Abstract:
Apparatus and method for a retrievable plug in coil tubing. A plug is disposed within a tubing and is set within the tubing by an anchoring element placed in gripping engagement with the tubing. The plug also has seal elements disposed therein that are placed in sealing engagement with the tubing. An orientation element on the plug positions the plug within the tubing with respect to the seam of the tubing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of, and incorporates by reference, provisional application Ser. No. 60/706,486, filed Aug. 8, 2005, and entitled “Retrievable Plug System.” 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       FIELD OF THE INVENTION  
       [0003]     The present invention relates generally to retrievable plugs and more particularly relates to retrievable plugs for placement in pressurized hydrocarbon wells to temporarily seal a portion of the well. Still more particularly, the present invention relates to a retrievable plug that can be oriented in coil tubing.  
       BACKGROUND  
       [0004]     During hydrocarbon drilling operations, it may become necessary to permanently or temporarily seal off a portion or various zones of a wellbore. Plugs are tools that are typically lowered into a cased hydrocarbon well and provide a seal to isolate two zones in the well when set in position inside the casing. Retrievable plugs provide temporary sealing and separation of zones during drilling and workover operations. Typically, conventional retrievable plugs are characterized by anchoring elements, such as conventional slips, and also generally include one of a variety of conventional rubber seal or packing elements.  
         [0005]     The anchoring elements are used to grip the inside surface of the well casing to prevent the set plug from moving within the casing. The seal or packing elements also engage the inside surface of the well casing to seal the annulus between the plug and well casing. A retrievable plug is removed from the well casing through the release and retraction of the anchoring elements and sealing or packing elements after the shear member is activated.  
         [0006]     Typically, retrievable plugs are designed for use with a range of large diameter casing tubing sizes. In some instances, a plug may be desired to seal sections of coil tubing, wherein the coil tubing may or may not include a longitudinal seam along the tubing inner surface. However, in coil tubing applications, where the tubing diameters can be smaller and the plugs are typically deployed at the bottom of the tubing, retrievable plugs have not been consistently utilized, especially where the coil tubing is characterized by a seam along the inner wall of the coil tubing. The presence of an inner wall seam spanning the length of the coil tubing makes it difficult to properly orient the plug and as a result to completely seal the annulus between the plug and coil tubing. Also, the presence of the inner wall seam makes retrieving the plug difficult and economically inefficient.  
         [0007]     Accordingly, there remains a need to develop new and improved systems and apparatus for a retrievable plug disposed in coil tubing near the surface that address certain of the foregoing difficulties.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0008]     The embodiments of the present invention are directed to methods and apparatus for plugging smaller-diameter coil tubing utilized in a wellbore. It is desired to provide a retrievable plug assembly for use in coil tubing characterized by a seam along the inner wall of the coil tubing. The embodiments of the retrievable plug assembly described herein may also be utilized in coil tubing without an inner wall seam.  
         [0009]     In one embodiment of the present invention, a retrievable plug assembly for isolating or sealing sections of coil tubing comprises a mandrel, seal elements, setting cones, and a slip mechanism. The retrievable plug assembly is anchored within the coil tubing by the slip mechanism, which includes slips, a slip cage, a locking ring, and an anti-setting ring.  
         [0010]     The retrievable plug assembly is lowered into coil tubing to the desired depth. In one embodiment, an orientation tool located on the plug assembly is used to ascertain the location and orientation of the seam of the coil tubing. In an alternative embodiment, a mule shoe orientation guide is used to position the plug assembly prior to insertion into the coil tubing so that the slips are positioned to engage the inner wall of the coil tubing between the seam of the coil tubing. An additional embodiment for locating the seam of the coil tubing includes making an prior trip into the wellbore with a separate tool on which an orientation tool is disposed before inserting the plug assembly.  
         [0011]     Once the retrievable plug assembly is positioned in the coil tubing at the desired depth and orientation, the slip mechanism is activated. In one embodiment, the slip mechanism is activated through the introduction of pressurized hydraulic fluid into the plug assembly. In another embodiment, applying a mechanical force to the plug assembly activates the slip mechanism. When the slip mechanism is activated, the slips are wedged between the mandrel and setting cone, causing the slips to extend radially outward and ultimately engage the inner wall of the coil tubing. In conjunction with the downward movement of the slips, the setting cone is forced downward, and the seal elements are compressed between the setting cone and a collar. As the seal elements are compressed, the seal elements are forced to expand radially until sealingly engaging the inner wall of the coil tubing, thereby creating a seal between the plug assembly and the coil tubing.  
         [0012]     To remove the retrievable plug assembly from the coil tubing, upward force is applied to the mandrel until a shear member located below the seal elements shears. The setting cones and slips become unwedged, allowing the slips to radially retract away from the inner wall of the coil tubing, thereby freeing the plug assembly from its anchored position. The anti-setting ring prevents the slips from re-setting during the removal of the plug assembly from the coil tubing.  
         [0013]     The retrievable plug assembly is configured such that all the critical anchoring elements are located above the seal elements. As a result, the anti-setting ring and slips cannot be damaged by hydrocarbons emanating from the wellbore. Additionally, the disposition of the seal elements downhole of the critical anchoring elements allows the plug assembly to remain in the wellbore for the life of the seal elements.  
         [0014]     Thus, the present invention comprises a combination of features and characteristics that are directed to overcoming various shortcomings of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein:  
         [0016]      FIG. 1A  is a cross-sectional elevation view of the hydraulically activated plug assembly with slips retracted;  
         [0017]      FIG. 1B  is a cross-sectional view of the plug assembly with slips retracted;  
         [0018]      FIG. 2A  is a cross-sectional elevation view of the hydraulically set plug assembly with slips extended;  
         [0019]      FIG. 2B  is a cross-sectional view of the plug assembly with slips extended;  
         [0020]      FIG. 3  is a cross-sectional elevation view of the hydraulically set plug assembly prior to removal;  
         [0021]      FIG. 4  is a cross-sectional elevation view of the hydraulically activated plug assembly during removal;  
         [0022]      FIG. 5A  is a cross-sectional elevation view of the plug assembly with mule shoe orientation guide;  
         [0023]      FIG. 5B  is a cross-sectional view of the mule shoe orientation guide;  
         [0024]      FIG. 6A  is a cross-sectional elevation view of the plug assembly with orientation tool;  
         [0025]      FIG. 6B  is a cross-sectional view of the orientation tool;  
         [0026]      FIG. 7  is a cross-sectional elevation view of the orientation assembly;  
         [0027]      FIG. 8  is a cross-sectional elevation view of the mechanically activated plug assembly with slips retracted; and  
         [0028]      FIG. 9  is a cross-sectional elevation view of the mechanically set plug assembly with slips extended. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, certain embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.  
         [0030]     Referring to  FIG. 1A , one embodiment of retrievable plug assembly  100  includes mandrel  10 , collar  12 , seal elements  14 , setting cone  16 , shear member  28 , and slip mechanism  40 . Slip mechanism  40  includes slips  42 , slip cage  44 , locking ring  46 , retaining ring  47 , and anti-setting ring  48 . Retrievable plug assembly  100  is disposed in coil tubing  30 . In certain embodiments, coil tubing  30  may be characterized by the presence of seam  32  along inner wall  34 , as shown in  FIG. 1B . Seam  32  is formed as a result of the rolling process used during the manufacturing of coil tubing  30 .  
         [0031]     Plug assembly  100  is positioned in coil tubing  30  at the depth desired for setting, and is set using an anchoring element such as slip mechanism  40 . While plug assembly  100  is lowered to the desired depth in coil tubing  30 , anti-setting ring  48  prevents setting cone  16  from traveling up mandrel  10  and prematurely engaging slips  42 . As a result, an early occurrence of extending slips  42  and setting plug assembly  100  is avoided. In certain embodiments slip mechanism  40  is activated through the introduction of pressurized hydraulic fluid from a source outside the wellbore (not shown). Hydraulic fluid is introduced through port  18  and applies pressure at cavity  20  that creates a downward force on slip cage  44 . Slip cage  44  is forced down, and the additional components of slip mechanism  40  match that downward movement with respect to mandrel  10 , setting cone  16 , and seal elements  14 .  
         [0032]     As slip mechanism  40  moves downwardly, it is prevented from moving up in coil tubing  30  with respect to mandrel  10  by locking ring  46 . Mandrel  10  has ratcheting teeth  22  that engage locking ring  46  to retain slip mechanism  40  in position. The downward motion of slip mechanism  40  forces slips  42  to engage the wedge surface on setting cone  16 , thereby ramping slips  42  to extend radially outward until slips  42  engage inner wall  34  of coil tubing  30  and placing plug assembly in set position, as shown in  FIGS. 2A and 2B . An upper portion of slips  42  protrude through slot  48  of slip cage  44 , thereby locking slips  42  into the set position between setting cone  16  and slip cage  44 . While slip mechanism  40  is forced downwardly and into the set position, seal elements  14  are compressed between setting cone  16  and collar  12 . The compression of seal elements  14  causes the seal elements  14  to expand radially to create a sealing engagement between seal elements  14  and inner wall  34  of coil tubing  30 .  
         [0033]     Referring now to  FIGS. 3 and 4 , when the removal of plug assembly  100  from coil tubing  30  is desired, a retrieving tool (not shown) is lowered into the wellbore and engages upper mandrel  26 . An upward force is applied to upper mandrel  26  through the retrieving tool, such that shear member  28  is sheared and mandrel  10  is detached from collar  12 . As a result of the upward movement of mandrel  10 , slips  42  are unwedged from setting cone  16  and retracted from engagement with inner wall  34  of coil tubing  30 . The retraction of slips  42  is aided by retaining ring  47 , which is comprised of an elastomer material and contracts around slips  42  to pull slips  42  away from inner wall  34  as slips  42  are unwedged from setting cone  16 . With the downward force on setting cone  16  released, seal elements  14  decompress, retract away from sealing engagement with inner wall  34  of coil tubing  30 , and expand back to their approximate original size and shape. Once slips  42  are retracted and seal elements  14  are relaxed from sealing engagement with inner wall  34  of coil tubing  30 , plug assembly  100  may be removed out of coil tubing  30 .  
         [0034]     An anti-setting element, including anti-setting ring  48 , prevents slips  42  from reengaging inner wall  34  and re-setting plug assembly  100  during the removal of plug assembly  100  from coil tubing  30 . Anti-setting ring  48  is disposed in a groove on the outer surface of mandrel  10  below ratcheting teeth  22 . As slips  42  are unwedged from setting cone  16  and pulled upward with the rest of slip mechanism  40 , slips  42  are maintained in a retracted position as a result of anti-setting ring  48  preventing the downward motion of locking ring  46 . By stopping locking ring  46 , anti-setting ring  48  also stops slip cage  44  from descending toward setting cone  16  and undesirably translating its motion to slips  42 .  
         [0035]     Referring again to  FIGS. 1B and 2B , plug assembly  100  is desired to be oriented when disposed in coil tubing  30  such that slips  42  are set in a manner that slips  42  do not engage seam  32 . In certain embodiments, orientation elements operate to orient plug assembly  100  and slips  42  in such a manner with respect to seam  32  in order to ensure that the centerline of plug assembly  100  matches that of coil tubing  30 . Further, by orienting plug assembly  100  in this manner, the ability of seal elements  14  to sealingly engage inner wall  34  concentrically and to force seal elements  14  to wrap around and surround seam  32  is assisted. The sealing interface between seal elements  14  and seam  32  is thereby ensured to be tight.  
         [0036]     Referring now to  FIGS. 5A, 5B ,  6 A, and  6 B, embodiments of plug assembly  100  that are constructed to include an orientation element for locating seam  32  are depicted. In the embodiment shown in  FIG. 5A , plug assembly  100  includes an orientation element in the form of mule shoe orientation guide  50 . Mule shoe orientation guide  50  may be utilized in embodiments where plug assembly  100  is run on a wireline. Mule shoe orientation guide  50  allows plug assembly  100 , and specifically slips  42 , to be properly oriented with respect to seam  32  at the surface and prior to insertion into coil tubing  30  such that slips  42  engage inner wall  34  in between seam  32 , as shown in  FIG. 2B . Mule shoe orientation guide  50  operates to orient plug assembly  100  with respect to seam  32  through the use of helical surface  51  and orienting groove  52 . Helical surface  51  guides mule shoe orientation guide  50  and plug assembly  100  during insertion into and while disposed in coil tubing  30  so that orienting groove  52  is keyed to seam  32 . In the present embodiment, it is preferred that orienting groove  52  and slips  42  are disposed on opposed radial sides of plug assembly  100  such that orienting grove  52  and slips  42  are neither aligned nor coplanar in order to ensure that slips  42  do not engage seam  32 . The inclusion of mule shoe orientation guide  50  on plug assembly  100  allows plug assembly  100  to be self-orienting and to be used in deeper wells without the requirement of manipulating the orientation of plug assembly  100  at the surface.  
         [0037]     Referring now to  FIG. 6A , in certain embodiments an orientation element in the form of orientation tool  60  is disposed on plug assembly  100 . Orientation tool  60  assists in the proper orientation of plug assembly  100  so that slips  42  do not engage seam  32 . Orientation tool  60  may be located at any point along plug assembly  100 , but is preferably located at the end of plug assembly  100  that is first inserted into coil tubing  30 . Orientation tool  60  locates the position of seam  32  along inner wall  34  of coil tubing  30  to ensure that slips  42  engage inner wall  34  of coil tubing  30  in between seam  32 , as shown in  FIG. 2B . Orientation tool  60  includes orientation key  62 , orientation tool body  64 , centralizing gauge rings  66 , and spring  68 .  
         [0038]     Plug assembly  100  and orientation tool  60  are lowered into coil tubing  30 , at which point orientation tool  60  is rotated until orientation key  62  catches seam  32 , as shown in  FIG. 6B . In the present embodiment, it is preferred that orientation key  62  and slips  42  are disposed on opposed radial sides of plug assembly  100  such that orientation key  62  and slips  42  are neither aligned nor co-planar in order to ensure that slips  42  do not engage seam  32 . Centralizing gauge rings  66  operate to align orientation tool body and plug assembly  100  with the longitudinal axis of coil tubing  30 . Orientation key  62  is kept in position to catch seam  32  by spring  68 . As a result of utilizing orientation tool  60  to locate seam  32 , there is no need for a prior additional trip down the wellbore with the purpose of finding seam  32  before inserting plug assembly  100 .  
         [0039]     Referring to  FIG. 7 , in an alternative embodiment orientation assembly  200  is utilized to locate seam  32  of coil tubing  30 . Disposed on orientation assembly  200  is orientation tool  60 , which includes orientation key  62 . Orientation assembly  200  and orientation tool  60  are lowered into coil tubing  30  in a separate trip prior to the insertion of plug assembly  100  into coil tubing  30 . Orientation assembly  200  and orientation key  60  are rotated until orientation key  62  catches seal  32 , as shown in  FIG. 6B , thereby indicating the location of seam  32  in coil tubing  30 . Orientation assembly  200  is removed from coil tubing  30 , and plug assembly  100  is lowered into coil tubing  30  in an orientation that prevents slips  42  from engaging seam  32 , as shown for example in  FIG. 2B , as a result of the prior location of seam  32  through the use of orientation assembly  200 .  
         [0040]     Referring to  FIG. 8  and  9 , in an alternative embodiment, slip mechanism  40  is set through the application of hydraulically assisted downward mechanical force. A hydraulically powered setting tool (not shown) is inserted into upper mandrel  26 . The setting tool applies a downward force, causing the downward motion of slip cage  44  with respect to mandrel  10 . As slip cage  44  is forced downward, the remaining components of slip mechanism  40  also move downwardly, causing slips  42  to ramp on setting cone  16 . Slips  42  extend radially and into engagement with inner wall  34  of coil tubing  30 , placing plug assembly  100  in the set position. As slip mechanism  40  is forced further downward, seal elements  14  are compressed and expand radially until reaching sealed engagement with inner wall  34  of coil tubing  30 .  
         [0041]     Referring now to  FIGS. 1A-9 , in certain embodiments seal elements  14  comprise rubber with 50 durometer hardness or less. The 50 durometer seal elements  14  are manufactured by Parker Seal. The industry standard rubber durometer for the sealing or packing elements in downhole packer/plug applications is in the range of 60 to 90 durometer, which indicates the use of a much harder rubber compound. In contrast, the softer rubber compound utilized in certain embodiments of the current invention is crucial in order to sufficiently expand seal elements  14  when compressed through the application of the setting force. As a result of being comprised of a softer rubber compound, seal elements  14  can be squeezed around seam  32  in coil tubing  30 , thereby creating a tighter pressure seal between plug assembly  100  and coil tubing  30 . Additionally, multiple seal elements  14  can be used to further assist in the forming of a tight seal.  
         [0042]     In alternative embodiments, the rubber compound consistency of seal elements  14  may be varied within the multiple seal element stack, with some seal elements  14  comprised of a rubber compound with hardness greater than 50 durometer. Use of seal elements  14  with a hardness greater than 50 durometer allows the plug assembly  100  to release when shear member  28  is sheared as a result of the application of upward force during removal of plug assembly  100 . Seal elements  14  that feature a 50 durometer hardness or less exhibit more difficulty in springing back to the original shape after being compressed to set plug assembly  100  in coil tubing  30  and to place seal elements  14  into sealing engagement with inner wall  34  of coil tubing  30 . The addition of seal elements  14  with a harder rubber compound and hardness over 50 durometer allows plug assembly  100  to release without surface manipulation since a higher durometer rubber compound more easily returns back to its original, pre-compressed form as slips  42  are released from the inner wall  34  of coil tubing  30 .  
         [0043]     Referring again to  FIG. 1A , slip mechanism  40  is located above, or upstream, from seal element  14 . As a result, the critical parts of slip mechanism  40  with regard to keeping plug assembly  100  anchored, such as slips  42 , locking ring  48 , and slip cage  44 , are isolated from the hydrocarbons which may be present in the wellbore. Exposure of the critical anchoring components to hydrocarbons such as sour gas or di-hydrogen sulfide can result in damage to the parts or deterioration of their optimal function. Therefore, plug assembly  100  may remain in coil tubing  30  for the life of seal elements  14 . Shear member  28  is exposed to sour gas and other hydrocarbons present in the wellbore due to the placement of shear member  28  below seal elements  14 . In one embodiment, shear member  28  is comprised of a corrosion resistant alloy, the use of which can extend the life of shear member  28 . Such corrosion resistant alloys are not as susceptible to experiencing changes in properties as a result of exposure to sour gas or other harmful hydrocarbons.  
         [0044]     While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching herein. The embodiments described herein are exemplary only and are not limiting. Because many varying and different embodiments may be made within the scope of the present inventive concept, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.