Patent Publication Number: US-8973680-B2

Title: Lockable reamer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of GB Patent Application No. 1013165.4, filed on Aug. 5,2010, the entire contents of which are hereby incorporated by reference. 
     FIELD OF THE INVENTION 
     This invention relates to a lockable downhole tool and in particular, but not exclusively, to a lockable reamer or under-reamer. The invention also relates to a method of using such a tool. 
     BACKGROUND OF THE INVENTION 
     In the oil and gas exploration and production industry, bores are drilled from surface to access sub-surface hydrocarbon bearing formations. The drilled bores are lined with tubing, known as casing or liner, and cement is injected into the annulus between the casing and surrounding bore wall. Typically, the bore is drilled in sections, and after drilling a section that section is lined with casing. Following cementing of the casing, the next section of bore is drilled. However, as the drill bit utilised to drill the next section must pass through the existing casing, the drill bit will of necessity be of smaller diameter than the drill bit used to drill the previous section. It is often considered desirable to enlarge the bore diameter below a section of casing beyond the drill bit diameter, and this is normally achieved by means of an under-reamer mounted above the drill bit. The under-reamer and drill bit may be arranged to cut rock simultaneously, or the under-reamer may be selectively activated to ream selected sections of an existing bore. 
     During reaming operations, rock cuttings and other debris are created and recovered from the well bore by circulating fluid down the drill pipe and returning the fluid up the annulus created between the drill pipe and the well bore casing. After all reaming operations have been completed, the drill pipe conveyed under-reaming tool is recovered from the well bore by pulling the drill pipe, in sections or stands, from the well bore. During recovery of the under-reaming tool it may be necessary to circulate fluid down through the drill pipe and subsequently up the annulus in order to clear obstructions caused by debris remaining in the annulus. Under these circumstances, a hydraulically activated under-reamer may experience sufficient differential pressure, between the internal tubing and the annulus, to activate the internal mechanism causing the cutters to move radially outwards and contact the casing lining the well bore. Simultaneous lateral or rotational movement of the under-reamer in this condition will cause damage to the casing or damage to the under-reaming tool. As it is common practice to rotate the drill pipe during debris clean-out operations so as to agitate the debris, an inappropriately extended reamer tool could cause significant and extensive damage. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention there is provided a downhole tool comprising: a body; at least one extendable cutting member operable to cooperate with a hydraulically actuated cam member, and a cam member lock configurable to be activated downhole to restrict movement of the cam member relative to the body and prevent extension of the cutting member. 
     According to another aspect of the invention there is provided a downhole operation comprising: 
     running a downhole tool into a bore; 
     extending a cutting member from a body of the tool; 
     retracting the cutting member; 
     activating a lock to prevent subsequent extension of the cutting member; and 
     retrieving the tool from the bore. 
     The invention facilitates retrieval of the tool, typically in the form of a reaming tool, more particularly an under reamer, with the cutting member locked in the retracted configuration. Embodiments of the invention allow an operator to circulate fluid through the locked tool, for example to facilitate hole cleaning, safe in the knowledge that the cutting member will be retained in the retracted position. 
     The cam member lock may take any appropriate form and in one embodiment may be a mechanical lock. The lock may be configurable to create a mechanical interference or lock between a part of the cam member and a part of the body. The lock may provide the interference directly, or may interact with another element, which may be an element of the body or the cam member to create or provide the interference. For example, the lock may support a dog or collet finger in a locking configuration. In other embodiments the lock may take other forms, for example a hydraulic or magnetic lock. 
     The cam member lock may include a portion adapted for location between the body and the cam member and configured to restrict movement therebetween. Said portion may include one or more collet fingers. The lock may be mounted in the body above the cam member and may be adapted to cooperate with an upper end portion of the cam member. This may facilitate retrofitting of the lock to an existing tool, where the upper end of one or both of the cam member and body may be modified to accommodate the lock. 
     The lock may be actuated by any appropriate means. In one embodiment, the lock may be configured to be activated by using a device dropped or pumped from surface, for example a ball or dart. The device may be configured to cooperate with a portion of the lock to permit creation of a differential pressure across the lock and permit hydraulic actuation of the lock, which may involve pressure-induced longitudinal translation of a portion of the lock. The lock may be initially retained in or biased towards an inactive configuration. The lock may define a fluid passage and the device may substantially occlude the passage. In one embodiment the lock may define a seat and the device may be configured to land on the seat to restrict or prevent flow through the lock. In moving the lock to the locking position a fluid flow path may be reestablished through the lock. 
     The cam member may be biased towards a configuration in which the cutters are retracted. The cam member and lock may be configured such that the cam member may move to cutter-retracted position while the lock is activated. Thus, the lock may be activated while the cutting member is extended and the cam member is permitted to return to the retracted configuration and is then latched or locked in the retracted configuration. This allows the lock to be activated without requiring fluid circulation to be stopped or reduced for an extended period. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects of the present will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional view of an existing hydraulic under-reamer; 
         FIG. 2  is a sectional view of a hydraulic under-reamer in accordance with an embodiment of the present invention; 
         FIG. 3  is an enlarged sectional view showing the lock closed mechanism of the under-reamer of  FIG. 2 ; and 
         FIG. 4  corresponds to  FIG. 3 , but showing the lock closed mechanism in the activated configuration. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Reference is first made to  FIG. 1  of the drawings, which is a sectional view of a conventional hydraulic under-reamer, such as supplied by the applicant. The reamer  10  is adapted to form part of a drill string and will be positioned towards the lower end of the string, above the drill bit. The reamer  10  comprises an elongate tubular body  12  formed from a number of connected parts. Windows  14  in the body  12  accommodate radially movable cutters  16  which co-operate with corresponding cam members  18 , whereby axial movement of the cam members  18  causes the respective cutters  16  to radially extend and retract. The cam members  18  form part of a central assembly  20  including an annular piston  22 , the piston seals  24 ,  25  being arranged such that an elevated internal pressure will tend to cause the assembly  20 , including the cam member  18 , to move axially downwards (from left to right in  FIG. 1 ) and extend the cutters  16 . An upper part of the assembly  20  features a funnel  26  which directs fluid flowing through the body  12  and through the center of the assembly  20 . A coil spring  28  is accommodated in an annulus  30  between the upper end of the assembly  20  and the body  12  and acts to urge the assembly  20  upwards relative to the body  12  and thus to move the cutters  16  towards the retracted configuration. 
     As described above, during recovery of the under-reamer  10  following completion of a reaming operation, fluid may be circulated down through the drill string and subsequently up the annulus. The drill string and the under-reamer  10  may be rotated as this fluid circulation takes place. If the differential pressure between the interior of the under-reamer and the annulus is sufficient, the differential pressure acting across the piston  22  may be sufficient to move the cam member downwardly and extend the cutters  16 , causing damage to the well bore casing. 
     Reference is now made to  FIGS. 2 ,  3  and  4  of the drawings, which illustrate an under-reamer  40  in accordance with an embodiment of the present invention. As will be described, the under-reamer  40  is configured to allow the reamer to be locked in the retracted and closed configuration such that fluid may be circulated through the under-reamer without any risk that the cutters will be extended. 
     The illustrated reamer  40  corresponds to a conventional reamer  10  which has been retrofitted with a lock arrangement in accordance with an embodiment of the present invention. Thus, the reamers  40 ,  10  share a number of common features. However, the upper or return sub  32  of the reamer  10  has been replaced with an alternative top sub  42  and pin sub  44  in the reamer  40 . Also, the funnel  26  has been replaced by a modified funnel  46  featuring an external shoulder  48  with a toothed surface. 
     The top sub  42  receives the modified funnel  46  and accommodates a cam member lock in the form of an activation piston  52 , shown in  FIG. 3  in an initial, inactive configuration. In this configuration the upper end of the piston  52  is in sealing engagement with a housing  54  which lines the top sub  42 . The piston  52  is initially fixed to the housing  54  by means of a shear pin  56 . 
     The lower end of the activation piston  52  is located within a lower housing  58  and includes a gripping collett  60  which is initially located above the funnel shoulder  48  and an opposing shoulder  62  formed on the lower housing  58 . 
     While the under-reamer  40  is in use, the activation piston  52  remains in the inactive configuration as illustrated in  FIG. 3 , and has no bearing on the operation of the under-reamer  40 . However, once all under-reaming activities have been completed and it is desired to lock closed the tool, a steel ball  64  is dropped through the drill string and lands on a seat  66  at the upper end of the activation piston  52 . The application of hydraulic pressure to the inside of the drill string will thus now generate a differential pressure across the ball and piston  64 ,  52  and the associated down force will shear the pin  56 . The piston  52  may then move downwards inside the upper and lower housings  54 ,  58  to the position as illustrated in  FIG. 4  of the drawings. The downwards motion of the activation piston  52  relative to the reamer body pushes the gripping collett  60  between the funnel and housing shoulders  48 ,  62 , such that the fingers of the collett  60  flex radially outwards to engage with the matching profile on the outer surface of the funnel  46 . The downward relative movement of the activation piston  52  also establishes a flow path around the ball  64  via an enlarged internal portion of the upper lockout housing  54  and flow ports  70  formed in the wall of the piston  52  so that fluid may still be circulated through the under-reamer  44  after the cutters have been locked closed. 
     Once the gripping collett  60  has engaged with the funnel shoulder surface, subsequent application of differential pressure across the under-reamer piston  22  will still urge the funnel  46  to move downwards. However, this force generates a radially inward acting reaction from the lower housing shoulder  62 , increasing the engagement between the gripping collett  60  and the funnel shoulder  48 . The funnel  46  and the other associated elements of the assembly  20 , including the cam member  18 , are thus locked against axial movement relative to the tool body. Accordingly, as the tool is recovered from the well bore, unrestricted fluid circulation through the drill string with simultaneous rotation and up and down movement of the drill string may be commenced without the risk of the cutters  16  extending and damaging the casing or the reamer  40 . 
     It should also be noted that the cam lock activation piston  52  may be moved downwards while the reamer cutters  16  are in the extended configuration, and the funnel shoulder  48  is not aligned with the housing shoulder  62 . However, once the differential pressure falls, the spring  28  lifts the assembly and positions the funnel shoulder  48  beneath the flexible gripping collett fingers  60 . The ratchet-like formations on the funnel shoulder surface and the gripping collett face will prevent subsequent movement of the funnel  46  in the downward direction. 
     It will be apparent to those of skill in the art that the above described embodiment is merely exemplary of the present invention, and that various modifications and improvements may be made thereto, without departing from the scope of the invention.