Abstract:
A wellbore cementing tool configured for placement in a drill string, and method of using same. The tool is lowered on a hollow, small-diameter stem into the drill string and contacts the bit, such that the downward pressure on the tool causes a shear pin to shear, resulting in upward movement of an outer sleeve relative to the central body of the tool. The outer sleeve normally holds outwardly biased locking members in a retracted position, but when the outer sleeve is upwardly displaced, slots in the outer sleeve align with the locking members and allow the locking members to extend outwardly through the slots to engage the inner wall of the drill string thereby locking the tool in place. When in position, cement can be injected through the tool and the bit, circulating up the wellbore annulus. The tool does not require rotation to engage the drill string.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Canadian Patent Ser. No. 2,790,548, filed Sep. 24, 2012, the entire contents of which are hereby incorporated by reference herein. 
     TECHNICAL FIELD 
     The invention relates to wellbore drilling technology, and specifically to tools and methods for cementing in a wellbore. 
     BACKGROUND 
     In the practice of borehole or wellbore drilling, a rotary drilling apparatus is employed to drill a hole downwardly into the ground, normally to either determine subsurface conditions, obtain samples of subsurface materials, or to extract natural resources located at depth. It is known to inject specialized cementitious material into the borehole to stabilize the hole walls or allow for isolation of certain subsurface strata. 
     Various cementing tools and methods have been developed over the years, often for mining or oil and gas drilling applications. While they have achieved generally widespread use and acceptance, it is known that certain drilling tools manifest potentially disadvantageous features. For example, some drilling tools are intended for deployment at a certain depth in the borehole, but locking them in place at that desired depth may require rotation of the tool and/or the string or stem used to deploy the tool, with the risk that threaded sections of drill pipe—in which the tool is being deployed—may be loosened at depth, a potentially serious occurrence. Also, some cementing tools can only be positioned when the drill string has first been removed from the hole, a practice known as tripping out the drill string. Tripping out the drill string can be time consuming and, in some contexts, otherwise unnecessary or undesirable. 
     It would therefore be desirable to have a wellbore cementing tool that could be employed without tripping out the drill string or requiring rotation that might destabilize the string in place. 
     SUMMARY 
     The present invention therefore seeks to provide a wellbore cementing tool and method for using same, where the tool can be deployed within an in-place drill string and locked in place at a desired depth without requiring tool rotation. 
     According to a first aspect of the present invention there is provided a wellbore cementing tool comprising an inner body and an outer sleeve disposed on an external surface of the inner body, the inner body supporting outwardly-biased locking members and the outer sleeve comprising apertures; wherein the outer sleeve is moved from a first downwardly disposed position to a second upwardly disposed position when the tool is lowered into a wellbore and contacts a downhole obstacle; wherein the locking members are held in a disengaged position by the outer sleeve when the outer sleeve is in the first position; and wherein the locking members extend through the apertures when the outer sleeve is in the second position. 
     According to a second aspect of the present invention there is provided a method for cementing a wellbore using the tool described above, wherein the method comprises the steps of: lowering the tool on a hollow stem into a drill string until the tool contacts a downhole obstacle; forcing the inner body of the tool downward relative to the outer sleeve; allowing the apertures of the outer sleeve to align with the locking members; allowing the locking members to be biased to pass outwardly through the apertures to engage the inner surface of the drill string; and injecting cementitious material down the hollow stem, through the tool, and through the lower end of the drill string such that the cementitious material passes out of the drill string and travels upwardly in the annulus between the drill string and the wellbore. The tool is preferably provided with a lower valve to prevent the cementitious material from flowing back into the tool, and a plug is preferably employed after injection of the cementitious material to plug the tool. 
     A detailed description of an exemplary embodiment of the present invention is given in the following. It is to be understood, however, that the invention is not to be construed as being limited to this embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, which illustrate an exemplary embodiment of the present invention: 
         FIG. 1  is a simplified sectional view of an upper portion of a tool according to the present invention; 
         FIG. 2  is a simplified sectional view of a middle portion of the tool of  FIG. 1 ; 
         FIG. 3  is a simplified sectional view of a lower portion of the tool of  FIG. 1 ; 
         FIG. 4 a    is a simplified sectional view showing the locking members in a disengaged position; 
         FIG. 4 b    is a simplified sectional view showing the locking members in an engaged position; and 
         FIG. 5  is a simplified sectional view of a plug according to the present invention. 
     
    
    
     Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings 
     DETAILED DESCRIPTION 
     In the following description, an exemplary tool according to the present invention is identified by the numeral  10 . Referring specifically to  FIGS. 1 to 3 , the tool  10  comprises an upper body  12 , a middle body  14 , and a lower body  16 , all threadably engaged in a manner well known in the art of drilling technologies. An upper metal sleeve  18  is disposed around the middle body  14  for movement relative thereto, as will be described below. A lower metal sleeve  20 , shown particularly in  FIG. 3 , is disposed around the lower body  16  and extends downwardly past the lowest extent of the lower body  16 , such that the lower sleeve  20  is the part of the tool  10  that contacts the downhole obstacle. 
     The tool  10  is provided with a threaded section  22  for engagement with a hollow stem (not shown); the threaded section  22  is preferably a left-hand thread to help avoid unwanted rotation of the adjacent drill string connections when the hollow stem is disengaged from the tool  10  after use. The hollow stem or string is used to lower the tool  10  into position within the drill string (not shown) and to flow cementitious material to the tool  10 . The tool  10  is provided with a central cavity  26  which extends from the upper end of the tool  10  to the lower body  16  where cementitious materials are allowed to exit through apertures  56 , and the cavity  26  comprises a larger chamber  24  in the upper body  12 . The chamber  24  is present to receive and retain a plug  64 , as is discussed below. 
     The upper body  12  is threadably engaged with the middle body  14 , as can be seen in  FIG. 1 , and the middle body  14  supports the means for securing the tool  10  in a desired location in the wellbore. The tool  10  of the exemplary embodiment is configured to be permanently secured inside the drill string, and so the desired location in this case would be the bottom of the hole at the desired drilling depth, with the downhole obstacle being the upper surface of the drill bit; however, it would be obvious to one skilled in the art that other configurations and other drilling applications are possible within the scope of the invention. 
     The securing means comprise four locking members  28  (two of which are visible in  FIG. 1 , the four locking members  28  being disposed at equal distances around the tool  10 ). The locking members  28  are pivotally mounted on the middle body  14  by means of pivot pins  30 , such that the locking members  28  are rotatable from a first position shown in  FIG. 1  to a second position rotated away from the middle body  14 . The locking members  28  are biased toward the second position by means of wedges  36  which are driven downwardly by springs  34 , the spring  34  in turn controlled by set screws  32 . The wedges  36  are driven downwardly by the springs  34 , but the angled contact face of the wedge  36  imparts an outward rotation of the locking member  28 . 
     In the position shown in  FIG. 1 , however, the locking members  28  cannot rotate outwardly due to the presence of the upper sleeve  18 . Turning now to  FIGS. 4 a  and 4 b   , the means for allowing the locking members  28  to rotate outwardly is illustrated. In  FIG. 4 a   , the upper sleeve  18  is disposed in a generally downward orientation, such that slots  38  in the upper sleeve  18  are positioned below the locking members  28 . When the slots  38  are not aligned with the locking members  28 , the locking members  28  cannot extend through the upper sleeve  18 . However, the upper sleeve  18  can be raised relative to the middle body  14 , such that the slots  38  align with the locking members  28  and allow the locking members  28  to extend through the upper sleeve  18 , as can be seen in  FIG. 4 b   . The mechanism for allowing the upper sleeve  18  to move upwardly relative to the middle body  14  and allow the locking members  28  to pass through the slots  38  is described below. 
     Turning now to  FIGS. 2 and 3 , the lower sleeve  20  is shown mounted on the middle body  14  and extending downwardly to cover the lower body  16 . As the lower sleeve  20  is the lowest part of the tool  10  when installed in a drill string, it is obvious that the lower end  62  of the lower sleeve  20  will be the part of the tool  10  that contacts the downhole obstacle (in this case a drill bit). The lower sleeve  20  is mounted on a steel bushing  42  which wraps around the middle body  14 , and the bushing  42  is secured to the middle body  14  by a shear pin  40 . The bushing  42  is overlain by rubber sleeves  44   a ,  44   b , and the uppermost rubber sleeve  44   a  is connected to the upper sleeve  18  by means of screws  48 . The rubber sleeves  44   a ,  44   b  are held in position by a plastic ring  46 . The lower body  16  is mounted at the lower end of the middle body  14  by means of a threaded engagement  50 . 
     The lower body  16  is illustrated in  FIG. 3  and functions both to allow passage of cementitious material to the bit and as a backflow preventer when the tool  10  is installed. The lower body  16  comprises a ball chamber  76  that is positioned at the lower extent of the cavity  26 . The ball chamber  76  houses a ball  54  which allows cementitious material to pass from the cavity  26  through four equally radially disposed apertures  56  and out of the tool  10 . In the event of backflow into the chamber  76 , the ball  54  instead presses upwardly against a hardened seat ring  52  and thereby prevents backflow into the cavity  26 . The ball  54  is biased upwardly by means of a spring  58 , which spring  58  is controlled by means of a pressure-adjusting screw  60  (which can be rotated by means of a hexagonal head  78 ). 
     Turning now to  FIG. 5 , a plug  64  is illustrated. The plug  64  is to be inserted into the tool  10  after injection of a desired volume of cementitious material. The plug  64  comprises an upper rubber member  66 , a shaft  68 , and a lower rubber member  70 . Each of the rubber members  66 ,  70  are provided with ribs or projections  72  of rubber to contact adjacent walls. The lower part of the plug  64  is inserted into the cavity  26  immediately below the chamber  24 , and is therefore provided with three O-rings  74 . 
     Use of the tool  10  will now be described. When a user wishes to cement a drilled borehole, the tool  10  is threadably connected to a hollow stem and then lowered into the interior of the drill string. When the tool  10  reaches the end of the drill string, the lower end  62  of the lower sleeve  20  strikes the drill bit. As downward force continues to be applied to the tool  10 , however, the central body of the tool  10  (specifically the threadably connected upper body  12  and middle body  14 ) is pushed downward relative to the lower sleeve  20  and the bushing  42  on which the sleeve  20  is mounted. This causes the shear pin  40  to rupture, allowing movement of the lower sleeve  20  and bushing  42  relative to the middle body  14 . As the bushing  42  has been freed to move upwardly relative to the middle body  14 , the bushing  42  presses upwardly against the rubber sleeves  44   a,b . This upward movement is now applied to the rubber sleeves  44   a,b , causing the plastic ring  46  to rupture and drive the upper sleeve  18  upwardly relative to the middle body  14 . The rubber sleeves  44   a,b  are also pressed outwardly toward the inner surface of the drill string due to the angled surface of the middle body  14 , thereby forming a seal against the drill string and preventing any backflow of cementitious material around the tool  10  and upwards within the drill string. 
     As the rubber sleeves  44   a,b  push the upper sleeve  18  upwardly relative to the middle body  14 , the upper sleeve  18  moves from the first position shown in  FIG. 4 a    to the second position shown in  FIG. 4 b   . When the slots  38  move into position adjacent the locking members  28 , the locking members  28  are outwardly biased through the slots  38  and engage the inner surfaces of the drill string. The tool  10  is then secured within the drill string immediately above the bit, and cementing can begin. 
     Cementitious material is then injected into the hollow stem, downwardly toward the tool  10 . The cementitious material passes into the chamber  24  and thence into the cavity  26 , ultimately passing out the apertures  56  and downwardly toward the bit, where it will pass through the bit and into the annulus between the drill string and borehole walls. 
     Once a volume of cementitious material has been injected that the user has determined will be adequate for the desired cementing activity, the plug  64  is sent down the hollow stem to the tool  10 . Once the plug  64  reaches the tool  10 , it presses into the chamber  24 , where the lower rubber member  70  terminates travel in the chamber  24  and the O-rings  74  seal against the upper end of the cavity  26 . The upper rubber member  66  helps to centralize and stabilize the plug  64 . Once in position, the plug  64  prevents any material from passing through the tool  10  to the bit. In addition, the ball  54  presses upwardly against the hardened seat ring  52  to prevent backflow into the cavity  26 , while the rubber sleeves  44   a,b  prevent backflow around the outside of the tool  10 . The hollow stem can then be disengaged from the threaded section  22  and tripped out of the hole, leaving the tool  10  in position adjacent the bit. 
     As can be readily seen, then, there are numerous advantages provided by the present invention. First, the tool can be deployed and allowed to engage the inner surface of a drill string without rotation of the tool. Also, the tool can be deployed in an in-place drill string, so no tripping out is required. The use of the ball valve and plug help prevent undesired flow of cementitious material in either direction, and the plug itself can be used to clean out the hollow stem as it travels downwardly toward the tool. 
     The foregoing is considered as illustrative only of the principles of the invention. Thus, while certain aspects and embodiments of the invention have been described, these have been presented by way of example only and are not intended to limit the scope of the invention. The scope of the claims should not be limited by the exemplary embodiments set forth in the foregoing, but should be given the broadest interpretation consistent with the specification as a whole.