Abstract:
A detonation transfer subassembly for coupling two detonation activated tools in a work sting such that the work string may be severed between the two detonation activated tools without risk of a detonation is disclosed. The detonation transfer subassembly comprises first and second explosive carrying members having a detonation transfer member disposed therebetween. The detonation transfer member defines a longitudinal passageway therein. A firing pin is disposed within the longitudinal passageway. The firing pin has a first position proximate the first explosive carrying member and a second position proximate the second explosive carrying member. The firing pin is propellable from the first position to the second position following a detonation within the first explosive carrying member such that the firing pin impacts an explosive disposed within the second explosive carrying member, thereby transferring detonation from the first explosive carrying member to the second explosive carrying member.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates, in general, to perforating a subterranean wellbore using shaped charges and, in particular to, a detonation transfer subassembly that is installed within a work string between loaded perforating guns to provide an area through which the work string may be severed without the potential for detonating the shaped charges carried in the perforating guns.  
         BACKGROUND OF THE INVENTION  
         [0002]    Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation using shaped charge perforating guns, as an example.  
           [0003]    After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.  
           [0004]    Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, numerous charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or the like. Once the charge carriers are properly positioned in the wellbore such that shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the carrier, creates a hydraulic opening through the casing and cement and then penetrates the formation forming a perforation therein.  
           [0005]    It has been found, however, that it may sometimes be necessary to shut in a well due to an out of control well situation while the tool string, including the perforating guns, is disposed within the well. For example, during a snubbing operation or after the well has been perforated. If live shaped charges remain in the perforating guns, it is possible that closing a set of shear rams on a live shaped charge or other explosive components could result in a detonation. If such a detonation occurs, the live shaped charge may fire causing damage and injury to well equipment and personnel.  
           [0006]    A need has therefore arisen for an apparatus that can be installed within the tool string between the loaded perforating guns to provide an area through which the tool string may be severed without the potential for detonating the shaped charges carried in the perforating guns. A need has also arisen for such an apparatus that can transfer detonation from one perforating gun to the next perforating gun such that the perforating guns may be fired in sequence.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention disclosed herein comprises a detonation transfer subassembly that can be installed within a tool string between two detonation activated tools, such as live perforating guns, that provide an area through which the tool string may be severed without the potential for detonating the detonation activated tools. The detonation transfer subassembly of the present invention also provides for the transfer of detonation from one detonation activated tool to another detonation activated tool such that the detonation activated tools may be detonated in sequence.  
           [0008]    The detonation transfer subassembly for the present invention comprises a first explosive carrying member and a second explosive carrying member. Each of these explosive carrying members has an explosive disposed therein. For example, the first explosive carrying member may have an explosive train including one or more boosters, a detonation cord and an unlined shaped charge. Similarly, the second explosive carrying member may have an explosive train including an initiator, one or more boosters and a detonation cord.  
           [0009]    Disposed between the first and second explosive carrying members is a detonation transfer member. The detonation transfer member has a longitudinal passageway. In one embodiment, the detonation transfer member may include a barrel disposed within a housing such that a vent chamber is defined therebetween. In this embodiment, the longitudinal passageway is disposed within the barrel. In addition, the barrel may include one or more vent ports that create a communication path between the longitudinal passageway and the vent chamber.  
           [0010]    A firing pin is disposed within the longitudinal passageway. The firing pin has a first position proximate the first explosive carrying member and a second position proximate the second explosive carrying member. The firing pin may be propelled from the first position to the second position in response to, for example, gas pressure generated by detonating the explosive disposed within the first explosive carrying member. Alternatively, a solid rocket propellant or other suitable propellant may be used or wellbore fluid pressure may be routed to the fire pin. In such an event, the firing pin impacts the explosive disposed within the second explosive carrying member, thereby transferring detonation from the first explosive carrying member to the second explosive carrying member.  
           [0011]    To assure that the firing pin impacts the explosive disposed within the second explosive carrying member with sufficient force to detonate this explosive, the first explosive carrying member may include an expansion chamber for the gas generated from the detonation of the explosive or ignition of a propellant in the first explosive carrying member. In addition, the firing pin may be initially fixed relative to the barrel by a shear pin that selective prevents movement of the firing pin relative to the barrel until the force is sufficient to shear the shear pin. Finally, as the firing pin travels from the first position to the second position, air in the longitudinal chamber vents to the vent chamber to avoid creating unnecessary resistance to the movement of the firing pin.  
           [0012]    As such, the detonation transfer subassembly of the present invention provides a region through which a tool string may be severed between two detonation activated tools that without the potential for detonating the detonation activated tools. Also, the detonation transfer subassembly of the present invention provides for the transfer of detonation from one detonation activated tool to another detonation activated tool through the detonation transfer member.  
           [0013]    The method of the present invention for operating the detonation transfer subassembly involves, disposing a detonation transfer member between first and second explosive carrying members, creating a detonation within the first explosive member, propelling a firing pin from a first position proximate the first explosive carrying member to a second position proximate the second explosive carrying member through a longitudinal passageway in the detonation transfer member and impacting an explosive disposed within the second explosive member with the firing pin, thereby transferring detonation from the first explosive carrying member to the second explosive carrying member.  
           [0014]    The method of the present invention for severing a work string between two detonation activated tools involves disposing a detonation transfer subassembly between the two detonation activated tools, positioning the detonation transfer member of the detonation transfer subassembly adjacent to shear rams of a blowout preventer and closing the shear rams of the blowout preventer, thereby severing the work string between the two detonation activated tools.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0016]    [0016]FIG. 1 is a schematic illustration of an offshore oil and gas platform operating a pair of detonation transfer subassemblies of the present invention that are disposed between successive perforating guns in a work string;  
         [0017]    [0017]FIG. 2 is a schematic illustration of an offshore oil and gas platform depicting a work string tripping into or out of a well such that a detonation transfer subassembly of the present invention is adjacent to a set of shear ram preventers;  
         [0018]    [0018]FIG. 3 is a schematic illustration of an offshore oil and gas platform depicting a work string after being severed by the shear ram preventers through a detonation transfer subassembly of the present invention;  
         [0019]    FIGS.  4 A- 4 B are half sectional views of successive axial sections of a detonation transfer subassembly of the present invention prior to transferring detonation;  
         [0020]    FIGS.  5 A- 5 B are half sectional views of successive axial sections of a detonation transfer subassembly of the present invention after transferring detonation;  
         [0021]    FIGS.  6 A- 6 B are half sectional views of successive axial sections of a detonation transfer subassembly of the present invention prior to transferring detonation; and  
         [0022]    FIGS.  7 A- 7 B are half sectional views of successive axial sections of a detonation transfer subassembly of the present invention after transferring detonation.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.  
         [0024]    Referring initially to FIG. 1, a pair of detonation transfer subassemblies of the present invention operating from an offshore oil and gas platform is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including subsea blow-out preventers  23 . Disposed on deck  20  is a surface installation  24  including shear ram preventers  25 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work sting  30 .  
         [0025]    A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . Work string  30  include various tools including shaped charge perforating guns  38 ,  40 ,  42  and detonation transfer subassemblies  44 ,  46 . When it is desired to perforate formation  14 , work string  30  is lowered through casing  34  until shaped charge perforating guns  38 ,  40 ,  42  are positioned adjacent to formation  14 . Thereafter, shaped charge perforating guns  38 ,  40 ,  42  are sequentially fired such that the shaped charges are detonated. Upon detonation, the liners of the shaped charges form jets that create a spaced series of perforations extending outwardly through casing  34 , cement  36  and into formation  14 .  
         [0026]    Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the detonation transfer subassemblies of the present invention are equally well-suited for use in deviated wells, inclined wells or horizontal wells. Also, even though FIG. 1 depicts an offshore operation, it should be noted by one skilled in the art that the detonation transfer subassemblies of the present invention are equally well-suited for use in onshore operations.  
         [0027]    In the event that the well traversing formation  14  become out of control while work string  30  include shaped charge perforating guns  38 ,  40 ,  42  and detonation transfer subassemblies  44 ,  46  are in the well, it may become necessary to shut in the well. For example, if the running of work string  30  into the well is a snubbing operation wherein another formation below formation  14  is live or if work string  30  is being tripped out of the well following the perforation operation and an uncontrolled situation occurs well, this could require a well shut in using shear ram preventers  25 . If the portion of work string  30  having shaped charge perforating guns  38 ,  40 ,  42  is adjacent to shear ram preventers  25  when the out of control situation occurs and if live shaped charges remain in perforating guns  38 ,  40  or  42 , closing shear ram preventers  25  could cause a detonation event. As illustrated in FIG. 2, using work string  30  having detonation transfer subassemblies  44 ,  46  positioned respectively between perforating guns  38 ,  40  and perforating guns  40 ,  42 , one of the detonation transfer subassemblies such as detonation transfer subassembly  46  may be positioned adjacent to shear ram preventers  25 . Once in this position, shear ram preventers  25  may be operated to shear through detonation transfer subassembly  46 , as best seen in FIG. 3, to shut in the well without the potential for causing an unwanted detonation.  
         [0028]    Referring now to FIGS.  4 A- 4 B, therein is depicted a detonation transfer subassembly of the present invention prior to transferring detonation that is generally designated  50 . Detonation transfer subassembly  50  includes an upper explosive carrying member  52  that has an upper pin end  54  that threadedly and sealingly couples with the lower box end of, for example, a perforating gun. Upper explosive carrying member  52  is a substantially cylindrical tubular member having a longitudinal bore  56  formed therein. Longitudinal bore  56  houses a holder member  58  which may be made from a suitable material such as steel or aluminum. Confined within holder member  58  is an explosive train that includes a booster  60 , a detonation cord  62  such as RDX plastic cover Primacord, an initiator booster  64  and an unlined shaped charge  66 . The lower portion of longitudinal bore  56  serves as an expansion chamber  68  the purpose of which will be explained in more detail below.  
         [0029]    It should be apparent to those skilled in the art that the use of directional terms such as top, bottom, above, below, upper, lower, upward, downward, etc. are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. As such, it is to be understood that the downhole components described herein may be operated in vertical, horizontal, inverted or inclined orientations without deviating from the principles of the present invention.  
         [0030]    Detonation transfer subassembly  50  also includes a detonation transfer member  70  that is threadedly and sealingly coupled to the lower end of upper explosive carrying member  52 . Detonation transfer member  70  is a substantially cylindrical tubular member having housing  72 . Housing  72  has a radially reduced exterior region  74  that is preferably aligned with the shear ram preventers if the well in which detonation transfer subassembly  50  is disposed must be shut in and the shear ram preventers must be used to shear detonation transfer member  70 . Housing  72  also has a longitudinal bore  76  formed therein. Disposed within longitudinal bore  76 , in a substantially annularly spaced apart relationship, is a barrel  78 . The annular space between longitudinal bore  76  and barrel  78  is a vent chamber  80 , the purpose of which will be explained in more detail below. Barrel  78  defines a longitudinal passageway  82  therein. Barrel  78  also defines a plurality of vent ports  84  that create a path for communication between vent chamber  80  and longitudinal passageway  82 . A firing pin  86  is disposed within longitudinal passageway  82 . Firing pin  86  is initially fixed relative to barrel  78  by shear pin  88 .  
         [0031]    Detonation transfer subassembly  50  also includes a lower explosive carrying member  90  that has a lower box end  92  that threadedly and sealingly couples with the upper pin end of, for example, a perforating gun. At its upper end, lower explosive carrying member  90  is threadedly and sealingly coupled with the lower end of detonation transfer member  70 . Lower explosive carrying member  90  is a substantially cylindrical tubular member having a longitudinal bore  94  formed therein. Longitudinal bore  94  houses a holder member  96  which may be made from a suitable material such as steel. Longitudinal bore  94  also houses a holder member  98  which may be made from a suitable material such as steel, aluminum or polymer. Disposed within longitudinal bore  94  above holder member  96  is a sealed initiator  100 . Confined within holder member  96  is a booster  102  and confined within holder member  98  is a booster  104 . Extending between booster  102  and booster  104  is a detonation cord  106 . Together, initiator  100 , booster  102 , detonator cord  106  and booster  104  form an explosive train.  
         [0032]    Under normal operation, detonation transfer subassembly  50  is used to transfer detonation from one detonation activated tool to another detonation activated tool such as from one shaped charge perforating gun to another as depicted in FIG. 1. This is achieved by receiving a detonation from the detonation activated tool that is threadedly and sealingly coupled to pin end  54  of upper explosive carrying member  52 . This detonation then travels through the explosive train within upper explosive carrying member  52 . Specifically, the detonation travels through booster  60 , detonation cord  62 , initiator booster  64  and finally to unlined shaped charge  66 . Upon detonation of unlined shaped charge  66 , a large volume of gas is generated that accumulates and pressurizes in expansion chamber  68 .  
         [0033]    When the gas pressure in expansion chamber  68  reaches a predetermined level, the force created by the gas pressure on firing pin  86  shears pin  88 . Once shear pin  88  has sheared, firing pin  86  is propelled from its position proximate upper explosive carrying member  52  through longitudinal passageway  82  until firing pin  86  impacts sealed initiator  100  in lower explosive carrying member  90 , as best seen in FIGS.  5 A- 5 B. Upon impact with sealed initiator  100 , seal initiator  100  detonates which in turn sends a detonation down the explosive train in lower explosive carrying member  90  including booster  102 , detonation cord  106  and booster  104 . Booster  104  then transfers the detonation to the detonation activated tool that is threadedly and sealingly coupled to box end  92  of lower explosive carrying member  90 . As such, detonation transfer subassembly  50  transfers detonation from one detonation activated tool to another detonation activated tool by transferring detonation from upper explosive carrying member  52  to lower explosive carrying member  92  through detonation transfer member  70 .  
         [0034]    Even though FIG. 4 has depicted the explosive train within upper explosive carrying member  52  as ending with unlined shaped charge  66  which generates the gas pressure in expansion chamber  68 , it should be noted by those skilled in the art that other techniques may be used to propel firing pin  86  from its position proximate upper explosive carrying member  52  to its position impacting sealed initiator  100  in lower explosive carrying member  90 . For example, the explosive train within upper explosive carrying member  52  could alternatively terminate in other types of propellants including, but not limited to, a solid rocket propellant. As another alternative, the explosive train within upper explosive carrying member  52  could terminate by opening a port to the exterior of detonation transfer subassembly  50  to allow high pressure fluid to enter expansion chamber  68  and provide the force to shear pin  88  and propel firing pin  88 .  
         [0035]    Importantly, the design of detonation transfer subassembly  50  assures that firing pin  86  impacts sealed initiator  100  with sufficient velocity to create detonation. Specifically, this is achieved by allowing gas generated by the detonation of unlined shaped charge  66  to expand and pressurize in expansion chamber  68 . In addition, this is achieved by selectively preventing movement of firing pin  86  relative to barrel  78  until the force created by the gas pressure in expansion chamber  68  is sufficient to shear pin  88 . Finally, this is achieved by allowing air in longitudinal chamber  82  to vent through ports  84  into vent chamber  80  as firing pin  86  travels through longitudinal chamber  82 . As such, firing pin  86  strikes sealed initiator  100  with sufficient force to cause sealed initiator  100  to detonate.  
         [0036]    Referring now to FIGS.  6 A- 6 B, therein is depicted a detonation transfer subassembly of the present invention prior to transferring detonation that is generally designated  150 . Detonation transfer subassembly  150  includes an upper explosive carrying member  152  that has an upper pin end  154  that threadedly and sealingly couples with the lower box end of, for example, a perforating gun. Upper explosive carrying member  152  is a substantially cylindrical tubular member having a longitudinal bore  156  formed therein. Longitudinal bore  156  houses a holder member  158  which may be made from a suitable material such as steel or aluminum. Confined within holder member  158  is an explosive train that includes a booster  160 , a detonation cord  162  such as RDX plastic cover Primacord, an initiator booster  164  and an unlined shaped charge  166 . The lower portion of longitudinal bore  156  serves as an expansion chamber  168 .  
         [0037]    Detonation transfer subassembly  150  also includes a detonation transfer member  170  that is threadedly and sealingly coupled to the lower end of upper explosive carrying member  152 . Detonation transfer member  170  is a substantially cylindrical tubular member having housing  172 . Housing  172  has a radially reduced exterior region  174  that is preferably aligned with the shear ram preventers if the well in which detonation transfer subassembly  150  is disposed must be shut in and the shear ram preventers must be used to shear detonation transfer member  170 . Housing  172  also has a longitudinal bore  176  formed therein. Disposed within longitudinal bore  176 , in a substantially annularly spaced apart relationship, is a barrel  178 . The annular space between longitudinal bore  176  and barrel  178  is a vent chamber  180 . Barrel  178  defines a longitudinal passageway  182  therein. Barrel  178  also defines a plurality of vent ports  184  that create a path for communication between vent chamber  180  and longitudinal passageway  182 . A firing pin  186  is disposed within longitudinal passageway  182 . Firing pin  186  is initially fixed relative to barrel  178  by shear pin  188 .  
         [0038]    Detonation transfer subassembly  150  also includes a lower explosive carrying member  190  that has a lower box end  192  that threadedly and sealingly couples with the upper pin end of, for example, a perforating gun. In the illustrated embodiment, lower explosive carrying member  190  is integral with detonation transfer member  170 . Lower explosive carrying member  190  has a bore  194  formed therein. Bore  194  houses a holder member  196  which may be made from a suitable material such as steel. Bore  194  also houses an alignment member  198  which may be made from a suitable material such as steel. Alignment member  198  receives the lower end of barrel  178  therein. Alignment member  198  is threadably coupled to holder member  196 . Disposed within holder member  196  is a sealed initiator  200 .  
         [0039]    Under normal operation, detonation transfer subassembly  150  is used to transfer detonation from one detonation activated tool to another detonation activated tool such as from one shaped charge perforating gun to another as depicted in FIG. 1. This is achieved by receiving a detonation from the detonation activated tool that is threadedly and sealingly coupled to pin end  154  of upper explosive carrying member  152 . This detonation then travels through the explosive train within upper explosive carrying member  152 . Specifically, the detonation travels through booster  160 , detonation cord  162 , initiator booster  164  and finally to unlined shaped charge  166 . Upon detonation of unlined shaped charge  166 , a large volume of gas is generated that accumulates and pressurizes in expansion chamber  168 .  
         [0040]    When the gas pressure in expansion chamber  168  reaches a predetermined level, the force created by the gas pressure on firing pin  186  shears pin  188 . Once shear pin  188  has sheared, firing pin  186  is propelled from its position proximate upper explosive carrying member  152  through longitudinal passageway  182  until firing pin  186  impacts sealed initiator  200  in lower explosive carrying member  190 , as best seen in FIGS.  7 A- 7 B. Upon impact with sealed initiator  200 , seal initiator  200  detonates which transfers the detonation to the detonation activated tool that is threadedly and sealingly coupled to box end  192  of lower explosive carrying member  190 . As such, detonation transfer subassembly  150  transfers detonation from one detonation activated tool to another detonation activated tool by transferring detonation from upper explosive carrying member  152  to lower explosive carrying member  192  through detonation transfer member  170 .  
         [0041]    Importantly, the design of detonation transfer subassembly  150  assures that firing pin  186  impacts sealed initiator  200  with sufficient velocity to create detonation. Specifically, this is achieved by allowing gas generated by the detonation of unlined shaped charge  166  to expand and pressurize in expansion chamber  168 . In addition, this is achieved by selectively preventing movement of firing pin  186  relative to barrel  178  until the force created by the gas pressure in expansion chamber  168  is sufficient to shear pin  188 . Finally, this is achieved by allowing air in longitudinal chamber  182  to vent through ports  184  into vent chamber  180  as firing pin  186  travels through longitudinal chamber  182 . As such, firing pin  186  strikes sealed initiator  200  with sufficient force to cause sealed initiator  200  to detonate.  
         [0042]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.