EP0391541A1 - Wear bushing retrieval tool - Google Patents

Abstract

A tool for use in retrieving a wear bushing from a wellhead assembly comprising a generally annular body portion (20) which can be located around a length of casing, means (16) for supporting the body portion relative to a length of casing so that it can be lowered into a wellhead with said casing, latching means (24) carried by body portion, said latching means being so shaped and arranged that it can engage a correspondingly shaped portion on said wear bushing, and means (32) for actuating the latching means to move it into engagement with the wear bushing.

Description

BACKGROUND
• This invention relates to the formation of oil and gas wells.
• In well drilling operations, during completion of a wellhead system lengths of casing are run through a casing or tubing spool. In order to protect the seal bore of the casing or tubing spool, it is known to provide a wear bushing which is located in a bowl formed on the wall of the spool bore in order to protect that well from damage which can be caused during drilling operations. The wear bushing normally has to be removed before a casing run is started. This means that the bore will be unprotected while lengths of casing are run through it.
• U. S. Patent No. 4,340,259 discloses a wear and guide bushing used to protect the casing head or tubing head bowl during drilling and includes an inner tapered ring to guide the casing sections and a plurality of outer lugs to support the ring in the bowl. This structure is to eliminate abrasion of the bowl by return flow of drilling fluid.
• U. S. Patent No. 3,247,914 discloses a protector which is run on the drill bit and landed in the casing head bowl. It is picked up by the bit for retrieval. The structure is provided to avoid tilting and jamming of the protector during removal.
• U. S. Patent No. 4,362,210 discloses a wear bushing which is landed within a wellhead on the casing which is supported by slips whose bowl are landed on the wellhead landing seat. The wear bushing includes annular packing for sealing between its exterior and the interior of the bushing and also a semicircular flange structure for engagement by a running and retrieving tool.
SUMMARY
• According to the present invention, there is provided a tool for use in retrieving a wear bushing from a wellhead assembly comprising a generally annular body portion which can be located around a length of casing, means for sup­porting the body portion relative to a length of casing so that it can be lowered into a wellhead with said casing, latching means carried by body portion, said latching means being so shaped and arranged that it can engage a corre­spondingly shaped portion on said wear bushing, and means for actuating the latching means to move it into engagement with the wear bushing.
• An object of the present invention is to provide a means for removing the wear bushing which allows such bushing to be removed at a relatively late stage in the completion of the wellhead system.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention will be described now by way of example only, with particular reference to the accompanying drawings wherein:
• Figure 1 is a partial sectional view of the improved wear bushing in position within the drilling riser for engagement therewith.
• Figure 2 is a similar view illustrating the first step in preparing for securing the wear bushing within the drilling riser.
• Figure 3 is another similar view illustrating the latching of the wear bushing within the drilling riser.
• Figure 4 is a partial sectional view of a modified form of wear bushing being positioned within the drilling riser.
• Figure 4A is a detail sectional view illustrating the structure to the latching means.
• Figure 5 is a partial sectional view of the wear bushing of Figure 4 with the latching dogs positioned within the latching recess.
• Figure 6 is a similar view illustrating further lowering of the latching ring so that its bent portion engages below the lower end of the tool body.
• Figure 6A is a detail sectional view to show the latching of the latching dogs within the latching recess.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Referring to Figure 1, there is shown a part of a wellhead system which includes a drilling riser through which lengths ofcasing 12 are run in order to complete the wellhead system. Thedrilling riser 10 is formed with a bowl into which fits wear bushing 14 in a manner which will be apparent to those skilled in the art. The wear bushing acts as a protector sleeve to protect the bore of the drilling riser from damage which could otherwise be caused as the lengths of casing are run through it.
• The present arrangement is concerned particularly with a tool which allows retrieval of the wear bushing 14 towards the end of the completion of the wellhead system. In this embodiment of the invention, the tool comprises anupper split ring 16 which can be attached to a casing length by means ofscrews 18. Anouter sleeve 20 is coupled to theupper split ring 18 by means ofshear pins 22. Theupper part 21 of the sleeve has a relatively thick wall while thelower part 23 has a relatively thin wall. Ashoulder 25 is defined between theparts 21 and 23. A segmentedlatching ring 24 is carried by theouter sleeve 20 within the annular space between that outer sleeve and the casing length. The segmented latching ring comprises an upper body part which is secured to the outer sleeve by means ofshear pins 26 and downwardly dependinglegs 28 which carry at their lower end enlargedfeet portions 30. The tool also includes anenergizing split ring 32 which can locate on acasing coupling 34 below thelatching ring 24 as shown in Figure 1 of the drawings. The inner surface of the energizing ring is tubular and generally of the same diameter as the outer surface of thecasing portion 12 while the outer surface of the energizing ring is generally frusto-conical, the arrangement being such that the wall thickness of the split ring increases gradually towards its lower portion. It will be seen from Figure 1 that the war bushing 14 has arecess 36 and thefoot 30 of the segmented latch ring is shaped to conform with the shape of therecess 36.
• In operation, a hole is drilled in a conventional manner through the wear bushing located in the bore defined through the drilling riser. The wear bushing remains in position as the casing lengths are run into the hole as will be apparent to those skilled in the art.
• At approximately 6 casing lengths from the required tube diameter, centralizers are not fitted to the casing lengths. The actual number of joints can vary depending upon the length of the blowout preventer stack and the drilling riser. At approximately three casing lengths from the required tube diameter, the tool of the present embodi­ment is secured to the outer surface of thecasing length 12 as shown in Figure 1 of the drawings. Initially, the energizing ring is located above thecasing collar 34 as shown in Figure 1, and then the remaining elements of the tool are secured to the outer surface of thecasing length 12 by means of thescrews 18. Thiscasing length 12 is then lowered in a conventional manner until the downwardly facingshoulder 25 on theouter sleeve 20 lands on top of the upwardly facing upper surface of the wear bushing 14. This position is illustrated in Figure 1 of the drawings. In this position, thefeet 30 are held away from the wear bushing by thesleeve part 28.
• Continued lowering of the casing from the position shown in Figure 1 initially causes thepins 22 to shear. This means that theupper ring 16 can move axially down­wardly relative to theouter sleeve 22 as illustrated by Figure 2 of the drawings. This further lowering causes thepins 26 to shear, and the result is that the segmented latch ring moves downwardly so that theelements 30 can move below thesleeve part 28 and outwardly into engagement with therecess 36 in the wear bushing.
• To retrieve the wear bushing from the position shown in Figure 3, the casing is pulled back to the surface to a position where access can be gained in order to retrieve the wear bushing. As shown in Figure 3 of the drawings, the outer surface of the energizingsplit ring 32 engages theelements 30 and causes them to positively engage in therecess 36 of the wear bushing. Although not necessarily required, continued lowering of the casing does not trans­mit the weight of the casing through the wear bushing as the upper split ring strips over the casing at thescrews 18. As will be apparent, raising of the casing will pull the wear bushing upwardly by virtue of the engagement of theelements 30 within therecess 36 of the bushing.
• It will be appreciated that on land wellhead applica­tions, the length of the blowout preventer stack and the drilling riser do not exceed the length of casing which can be handled in a rig derrick. It should therefore not be necessary to break out casing joints when retrieving the wear bushing.
• Once retrieved, the tool shown in Figures 1 to 3 is removed, and further stands of casing are lowered through the wear bushing. The wear bushing is removed over the exposed casing connector prior to attachment of the casing hanger to complete the wellhead operations in a convention­al manner.
• A second embodiment of the invention is shown in Figures 3 to 6. In this embodiment of the invention, the casing is run through adrilling riser 110 in a manner similar to that described for the first embodiment. Thedrilling riser 110 supports a wear bushing 114 as described also for the first embodiment. The wear bushing has a similarshaped recess 136.
• The wear bushing retrieval tool of the second embodi­ment comprises a generallyannular body portion 120 to the upper portion of which are connected upwardly extendinglines 122. Thetool body 120 has a first upper relativelythick body portion 121, an intermediatethinner body portion 124 and a lower relativelythin body portion 126. A downwardly facingshoulder 128 is formed at the junction of the upper and intermediate portions, and a second down­wardly facingshoulder 130 is formed at the junction of the intermediate and lower portions. The intermediate body portion has radial through bores 132, only one of which is shown in Figure 4. The radial through bore is in communi­cation with an upwardly extendingclosed bore 134. The radial through bores accommodate latching dogs 138. The outwardly facingsurface 133 of each latching dog is shaped to conform generally to the shape of therecess 136 formed in the wear bushing. The inwardly facingsurface 135 of the latching dog is generally frusto-conical. The upper surface of each latching dog is stepped at 139. The upward­ly extendingclosed bore 134 accommodates apin 140 which is biased downwardly by means of aspring 142. In the position shown in Figure 4A thepin 140 is in contact with the raised part of the stepped upper surface of the latch­ing dog. As shown in Figure 4(A) the lower surface of each latching dog 138 has a cut-away portion which accommodates an upwardly projectingpin 144.
• Thelower section 126 of the body portion has a throughbore 150 which can receivescrews 152 to enable the tool body to be secured to acasing collar 156.
• The tool also includes an energizing and latchingring 160 which can be located between thetool body 120 and the outer surface of thecasing portion 112. The energizing and latching ring is generally annular, but has a lowerchamfered portion 162 on its outer surface. The energizing and latching ring can be secured to the outer surface of thecasing length 112. The energizing and latching ring has an upwardly extendingportion 164 which is inclined slightly outwardly and upwardly.
• In operation casing lengths are run through the drilling riser in the conventional manner with thewear bushing 114 in place. This is carried out until approxi­mately five joints from the required total depth. It should be noted that centralizers are not fitted to the last run of casing. At approximately three casing lengths from the required tube diameter the tool, shown in Figure 4, is fitted to the outer diameter of acasing collar 156 by the means of screws, as shown in Figure 4. The energizing and latchingring 160 is located in the annular space between thetool body 120 and the outer surface of thecasing length 112. It will be noted that in this position the latching dogs 138 do not protrude beyond the outer surface of theintermediate body portion 124 and are held bypins 144. Figure 4 shows one length ofline 122 attached to thebody portion 120, but it should be appreciated that there are three such lengths spaced angularly around the body. The casing is then run into the hole in a conventional manner, care being taken to monitor the feed of thelines 122. The length of line is monitored as the casing is lowered and when theshoulder 130 lands on thewear bushing 114, the line ceases to travel, thereby indicating that the tool has correctly landed on the wear bushing. This position is illustrated in Figure 4 of the drawings. Continued lowering of the casing causes the screws coupling the tool body to the casing coupling to be stepped through so that the casing can then pass axially downwardly relative to the tool body. Continued downward movement of the casing causes the energizing and latching ring to engage the frusto-conical surface 138 on the latchingdogs 130, thereby forcing the latching dogs radially outwardly into therecess 136 formed in the wear bushing. This is illustrated in Figure 5 of the drawings. It should be noted that there are approximately eight latching dogs spaced equally angularly around the body of the retrieval tool. As the dogs are displaced radially outwardly, the upper portions of thepins 144 are sheared and the retaining pins 132 move axially downwardly to engage the lower part of the stepped surface of the latching dogs under the action of thespring 134 and thereby retain the latching dogs in their outer position. This is illustrated best in the enlarged view shown in Figure 6A of the drawings.
• The tool and wear bushing can then be retrieved to the surface by pulling on thelines 122. The wear bushing is removed over any exposed casing connector prior to attach­ment of a casing/tubing hanger for completion of the opera­tions in a conventional manner.
• It will be apparent that the second embodiment of the invention has a significant advantage over the first embodiment in that it does not require the casing to be pulled in order to retrieve the wear bushing. The wear bushing can be retrieved to the surface without the need to pull back the casing.
• It will be appreciated that the present tool can be adapted for use with a bowl protector in any size of casing or tubing.

Claims (12)

1. A tool for use in retrieving a wear bushing from a wellhead assembly comprising a generally annular body portion which can be located around a length of casing, means for supporting the body portion relative to a length of casing so that it can be lowered into a wellhead with said casing, latching means carried by body portion, said latching means being so shaped and arranged that it can engage a correspondingly shaped portion on said wear bushing, and means for actuating the latching means to move it into engagement with the wear bushing.

2. A tool according to claim 1, wherein said body portion comprises a ring-like part securable to a length of casing by a frangible means, and an outer sleeve carried by said ring-like part and connected thereto by frangible means, said outer sleeve incorporating means for engaging the wear bushing to correctly position the tool relative to the wear bushing.

3. A tool according to claim 2, wherein said engag­ing means comprises a shoulder formed on the outer surface of the sleeve.

4. A tool according to claim 2 wherein said latching means comprises segmented latch ring disposed intermediate said casing and said sleeve and having a plurality of downwardly depending legs which have latching heads for engaging the wear bushing.

5. A tool according to claim 3 wherein said latching means comprises segmented latch ring disposed intermediate said casing and said sleeve having a plurality of downwardly depending legs which have latching heads for engaging the wear bushing.

6. A tool according to claim 4, wherein said actuat­ing means comprises a ring shaped member locatable around said casing such that it can be supported by a casing coupling element beneath said body portion, said ring shaped member having a generally frusto-conical outer surface arranged to engage said legs of said latching means and urge said latching heads into engagement with the wear bushing by a wedging action.

7. A tool according to claim 1, wherein said body portion is suspended from one or more lines or cables and said body portion includes means for engaging the wear bushing to correctly position the tool relative to the wear bushing.

8. A tool according to claim 7, wherein said engag­ing means comprises a shoulder formed on the outer surface of the body.

9. A tool according to claim 7, wherein said latch­ing means comprise a plurality of latching dogs carried by said body portion, said latching dogs being movable radially outwardly to engage a recess in said wear bushing.

10. A tool according to claim 8, wherein said latching means comprise a plurality of latching dogs carried by said body portion, said latching dogs being movable radially outwardly to engage a recess in said wear bushing.

11. A tool according to claim 9, wherein said actuating means comprises an energizing ring movable axially relative to the body portion so that it can contact said latching dogs to move them to their radially outward position.

12. A tool according to claim 11, wherein said body portion includes retaining means operable to retain the latching dogs in their radially outward position.

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