WO1998038411A2

WO1998038411A2 - Apparatus for use in drilling operations

Info

Publication number: WO1998038411A2
Application number: PCT/GB1998/000634
Authority: WO
Inventors: David George Knowles; John Milne
Original assignee: Ocre (Scotland) Limited
Priority date: 1997-02-28
Filing date: 1998-03-02
Publication date: 1998-09-03
Also published as: GB2338738A; WO1998038411A3; GB9920347D0; GB9704213D0; AU6736498A

Abstract

A method of facilitating fluid circulation may be utilised during a drilling operation in which drilling fluid is circulated downwardly through a small diameter drill support, such as coiled tubing (22), and upwardly through an annulus (44) between a lined bore wall (38) and the drill support (22). The method comprises providing a sleeve (48) between the bore wall (38) and the drill support (22) to reduce the annulus flow area to facilitate maintaining the drilling fluid flow speed in the annulus at a level sufficient to maintain entrainment of drilling cuttings. Further provided is a method of protecting a well head tree and safety valve from erosion by drilling fluid by hanging a protection sleeve above the tree (or safety valve) and sealing above and below the tree (or safety valve).

Description

APPARATUS FOR USE IN DRILLING OPERATIONS

This -invention relates to apparatus for use in drilling operations. In particular, but not exclusively, the present invention relates to apparatus for use in drilling operations utilising coil tubing or small diameter ("slimline") drillpipe.

In the oil and gas exploration and extraction industries, boreholes are drilled to gain access to hydrocarbon-bearing formations. The boreholes, which are typically several thousand metres long, are lined with steel casing and may be provided with various devices, profiles and valves. From time-to-time problems may be encountered in a section of the borehole or the area of the formation intersected by the borehole and it may become necessary to access a different area of the hydrocarbon- bearing formation. Rather than drill a new borehole from the surface, it is often possible to utilise a section of the existing borehole by sealing off the lower end of the borehole and then "side-tracking" or drilling through a portion of the existing borehole wall and drilling a new, relatively short section of bore to access the formation at a different location.

If this drilling operation is carried out using traditional drillpipe it is first necessary to "kill" the well and substantially modify or remove much of the wellhead apparatus; in offshore operations much of the subsea wellhead apparatus, notably the "tree", must be removed to accommodate the drillpipe, and then restored before other operations may commence once more. Clearly, such removal and restoration operations are expensive and time-consuming. Many of these difficulties may be avoided by utilising smaller diameter drilling supports in place of drillpipe, that is coil tubing or slimline drillpipe, which may pass through the tree .

It is among the objectives of embodiments of the present invention to provide apparatus to facilitate drilling operations using coil tubing and slimline drillpipe .

According to a first aspect of the present invention there is provided a method of facilitating fluid circulation during a drilling operation in which drilling fluid is circulated downwardly through a drill support and upwardly through an annulus between bore casing and the drill support, the method comprising: providing a sleeve between a bore casing and a drill support to reduce the annulus flow area such that drilling fluid flow speed in the annulus may be maintained at a level sufficient to maintain entrainment of the drilling cuttings.

According to another aspect of the present invention there is provided apparatus for facilitating fluid circulation during a drilling operation in which drilling fluid is circulated downwardly through a drill support and upwardly through an annulus defined between bore casing and the drill support, the apparatus comprising: a sleeve for location between a drill support and bore casing to reduce the annulus flow area such that drilling fluid flow speed may be maintained at a level sufficient to maintain the entrainment of cuttings.

These aspects of the present invention overcome a problem encountered when utilising a relatively small diameter drill support, typically coil tubing: the flow rate of drilling fluid from the surface to the drill bit is restricted by the internal diameter and mechanical limitations of the tubing, such that the flow speed of the fluid from the bit to the surface through the larger area annulus is relatively low. The slow-moving fluid may be unable to maintain the entrainment of cuttings such that the annulus becomes blocked, particularly at locations where step increases in bore diameter occur. Preferably, the sleeve comprises outer seal means for preventing upward fluid flow through an outer annulus between the sleeve and bore casing.

Preferably, the sleeve is adapted to extend through a tree of a wellhead assembly. Preferably also, the apparatus further comprises a sleeve hanger. Most preferably, the hanger is adapted for location above the tree of the wellhead assembly. Shear seal blow out preventers (BOPs) may be provided between the hanger and the tree. Conveniently, the sleeve hanger is provided on a hanger support assembly or spool which defines a fluid outlet in communication with the annulus, through which the drilling fluid and entrained cuttings may flow. If desired, supplementary fluid may be introduced below the hanger, to flow downwardly in an outer annulus between the sleeve and bore casing and to combine with primary drilling fluid, which has passed through the drill support, to increase the fluid flowrate upwardly through an inner annulus between the sleeve and the drill support. Conveniently, the supplementary fluid is introduced into the outer annulus via an existing fluid port in the tree, which, in the absence of the sleeve, normally serves as a drilling fluid outlet. Preferably also, the sleeve hanger is configured to release the sleeve and permit the sleeve to drop into the bore, clear of selected elements of the tree. Thus, in an emergency situation, the valves and other devices provided on the tree, such as BOPs, may be operated and utilised as necessary. Most preferably, the sleeve defines a shoulder or no-go dimensioned to engage a production tubing hanger which is typically provided below the tree, such that the sleeve will only drop a limited distance and may be retrieved without difficulty. Preferably also, the sleeve hanger includes one or more radially movable members for selectively supporting the sleeve. Most preferably, the supporting members are keys which, with the hanger in a first configuration, are radially supported and will engage a sleeve shoulder to support the sleeve, and with the hanger in a second configuration are unsupported, allowing the keys to be deflected outwardly by the shoulder. Support for the keys may be provided by an axially movable piston. Preferably also, the sleeve hanger and sleeve include a member for restraining the sleeve against upward movement. ^'-The member may be in the form of a snap ring on the sleeve for co-operating with radially movable keys provided on the hanger.

In certain embodiments the sleeve is adapted to extend beyond a bore safety valve, and thus protects the valve seal bore. Accordingly, it is not necessary to run-in a separate sleeve to protect the seal bore from scoring and the like.

According to another aspect of the present invention there is provided a tree saver comprising: a hanger for location above a wellhead tree; a sleeve adapted to be supported by the hanger and extend through a tree bore; and seals for location above and below the tree to isolate the tree bore .

According to another aspect of the present invention there is provided apparatus for protecting a valve assembly of a wellhead assembly during a downhole drilling operation utilising a rotating drill support member which extends through the valve assembly, the apparatus comprising: a protective sleeve for location within a wellhead assembly defining a borewall, the upper end of the sleeve being adapted to sealingly engage the borewall above the valve assembly and the lower end of the sleeve being adapted to sealingly engage the borewall below the valve assembly.

In use, the apparatus protects the valve assembly from contact with the rotating drilling support and also protects any seals provided on the valve assembly from contact with drilling fluid and cuttings carried thereby.

Preferably, the apparatus of this and the other aspects of the invention includes a sleeve hanger including anti -rotation means for engaging the wellhead assembly, such that the hanger and sleeve will not rotate in the bore with the drill support member.

In one embodiment of this aspect of the invention the sleeve is adapted to extend to or beyond a casing safety valve nipple, and thus also protect the safety valve nipple from contact with the rotating drill support and from abrasion by the upwardly flowing drilling fluid.

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a wellhead assembly including apparatus for facilitating fluid circulation during a drilling operation in accordance with an embodiment of a first aspect of the present invention; Figure 2 is a sectional view of part of the assembly of Figure 1, shown somewhat enlarged;

Figure 3 is a further enlarged cross-sectional view of the apparatus of Figure 1, including internal details and showing a running tool; Figure 4 is a sectional side view corresponding to a portion of Figure 3;

Figures 5, 6, 7 and 8 are sectional views of the apparatus of Figure 1 and illustrating the running sequence of the apparatus ;

Figure 9 is a sectional view illustrating the retrieval of the apparatus of Figure 1;

Figure 10 is a sectional view illustrating the emergency release of part of the apparatus of Figure 1; and

Figures 11 and 12 are sectional views of a tree-saver in accordance with an embodiment of a further aspect of the present invention.

Reference is first made to Figure 1 of the drawings, which is a diagrammatic representation of a wellhead assembly 20 including apparatus for facilitating fluid circulation during a drilling operation in accordance with an embodiment of a first aspect of the present invention.

The Figure illustrates a drilling operation in which a drill bit (not shown) is mounted on the lower end of a length of coiled tubing 22 which is shown being fed from a coiled tubing reel 24. The coiled tubing 22 passes down through a set of blind ram blowout preventers (BOPs) 26, a support spool 28 forming part of the apparatus of the invention, shear seal BOPs 30, a Christmas tree 32 and a production tubing hanger 34. In an offshore drilling operation the BOPs 26, 30, support spool 28 and tubing hanger 34 will normally be located on or above the sea floor. Below the production tubing hanger 34, the bore 36 extends towards a hydrocarbon-bearing formations, and is lined for most of its length with steel casing 38.

During a drilling operation, drilling fluid or "mud" is pumped through the coiled tubing 22, the mud being drawn from mud pits 40 and pumped into the tubing 22 using an appropriate cement unit 42. The drilling mud passes downwardly- _ through the tubing 22 and exits at nozzles provided in the drill bit.- The drilling mud lubricates and cools the drill bit, assists in dislodging material from the cutting face and then carries drilling cuttings and other debris away from the cutting face. The mud and entrained cuttings pass upwardly through an annulus 44 defined between the coiled tubing 22 and the casing 38 before passing through an outlet 46 in the support spool 28. The mud is then treated to remove the cuttings and other impurities before being returned to the mud pits 40, ready for re-use.

When drilling with smaller diameter drill supports, such as coiled tubing 22, the cross-sectional area of the annulus 44 is considerably larger than the internal cross- section of the coiled tubing 22. Accordingly, the upwards speed of flow of the drilling mud through the annulus 44 is relatively slow, and in some cases may not be sufficient to maintain entrainment of the cuttings, resulting in blocking of the annulus. As will be described in greater detail below, this embodiment of the present invention aims to avoid this difficulty by reducing the cross-sectional area of the annulus 44. This is achieved by locating a sleeve 48 in the bore, the upper end of which is mounted in and sealed to the support spool 28 below the mud outlet 46. Accordingly, the provision of the sleeve 48 reduces the flow area of the annulus 44, increases the speed of the return mud flow, and thus ensures entrainment of the drilling cuttings in the mud.

Reference is now also made to Figures 2, 3 and 4 of the drawings, which illustrate the support spool 28 and the upper end of the sleeve 48 in more detail. The support spool 28 is adapted to be bolted directly to the shear seal BOP 30 and has a tubular body 50 defining various fluid ports, as will be described. Towards the lower end of the spool bore 52 is a shoulder 54 which supports a sleeve hanger 56. A number of keys 58 are provided in the hanger 56 and when radially supported the keys collectively define a shoulder for supporting the sleeve upper end 60. The keys 58 are located in apertures circumferentially spaced around the hanger 56. An annular groove 64 is formed behind the apertures and accommodates an annular actuator sleeve 66. The volumes above and below the sleeve 66 are in communication with respective hydraulic fluid ports 68, 69, such that application of fluid pressure through one of the ports 68, 69 will move the actuator sleeve 66 axially to support the keys 58, as illustrated in the lower half of Figure 4, or to allow retraction of the keys 58, as illustrated in the upper half of Figure 4.

The sleeve upper end 60 is of larger external diameter than the remainder of the sleeve 48 and defines an external shoulder 70 for engaging the keys 58. Below the shoulder 70 is an annular slot 72 which accommodates a snap-ring 74 having a chamfered lower outer corner 76 which allows the snap-ring 74 to deflect and pass over the extended keys 58. However, the snap-ring 74 prevents the sleeve 48 being lifted from the hanger 56 when the keys^' 58 are extended radially inwardly. The sleeve upper end 60 also carries a spring loaded anti-rotation dog 78 for engaging an axial groove 80 in the hanger 56.

Figure 3 illustrates the running tool 82 which is used to locate the sleeve 48 in the hanger 56. The sleeve 48 engages the running tool 82 in a somewhat similar manner to the engagement between the sleeve 48 and the hanger 56, that is the running tool head 83 carries a number of radially movable keys 84 which are selectively supportable by an actuator sleeve 86. The keys 84 engage a snap-ring 88 provided internally on the sleeve upper end 60 such that the running tool 82 may be stabbed into the sleeve upper end 60 with the keys 84 in the radially extended position, as illustrated in the lower half of Figure 3. To release the running tool 82 from the sleeve 48, fluid pressure is applied through the hollow running tool support mandrel 87 to lift the actuating sleeve 86, allowing the keys 84 to move inwardly and clear the snap-ring 88.

Reference will now also be made to Figures 5 through 8 of the drawings which illustrate the running sequence of the sleeve 48. Firstly, the support spool 28 and shear seal BOPs 30 must be fitted to the existing subsea assembly, above the tree 23. The tubular sections which form the sleeve 48 are made up and run into the bore. The uppermost tubing section includes the enlarged cross- section end portion 60, and once this has been made up to the remainder of the sleeve 48, the running tool 82 is stabbed into the sleeve 48. Initially, the running tool actuating sleeve 86 is in the lower position such that the keys 84 are in the radially extended position and thus engage beneath the sleeve snap-ring 88.

The running tool 82 and sleeve 48 are then run into the support spool 28. The sleeve hanger 56 has already been positioned in the support spool 28, and the actuating sleeve 66 positioned such that the keys 58 extend into the hanger bore and will engage the sleeve shoulder 70 (Figure 6) . The sleeve 48 is then stabbed into the support spool 28, where it is locked in by the snap-ring 74. The running tool 82 and sleeve 48 are then rotated to engage the anti- rotation dog 78. The integrity of the seal between the sleeve 48 and the sleeve hanger 56 is then tested by applying fluid pressure through support spool port 90.

The running tool 82 is released from the sleeve 48 by applying pressure through the running tool support mandrel 87 to move the actuating sleeve 86 upwardly, and allow the keys to collapse inwardly. The running tool 82 may then be lifted from the upper end of the sleeve 48. The drilling apparatus and coiled tubing may then be run into the bore, through the sleeve 48, as illustrated in Figure 1.

As described above, drilling mud is pumped downwardly through the coiled tubing 22 and then passes upwardly from the drill bit through the annulus 44, including the reduced cross-sectional area annulus portion formed by the sleeve 48, to exit at the mud outlet 46 provided in the support spool 28 .

In the event that it is desired to increase the rate of flow of. drilling mud upwardly through the sleeve 48, supplementary fluid may ^" be introduced into the outer annulus 92 formed between the casing 38 and the sleeve 48. The supplementary mud is pumped using a second cement unit 94 to pump mud through an existing branch 96 in the tree 32, which, in the absence of the sleeve 48, would normally serve as the drilling mud outlet. The supplementary mud flows down the annulus 92 to the end of the sleeve 48 and then joins the primary flow of mud upwardly through the annulus 44. The resulting increase in mud flow in the annulus 44 assures entrainment of drilling cuttings upwardly to the outlet 46. After a drilling operation has been completed, the sleeve 48 may be retrieved, as illustrated in Figure 9 of the drawings, by stabbing in the running tool 82 to engage the sleeve 48, and then moving the support spool actuating sleeve 66 upwardly by application of fluid pressure through the port 69, such that the keys 58 may move radially outwardly, allowing the snap ring 74 to move upwardly past the keys 58. The sleeve 48 may then be lifted through the support spool 28.

In the event of an emergency and when, for example, it is desired to operate the shear seal BOPs 30, the sleeve 48 may be released from the support spool 28 by applying pressure through the port 69 to move the actuating sleeve 66 to allow the keys 58 to move outwardly, as illustrated in Figure 10. However, the sleeve 48 will only drop as far as the existing production tubing hanger 34, where the sleeve shoulder 70 engages a hanger no-go. Thus, once the emergency situation has ^" passed, the sleeve 48 may be retrieved without difficulty.

Reference is now made to Figures 11 and 12 of the drawings, which illustrate a tree protection sleeve 110 in accordance with an embodiment of a further aspect of the present invention. The sleeve 110 is substantially similar to the sleeve 48 described above, however the tree protection sleeve 110 is considerably shorter than the sleeve 48, only extending as far as the production tubing hanger 34, and the sleeve support spool 28 is bolted directly to the tree 32. Like the sleeve 48, the tree protection sleeve 110 is provided with an upper seal 112 for sealing engagement with the sleeve hanger 56, but also includes a lower seal 114 for sealing engagement with the wall of the production tubing hanger 34.

The tree protection sleeve 110 will tend to be provided for use in combination with small diameter support strings, such as coiled tubing 22, and in particular with rotating support strings such as slimline drillpipe, which pass through the tree 32. The primary function of the sleeve 110 is to protect the tree 32 from damage sustained by contact with the rotating string.

In an embodiment of a further aspect of the present invention, a longer sleeve (for example 700m) is provided which extends downwardly through the safety valve bore . The sleeve is provided with a seal stack which cooperates with the seal stack of the safety valve, and somewhat like the sleeve ^'protection sleeve 110 described above, protects the valve seal bore from physical damage from the drill support, and also protects the seal bore from erosion by the flow of drilling mud over the bore. Further, the provision of an anti -rotation lock prevents the sleeve from rotating with the drill support; this is in contrast to existing safety valve nipple protection sleeves which tend to rotate with the drill pipe, resulting in wear and damage to the nipple.

It will be clear to those of skill in the art that the above-described embodiments are merely exemplary of the various aspects of the present invention, and that modifications and improvements may be made thereto without departing from the scope of the invention.

Claims

1. A method of facilitating fluid circulation during a drilling operation in which drilling fluid is circulated downwardly through a drill support and upwardly through an annulus between a lined bore wall and the drill support, the method comprising: providing a sleeve between a bore wall and a drill support to reduce the annulus flow area to facilitate maintaining the drilling fluid flow speed in the annulus at a level sufficient to maintain entrainment of drilling cuttings.

2. The method of claim 1, further comprising providing a small diameter drill support.

3. The method of claim 2, wherein the drill support is coil tubing.

4. The method of any of the preceding claims, further comprising sealing the sleeve to the bore wall to preventing upward fluid flow through an outer annulus between the sleeve and bore wall.

5. The method of any of the preceding claims, wherein the sleeve extends through a tree of a wellhead assembly.

6. The method of any of the preceding claims, further comprising supporting the sleeve on a sleeve hanger located above the tree of a wellhead assembly.

7. The method of claim 6, further comprising introducing supplementary fluid below the hanger, to flow downwardly in an outer annulus between the sleeve and bore wall and to combine with primary drilling fluid, which has passed through the drill support, to increase the fluid flowrate upwardly through an inner annulus between the sleeve and the drill support .

8. The method of claim 7, wherein the supplementary fluid is introduced into the outer annulus via an existing fluid port in the tree.

9. The method of any of the preceding claims, further comprising providing a sleeve which extends beyond a bore safety valve to protect the safety valve seal bore.

10. Apparatus for facilitating fluid circulation during a drilling operation in which drilling fluid is circulated downwardly through a drill support and upwardly through an annulus defined between bore casing and the drill support, the apparatus comprising: a sleeve for location between a drill support and bore casing to reduce the annulus flow area to facilitate maintaining drilling fluid flow speed in the annulus at a level sufficient to maintain entrainment of cuttings.

11. The apparatus of claim 10, wherein the sleeve comprises outer seal means for engaging a bore wall and preventing- .upward fluid flow through an outer annulus between the sleeve and bore casing.

12. The apparatus of claim 10 or 11, wherein the sleeve is adapted to extend through a tree of a wellhead assembly.

13. The apparatus of claim 10, 11 or 12, wherein the apparatus further comprises a sleeve hanger.

14. The apparatus of claim 13 , wherein the hanger is adapted for location above the tree of a wellhead assembly.

15. The apparatus of claim 14, wherein shear seal blow out preventers (BOPs) are provided below the hanger.

16. The apparatus of claims 13, 14 or 15, further comprising a hanger support assembly defining a fluid outlet for communication with the annulus.

17. The apparatus of any of claims 13 to 16, wherein the sleeve hanger comprises means for selectively releasing the sleeve to permit the sleeve to drop into the bore.

18. The apparatus of claim 17, wherein the sleeve defines a shoulder or no-go dimensioned to engage a production tubing hanger.

19. The apparatus of claim 17 or 18, wherein the sleeve hanger includes one or more radially movable supporting members fo _ selectively supporting the sleeve.

20. The apparatus of claim 19, wherein the supporting members are keys which, with the hanger in a first configuration, are radially supported and will engage a sleeve shoulder to support the sleeve and with the hanger in a second configuration are unsupported, allowing the keys to be deflected outwardly by the shoulder.

21. The apparatus of claim 20, further comprising an axially movable piston for selectively supporting the keys.

22. The apparatus of any of claims 13 to 21, wherein the at least one of the sleeve hanger and sleeve include a member for restraining the sleeve against upward movement .

23. The apparatus of claim 22, wherein the member for restraining the sleeve against upward movement is a snap ring on the sleeve for co-operating with radially movable keys provided on the hanger.

24. A method of drilling a bore comprising the steps: locating a drill support in a bore; circulating drilling fluid downwardly through the drill support and then upwardly through an annulus between the wall of the bore and the drill support; and providing a sleeve between the bore wall and the drill support to reduce the annulus flow area to facilitate maintaining. the drilling fluid flow speed in the annulus at a level sufficient to maintain entrainment of drilling cuttings.

25. Tree saver apparatus comprising: a hanger for location above a wellhead tree; a sleeve adapted to be supported by the hanger and extend through a tree bore; and seals for location above and below the tree to isolate the tree bore from drilling fluid passing through the tree bore .

26. A method of protecting well head tree from erosion by drilling fluid, the method comprising: providing a hanger above a wellhead tree defining a through bore forming part of a wellbore; supporting a sleeve on the hanger, the sleeve extending through the tree bore; and sealing the sleeve in the wellbore above and below the tree to isolate the tree bore from drilling fluid passing therethrough.

27. Apparatus for protecting a valve assembly of a wellhead assembly during a downhole drilling operation utilising a rotating drill support member which extends through the valve assembly, the apparatus comprising: a protective sleeve for location within a wellhead assembly defining a part of a borewall, the upper end of the sleeve being adapted to sealingly engage the borewall above the valve assembly and the lower end of the sleeve being adapted to sealingly engage the borewall below the valve assembly. -.

28. The apparatus of claim 25 or 27, further comprising a sleeve hanger including anti-rotation means for engaging a wellhead assembly, such that the hanger and sleeve will not rotate in the bore with the drill support member.

29. The apparatus of claim 25, 27 or 28, wherein the sleeve is adapted to extend to or beyond a casing safety valve nipple.