Abstract:
An embodiment of a downhole tool for use with a workstring in a wellbore includes a first section, a second section, and a coupling mechanism adapted such that in a first configuration the coupling mechanism couples the first section to the second section. In a second configuration, the coupling mechanism does not couple the first section to the second section. Also disclosed is a method for creating a plug in a wellbore, the method comprising: injecting a slurry into the workstring to form a plug in the wellbore, positioning a flow preventing mechanism into the workstring to prevent fluid flow from exiting the workstring, inducing a coupling mechanism to uncouple a portion of the workstring such that the portion remains with the slurry to create the plug in the wellbore, and removing the first section from the wellbore.

Description:
BACKGROUND 
     This invention pertains to apparatuses and methods of removing tail pipes when conducting downhole operations in boreholes which penetrate subterranean earth formations. 
     When drilling a borehole which penetrates one or more subterranean earth formations, it may be advantageous or necessary to create a hardened plug in the borehole. Such plugs are used for abandonment of the well, wellbore isolation, wellbore stability, or kick-off procedures. For instance, it is sometimes necessary to change the direction of the borehole as it is being drilled. In order to change direction, a harden mass of cement is often placed in the borehole in the vicinity of the location where the change in drilling direction is to begin. This hardened mass of cement is referred to in the art as a sidetrack plug or as a kickoff plug. 
     The specific function of a kickoff plug is to cause the drill bit to divert its direction. Accordingly, if the plug is harder than the adjacent formation, then the drill bit will tend to penetrate the formation rather than the plug and thereby produce a change in drilling direction. However, a kickoff plug may fail to cause the drill bit to change direction if the plug is unreasonably contaminated with a foreign material, such as drilling mud or fluid. Drilling fluid, when mixed in the unset cement, can render the set mass softer than the adjacent formation. Thus, extreme care and expense is usually taken to make sure that the drilling fluid does not mix with the cement plug. 
     Typically, a cement plug may be set in a borehole by pumping a volume of spacer fluid compatible with the drilling mud and cement slurry into the workstring. Then a predetermined volume of cement slurry is pumped behind the spacer fluid. The cement slurry travels down the workstring and exits into the wellbore to form the plug. The cement slurry typically exits through one or more openings located at the end of the workstring. In this context, the end of the workstring is usually referred to as the “tail pipe.” Drilling fluid is usually pumped behind cement slurry to maintain pressure within the workstring. 
     At this point, the workstring is raised within the wellbore to permit the entire volume of cement slurry inside the conduit to flow out of the bottom of the tail pipe. However, the tail pipe must be raised very slowly or the cement slurry and the drilling fluid will mix, which may destroy the integrity of the plug. The process of raising the tail pipe generally causes some damage to the plug because as the tail pipe is raised the drilling fluid in the workstring mixes with the cement slurry. What is needed therefore, is a method and apparatus to keep the drilling fluid in the tail pipe from mixing with the cement slurry as the tail pipe is removed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross section of one embodiment of the present invention showing the embodiment in a running configuration. 
     FIG. 2 is a longitudinal cross section of the embodiment of FIG. 1 showing the embodiment in a disconnected configuration. 
     FIG. 3 a  is a cross section of one embodiment of the present invention in a wellbore when the embodiment is in a running configuration. 
     FIG. 3 b  is a cross section of the embodiment of FIG. 3 a  showing the embodiment with a plug. 
     FIG. 3 c  is a cross section of the embodiment of FIG. 3 a  showing the embodiment in a disconnected configuration. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIGS. 1 and 2, there is a downhole or tubing release tool  10 . As will be explained below with reference to the operation of the tubing release tool  10 , the tubing release tool  10  comprises a first or “upper” tubular section  10   a  and a second or “lower” tubular section  10   b . FIG. 1 illustrates a first or “running” configuration where the upper section  10   a  and lower section  10   b  are coupled together. In contrast, FIG. 2 illustrates a second or “disconnected” configuration where the upper section  10   a  and lower section  10   b  are separated. As will be explained in detail below, a coupling mechanism is provided such that in the running configuration the coupling mechanism couples the upper section  10   a  to the lower section  10   b , and in the disconnected configuration the coupling mechanism does not couple the upper section  10   a  to the lower section  10   b . The individual components of the tubing release tool  10  will now be discussed with reference to both FIG.  1  and FIG.  2 . 
     The tubing release tool  10  has an outer housing  12  which is generally cylindrical in shape and encloses the various modules and components of one embodiment of the present invention. In the illustrative embodiment, the upper end of the outer housing  12  is comprised of an upper connecting body  14 . The upper connecting body  14  connects to a collet retainer  16 . In the running configuration, the collet retainer  16  is disposed above a spacer housing  18 , but the collet retainer  16  does not directly connect to the spacer housing  18 . A lower connecting body  20  is positioned below the spacer housing  18 . Thus, in the running configuration, the outer housing  12  comprises the upper connecting body  14 , collet retainer  16 , spacer housing  18 , and lower connecting body  20 . 
     The Upper Section: 
     A top end of the upper connecting body  14  defines a top opening  22 . The top opening  22  is a top end of a concentric bore  24  that runs longitudinally through the upper connecting body  14 . The top opening  22  also defines a top of fluid passageway or central bore  26  which generally runs entirely through the tubing release tool  10  along a longitudinal axis  28 . Thus, the bore  24  forms a top portion of the central bore  26 . 
     The upper connecting body  14  may be adapted for connecting to a workstring (not shown in FIG. 1 or FIG. 2) in a conventional manner. For instance, in the illustrated embodiment, the upper connecting body  14  has an interior threaded surface  30  to connect to the workstring. The illustrative embodiment also has an annular groove  32  defined in the bore  24  below the interior threaded surface  30 . The annular groove  32  is a relief space to allow internal threads to be cut in the upper connecting body  14 . A lock ring  34  is positioned in another annular groove  36 , which is located below annular groove  32 . The diameter of the bore  24  remains constant below the annular groove  36  until the diameter of the bore  24  abruptly narrows to create an upward facing shoulder or seat  40  within the bore  24 . 
     The lock ring  34  holds a secondary releasing sleeve  38  in place during assembly. The secondary releasing sleeve  38  is a cylindrical shaped sleeve which is slidably disposed within the bore  24 . As will be explained below with reference to the operation of the tubing release tool  10 , the secondary releasing sleeve  38  slidably moves along the axis  28  within the bore  24 . A top end of the secondary releasing sleeve  38  has an exterior rim  42 , the diameter of which is slightly smaller than the interior diameter of the bore  24 . A sealing means, such as an O-ring  44  provides a sealing engagement between the rim  42  and an interior surface  46  of the bore  24 . 
     In some embodiments, the upper connecting body  14  has a screw hole  48  which allows a user to fill a cavity  50  with a lubricating agent, such as grease. The cavity  50  is defined by a space between the interior surface  46  and an exterior surface  47  of the secondary releasing sleeve  38 . The secondary releasing sleeve  38  may have one or more longitudinal grooves (not shown) defined within its exterior surface  47  to create a flow path for the lubricating agent. Consequently, as the secondary releasing sleeve  38  travels longitudinally, the lubricating agent can escape. Without such longitudinal grooves, the secondary releasing sleeve  38  could become fluid locked and unable to travel. 
     In other embodiments, the upper connecting body  14  may be fitted with a fluid releasing device, such as a rupture disk assembly  51  that is ruptured at a predetermined pressure level. As will be explained in greater detail later, the rupture disk assembly  51  allows some of the drilling fluid in the workstring to escape after the cementing is completed. Consequently, the operator does not have to pull up a workstring full of drilling fluid. In yet other embodiments, the upper connecting body  14  may also be fitted with a pressure monitoring mechanism, such as a nozzle  52 . The nozzle  52  allows a controlled amount of fluid to escape which allows the operator to monitor the backpressure inside of the tubing release tool  10 . 
     At the top end of the secondary releasing sleeve  38  there is a radially inwardly beveled surface  53  which defines an opening  54 . The opening  54  turns into a top end of a concentric bore  56  that generally runs longitudinally through the secondary releasing sleeve  38 . The bore  56  is in communication with the bore  24  of the upper connecting body  14  and also forms a portion of the central bore  26 . The secondary releasing sleeve  38  may also have one or more vent ports  60   a  and  60   b  to allow the lubricating agent to flow into bore  56 , indicating the cavity  50  is filled to capacity. 
     In the illustrative embodiment, the upper connecting body  14  couples to the collet retainer  16  via a threaded connection  62 . A concentric bore  64  (FIG. 2) runs longitudinally through the collet retainer  16 . Below the threaded connection  62 , the bore  64  abruptly narrows in a radial inward direction to create an inwardly protruding circumferential lip or seat  68 . 
     The collet retainer  16  may have at least one screw hole  72  which allows a user to lubricate the bore  64  with a lubricating agent, such as grease. A one-way seal, such as a debris seal  74  may be positioned within an annular groove  70  which is defined in the bore  64  at a predetermined distance below the seat  68 . The debris seal  74  is used during the running configuration to allow the lubricating agent to escape, and to prevent drilling fluid from seeping into the bore  64 . 
     Thus, in the illustrative embodiment, the upper section  10   a  includes the upper connecting body  14 , the collet retainer  16 , and the secondary releasing sleeve  38 . 
     The Lower Section: 
     As explained previously, the spacer housing  18  is disposed below the collet retainer  16  (of the upper section  10   a ) when in the running configuration. The spacer housing  18  is generally in the shape of a hollow cylinder. The interior diameter of spacer housing  18  is slightly larger than the exterior diameter of a releasing collet  75  such that the spacer housing  18  surrounds a portion of collet  75 . In the illustrated embodiment, the spacer housing  18  also has two screw holes  76   a  and  76   b  (screw hole  76   b  is not shown) to hold the spacer housing  18  on the collet  75  during assembly. 
     The collet  75  is generally cylindrical shaped and has a concentric bore  78  running longitudinally through the collet  75 . In the running configuration (FIG.  1 ), a lower portion of the bore  78  becomes a portion of the central bore  26 . At a top end of the collet  75 , there is an outwardly protruding rim  80  which circumferentially extends around the top end of collet  75 . Below the rim  80 , there is a flexible or top section  82  of the collet  75 . Below the top section  82 , there is a lower section  84  of the collet  75 . The wall thickness of the top section  82  is narrow relative to the lower section  84 . There are also a predetermined number of longitudinal slots extending from the top of the rim  80  through the top section  82 . For instance, slots  85   a  and  85   b  are shown in FIG.  2 . Preferably these slots will be equally spaced around the periphery of the rim  80 . As will be explained below in relation to the operation of the tubing release tool  10 , the combination of the slots  85   a  and  85   b  and the narrowed wall thickness of the top section  82  allow the diameter of the rim  80  to decrease when the rim  80  is not radially supported by a supporting mechanism. Thus, the rim  80  can be considered “flexible” in that it can contract from a first radial position of a particular diameter to a second radial position of a lesser diameter. 
     The interior of the lower section  84  of the collet  75  abruptly narrows to create an upward facing shoulder or seat  86 . The lower section  84  has external threads  88  to mate with interior threads  89  of the lower connecting body  20 . 
     A support mechanism, such as a primary releasing sleeve  90  is slidably disposed within the bore  78  of the collet  75 . The primary releasing sleeve  90  is generally cylindrical in shape and has a concentric bore  92  running along the primary releasing sleeve&#39;s  90  longitudinal axis. In the running configuration (FIG.  1 ), the bore  92  is in communication with the bore  56  of the secondary releasing sleeve  38  and is a portion of the central bore  26 . The exterior diameter of the primary releasing sleeve  90  is slightly smaller than the diameter of the bore  78  of the collet  75 . In the running configuration, primary releasing sleeve  90  “radially supports” the collet  75  in that it prevents the rim  80  from radially contracting to a smaller diameter. 
     As illustrated in FIG. 1, the primary releasing sleeve  90  is in a first position. The primary releasing sleeve  90  is maintained in this first position by a positioning mechanism, such as a shearing mechanism. In the illustrative embodiment, the shearing mechanism is a plurality of radially spaced shear pins  100   a  through  100   c  which extends through the primary releasing sleeve  90  and the collet  75 . In other embodiments, the shearing mechanism could be a single shear pin. The shear mechanism is shearable at a predetermined force, which in the illustrative embodiment, is applied by the primary releasing sleeve  90 . As will be explained below in relation to the operation of the tubing release tool  10 , once the shear pins  100   a  through  100   c  have sheared, thus disabling the positioning mechanism, the primary releasing sleeve  90  is free to slidably move along the longitudinal axis  28  to a second position, which is illustrated in FIG.  2 . 
     In the running configuration (FIG.  1 ), there is a means to provide a sealing engagement between the exterior of the primary releasing sleeve  90  and an interior surface of the bore  24  of the upper connecting body  14 . In the illustrative embodiment, this sealing means is an O-ring  102  positioned in an annular groove  104 , which is defined in the bore  24 . Similarly, there is also a sealing means providing a sealing engagement between the exterior of the primary releasing sleeve  90  and an interior surface of the bore  78  of the collet  75 . This sealing means may be an O-ring  106  positioned within an annular groove  108  of the exterior surface of the primary releasing sleeve  90 . 
     As discussed above, the lower connecting body  20  is disposed below the spacer housing  18  and connects to the collet  75 . The lower connecting body  20  is generally cylindrical in shape and also has a concentric bore  110  running along its longitudinal axis. The bore  110  is in communication with the bore  78  of the collet  75  and is a portion of the central bore  26 . The lower connecting body  20  has a top opening  112  which is adapted to mate with the external threads  88  of the collet  75  via internal threads  114 . The lower connecting body  20  may also be adapted to connect in a conventional manner to another downhole tool which may be positioned lower in the workstring than the tubing release tool  10 . For instance in the illustrative embodiment, the lower connecting body  20  has external threads  116  designed to mate with another workstring tool (not shown). In the illustrative embodiment, the exterior diameter of the lower connecting body  20  also narrows to allow the other workstring tool to conveniently mate with the lower connecting body  20 . 
     In sum, in the illustrative embodiment, the lower section  10   b  includes the primary releasing sleeve  90 , the collet  75 , the spacer housing  18 , and the lower connecting body  20 . 
     Operation of the Invention 
     Referring to FIGS. 3 a  through  3   c , the operation of the tubing release tool  10  will now be discussed. In operation, the upper connecting body  14  of the tubing release tool  10  is connected to a workstring  120 . In the illustrative embodiment, the lower connecting body  20  is also connected to an extension tube  122 . The entire workstring is then lowered into a wellbore  124 . Drilling fluid is circulated through the workstring  120  and the tubing release tool  10  as it is lowered into the wellbore  124 . Once the tubing release tool  10  reaches the desired depth, a volume of spacer fluid compatible with the drilling fluid may be introduced into the workstring  120 . 
     A predetermined volume of cementitious fluid, such as cement slurry can then be pumped behind the spacer fluid. The cementitious fluid may be comprised of any slurry capable of forming a hardened plug. For instance, cement slurry may be comprised of cement and sufficient water to form a pumpable slurry. The cement slurry may also include additives to accelerate the hardening time, to combat or otherwise prevent fluid loss and gas migration, and to resist loss in compressive strength caused by high downhole temperatures. Such cementitious fluids and slurry compositions are well known in the art. 
     The cement slurry will flow through the workstring  120  and enters the tubing release tool  10  through the top opening  22  of the upper connecting body  14 . The cement slurry flows through the central bore  26  and into the extension tube  122 . The cement slurry exits the extension tube  122  into the wellbore  124 . The cement slurry will fill a portion of the wellbore  124  to create a cementitious plug  126  at the desired depth within the wellbore  124 . 
     At this point, it is desirable to switch from the running configuration to the disconnected configuration. In the running configuration, the collet  75  acts as the coupling mechanism between the upper section  10   a  and the lower section  10   b  of the tubing release tool  10 . The coupling or connection between the upper section  10   a  and the lower section  10   b  occurs because the diameter of the rim  80  of the collet  75  is larger than the diameter of the lip  68  of the collet retainer  16 . Thus, as long as the exterior diameter of the rim  80  is larger than the interior diameter of the lip  68 , the collet  75  is “retained” in the bore  64  of the collet retainer  16 . On the other hand, if the exterior diameter of the rim  80  becomes smaller than the interior diameter of the lip  68 , there is nothing to prevent the collet  75  from slipping past the lip  68  and out of the collet retainer  16 . 
     In order to switch from the running configuration to the disconnected configuration, a flow prevention mechanism may be introduced into the workstring  120 . Referring now to FIG. 3 b , a plug  128  has been introduced into the workstring  120  and has moved downward within the workstring  120  by drilling fluid which is introduced behind the plug  128 . The plug  128  may be any conventional plug, such as drill pipe dart or phenolic ball that would provide a hydraulic seal upon reaching the secondary releasing sleeve  38 . The plug  128  could also be a combination of plugs or balls. For instance, a foam ball (not shown) could be introduced into the workstring  120  to clean or wipe the inside of the workstring  120 . Then, a phenolic ball (not shown) could be introduced to begin the disconnecting procedure (as will be explained below). The combination of the foam ball and the phenolic ball could act as the plug  128 . 
     When the plug  128  engages the tubing release tool  10 , the plug  128  moves through the central bore  26  until it sealingly engages the opening  54  of the secondary releasing sleeve  38  such that the drilling fluid behind the plug  128  is prevented from exiting the workstring  120 . Backpressure is thereby increased as additional drilling fluid is pumped into the workstring  120 . 
     The backpressure inside the workstring  120  causes the plug  128  to exert an axial force on the beveled surface  53  of the secondary releasing sleeve  38 . In response, the secondary releasing sleeve  38  pushes on the primary releasing sleeve  90 , transferring the axial force from the secondary releasing sleeve  38  to the primary releasing sleeve  90 . In turn, the primary releasing sleeve  90  exerts a shearing force on the shearing pins  100   a  through  100   c  which are maintaining the primary releasing sleeve  90  in the first position within the bore  78 . Thus, when the backpressure inside the workstring  120  reaches a first predetermined pressure, the shear force exerted on the shear pins  100   a  through  100   c  will be great enough to cause the shear pins  100   a  through  100   c  to fail. This shearing allows the releasing sleeves  38  and  90  to move longitudinally downward until the primary releasing sleeve  90  rests on the seat  86 . In some embodiments, the secondary releasing sleeve  38  is vertically supported by the primary releasing sleeve  90 . Thus, when the primary releasing sleeve  90  moves longitudinally downward, the secondary releasing sleeve  38  will also move downward until the rim  42  engages the seat  40  of the upper connecting body  14  as shown in FIG. 3 c  and FIG.  2 . 
     As discussed previously, longitudinal slots  85   a  and  85   b  in the top section  82  of the collet  75  allow the rim  80  to move in a radially inward direction when the rim  80  is not radially supported by the primary releasing sleeve  90 . Thus, once the primary releasing sleeve  90  has moved downward from a first position (as shown in FIG. 3 b ) to a second or lower position (as shown in FIG. 3 c ), the rim  80  is no longer radially supported and is free to move inwardly in a radial direction. When the rim  80  moves inwardly, it no longer engages the seat  68  of the collet retainer  16 . When the seat  68  is no longer engaged with the rim  80 , the upper section  10   a  of the tubing release tool  10  is no longer coupled to the lower section  10   b . The hydraulic force applied to secondary releasing sleeve  38 , forces lower section  10   b  free from upper section  10   a , completing the uncoupling or disconnect between the upper section  10   a  and the lower section  10   b.    
     Once the upper section  10   a  is no longer coupled to the lower section  10   b , the workstring  120  may be removed. The lower section  10   b  will remain in the cementitious plug  126  and the upper section  10   a  will remain connected to the workstring  120 , and thus, will be removed as the workstring  120  is removed. Turning now to FIG. 3 c , as the workstring  120  is moved up, the plug  128  sealingly engages the beveled surface  53  of the secondary releasing sleeve  38  such that the drilling fluid in the workstring  120  will remain in the workstring  120 . Thus, as the workstring  120  is raised, the drilling fluid will not intermix with the cement slurry nor apply a hydrostatic load to the cementitious plug  126 . The operator, therefore, may significantly reduce current precautions to decrease the intermixing of the drilling fluid with the cement slurry, such as waiting for several hours for the cement slurry to thicken. The cement slurry is, therefore, free to set into a hard impermeable mass. 
     Once the disconnect is completed, the operator may remove a portion of the wet workstring  120  or wait a predetermined length of time, for instance 20 to 30 minutes until the cementitious plug  126  begins to harden. At that point, continued pumping of drilling fluid will create an increase in backpressure of the workstring  120 . When the back pressure reaches a second predetermined pressure, such as 4000 psi, the rupture disk assembly  51  will rupture, allowing the drilling fluid to exit from the side of the tubing release tool  10  through the rupture disk assembly  51 . By allowing the drilling fluid to exit the tubing release tool  10 , the operator avoids pulling up the workstring  120  when it is full of drilling fluid. 
     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. For instance, the use of the nozzle  52  allows the operator to monitor the backpressure inside of the tubing release tool  10 . When the lower section  10   b  disconnects from the upper section  10   a , there will be a momentary drop in pressure within the tubing release tool  10 . By monitoring the backpressure, the operator can determined when disconnect occurs. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.