sleeve is locked to both the larger diameter casing and to the smaller diameter casing.
4. A cap as claimed in Claim 2 or Claim 3, wherein the means for locking the sleeve to the larger diameter casing is provided on a cuff which has limited axial freedom of movement on the sleeve.
5. A cap as claimed in Claim 4, wherein the cuff is adapted to be initially latched to the sleeve in one end position, in which position the locking means is not actuated, and to be unlatched by the action of positioning the cap in the well, whereupon the cuff moves to a second position in which the locking means are automatically actuated.
6. A cap as claimed in any one of Claims 2 to 5, wherein the sleeve is provided with a ratchet type threaded ring for engagement with threads in the wall of the smaller diameter casing, to lock the sleeve to the smaller diameter casing.
7. A cap as claimed in any one of Claims 2 to 6, wherein the port is opened and closed by a screw-threaded sleeve which can be rotated on its thread to obscure or to reveal the port.
8. A cap for temporarily sealing an annulus in an oil well, the cap being substantially as herein described with reference to the accompanying drawings.