Abstract:
A protection sleeve ( 12 ) for locking over a seal ( 72 ) in a wellbore is described. The sleeve ( 12 ) is adapted for releasable engagement to a running tool ( 14 ) and has a locking mechanism ( 28 ) comprising first and second tubula members and a collet ( 56 ) is provided. One tubular member includes a profile adapted to mate with a profile of the seal ( 72 ). The sleeve ( 12 ) may be located on a work string ( 14 ), including a rotary drill string, and the invention also relates to methods of running in, setting, carrying out an intervention operation and retrieving the sleeve in a single run. The invention has particular application in Through Tubing-Rotary Drilling (TTRD).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase, pursuant to 35 U.S.C. §371, of International Application No. PCT/GB2006/001233, published in English on Oct. 5, 2006 as International Publication No. WO 2006/103477 A1, which claims the benefit of British Application Ser. No. GB 0506640.2, filed Apr. 1, 2005. The content of each of the above-mentioned applications are incorporated by reference herein. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to well tools and more particularly relates to a protection sleeve used to straddle seal bores such as those in tubing hangers, downhole safety valves and nipples, prior to well intervention operations. 
     2. Description of Related Art 
     In oil and gas well production, once a well is completed it may be necessary to re-enter the well to service or adjust equipment and optimise the performance of the well. Such re-entry is termed well intervention. During intervention it is necessary to run protection sleeves which cover seal bores within the existing well completion. These seal bores would typically be part of a tubing hanger, downhole safety valve or nipple. Without protection such seals may be damaged as further equipment is run through the completion. Once located in position, the sleeves allow access into the wellbore during the intervention and are then removed for production of the well to recommence. 
     Current protection sleeves are wireline conveyed or work string conveyed. Both these typically require a dedicated run to set the sleeve and a dedicated run to remove the sleeve. Once the sleeve is in position, the intervention is carried out via a wireline, coiled tubing or drill string. These provide the necessary clearance between the inner surface of the sleeve and the intervention work string. 
     Recently, new drilling techniques have placed a higher requirement on these protection sleeves. Due to the maturity of North Sea fields, the number of slots available to drill new wells is limited by the aging infrastructure. To address this, the industry has developed new drilling techniques to use the existing wellhead slots. This technique is termed Through Tubing Rotary Drilling (TTRD). The technique involves drilling a new section of the well through the existing well without having to pull the completion first. The point at which the new section of well is to be started is termed the kick off point. A whipstock packer is set at the predetermined location within the well and this is used to divert the drill string in the new direction. Conventional drillpipe, of smaller outer diameter (“OD”), is then run into the well through the existing tubing string until the whipstock is reached. At this stage the milling operation will commence, drilling a window through the existing tubing and casing to create a ‘sidetrack’ where the new well section is drilled. 
     As with previous intervention jobs a protection sleeve has to be run to prevent damage to the seal bores within the existing well completion. In the TTRD wells, the protection sleeve now has to protect against rotating drillpipe where non-rotating wireline or coiled tubing was previously used. Further as the milling operation takes place large amounts of debris and metal cuttings will need to be circulated past the sleeve. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a protection sleeve and protection sleeve assembly, with a method for running, setting and retrieving a protection sleeve in a wellbore on a work string. 
     It is an object of at least one embodiment of the present invention to provide a protection sleeve that may be coupled to a drill string to mitigate the need for a dedicated run to set the protection sleeve. 
     It is a further object of at least one embodiment of the present invention to provide a protection sleeve including a lock mechanism, the lock mechanism preventing the sleeve being pulled out of position as the drill pipe is operated. A further object of the invention is to provide a protection sleeve and/or locking mechanism with improved debris tolerance. 
     It is a still further object of the present invention to provide a method of running and setting a protection sleeve while creating a sidetrack in a wellbore. 
     According to a first aspect of the present invention there is provided a method of setting and unsetting a protection sleeve on a work string comprising the steps:
         (a) mounting a protection sleeve on a running tool, the running tool being located in a work string;   (b) running the work string in a wellbore until a profile of the sleeve abuts a profile of a seal bore;   (c) locking the protection sleeve to the seal bore;   (d) releasing the running tool;   (e) running the work string with the running tool through the protection sleeve into the wellbore to perform an operation in the wellbore beyond the seal bore;   (f) pulling the work string from the wellbore so that the running tool engages the protection sleeve;   (g) releasing the protection sleeve from the seal bore; and   (h) retrieving the protection sleeve on the running tool as the work string is pulled from the well.       

     In this way, separate trips are not required into the wellbore to locate and retrieve the protection sleeve during intervention. 
     Preferably the method includes the step of applying an over pull to the sleeve to verify it is properly set. 
     Preferably the work string comprises a series of tubing sections rotatable in the wellbore. In this way, the work string may be a rotating drill pipe so that the invention is not limited to wireline and coiled tubing intervention. 
     Preferably the step of releasing the sleeve from the seal bore includes the step of over pulling the protection sleeve via the running tool. Preferably also this step includes trapping the lock in an unset position so that the lock cannot reset and become jammed in the well. 
     Preferably the method may include the additional step of noting that the lock has jammed and applying a high over pull to release the sleeve. 
     Preferably the method includes the further steps of resetting the lock and repeating steps. 
     According to a second aspect of the present invention there is provided a protection sleeve for locking over a seal in a wellbore, the sleeve comprising a substantially tubular body having a bore therethrough adapted for the clear passage of a work string, the body including a first sleeve member adapted for releasable engagement to a running tool and a locking mechanism, the locking mechanism comprising first and second tubular members, engaging means to releasably engage the tubular members to each other, and a collet having a plurality of fingers retained within the body in a first position; held in an expanded configuration, proud of the body, in a second position; and released back within the body in a third position, wherein the second tubular member includes a profile adapted to mate with a profile of the seal and in the second position, the fingers locate within the profile of the seal. 
     In this way, the fingers lock the sleeve to the seal bore so that its passage is prevented in either direction. An over pull on the work string can be used to ensure the lock is set i.e. that the fingers are located within the seal profile. Release of the running tool then allows the work string to pass through the sleeve. Additionally by releasing the fingers back within the sleeve body, the sleeve can be removed when the work string is removed from the wellbore. 
     Preferably the first sleeve member includes a shoulder adapted for engagement to a surface of a running tool. The running tool can then be used to pick up the protection sleeve when the work string, including the running tool, is pulled from the wellbore. 
     Preferably the engaging means is a shearable means. The shearable means may be by pins, shear ring, or the like. Most preferably the engaging means is a shear ring. 
     Preferably the sleeve further comprises one or more windows, the windows providing a fluid flow passage between the outside of the sleeve and the bore. More preferably the windows are located at the collet. In this way debris is prevented from building up within the collet and preventing the fingers from moving to the third position to unset the lock. 
     Preferably the locking mechanism further comprises a trap to prevent the lock moving from the first or third positions. Preferably the trap comprises a c-ring locatable in a recess. This prevents the lock from setting as a result of movement of the mechanism, for instance, when the being used on a floating oil rig. 
     According to a third aspect of the present invention there is provided a protection sleeve assembly adapted for connection in a work string, the assembly comprising a protection sleeve according to the second aspect and a running tool, the running tool including connection means for locating in a work string, engaging means for releasably attaching the protection sleeve during run in and a shoulder to pick up the protection sleeve when the work string is removed from the wellbore. 
     Preferably the engaging means is a shearable means. The shearable means may be by pins, shear ring, or the like. Most preferably the engaging means is a shear ring. 
     Preferably the shear ring is rated to release after the lock has been set, that is when the sleeve is in the second position. 
     Preferably the running tool includes a plurality of upsets on an outer surface. These upsets ensure the sleeve is properly centralised when both running in the well and being pulled from the well. 
     According to a fourth aspect of the present invention there is provided a method of creating a sidetrack in a completed wellbore;
         (a) mounting a protection sleeve on a running tool, the running tool being located in a drill string;   (b) running the drill string in a wellbore until a shoulder of the sleeve abuts a shoulder of a seal bore;   (c) locking the protection sleeve to the seal bore;   (d) releasing the running tool;   (e) running the drill string with the running tool through the protection sleeve into the wellbore to a whipstock in the wellbore;   (f) drilling a window to create a sidetrack;   (g) drilling the sidetrack wellbore;   (h) pulling the drill string from the wellbore so that the running tool engages the protection sleeve;   (i) releasing the protection sleeve from the seal bore; and   (j) retrieving the protection sleeve on the running tool as the drill string is pulled from the well.       

     Preferably also the running tool is located near the drill bit. More preferably the distance between the drill bit and the running tool is less than the distance between the seal bore and the whipstock. In this way the running tool is designed to pass through the milled window. 
     Preferably the method includes the step of applying an over pull to the sleeve to verify it is properly set. 
     Preferably the step of drilling is achieved by rotation of at least a portion of the drill string on the wellbore. 
     Preferably the step of releasing the sleeve from the seal bore includes the step of over pulling the protection sleeve via the running tool. Preferably also this step includes trapping the lock in an unset position so that the lock cannot reset and become jammed in the well. 
     Preferably the method may include the additional step of noting that the lock has jammed and applying a high over pull to release the sleeve. 
     Preferably the method includes the further steps of resetting the lock and repeating the steps. 
     According to a fifth aspect of the invention there is provided a method of carrying out a downhole operation, the method comprising the steps of:
         (a) forming an assembly from a protection sleeve and a running tool, the running tool adapted to be part of a work string;   (b) running a work string including the assembly in a wellbore until a profile of the assembly abuts a profile of a seal bore;   (c) releasably engaging the protection sleeve with the seal bore;   (d) releasing the running tool from the protection sleeve;   (e) running the work string with the running tool through the protection sleeve into the wellbore to perform an operation in the wellbore beyond the seal bore.       

     According to a sixth aspect of the invention there is provided a method of carrying out a downhole operation, the method comprising the steps of:
         (a) Performing an operation using a workstring at a wellbore location below a seal bore;   (b) pulling the work string from the wellbore so that a running tool on the workstring engages a protection sleeve at the seal bore;   (c) releasing the protection sleeve from the seal bore; and   (d) retrieving the protection sleeve on the running tool as the work string is pulled from the well.       

     The fifth and sixth aspects of the invention may be combined with optional and preferred features of the embodiments of any of the first to fourth aspects of the invention defined above. 
     An embodiment of the present invention will now be described, by way of example only, with reference to the following Figures of which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(   a ), ( b ) and ( c ) are part cross-sectional views through a work string including a protection sleeve and running tool, where the sleeve is in the (a) first, (b) second and (c) third positions; 
         FIGS. 2(   a ), ( b ) and ( c ) are part cross-sectional views through the (a) sleeve, (b) the running tool and (c) the protection sleeve assembly of  FIG. 1 ; 
         FIGS. 3(   a ), ( b ) and ( c ) are schematic illustrations of the locking mechanism in the (a) first, (b) second and (c) third positions, of the protection sleeve of  FIG. 1 ; and 
         FIG. 4  is a schematic illustration of a wellbore in which a sidetrack is being drilled through a completion using the protection sleeve of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is initially made to  FIG. 1  of the drawings which illustrates a protection sleeve assembly, generally indicated by reference numeral  10 , in accordance with an embodiment of the present invention. Assembly  10  comprises a protection sleeve  12  and a running tool  14 . The running tool  14  is connected in a work string (not shown) via pin section  16  and box section  18 . The running tool  14  is releasably connected to the sleeve  12  by a shear ring  20 . 
     Reference is now made to  FIG. 2  of the drawings which illustrates the parts  12 ,  14  in greater detail.  FIG. 2(   a ) illustrates the protection sleeve  12 . Sleeve  12  comprises a tubular body  22  having a bore  24  therethrough. Body  22  is relatively thin-walled to provide a large cross-sectional area for the bore so that work strings can pass through the bore  24  without hindrance. Body  22  is made up of a sleeve assembly  26  and a locking mechanism  28 . Sleeve assembly  26  comprises a bottom sub  30 , a straight section  32 , a milled section  34  and a top sub  36 . The subs  30 ,  36  and sections  32 ,  34  are all annular and joined by threaded connections. Of note is that the bottom sub  30  is left hand threaded at the connection. This is done to prevent the bottom sub  30  from unscrewing when rotating drill pipe passes through the sleeve  12 . The bottom sub  30  also includes a circumferentially arranged shoulder  38  at its base  40 . This is designed so that the sleeve  12  can be picked up easily by the running tool  14 . 
     Milled section  34  includes five windows  42   a - e  arranged circumferentially around the section  34 , co-linearly with the axis of the bore  24 . Each window has a first elongate opening  44  and a smaller square opening  46 . The opening  44 ,  46  are separated by a tab  48 . Tab  48  is a portion of the sleeve section  34 , typically of metal, which is shearable under high loading. The purpose of the windows  44  and the tabs  48  will be described hereinafter with reference to the locking mechanism  28 . 
     Locking mechanism  28  consists of five tubular members  50   a - e . The members  50   a - e  are all fixed, typically by screw thread, to the adjacent member except for members  50   c  and  50   d . These features are best seen with the aid of  FIG. 3 . Like parts have been given the same reference numeral throughout the Figures to aid clarity. 
     On the member  50   d  there is located a recess  52  into which a c-ring  54  can locate when they are arranged over each other. The ring  54  is initially held in the member  50   c . The depth of the recess  52  is less than the height of the ring  54 , so that when the ring  54  lands in the recess  52 , the ring  54  abuts the member  50   c  and the members  50   c, d  will move together. 
     Protruding from member  50   b  are five collet fingers  56 . The fingers  56  are arranged equidistantly around the body  22 . Each finger naturally lies within the wall of the sleeve, being bounded by the milled section  34  and tubular member  50   a . The fingers  56  may thus be considered as a reverse collet as they are not forcibly retained in their first position. 
     The locking mechanism  28  is initially held to the sleeve assembly  26  by virtue of a shear ring  60  located across the member  50   a  and the milled section  34 , the ring  60  being shearable to release the member  50   a  and section  34  from each other under a predetermined force. Further a c-ring  62  which is located within the section  50   e  against the milled section  34 , can be moved into a recess  64  on the milled section  34 . Such movement is in a reverse direction to that used between the members  50   c, d  using ring  54  in recess  52 . C-ring  62  is thus used to hold the locking mechanism  28  in a position, termed the second position, while c-ring  54  is used to hole the locking mechanism  28  in a further position, termed the third position. 
     It will be appreciated that the running tool  14  used with the present invention could encompass several variations. In this embodiment, the tool is of two-part construction so that the shear ring  20  can be easily inserted to hold the sleeve  12  to the tool  14  during initial installation or assembly. On an outer surface is an upward directed ledge  80  designed to abut the sleeve  12 . The tool  14  has a bore  64  to provide a continuous path through the work string to which it is attached. The bore  64  is preferably of the same cross-sectional area or greater than the bore of the work string to which it is attached. The outer surface of the tool  14  is provided with upsets  66 ,  68  to ensure the sleeve  12  mounted thereon is properly centralised. Generous radii are provided on all upsets on the running tool  14  and the sleeve  12 . This is to address the potential for hanging up on the well profile when running in and out of the well. 
     Referring back to  FIGS. 1(   a ) to  1 ( c ), in use, the bottom sub is located on the running tool  14  so that the shoulder  38  abuts the ledge  80 . Shear ring  20  is located between the sub  30  and the tool  14 . The remaining parts of the sleeve  12  are then located onto the running tool  14 . These parts may be pre-connected or may be connected as they are located on the tool  14 . The collet fingers  56  are arranged such that the head  58  of each finger  56  lies within the square window  46 . Each tab  48  is arranged behind the finger  56  adjacent to the head  58 . C-ring  54  is held within the member  50   c  and c-ring  62  is held within the member  50   e . Shear ring  60  is located between the sleeve assembly  26  and the locking mechanism  28  holding these parts together. This configuration is referred to as the first position. The running tool  14  is connected in a work string and the whole assembly  10  is run into a completed well. This is as illustrated in  FIG. 1(   a ). 
     On reaching a seal within the wellbore, an outer profile  70  on the catches a profile, such as a nipple profile  72 , within the wellbore. The member  50   c  is held at the profile  72 . As the work string continues to move into the well, force is applied between the member  50   c  and the sleeve assembly  26  such that the shear ring  60 , therebetween, shears and the parts separate. Note that the sheared sections are held within the members  50   c  and section  34  so that they cannot become jammed any where in the assembly  10 . These sheared parts may be retrieved later when the assembly  10  is brought to the surface. 
     When ring  60  shears, the locking mechanism  28  moves relative to the sleeve assembly  26 . This causes the tabs  48  to be pushed under the collet heads  58  and thereby force the collet radially outwards. The collet heads  58  then locate within a recess  74  of the nipple profile  72 . At the same time, c-ring  62  is pushed into the recess  64  so that the locking mechanism  28 , via the member  50   e , is locked to sleeve assembly  26 . This locks the tabs  48  behind the collet heads  58  and effectively locks the sleeve  12  to the nipple profile  72 . At this point an over pull on the work string will indicate that the sleeve  12  is locked in position against the nipple profile  72  and the seal bore is therefore protected. This is as illustrated in  FIG. 1(   b ). 
     In this, the second position, the work string can be run through the sleeve  12 . With the sleeve  12  locked in position against the nipple profile  72 , a downward force from the work string will cause shear ring  20  to shear, so that the running tool  14  and work string can pass through the sleeve  12  to a greater depth within the wellbore. It will be appreciated that the string may contain further tools such that intervention work can be performed below the level of the nipple profile  72 . 
     When the intervention work is complete, the work string is pulled from the wellbore. As the running tool  14  reaches the sleeve  12 , the ledge  80  on the running tool  14  is brought up and contacts the shoulder  38  on the sleeve  12 . There is no requirement for a special mating arrangement, this simple contact can be used to release the sleeve  12 . When the contact is made, an over pull is applied to the work string. This overpull will move the member  50   d  relative to the member  50   c . Movement of the member  50   d  moves the milled section  34  as the two are engaged via the c-ring  62 . As the tabs  48  are on the milled section  34 , these tabs  48  move from under the collet heads  58  and consequently the collet retracts back into the sleeve body  22 . This effectively releases the lock and the sleeve  12  is unset. During the movement, c-ring  54  will be located over recess  52  and seat therein to join the members  50   c  and  50   d  together. This will halt the passage of the tabs  48  so that they rest behind the fingers  56  as for the first position. The lock mechanism  28  is thus trapped in the unset position and cannot move back to the locked position. This is especially applicable when the sleeve is used on a floating oil rig. Without this mechanism the up and down motion of the oil rig may cause the lock to reset and become jammed in the well. 
     Further pulling on the work string will now move the sleeve  12  with the running tool  14 , so that the sleeve  12  is retrieved to the surface of the well. This is as illustrated in  FIG. 1(   c ) and referred to as the third position. 
     Once on the surface, the sleeve  12  and running tool  14  can be reset by replacement of the shear rings  20 ,  60  and repositioning of the c-rings  54 ,  62 . Advantageously milled windows in the outer housings covering the c-rings  54 ,  62  allow for easy resetting of the lock mechanism  28  for re-run in the well. Access can still be gained to the c-rings if they become jammed with debris and the lock cannot be reset. 
     A further feature of the protection sleeve  12  is that it is debris tolerant. The milled slots or windows  44  under each finger  56  gives nowhere for the debris to jam and prevent the lock mechanism from unsetting. Additionally, the tabs  48 , which support each finger  56  in the set position, are calibrated to shear out at a predetermined value so that they form an emergency shear out facility for the locking mechanism  28 . If the locking mechanism  28  jams for some reason then a high value over pull will shear out the tabs  48  and de-support the collet fingers  56  allowing the sleeve  12  to be pulled from the well. 
     A yet further feature of the protection sleeve  12  is that, if necessary, it can be retrieved for the well using a fishing tool as is known in the art. The fishing tool would latch into the fishing neck  37  provided on the top sub  36  and the sleeve  12  would then be pulled to the surface. Such a procedure is likely to be required in the event that the work string parts and the running tool are lost downhole. 
     The present invention is especially suitable for creating sidetracks in existing wellbore completions. This is as illustrated in  FIG. 4 . In an existing completed wellbore  100 , there is typically located a cemented casing string  102  with a production tubing  104  arranged within. Near the surface  106  of the well  100  is a seal bore  108 , which may be a safety valve. In order to provide a side track  110 , a drill string needs to be inserted through the completion and sidetracked through the casing  102 . This form of intervention requires a protection sleeve to be inserted over the seal bores  108  to prevent them from being damaged by the passage of the drill string and by the returned mud and cuttings during drilling. In the prior art an initial run would be required to locate a protection sleeve over the seal bore. Indeed an individual run would be needed for each seal bore in the completion. With the present invention the sleeve  112  or sleeves, as appropriate, are located on running tools  114  which form part of the drill string  116 . Thus a single trip into the completed well can be made to both set the sleeves and drill the side track. With a whipstock packer  118  located in the wellbore, the drill string  116  is run into the completion. The running tool  114  is located near the drill bit  120 , so that the sleeve  112  is set as early as possibly to reduce the potential damage on the seal bore  108 . The/or each sleeve  112  is set and locked in position as described herein with reference to  FIGS. 1 to 3 . Once locked the drill string continues to run into the well, through the protection sleeve. The slimline design of the sleeve and in particular the lock mechanism allows a larger size of drill pipe to be run through it than a conventional lock design would. Additionally, an over pull can be applied to check that the sleeve  112  has been locked in position before continuing into the well. 
     The drill bit  120  is diverted via the whipstock  118  and mills a window  122  through the tubing  104  and casing  102 . The running tool  114  is essentially part of the drill string  116 . The running tool  114  is run into the remainder of the well and performs as per the drill pipe  116  and any bottom hole assembly  120 . This is possible as the running tool  114  is of simple construction and has no moving parts. This allows the running tool  114  to enter through the milled window section  122  without risk of damage to the running tool  114  or milled window  122 . More complicated running tools may not pass through this window  122  without risk of damage to the running tool or window. In that case the running tool would have to be spaced out properly on the drill string so it never reached the window once the side track had been entirely drilled. The down side to spacing the sleeve in this fashion is that long sections of the drill pipe have to pass through the seal bore before the protection sleeve can be locked in place which results in damage to the seal bore. Preferably also the running tool is located near the drill bit. Thus in this design the distance between the drill bit and the running tool, A, is less than the distance between the seal bore and the whipstock, B. In this way the running tool is designed to pass through the milled window. 
     Once the sidetrack is drilled, the drill pipe  116  is pulled from the well  100 . When the running tool  114  reaches the sleeve  112 , the sleeve  112  is unlocked and picked up on the tool  114  as described above. The sleeve  112  is then retrieved to the surface. 
     The principal advantage of the present invention is that it provides a protection sleeve and protection sleeve assembly, with a method for running, setting and retrieving a protection sleeve in a wellbore on a work string in a single trip. 
     A further advantage of the present invention is that it provides a protection sleeve which is locked in position against a seal bore. The lock is effected in both the set and unset positions which allows the assembly to be used on floating oil rigs where the up and down movement might otherwise cause a lock to reset. The lock can be checked by a simple over pull on the string. 
     A yet further advantage of the present invention is that it provides a protection sleeve assembly in which shear rings are used so that, once parts are separated the sheared portions remain within the assembly and cannot cause the string to jam in the wellbore. 
     Modifications may be made to the invention herein described without departing from the scope thereof. For example, multiple sleeves may be set from a single work string by correctly spacing out running tools on the string.