Abstract:
A sealed perforating gun assembly for use with automatic pipe handling equipment on oil and gas drill rigs. An upper sealed connector and a lower sealed connector have sealed threaded connections for mating with ends of a perforating gun. The connectors have external dimensions equivalent to the external dimensions of standard drill pipe and have standard tapered thread couplings. Ignition transfer explosives are carried within cavities in the connectors. The cavities are sealed on their drill pipe coupling ends. The ignition transfer explosives are adapted to penetrate the seals so that ignition can be transferred between the gun assembly and adjacent sections of the gun string. Since the external dimensions of the sealed connectors correspond to the external dimensions of drill pipe, automatic drill pipe handling equipment can handle the gun assemblies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    None.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         REFERENCE TO A MICROFICHE APPENDIX  
         [0003]    Not applicable.  
         FIELD OF THE INVENTION  
         [0004]    This invention relates to perforating guns for use in hydrocarbon wells and more particularly to an assembly of sealed connectors and perforating guns which allow perforating guns to be handled by automatic pipe handling apparatus.  
         BACKGROUND OF THE INVENTION  
         [0005]    The completion of oil and gas wells by gun perforating is well known in the art. A work string including one or more perforating guns is lowered into a well casing cemented into the wellbore. The perforating guns are positioned adjacent to the formation to be perforated. The perforating guns are fired to penetrate the casing and cement and form perforations into the producing formation for recovery of the desired fluids. These perforating guns typically utilize shaped charges to form the perforations.  
           [0006]    Typically, a firing head is positioned at the top of the string of guns and is connected to the uppermost gun of a string of guns. A time domain firer (TDF) is positioned between adjacent pairs of guns. When the firing head is triggered, the uppermost gun is then fired, and the time domain firers then cause the string of guns to be fired sequentially from top to bottom. On occasion, the firing sequence is from bottom to top.  
           [0007]    There is inherent risk in handling the explosive components which must be assembled to make a perforating gun. Even after the guns are assembled, there is risk in handling the completed guns. The assembled guns are typically connected to a drill string for placement in the borehole. Safety regulations increasingly discourage or prohibit the manual handling of perforating guns on drill rigs due the risks involved. As a result, there is a need for apparatus and methods which allow perforating guns to be handled automatically on drill rigs.  
         SUMMARY OF THE INVENTION  
         [0008]    One embodiment of the present disclosure provides a perforating gun assembly having external dimensions corresponding to the dimensions of standard drill pipe joint couplings, and adapted for handling by automatic drill pipe handling systems. One or more conventional perforating guns is assembled with two sealed subs having pipe joint threaded couplings.  
           [0009]    In one embodiment, the interior of each sealed sub carries a bi-directional explosive for transferring a detonation to or from the perforating gun.  
           [0010]    The perforating gun assembly of the present disclosure is assembled into a drill string with conventional drill pipe handling equipment. Multiple assemblies may be connected together like standard drill pipe joints. When the guns are fired, the explosive transfer path couples the detonation to successive guns to fire the entire string. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is generalized illustration of a borehole in the earth with a pipe string carrying a perforating gun assembly according to the present invention.  
         [0012]    [0012]FIG. 2 is a cross sectional illustration of an upper sealed connector and a portion of a perforating gun according to the present invention.  
         [0013]    [0013]FIG. 3 is a cross sectional illustration of a lower sealed connector and a portion of a perforating gun according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    In the following description, the terms “upper”, “upward”, “uphole”, “lower”, “above”, “below”, “downhole”, and the like, as used herein shall mean in relation to the bottom, or furthest extent as measured from the surface location, of the wellbore even though portions of it may be deviated from vertical or may be horizontal. These terms are intended to describe the relative position of a perforating gun in the vertical position normally used for assembling the gun into or as part of a drill string or work string for lowering into a borehole. Boreholes are normally essentially vertical at their surface location. Work strings and drill strings are normally connected together joint by joint or section by section at the borehole surface location as they are lowered into the borehole. While perforating guns may be lowered into a borehole on a string of drill pipe, it is understood that perforating gun assemblies are not designed to withstand the torque normally encountered during drilling operations and would not be present during drilling operations. These terms are used for convenience in describing the invention and are not intended to be limiting.  
         [0015]    [0015]FIG. 1 illustrates a borehole  10  passing through an earth formation  12 , from which it may be desired to produce fluids. The borehole  10  is lined with a casing  14  which is set in the borehole  10  with cement  16 . Two perforating guns  18  and  20  are shown positioned in the borehole  10  within the zone  12  in preparation for forming perforations through the casing  14  and cement  16  to allow fluids to flow from formation  12  into the casing  14 .  
         [0016]    A perforating gun assembly  22  according to the present invention includes the perforating gun  18 . It also includes an upper sealed connector  24  and a lower sealed connector  26 . The upper connector  24  includes a drill pipe box coupling  28  having an internal tapered thread. The external dimensions of coupling  28  are within the tolerances for a standard box coupling of standard drill pipe. As a result, tools designed for handling of standard drill pipe are capable of handling the gun assembly  22  as if it were a drill pipe joint.  
         [0017]    The lower sealed connector  26  includes a drill pipe pin coupling having an external tapered thread, not shown in this figure. The external dimensions of this coupling, in particular the external upset, are within the tolerances for a standard pin coupling of standard drill pipe. As a result, standard drilling equipment, e.g. an iron roughneck, can grip the coupling  26  for making or breaking a threaded joint.  
         [0018]    The assembly  22  is suspended in the borehole  10  by a drill string including a pipe joint  30  which may include a firing assembly and detonator for the gun modules  18  and  20 . The lower end of joint  30  includes a standard pin coupling connected to the upper sealed connector  24 . Another section of drill pipe  32  may have an upper box coupling connected to lower sealed connector  26 . A lower pin coupling  36  of joint  32  may be connected to an upper sealed connector  38  forming part of a second perforating gun assembly according to the present disclosure including the perforating gun  20 . The section  32  may include detonating cord running from end to end to transfer ignition between gun modules  18  and  20 .  
         [0019]    [0019]FIG. 2 provides a cross sectional illustration of the upper sealed connector  24  and a portion of the perforating gun  18  according to the present invention. As discussed above, most of the external dimensions and shape of the upper connector  24  are equivalent to standard drill pipe, or tool, joints. For example, the main body  40  of connector  24  may be a cylinder having a nominal outer diameter of 3.5 inch, as used in standard 3.5 inch drill pipe. In this embodiment, this main body  40  has a length of about thirteen inches. At the upper end of body  40  is a external upset  28  having an external nominal diameter of about 4.75 inch. As illustrated, the upset portion  28  has a standard tapered internal thread  42  complementary to standard drill pipe pin couplings. On the lower end of body  40  is another upset  44  adapted for coupling to a standard perforating gun module  18  female threaded end. The upset  44  includes a straight section  46  having external acme threads complementary to internal acme threads  48  on the upper end of gun module  18 . The upset  44  has two grooves  50  in which are carried O-rings  52  to form a fluid tight seal with the gun  18 .  
         [0020]    The upper connector  24  has a central cavity  54  extending from its lower end in upset  44  almost to the bottom of the box thread  42  in the upper end of the connector  24 . The cavity  54  is closed at its upper end by a thin wall  56  forming part of the bottom of the box coupling  42 .  
         [0021]    An explosive device  58  is disposed in housing cavity  54  and is adapted to provide an explosive transfer in either direction between the upper end of connector  24  and the perforating gun  18 . Device  58  may comprise an insert  60  which is held in the upper end of cavity  54  by a retaining means, such as the frictional engagement of an O-ring. A booster charge  64  is disposed in the lower end of insert  58 . Booster  64  has a metallic portion  66  which is crimped around the lower end of a length of detonating cord  68 . A detonating cord initiator  70  has a metallic portion  72  which is crimped around the upper end of detonating cord  68 . The detonating cord  68  is carried loosely within the cavity  54  and is held in place by connection to the booster charges at its ends. Detonating cord initiator  70  also includes a powder charge  74 . A shaped charge  76  having a conical cavity  78  is positioned adjacent to the charge  74 . The shaped charge  76  cavity  78  is directed toward the wall  56  closing the upper end of cavity  54 . The charge  76 , upon detonation, will perforate the wall  56  in order to transfer ignition to devices connected above the connector  24 . Alternatively, a detonator or other ignition transfer device above connector  24  may have a similar shaped charge which can perforate wall  56  to ignite the shaped charge  76  and the rest of device  58  to transfer ignition to the perforating gun  18 .  
         [0022]    The perforating gun  18  is connected to the lower end of upper connector  24  by the threaded joint  46 ,  48 . A fluid tight seal for the joint is provided by the O-rings  52 . A booster  80  is positioned in gun  18  adjacent the booster  64  in the lower end of upper connector  24 . The booster  80  is connected to a detonating cord  82 , which is coupled to perforating charges, preferably shaped charges, in the gun  18 . There are no seals or metal walls separating the booster charges  64  and  80 . Upon ignition of either charge, the ignition will be transferred to the other charge.  
         [0023]    [0023]FIG. 3 provides a cross sectional illustration of the lower sealed connector  26  and a lower portion of the perforating gun  18  according to the present invention. The lower connector  26  has external dimensions equivalent to standard drill pipe, or tool, couplings. For reasons which will become apparent, in this embodiment, the lower connector  26  does not have a body portion having the nominal drill pipe diameter. Instead, it has an upset portion  84  having a nominal diameter of 4.75 inch corresponding to standard drill pipe pin coupling upsets. Below the upset  84  is a tapered thread pin coupling  86 . The upset  84  and coupling  86  have dimensions corresponding to standard drill pipe, or tool joint, pin couplings. Above the upset  84  is a straight threaded section  85  adapted for forming a sealed connection with a female end of perforating gun  18 . The section  85  has an acme threaded section  90  and O-ring section  92  for making a sealed threaded connection to the lower end of gun  18 .  
         [0024]    The lower connector  26  has an internal cavity  94  extending from the upper end of the threaded section  85  to a thin wall  96  at the lower edge of pin coupling  86 . Carried within cavity  94  is an explosive device  96  which may be essentially identical to the explosive device  58  carried within the upper connector  24 . The detonating cord  98  in lower connector  26  is somewhat shorter than the cord  68 , since the lower connector  26  can be shorter than the upper connector  24 .  
         [0025]    The lower end of gun  18  carries a booster charge  100  positioned opposite the explosive device  96  in the lower connector  26 . It also includes the other end of detonating cord  82 . The charge  100  is adjacent the device  96  in the lower connector. There are no seals or metal walls separating the charges  96  and  100 . Upon ignition of either charge, the ignition will be transferred to the other charge.  
         [0026]    In this embodiment, the connectors  24 ,  26  each have a male threaded section  46 ,  85  adapted for threaded coupling to a female threaded end of a perforating gun unit. This arrangement is preferred because the most common gun units have female threaded couplings on both ends. It is apparent that the ends of connectors  24 ,  26  adapted for connection to the perforating gun may be provided with a female threaded coupling if needed for perforating guns which may have a male threaded coupling, or which may be assembled with a tandem coupler.  
         [0027]    The present disclosure allows for safe handling of perforating guns on drilling rigs. It allows the guns to be assembled into work strings and lowered into a borehole automatically so that workers are not exposed to injury from accidental ignition of the guns. The assembly of a perforating gun  18  with an upper connector  24  and a lower connector  26  can be carried out in a controlled environment in a building away from the drill rig. If desired, more than one gun  18  can be connected into a gun assembly with one upper connector  24  and one lower connector  26 . In some embodiments a conventional tandem gun connector may be used for mechanically and explosively coupling successive guns. In any case, the completed assembly is completely sealed. That is, all explosive components are encased in metal housings. The upper and lower ends are sealed by the walls  56  and  96  in upper and lower connectors  24  and  26 . This greatly reduces the chance of accidental ignition as a result of accidental mechanical contact, flame or electrical spark. The completed assembly can be pressure tested at the factory to check for fluid leaks. There is no need to open the completed gun assembly after testing. This helps a void damage by leakage of drilling fluids when the gun  18  is positioned in a borehole.  
         [0028]    The completed gun assembly, with upper and lower connectors  24 ,  26 , can be transported to the drill site like other tubular goods. It can be handled with the same pipe handling equipment used to handle drill pipe, tool joints, etc. When it is time to install the gun or guns in a borehole for firing, the gun assembly is automatically lifted into position on the drill rig without need for human contact or exposure. Automatic elevators are designed to grip the upper end of drill pipe joints with bushings shaped to fit the upper external upset of the upper coupling and a length of the joint below the upset. The upper connector  24  body section  40  preferably has a length sufficient to be gripped in this manner by conventional elevator equipment. The disclosed embodiment length of about thirteen inches was selected based on the dimensions of such elevator equipment. The outer diameters of the upsets  28  and  84  are of the standard diameters for which iron roughneck tools are designed to grip for making up threaded joints as pipe is run in the borehole or breaking those joints when pipe is being removed from the borehole.  
         [0029]    As illustrated in FIG. 1, two gun assemblies  18  and  20  may be separated by a spacer section  32 . The section  32  normally would carry an ignition coupling charge. The section  32  may be made of a conventional ignition coupling device between an upper connector  24  and lower connector  26  according to the present disclosure. This arrangement allows the ignition coupling joint  32  to also be handled and assembled into the pipe string entirely by automatic equipment on the drill rig.  
         [0030]    While the present invention has been illustrated and described with respect to certain specific apparatus and methods of operation, it is apparent that various changes can be made within the scope of the present invention as defined by the appended claims.