Abstract:
A connection system to be used in conjunction with a perforating gun comprising a top sub formed to receive one end of a gun body of a perforating gun, a circumferential groove disposed on the outer surface of the gun body, and a collet secured to the top sub. The collet has at least one finger that engages the groove. Engaging the groove with the at least one finger of the collect connects the gun body to the top sub. A cover sleeve is included that retains the finger in connective engagement with the groove.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority from co-pending U.S. Provisional Application No. 60/424,486, filed Nov. 7th,  2002 , the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates generally to the field of oil and gas well services. More specifically the present invention relates to a connector assembly for a perforating gun that is quick, reliable, and simple to use.  
         [0004]     2. Description of Related Art  
         [0005]     Perforating guns containing shaped charges are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations. These perforations hydraulically connect predetermined zones of the earth formations to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore where the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. Without perforations, the hydrocarbons entrained in the formations surrounding the wellbore could not flow into the wellbore.  
         [0006]     Many different types of perforating guns exist, but most have the same basic components. Those components are, shaped charges, a gun tube, a gun body, a top sub or connector, a detonator, and a bottom sub. Typically the shaped charges are disposed within the gun tube, and the gun tube is inserted into the gun body. The top sub is attached to the upper portion of the gun body and connects the perforating gun to a means for raising and lowering the perforating gun into a wellbore. The bottom sub generally attaches to the lower end of the gun body. Often, the bottom sub houses the detonator within a recess located inside of its body.  
         [0007]     When the perforating gun is situated in the portion of the wellbore where a perforation is desired, the shaped charges within the perforating gun are detonated. This in turn produces perforations through the cemented casing lining the wellbore and into the surrounding formation. As is well known in the art, each time a perforating gun is used to produce perforations inside of a wellbore, some of the components of the perforating gun are either expended or fully destroyed. Thus before perforating guns can be reused, they must be returned to the surface and refurbished to replace the parts destroyed or used up during the previous perforation. During its refurbishment the perforating gun usually must be disassembled and reassembled prior to its next deployment.  
         [0008]     Part of the disassembly and reassembly process of the perforating gun involves disconnecting the perforating gun from its raising/lowering means; which is typically a wireline. The wireline is attachable to a cablehead, which provides the connection between the perforating gun and the wireline. Wirelines can also serve to provide a signal conduit from the surface to the perforating gun to actuate detonation of the shaped charges. Generally the wireline cablehead is affixed to the upper sub of the perforating gun and is detached during refurbishment of the perforating gun. Additionally, the upper sub is disconnected from the gun body when the expended portions of the perforating gun are replaced. Thus to help minimize the time and expense of refurbishing perforating guns between subsequent uses, it is important that disconnecting and reconnecting the upper sub to the gun body be quick, simple, and be capable of being done at or close to the wellbore.  
         [0009]     Often, because of special or uniquely sized components used for a specific perforating application, the perforating gun must be transported to a central processing facility for refurbishment instead of the site where the perforations are performed, i.e. the field. Transportation to and from the field to a central processing facility can be financially expensive as well as costly from a lost time standpoint. On the other hand, if a perforating gun could be refurbished for reuse at a field location, the added expense and time of transportation to a central processing facility could be avoided.  
         [0010]     Some examples of perforating guns having connection means can be found in Hromas et al., U.S. Pat. No. 6,098,716, Burleson et al. U.S. Pat. Nos. 5,778,979, 5,823,266, and 5,992,523, and Huber et al., U.S. Pat. No. 6,059,042. However each of these suffer from the drawbacks that they are complex and the connection mechanisms disclosed therein contain multiple moving parts. Additional components add complexity, which reduces reliability and adds capital and maintenance costs. Further, none of the above noted references appears to have the capability of being refurbished or modified in the field, which limits their application to single uses and reduces their flexibility of use.  
         [0011]     Therefore, there exists a need for a device or system in connection with perforating guns that provides for a fast and simple method of connecting and disconnecting perforating guns from a wireline. Also the system should allow for the perforating guns to be prepared at a field site, provide for multiple gun lengths, minimize the time required to assemble the perforating gun assembly, and include a proven way of sealing the perforating guns from wellbore fluids.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     One embodiment of the present invention discloses a connection system for a perforating gun comprising a top sub formed to receive one end of the gun body of a perforating gun. Disposed on the outer surface of the gun body is a circumferential groove. A collet is securable to the top sub where the collet has at least one finger formed onto its body. The collet finger is produced to engage the gun body groove, which in turn connects the gun body to the top sub. Further included with the present invention is a cover sleeve that circumscribes the finger wedging the finger between the cover sleeve and the groove. Also included with the connection system of the present invention is a seal disposed between the top sub and the perforating gun.  
         [0013]     A fastener, such as threaded bolt, screw, rivet, or pin, can be used to secure the collet and cover sleeve to the top sub. The cover sleeve should be freely slideable along the axis of the perforating gun and formed to simultaneously circumscribe the collet and the perforating gun. The magnitude of the inner diameter of the cover sleeve is substantially uniform along its axis up until it reaches a lip of the cover sleeve. The cover sleeve lip is located on the end opposite where the cover sleeve is attached to the collet. The lip protrudes inward toward the axis of the cover sleeve and axially contacts at least one finger.  
         [0014]     An alternative embodiment of a connection system for a perforating gun comprises a top sub formed to receive one end of a gun body of a perforating gun. A groove is circumferentially disposed on the outer surface of the gun body. Also included is a cover sleeve attachably detachable to the top sub on one end and having an inwardly protruding lip on the other end. Mating threads on the cover sleeve and on the top sub can be used to secure the cover sleeve to the top sub. A ring is disposed within the groove having an outer diameter that is at least equal to the inner diameter of the lip. Thus upon attachment of the cover sleeve to the top sub, the lip engages the ring. The engagement of the lip to the ring secures the gun body to the top sub. The ring is comprised of at least two hemispherical sections.  
         [0015]     One of the many features of the present invention involves providing a fast and simple method of connecting perforating guns. The present invention also provides for perforating guns to be assembled at field locations and allows for random length of gun hardware. Further, the time and expense required to assemble/reassemble perforating guns is reduced by utilization of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0016]      FIG. 1  illustrates a partial cross-sectional view of a perforating gun connection assembly having a split ring.  
         [0017]      FIG. 2  depicts a cross-sectional view of a perforating gun connection assembly having a collet.  
         [0018]      FIG. 3A  illustrates a cross-sectional view of a collet.  
         [0019]      FIG. 3B  illustrates an axial view of a collet.  
         [0020]      FIG. 4  illustrates a cross-sectional view of a gun body.  
         [0021]      FIG. 5  illustrates a cross-sectional view of a cover sleeve.  
         [0022]      FIG. 6A  illustrates an axial view of a ring.  
         [0023]      FIG. 6B  illustrates a cross-sectional view of a ring. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     With reference to the drawings herein, a perforating gun quick disconnect system according to one embodiment of the present invention is illustrated in  FIG. 1 . For purposes of reference, bottom or lower refers to portions of the perforating gun located closer to the bottom of the wellbore, whereas top or higher refers to portions of the perforating gun situated closer to the wellbore opening. In one embodiment of the invention as shown in  FIG. 1 , a top sub  10  is secured to the upper end of a gun body  50 . Seals  16  are provided on the outer radius of the top sub  10  and contact the inner radius of the upper section of the gun body  50 .  
         [0025]     In the embodiments illustrated in  FIGS. 1 and 2 , the top sub  10  is substantially cylindrical with a varying diameter, and preferably with its diameter being largest at its mid-section. With regard to the embodiment of  FIG. 2 , it is preferred that the diameter of the top sub  10  be substantially equal to the collet base  41 . Just below the top sub  10  mid-section, its diameter reduces to form a shoulder  12  on which the collet base  41  is secured. An annular retainer  25  is attachable to the lower portion of the top sub  10 . It is preferred that the outer radius of the upper section of the retainer  25  be substantially the same as the inner radius of the collet fingers  42 . However, the radius at the lower section of the retainer  25  should be smaller than the radius of the collet fingers  42 . The reduced diameter along the lower section of the retainer  25  creates an annular space between the collet fingers  42  and the retainer  25 . That annular space should be formed such that it is capable of accommodating the upper portion of the gun body  50  along a portion of its lenght.  
         [0026]     In an embodiment of the invention of  FIG. 1 , a ring  30  is shown situated inside of a groove formed on the outer radius of the upper section of the gun body  50 . The ring  30  is preferably comprised of at least two hemispherical sections that when placed into the groove on the gun body  50 , the ring  30  can circumscribe substantially the entire diameter of the gun body  50 . Alternatively the ring  30  can be comprised of a single section that is press fit into the groove, or be of three or more sections. A cover sleeve  20  is shown circumscribing a portion of the top sub  10  and a portion of the gun body  50 . A cover sleeve lip  21  is formed on the bottom of the cover sleeve  20  having a radius substantially similar to the radius of the ring  30 . The cover sleeve lip  21  protrudes inward toward the axis of the cover sleeve  20 . The presence of the cover sleeve lip  21  adjacent the ring  30  can prevent the ring  30  from axially moving downward past the cover sleeve lip  21 . Threads  22  on the top of the cover sleeve  20  at its inner diameter are formed to mate with corresponding threads located on the outer diameter of the top sub  10 , thus providing a threaded connection between the cover sleeve lip  21  and the top sub  10 . It is important that the cover sleeve  20  inner radius be formed to allow it to easily axially traverse the gun body  50 , and yet leave only a small clearance between it and the outer diameter of the ring  30 .  
         [0027]     Also included with this embodiment of the invention are a shaped charge  54 , a gun tube  52 , and a detonator  56 . The form and type of the top sub  10 , lower sub  11 , seals  16 , detonating cord  57 , gun body  50 , and detonator  56  can vary from those illustrated here without departing from the spirit of the present invention.  
         [0028]     Assembly of the perforating gun of  FIG. 1  generally involves first loading the gun tube  52  with shaped charges  54  using approved ballistic procedures. The detonator cord  57  and associated electrical wire  58  is routed along the path of the ignition points of the charges. The gun tube  52  is then inserted into the gun body  50 . The cover sleeve  20  is slid over the gun body  50  and the top sub  10  is inserted into an opening on the upper portion of the gun body  50 . The ring  30  is placed into the groove  51  on the gun body  50 . The presence of the ring  30  prevents the cover sleeve lip  21  from sliding above the ring  30 . Due to the small clearance between the inner diameter of the cover sleeve  20  and the outer diameter of the ring  30 , the ring  30  is secured in place inside of the groove  51 . It is to be understood that one skilled in the art can determine the clearance between the ring  30  and the cover sleeve  20  necessary to secure the ring  30  within the groove  51 .  
         [0029]     To complete the assembly process, the cover sleeve  20  is slid upwards toward the top sub  10  and screwed onto the top sub  10  by virtue of the threads  22  disposed on the cover sleeve  20  and the top sub  10 . It is important that the sub seals  16  mate up against the inner diameter of the opening of the gun body  50  to prevent fluid leakage from the wellbore to the inside of the gun body  50 . As is well known, if wellbore fluids enter the inside of the gun body  50 , the fluids can either damage the shaped charges  54  before detonation, or cause the gun body  50  to split upon detonation of the shaped charges  54 .  
         [0030]     Another embodiment of the present invention is illustrated in  FIG. 2 . In this embodiment, the ring  30  and threads  22  of the embodiment of  FIG. 1 , are replaced by a collet  40  and a collet fastener  46 . The collet  40  is formed to fit over a portion of the top sub  10  and is securable to the top sub  10 . The features of the collet  40  include a collet finger  42  with a collet finger insert  44 . The collet finger insert  44  is fashioned to fit within the groove  51  formed on the upper portion of the top sub  10 . Also included with this embodiment is a cover sleeve  20  having inner diameter that is sufficiently large to easily slide over the collet finger  42 . While the present invention can be equipped with one or more collet fingers  42 , it is preferred that the number of collet fingers  42  be six. Further, it is also preferred that the collet fingers  42  be radially displaced around the collet  40  with an equal distance between each adjacent collet finger  42 .  
         [0031]     Assembly of the embodiment of the invention shown in  FIG. 2  is much the same as the embodiment of  FIG. 1 . The difference lies in how the gun body is secured to the top sub  10 . In the embodiment of the invention illustrated in  FIG. 2 , the collet  40  is secured to the top sub  10  before insertion of the gun body  50  into the top sub  10 . Insertion of the gun body  50  into the top sub  10  positions the collet finger insert(s)  44  adjacent the groove  51  on the gun body  50  where the collet finger insert(s)  44  can then fit into the groove  51 . As can readily be seen from  FIG. 2 , upon assembly of the present invention, the axis of the collet  40  should be substantially aligned with the axis of the gun body  50 .  
         [0032]     Because the collet finger insert(s)  44  is designed to mate inside of the groove  51 , the distance from the collet axis to the collet finger insert(s)  44  is equal to the distance from the groove  51  to the collet axis. Since the outer radius of the gun body  50  is greater than the distance from the groove  51  to the collet axis, the collet finger insert(s)  44  must be urged axially outward before the gun body  50  is inserted into the top sub  10 . Application of a sufficient upward axial force to the gun body  50  will temporarily bend the collet finger insert(s)  44  outward; thus out of the way of the gun tube  50 . Radial displacement of the collet finger insert(s)  44  allows the gun tub  50  to fit inside of the top sub  10 . To ensure ease of use and a quick turnaround time, the force required to insert the gun body  50  within the collet finger(s)  42 , or retract the gun body  50  from the grasp of the collet finger(s)  42 , should not exceed approximately 50 pounds force. Thus material selection of the collet finger(s)  42  as well as the size of the collet finger(s)  42  is dictated by this requirement. It is believed that one skilled in the art can choose the proper dimensions and material of a collet finger(s)  42  without undue experimentation.  
         [0033]     Once the collet finger insert(s)  44  are within the groove  51 , the cover sleeve  20  can then be slid upward such that the body of the cover sleeve  20  surrounds the collet finger(s)  42  and collet finger insert(s)  44 . The inner diameter of the cover sleeve  20  retains the collet finger insert(s)  44  within the groove  51  on the gun body  50 . The cover sleeve  20  can be secured to the collet  40  by a threaded fastener  46 . However any number of other attachment devices can be employed, such as rivets, pins, or a series of mating threads on the inner diameter of the cover sleeve  20  and the outer diameter of the collet  40 . Firmly securing the collet finger insert(s)  44  inside the groove  51  provides a connection between the top sub  10  and the gun body  52 . This in effect connects the perforating gun to the wireline.  
         [0034]     The present invention could employ a single cover sleeve  20  in conjunction with a single groove  51  formed on the upper or the lower portion of the gun body  50 . This would result in a quick disconnect system for either the top sub  10  or the bottom sub  11 , but not both subs simultaneously. However, a cover sleeve  20  and groove  51  on both ends of the gun body  50  allows for quick and simple removal, as well as attachment, of both the top sub  10  and the bottom sub  11  from the gun body  50 . Thus, it is preferred that the grooves  51  be provided on the gun body  50  at both its upper and its lower end.  
         [0035]     Assembly of a perforating gun could be done with a groove  51  far from either end, but this would require a long collet finger(s)  41  and an elongated cover sleeve  20 . Since a long collet finger(s)  41  or a long cover sleeve  20  can increase the time and effort required to assemble and disassemble the perforating gun, it is preferred that the groove  51  be positioned close to its associated sub.  
         [0036]     One of the many advantages of the present invention is realized during disassembly of the associated perforating gun. Just as the perforating gun having the present invention can be quickly and easily assembled, it can also be quickly and easily disassembled. Once the shaped charges  54  have discharged and the perforating gun is removed from the wellbore, the collet fastener  46  can be removed and the gun body  50  can be detached from the top sub  10 . Detaching the gun body  50  from the top sub  10  of the present invention does not involve the use of tools but instead can be performed manually—simply by pulling the gun body  50  away from the top sub  10 . More importantly, this function can be done in the field, thus eliminating the need to transport the perforating gun to a central processing facility. A loaded perforating gun can then be reattached to the top sub  10  and the perforating process can be repeated immediately.  
         [0037]     The material selection of the gun body  50 , ring  30 , and collet  20  is important. Due to the large impulse forces encountered during use by each of these components, they should be constructed of a material that does not easily yield, either momentarily or permanently. Even small amounts of yield during use can cause the gun body  50  to bond to the collet finger insert(s)  44 . Which is highly undesirable since quick disassembly is important when refurbishing perforating guns. The proper material of the gun body  50 , ring  30 , and collet  20  can be determined by one skilled in the art and without undue experimentation.  
         [0038]     The bottom sub  11  of the embodiment of the present invention of  FIG. 2  can be attached to the gun body  50  in much the same fashion as the top sub  10 . However, because of the detonator  56 , safety procedures typically require that the detonator  56  be connected while the detonator  56  is in a blast shield outside of the gun assembly. The detonator  56  is then connected to the detonating cord  57 .  
         [0039]     One of the many advantages of the present invention is the efficient manner in which the perforating gun can be assembled and disassembled, either for its initial use or for subsequent uses. The present invention enables the assembly/disassembly of the perforating guns to be done at either a primary manufacturing site, or in a remote field site. Thus use of the present invention eliminates time wasted to transport perforating guns to a primary manufacturing site for processing, saves money associated with transporting perforating guns, and reduces the time and effort required to assemble/disassemble perforating guns, either in the field, or at a manufacturing facility. For example, the present invention allows the user the flexibility of forming the groove  51  onto the gun body  50  in the field with a lathe or other machining device. The gun body  50  with its newly formed groove  51  can then be attached to the top sub  10 , while still in the field, inserted into a wellbore, and have the shaped charges within the gun body  50  detonated. After the perforating gun is raised up and out of the wellbore, a new gun body  50 , with a newly formed groove  51  can be switched into the present invention and the perforating process repeated. This provides one example of how use of the present invention allows many functions to take place in the field and reduces the need for machining at a manufacturing site, which in turn reduces costs, effort, and time associated with transportation and engineering coordination.  
         [0040]     A further advantage of the present invention is that the top sub  10  can be disconnected from the perforating gun without the need to disconnect the wireline. This not only saves time, but can reduce possible infield anomalies caused by mistakes in the attachment/detachment during use of the perforating gun. In addition to a cost and time savings, the present invention also is flexible in its application. Use of the present invention is not limited to a single perforating gun of a single length. Instead the present invention can be implemented on perforating guns of any length.  
         [0041]     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes are possible in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.