Abstract:
A release tool and method of use for releasing tools (such as perforating guns) from tool strings (such as perforating strings) after use in well bore operations. It is emphasized that this abstract is provided to comply with the rules requiring an abstract, which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
[0001]     The present application claims benefit of U.S. Provisional Application Ser. No. 60/522,253, filed Sep. 7, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Technical Field  
         [0003]     The present invention relates generally to hydrocarbon well operations and equipment, and more particularly to a releasable connector assembly for a perforating gun and method of use.  
         [0004]     2. Background  
         [0005]     It is often desirable to automatically disconnect a tool from a string in a well after completion of a particular operation. For example, once a perforating gun suspended in a wellbore on a conveyor line (e.g., wireline, tubing, jointed tubing, coiled tubing, or slickline) has been detonated to achieve perforation of a target well zone, it may be advantageous for the perforating gun to automatically disconnect from the conveyor line. This is especially true in permanent completions where no additional conveyor line runs are desired. The automatic disconnection of the perforating gun from the conveyor line may be desirable because in certain formations, an inflow of formation fluids follows detonation and may cause the perforating gun to “sand up” and become stuck in the casing. Many such automatic releases are available from various manufacturers. A difficulty with some of these conventional automatic releases is that the perforating gun typically falls to the bottom of the well after detonation, and thus, the perforating gun is not recoverable.  
         [0006]     To address this problem, some perforating gun strings may include modular perforating gun sections that automatically disconnect in a manner that allow the sections to be retrieved from the well after detonation. However, a problem with this approach is that the detonation of downhole explosives and/or the in-rush of well fluid may propel the disconnected sections up the wellbore and damage or “blow up” the well. Moreover, some existing gun release systems may not be useable in closed tubing applications where the pressure within the tubing string is less than the pressure in the wellbore.  
         [0007]     Thus, there exists a continuing need for a perforating system having sections that automatically disconnect after detonation and yet do not pose a great danger to the well after disconnection.  
       SUMMARY  
       [0008]     Generally, in one embodiment of the invention, an apparatus for releasably coupling a perforating gun to a tubing string includes a latching mechanism to couple the perforating gun to the string. The latching mechanism connects the perforating gun to the tubular member before detonation of the perforating gun. In response to the detonation of the perforating gun, the latch automatically disconnects the perforating gun from the tubular member after the expiration of a duration of time.  
         [0009]     In another embodiment, the apparatus further includes a balancing assembly to substantially balance the pressure forces inside the tubing with the pressure forces in the wellbore. This is particularly significant when tubing pressure is less than wellbore pressure. This embodiment may further include a sealing assembly to seal the tubing from the wellbore.  
         [0010]     Another embodiment of the present invention include a method for connecting a perforating gun to a string, detonating the perforating gun, and disconnecting the perforating gun from the string in response to the detonation. In some embodiments, the method includes equalizing the pressure within the tubing with the pressure outside the tubing such that the weight of the perforating gun causes the perforating gun to release from the tubing string.  
         [0011]     Other or alternative features will be apparent from the following description, from the drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The manner in which these objectives and other desirable characteristics can be obtained is explained in the following description and attached drawings in which:  
         [0013]      FIG. 1  illustrates a profile view of a gun system being deployed in a wellbore, the gun system being coupled to a tubing by an embodiment of a connector assembly of the present invention.  
         [0014]      FIG. 2  illustrates a profile view of the gun system of  FIG. 1  being disconnected from a tubing in a wellbore.  
         [0015]      FIG. 3  illustrates a cross-sectional view of an embodiment of a connector assembly for use in releasably connecting a perforating gun to a tubing.  
         [0016]      FIGS. 4A-4C  illustrate an embodiment of the equalizing mechanism in accordance with the present invention.  
         [0017]      FIG. 5  illustrates an enlarged cross-sectional view of an embodiment of a connector assembly for use in releasably connecting a perforating gun to a tubing.  
     
    
       [0018]     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.  
         [0020]     In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate.  
         [0021]     Some prior gun release tools have proved to instantly and reliably drop off perforating gun strings at very high deviations. For example, a prior art gun release sub may be run on new wells where a ported sub is incorporated above the release sub; therefore, the tubing pressure and the rathole pressure are equalized. However, for operations requiring the tubing to be closed and sealed against rathole pressure, an upward force is created by the differential pressure against the seal diameter in the release housing of the release sub. If the tubing pressure is substantially less than the rathole pressure and gun weight (deviation reduces the gun weight) is insufficient to overcome the differential pressure force, the tool will not drop the guns. In this case, the release sub acts like a plug in the end of the tubing. Even though the guns can be detonated, if the release sub does not drop off, hydrocarbons may not flow up in the tubing to surface. The focus of the proposed invention is an automatic gun drop tool that is pressure/force balanced to pressure differentials between rathole and tubing, therefore allowing the gun string to drop.  
         [0022]     Generally, with reference to  FIGS. 1 and 2 , an embodiment of the present invention includes a connector assembly  10  for coupling a perforating gun  20  (or other completion tool actuated by a detonation such as a tubing cutter) to a tubing string  30  (or other downhole string such as a tool string) suspended in a wellbore  40 . The connector assembly  10  includes: (1) a latching mechanism for releasing the gun  20  from the tubing string  30  when the gun is detonated; and (2) an equalizing mechanism for equalizing the pressure between the inside of the tubing  30  and the wellbore  40  such that the gun  20  may release from the tubing in closed tubing applications (e.g., where the pressure inside the tubing may be less than the pressure outside of the tubing).  FIG. 1  illustrates the perforating gun  20  being coupled to the tubing string  30  via the connector assembly  10 .  FIG. 2  illustrates the perforating gun  20  being released from the tubing string  30  post-detonation.  
         [0023]     In operation, the perforating gun  20  is fixedly secured to the connector assembly  10  and the gun is run downhole on the tubing string  30  to a target formation interval  50  of a wellbore  40 . At this target formation interval  50 , the perforating gun  20  is detonated. When the perforating gun  20  detonates, the latching mechanism of the connector assembly  10  automatically disconnects (immediately or after a duration of time, as described below) the perforating gun by releasing the latch&#39;s hold on the tubular string  30 . In alternative embodiments, a plurality of perforating guns may be connected to a tubing string via a plurality of connector assemblies arranged in series whereby the guns are detonated. In other embodiments, the perforating gun section  20  may be retrieved after the perforating gun detonates. In these embodiments, the perforating gun may be of sufficiently short length (e.g., 40 feet) to allow the perforating gun to be retrieved into a riser of a well without killing the well.  
         [0024]     Various embodiments of the connector assembly of the present invention include a latching mechanism and an equalizing mechanism. Embodiments of such a latching mechanism are described in U.S. Pat. No. 5,293,940, which is incorporated herein by reference.  
         [0025]     With respect to  FIG. 3 , in one embodiment of the connector assembly  10 , a release housing  10 A is adapted to be connected to a tubing  30 . A first sub or fill sub  61  having at least one firing head  18  arranged therein is connected to a latching mechanism releasably engaging the housing  10 A. The latching mechanism (including a frangible breakup plug  12 , a release piston  14 , and collet fingers  16 ) is adapted to be disposed within the release housing  10 A and is connected to a second sub  10 B. The second sub  10 B is adapted to be connected to a perforating gun  20 . In operation, when a detonation wave from the firing head  18  passes through the frangible breakup plug  12 , the frangible breakup plug shatters; and, when the breakup plug shatters, the release piston  14  moves down and the latching mechanism disconnects the second sub  10 B (including the attached perforating gun  20 ) from the release housing  10 A and allows the perforating gun  20 , second sub  10 B, release piston  14 , collet fingers  16  and fill sub  61  and firing head  18  to withdraw from within the release housing  10 A and away from the tubing  30 .  
         [0026]      FIG. 4A  illustrates an embodiment of the equalizing (or pressure balancing) mechanism of the connector assembly  10 . The equalizing mechanism includes a balance mandrel  60 , a lower piston  70 , and an upper seal sleeve  80 . The lower section of the balance mandrel  60  is connected to the second sub  10 B (e.g., a perforating gun adapter) and includes a seal diameter D 1  for sealing with the lower piston  70  and a larger seal diameter D 2  for sealing inside a release housing  10 A. The release housing  10 A defines an axial bore therein. The gun adapter  10 B is butted up against the lower piston  70 , which is butted up to a shoulder  72  inside the release housing  10 A and seals with the axial bore of the release housing. The upper end of the balance mandrel  60  includes a larger seal diameter D 2 , which also seals inside the release housing  10 A and opposite of the lower piston  70 . The annular gap between the larger seal diameter D 2  and the smaller seal diameter D 1  on the balance mandrel  60  defines an area A 1  against an air chamber (or other low pressure/compressible fluid chamber), which is approximately equal to the area defined by the smaller diameter D 1  of the balance mandrel  60 . Fluid holes  74  in the release housing  10 A expose the volume inside the release housing to the wellbore and allow wellbore fluid pressure to act against the annular area A 2 . Therefore, the pressure force up against the area A 1  is equal to the pressure force against the area A 2 , which balances the connector assembly (assuming that the pressure in the sealed off tubing is equal to zero). The internal seal diameter of the upper seal sleeve  80 , which seals off the wellbore pressure from the tubing pressure, is the same area A 1  as on the balance mandrel  60 . The upper seal sleeve  80  butts up to another shoulder  76  within the release housing  10 A and seals inside the release housing. Thus, wellbore fluid pressure cannot push the upper seal sleeve  80  upward. As shown in FIGS.  4 B-C, if the tubing pressure is greater than zero (e.g., the weight of the gun), an additional downward force is created to aid pushing the balance mandrel  60  out of the release housing  10 A. As the balance mandrel  60  disengages from the release housing  10 A, the lower piston  70  and upper seal sleeve  80  are displaced by elements  64  and  66  on the balance mandrel  60 , respectively, to facilitate full release of the gun adapter  10 B (and perforating gun). In some embodiments, the elements  64 ,  66  have a cross-sectional diameter larger than the diameter of the balance mandrel  60  but equal to or smaller than the diameter of the bore of the release housing  10 A below the upper seal sleeve  80 .  
         [0027]     Still with respect to  FIGS. 4A-4C , in some embodiments, the balance mandrel  60  includes one or more equalizing slots  62  formed in the upper balance section  60 A for balancing the tubing pressure with the wellbore pressure. Initially, the slots  62  are positioned above the upper seal sleeve  80  (as shown in  FIG. 4A ). As the balance mandrel  60  begins to move axially downward, the slots  62  uncover the inner seal of the upper seal sleeve  80  (as shown in  FIG. 4B ). This allows the tubing pressure to balance with the wellbore pressure thus facilitating the gun adapter  10 B to drop out of engagement with the release housing  10 A (as shown in  FIG. 4C ).  
         [0028]     Referring to  FIG. 3 , an embodiment of the initiation device as adapted to the connector assembly of the present invention is illustrated. The release housing  10 A is adapted to be connected to the tubing  30 . A fill sub  61  is provided for enclosing one or more firing heads  18 . A firing head adapter  100  and transfer housing  110  receive the firing head  18  and connect the firing head to a balance mandrel  60 . A detonating cord  115  is connected to a perforating gun  20 , which is disposed on the other side of the connector assembly. The detonating cord  115  passes through the center of the connector assembly  10 , and extends from the firing head  18 , on one side, to the perforating gun  20 , on the other side.  
         [0029]     With respect to  FIGS. 3 and 5 , an embodiment of the connector assembly  10  of the present invention comprises: (1) a release piston  14  sealingly connected to the transfer housing  110 , the release piston  14  having a protruded portion or locking upset  14 A; (2) collet fingers  16  each having an end  16 A which is adapted to contact the locking upset  14 A of the release piston  14 , on one side, and adapted to contact a threaded connection  111  disposed on an internal periphery of the release housing  10 A, on the other side, when the end  16 A contacts the locking upset  14 A, the collet fingers  16  being ultimately operatively connected to the transfer housing  110  via a release collet  120 ; (3) a set of release pins  15  arranged between the collet fingers  16  and the release piston  14 , the release pins  15  holding the collet fingers  16  radially outward into engagement with the internal periphery of the release housing  10 A when adjacent to the locking upset  14 A of the release piston  14 ; (4) a release collet  120  integrally connected to the collet fingers  16  and sealed against the release housing  10 A, the release collet  120  being supported from below by the lower section  60 B of the balance mandrel  60 ; (5) locking screws  132  for securing an anti-rotation lock  130  to the gun adapter  10 B, the anti-rotation lock  130  preventing the gun adapter  10 B (and thus the gun) from rotating relative to the release housing  10 A; (6) a breakup plug  12  fabricated from any frangible material (e.g., ductile iron, cast iron, ceramic, and so forth) being sealingly connected to the release piston  14 , one end  14 B of the release piston  14  being sealingly disposed between one end of the frangible breakup plug  12  and the release collet  120 , the other end of the frangible breakup plug  12  being sealingly disposed against the lower balance section  60 B of a balance mandrel  60 ; (7) an air chamber  140  formed around the frangible breakup plug  12 ; (8) a balance mandrel  60  (having an upper balance section  60 A and a lower balance section  60 B) including one or more equalizing slots  62  formed in the upper section  60 A, the balance mandrel  60  being arranged between the release piston  14  and the transfer housing  110 ; (9) a moveable lower piston  70  sealing beween the release housing  10 A and the lower balance mandrel  60 B; (10) an upper seal sleeve  80  sealing beween the release housing  10 A and the upper balance mandrel  60 A; and (11) a bottom sub or gun adaptor  10 B operatively connected to the release collet  120  via the lower section  60 B of the balance mandrel  60 , the bottom sub  10 B being connected to the perforating gun  20 .  
         [0030]     In  FIG. 5 , in some embodiments of the connector assembly  10 , a wireline re-entry guide  140  represents the actual shape of the end of the production tubing or alternatively the release housing  10 A. The wireline re-entry guide  140  is sometimes called a “muleshoe” and is shaped at an angle, having an internal bevel to provide for easy re-entry of wireline tools into the tubing after the tools have run out of the end of the tubing. The purpose of guide  140  is to reduce the chance of hanging up wireline tools when re-entering tubing.  
         [0031]     With reference to  FIGS. 3 and 5 , in operation, an embodiment of a perforating gun system in accordance with the present invention includes providing a connector assembly (as described above in various embodiments) to releasably connect a tubing  30  to a perforating gun  20 . Once connected, the gun system is lowered into a wellbore to target perforating depth. Other perforating accessories, such as a packer, may be placed above the connector assembly in the wellbore. Wellbore fluid enters the release housing  10 A via ports  17  and surrounds the firing head  18  and release piston  14 . Hydrostatic pressure tends to force the release piston  14  downwardly into the air chamber  141 , which chamber  141  is sealably formed, at one end, by the lower end of the release piston  14 , which has a cross sectional area of “A 2 ”, and the inside portion of the balance mandrel  60 . The upper end of the release piston  14  has a cross section area of “A 1 ”. The release piston  14  is forced downwardly by a force, which is equal to the area (A 2 −A 1 ) times the hydrostatic pressure. However, initially, the release piston  14  cannot move downwardly because the frangible breakup plug  12  rigidly positions the piston  14  in place by abutting against the bottom of piston  14 , on one end, and against a shoulder inside the balance mandrel  60 , on the other end. The downward pressure force induced on the release piston  14  induces a downward compressive force on the frangible breakup plug  12 . The frangible breakup plug  12  is designed to be stronger than any compressive force that can be induced by the release piston  14 . Therefore, the release piston  14  is rigidly held in position by the frangible breakup plug  12 , and the locking upset  14 A of release piston  14  is positioned adjacent to the release pins  15  and the end  16 A of collet finger  16 ; as a result, the collet fingers  16  are prevented from collapsing, and the gun adapter  10 B is locked to the release housing  10 A. A fluid leak in the gun string prior to initiating the firing head  18  cannot move the release piston  14  and prematurely release the perforating gun from the tubing  30  because the frangible breakup plug  12  rigidly prevents the release piston  14  from moving.  
         [0032]     However, when the firing head  18  is initiated, a detonation wave is initiated within the detonating cord  115 , the detonation wave propagating from the firing head  18 , through the firing head adaptor  100 , transfer housing  110 , release piston  14 , frangible breakup plug  12 , balance mandrel  60 , and gun adapter  10 B, shooting the perforating gun  20 . When the detonation wave propagating in the detonating cord  115  passes through the frangible breakup plug  12 , the resultant shock wave and pressure from the detonation wave shatters the breakup plug  12 , which is made of a frangible material that shatters in response to the shock wave from the detonating cord  115 . The breakup plug  12  shatters into small pieces. As a result, the release piston  14  is no longer supported and held in position by the breakup plug  12 . The pressure force pushing down on the release piston  14  forces the piston  14  down into the air chamber  140 . The locking upset  14 A on the release piston  14  moves out from under the end  16 A of the collet fingers  16 . The weight of the perforating gun connected to the gun adapter  10 B causes the collet fingers  16  to collapse inwardly thereby disengaging the release collet  120  from the release housing  10 A (the collet fingers  16  collapse inwardly due to the angle of the threads on the inside of the release housing  10 A and the mating threads on the outside of the collet fingers  16 ).  
         [0033]     Initially, the equalizing slots  62  in the upper section  60 A of the balance mandrel  60  are positioned above the upper seal sleeve  80 . However, as the release piston  14  begins to move axially downward, the balance mandrel  60  shifts downward such that the slots  62  uncover the inner seal of the upper seal sleeve  80 . This allows the tubing pressure to balance with the wellbore pressure thus facilitating the release of the release piston  14 .  
         [0034]     When the release collet  120  is disengaged from the release housing  10 A, the following equipment falls to the bottom of the wellbore: the perforating gun  20 , the gun adapter  10 B, the lower piston  70 ; the lower balance section  60 B, the release collet  120  and collet fingers  16 , the release piston  14 , the upper seal sleeve  80 , the upper balance section  60 A, the transfer housing  110 , the firing head adapter  100 , and the fill sub  61  with the firing head  18 .  
         [0035]     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. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.