Abstract:
The present invention provides for a perforating gun having stackable sections that latch, enabling the gun string to carry both compressive and tensile loads. This allows for the downhole assembly of guns of any desired length, and for the entire gun string to be removed after firing.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application 60/369,424 filed Apr. 2, 2002. 
     
    
     
       BACKGROUND  
         [0002]    1. Field of Invention  
           [0003]    The present invention pertains to perforating guns used in subsurface wells, and particularly to perforating guns having stackable sections.  
           [0004]    2. Related Art  
           [0005]    It is often desirable to perforate zones of interest in a subterranean well with very long gun strings to maximize production of well fluids, such as hydrocarbons. This is particularly true in horizontal or highly deviated wells. Gun strings may range in length from a few hundred feet to several thousand feet. Perforating guns are often run into the well using coiled tubing, though drill string may be used if a rig is present at the well site.  
           [0006]    Generally, it is faster and safer to run and retrieve a gun string in an underbalanced well using coiled tubing. (Underbalanced operations help prevent damage to formations.) If drill string is used, a snubbing unit must also be used to seal and control pressure from well fluids. Though coiled tubing may be faster and safer, its use may limit the length of the gun string because the coiled tubing can only push so much load before its buckling strength is exceeded. This is particularly true in horizontal or nearly horizontal wells.  
           [0007]    There are existing systems for downhole stacking of guns. U.S. Pat. No. 6,098,716, assigned to Schlumberger Technology Corporation, is one example. However, those prior art systems have sections that are intended to be stacked in vertical or nearly vertical holes, not horizontal holes. The Schlumberger system uses a connector that mechanically latches in compression, but is not designed to carry a tensile load. Other prior art systems stack, but do not latch at all, and thus can carry neither compressive nor tensile loads. Thus, there is a continuing need for improved sectional perforating guns.  
         SUMMARY  
         [0008]    The present invention provides for a perforating gun having stackable sections that latch, enabling the gun string to carry both compressive and tensile loads. This allows for the downhole assembly of guns of any desired length, and for the entire gun string to be removed after firing.  
           [0009]    Advantages and other features of the invention will become apparent from the following description, drawings, and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]    [0010]FIG. 1 is a schematic diagram of a perforating gun assembly constructed in accordance with the present invention, showing the placement of the lowermost section.  
         [0011]    [0011]FIG. 2 is a schematic diagram of the gun assembly of FIG. 1 showing the addition of another section.  
         [0012]    [0012]FIG. 3 is an enlarged view of a connector, shown in its unconnected state, used to join the sections of the gun assembly of FIG. 2.  
         [0013]    [0013]FIG. 4 is an enlarged view of the connector of FIG. 3, shown in its connected state, used to join the sections of the gun assembly of FIG. 2. 
     
    
     DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 shows a completion assembly  10  including a perforating gun string  12 . Gun string  12  is disposed in a lower portion of a horizontal or highly deviated well bore  14 . Gun string  12  comprises sections  16  (FIG. 2), and each section  16  further comprises subsections  18 . Subsections  18  may be joined using specialized connectors  20 , such as the Completions Insertion and Retrieval Under Pressure Connectors disclosed in U.S. Pat. No. 6,059,042, to permit assembly and disassembly of sections  16  while maintaining well bore  14  in an underbalanced state. FIG. 1 shows coiled tubing  22  being used to place section  16  in well bore  14 , though drill string (not shown) may also be used.  
         [0015]    Coiled tubing  22  has a disconnector  24  on its lower end. Disconnector  24  may be hydraulically or mechanically actuated, as is well known in the art, and can releasably engage each section  16 , as described further below. FIG. 2 shows a subsequent, adjoining section  26  run in and mechanically and ballistically connected to section  16  using a connector  28 . Swivels and weighted spacers may be incorporated in strategic locations of gun string  12  to allow the charges to align in a particular plane, should that be desired.  
         [0016]    [0016]FIG. 3 shows connector  28  in its unconnected state. The upper portion  30  of connector  28 , located on the lower end of section  26 , comprises an overshot  32 , a C-ring  34 , and a donor portion  36  of a sealed ballistic transfer  38 . Overshot  32  helps guide upper portion  30  onto a lower portion  40  of connector  28 . Lower portion  40  is located on the upper end of section  16 .  
         [0017]    C-ring  34  incorporates internal buttress threads  42  that allow C-ring  34  to slide onto a mating set of buttress threads  44  in one direction, but prevent C-ring  34  from coming off in the opposite direction. C-ring  34  is split to allow it to expand and contract to engage mating threads  44 . C-ring  34  is constrained to remain within upper portion  30 , but is allowed to ‘float’ for alignment and engagement purposes. Once engaged with mating threads  44 , C-ring  34  and upper portion  30  cannot be disconnected from lower portion  40  while in well bore  14 .  
         [0018]    [0018]FIG. 4 shows connector  28  in its connected state. As mentioned above, lower portion  40  of connector  28  contains mating buttress threads  44  for C-ring  34 . Lower portion  40  also has an internal running/retrieving profile  46  and a receptor portion  48  of sealed ballistic transfer  38 . Disconnector  24  engages and disengages with profile  46  to connect or release coiled tubing  22  from each section  16 . External buttress threads  44  provide a latching point for C-ring  34 . Receptor portion  48  allows for the continuation of the ballistic train from gun section  26  to gun section  16 . A blank section (devoid of charges) of tubing having connector  28  can be inserted in gun string  12  between charge-bearing sections so long as the ballistic train is maintained therethrough.  
         [0019]    In operation, an appropriate length for section  16  is determined to prevent coiled tubing  22  from buckling and locking up during insertion of section  16  into well bore  14 . The first gun section  16  to be run into well bore  14  is picked up, disconnector  24  is latched into profile  46 , and section  16  is run in to the desired depth. Disconnector  24  is then actuated to release section  16 . For example, if disconnector  24  is hydraulically actuated, fluid is pumped down an interior passageway of coiled tubing  22  to release disconnector  24 . Coiled tubing  22  is then removed from well bore  14 . The next gun section  16  (e.g., section  26 ) is picked up and run in the same way, and latched onto the lower portion  40  of connector  28 . Subsequent gun sections  16  are run in as required until a desired length is reached. A firing head  50  (FIG. 1) is attached to coiled tubing  22  or uppermost gun section  16 . This terminal section  16  is run in well bore  14  and latched onto the adjoining lower section  16 .  
         [0020]    Gun string  12  can be fired in various ways, depending on the type of firing head  50  used. For example, to fire gun string  12  using a pressure-actuated firing head  50 , a ball (not shown) is pumped down coiled tubing  22  until it lands in a seat (not shown) in firing head  50 . Pressure is increased to a predetermined level to shear a shear pin and initiate firing. Gun string  12  then fires along its entire length. Other firing head options are feasible, such as a hydraulic delay firing head. The coiled tubing  22  can remain attached or be disconnected and removed from well bore  14  before firing.  
         [0021]    After firing, well bore  14  is perforated. The entire gun string  12  can be retrieved to surface and gun sections  16  can be removed from well bore  14 . If specialized connectors  20  were used to assemble sections  16 , the sections can be removed without killing the well.  
         [0022]    An alternative operation would be to run the entire gun string  12  into well bore  14  with drill pipe (not shown), disconnect with disconnector  24 , fire gun string  12 , and retrieve the entire gun string  12  with coiled tubing  22  using specialized connectors  20 . The drill pipe is strong enough to allow the entire gun string  12  to be run in all at one time, or it can be run in in sections as described above. If drill pipe is used to retrieve the guns after perforating, a snubbing unit is required to remove sections  16  without killing the well.  
         [0023]    Although only a few example embodiments of the present invention are described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example 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. 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.