Patent Publication Number: US-8991496-B2

Title: Firing head actuator for a well perforating system and method for use of same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119 of the filing date of International Application No. PCT/US2013/036528, filed Apr. 15, 2013. 
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates, in general, to equipment utilized and operations performed in conjunction with completing a subterranean well for hydrocarbon fluid production and, in particular, to a firing head actuator for a well perforating system and method for operating the firing head actuator. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the present invention, its background will be described with reference to perforating a hydrocarbon bearing subterranean formation with a shaped charge perforating gun apparatus, as an example. After drilling a section of a subterranean wellbore that traverses a hydrocarbon bearing subterranean formation, individual lengths of 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 through which fluids from the formation may be produced to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string or to place addition cement behind the casing string, hydraulic openings or perforations must be made through the casing string and a distance into the formation. 
     Typically, these perforations are created by detonating a series of shaped charges located within one or more perforating guns that are deployed within the casing string to a position adjacent to the desired location. Conventionally, the perforating guns are formed from a closed, fluid-tight hollow carrier gun body adapted to be lowered into the wellbore on a conveyance such as coiled tubing, a jointed tubing or the like. Disposed within the hollow carrier gun body is a charge holder that supports and positions the shaped charges in a selected spatial distribution. The shaped charges have conically constrained explosive material therein. A detonating cord that is used to detonate the shaped charges is positioned adjacent to the initiation ends of the shaped charges. The detonating cord is typically activated by a firing head when it is desired to initiate the perforating guns. 
     Many conventional firing heads are operated in response to pressure applied to the firing head from a remote location. For example, many pressure operated firing heads rely on shear pins to select a pressure which, when applied to the firing head, shears the pins and initiates the detonation sequence. With pressure actuated firing heads, the pressure required to trigger actuation must typically be the highest pressure required to trigger actuation of any pressure actuated component in the well. It has been found, however, that the perforation event may require a wellbore pressure that is not consistent with the actuation pressure of the firing head. Depending upon the particular design of the completion, it may be desired to create an underbalanced pressure condition in the wellbore, a balanced pressure condition in the wellbore or a particular overbalanced pressure condition in the wellbore prior to the perforation event. Accordingly, pressure in the wellbore must be reduced after the pressure event that actuates the firing head but before the perforation event. 
     Efforts have been made to overcome this pressure balance issue using time delay devices, which may be added to a firing head to extend the time period between the pressure event and the perforation event. Convention time delay devices use pyrotechnic time delay fuses that provide delays in the order of minutes. To create a longer delay, more than one pyrotechnic time delay fuse may be added to the firing head. It has been found, however, that in certain installations wherein a time delay in the order of hours is desired, the number of pyrotechnic time delay fuses required the achieve such a time delay and the connections required between the pyrotechnic time delay fuses make these systems unreliable. In addition, the length of a system of pyrotechnic time delay fuses needed to achieve such a time delay makes such a system unfeasible. 
     A need has therefore arisen for an improved firing head that is operable to provide a time delay between the pressure event and the perforation event. In addition, a need has arisen for such an improved firing head that does not require numerous time delay elements to provide sufficient time for pressure balancing the well prior to the perforation event. Further, a need has arisen for such an improved firing head that does not require time delay elements having an unfeasible length to provide sufficient time for pressure balancing the well prior to the perforation event. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises a firing head actuator that is operable to provide a time delay between the pressure event and the perforation event. In addition, firing head actuator of the present invention does not require numerous time delay elements to provide sufficient time for pressure balancing the well prior to the perforation event. Further, firing head actuator of the present invention does not require time delay elements having an unfeasible length to provide sufficient time for pressure balancing the well prior to the perforation event. 
     In one aspect, the present invention is directed to a firing head actuator for a well perforating system. The firing head actuator includes a housing assembly. A first impact piston is initially secured to and slidably disposed within the housing assembly. An electronic time delay assembly is disposed within the housing assembly. A trigger assembly is disposed within the housing assembly. A second impact piston is initially secured within and slidably disposed within the housing assembly. An initiator is disposed within the housing assembly such that a pressure signal of a predetermined threshold actuates the first impact piston, the first impact piston mechanically actuates the electronic time delay assembly, after a predetermined time period, the electronic time delay assembly sends an electric signal to actuate the trigger assembly, the trigger assembly mechanically releases the second impact piston and pressure shifts the second impact piston into contact with the initiator. 
     In certain embodiments, a plurality of shear pins may initially secure the first impact piston to the housing assembly. In some embodiments, the electronic time delay assembly may include a signal detector, a control circuit, a power supply, an electronic timing device and an output signal generator. In one embodiment, the trigger assembly may include a release piston slidably and sealingly disposed within the housing assembly and selectively moveable between first and second positions. In the first position, the release piston secures the second impact piston within the housing assembly. In the second position, the release piston is remote from the second impact piston. In this embodiment, a barrier is disposed within the housing assembly that selectively separates first and second chambers within the housing assembly such that a fluid may be contained in the first chamber between the barrier and the release piston. The fluid is operable to selectively retain the release piston in the first position. A piercing assembly is disposed within the housing assembly such that, responsive to the electric signal from the electronic time delay assembly, the piercing assembly penetrates the barrier allowing at least a portion of the fluid to flow from the first chamber to the second chamber and allowing pressure to shift the release piston from the first position to the second position. Also, in this embodiment, the piercing assembly may penetrate the barrier responsive to pressure generated by combustion of a chemical element in response to electronic actuation of an ignition agent. In another embodiment, the trigger assembly may include an electric motor disposed within the housing assembly and a release piston operably associated with the electric motor. The release assembly may be slidably disposed within the housing assembly and selectively moveable between first and second positions. In the first position, the release piston secures the second impact piston within the housing assembly. In the second position, the release piston is remote from the second impact piston. In this embodiment, responsive to the electric signal from the electronic time delay assembly, the electric motor retracts the release piston from the first position to the second position. In either of these embodiments, at least one retainer element may be disposed between the release piston and the second impact piston to initially secured the second impact piston within the housing assembly. 
     In another aspect, the present invention is directed to a well perforating system. The well perforating system includes a tubular string, a perforating gun disposed within the tubular string and a firing head actuator disposed within the tubular string and operably associated with the perforating gun. The firing head actuator includes a housing assembly, a first impact piston initially secured to and slidably disposed within the housing assembly, an electronic time delay assembly disposed within the housing assembly, a trigger assembly disposed within the housing assembly, a second impact piston initially secured within and slidably disposed within the housing assembly and an initiator disposed within the housing assembly, such that a pressure signal of a predetermined threshold actuates the first impact piston, the first impact piston mechanically actuates the electronic time delay assembly, after a predetermined time period, the electronic time delay assembly sends an electric signal to actuate the trigger assembly, the trigger assembly mechanically releases the second impact piston and pressure shifts the second impact piston into contact with the initiator, thereby initiating a detonation event in the perforating gun. 
     In a further aspect, the present invention is directed to a method for initiating a well perforating system. The method includes providing a firing head actuator including a housing assembly, a first impact piston initially secured to and slidably disposed within the housing assembly, an electronic time delay assembly disposed within the housing assembly, a trigger assembly disposed within the housing assembly, a second impact piston initially secured within and slidably disposed within the housing assembly and an initiator disposed within the housing assembly; operably associating the firing head actuator with a perforating gun disposed within a tubular string; positioning the firing head actuator and the perforating gun at a target location in a well; generating a pressure signal of a predetermined threshold to actuate the first impact piston; mechanically actuating the electronic time delay assembly with first impact piston; after a predetermined time period, sending an electric signal from the electronic time delay assembly to actuate the trigger assembly; mechanically releasing the second impact piston with the trigger assembly; responsive to pressure, shifting the second impact piston into contact with the initiator; and initiating a detonation event in the perforating gun. 
     The method may also include penetrating a barrier with a piecing assembly; flowing fluid from a first chamber to a second chamber within the housing assembly through the barrier; responsive to pressure, shifting a release piston from a first position, wherein the release piston secures the second impact piston within the housing assembly, to a second position, wherein the release piston is remote from the second impact piston; generating pressure by combustion of a chemical element responsive to electronic actuation of an ignition agent by the electric signal from the electronic time delay assembly and/or retracting a release piston from a first position, wherein the release piston secures the second impact piston within the housing assembly, to a second position, wherein the release piston is remote from the second impact piston with an electric motor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a schematic illustration of an offshore oil and gas platform operating a well perforating system according to an embodiment of the present invention; 
         FIGS. 2A-2C  are partial cross sectional views of consecutive axial sections of a firing head actuator for use in a well perforating system according to an embodiment of the present invention prior to actuation; 
         FIGS. 3A-3C  are partial cross sectional views of consecutive axial sections of a firing head actuator for use in a well perforating system according to an embodiment of the present invention after actuation; 
         FIGS. 4A-4C  are partial cross sectional views of consecutive axial sections of a firing head actuator for use in a well perforating system according to an embodiment of the present invention prior to actuation; and 
         FIGS. 5A-5C  are partial cross sectional views of consecutive axial sections of a firing head actuator for use in a well perforating system according to an embodiment of the present invention after actuation. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. 
     Referring initially to  FIG. 1 , a well perforating system being operated 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 blowout preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as a work string  30 . 
     A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is secured within wellbore  32 . Work string  30  includes various tools such as a firing head actuator  36  and a shaped charge perforating gun apparatus tandem  38 . When it is desired to perforate wellbore  32  proximate formation  14 , work string  30  is lowered through casing  34  until perforating gun tandem  38  is positioned adjacent to formation  14 , as illustrated. Thereafter, a pressure signal is sent from the surface to firing head actuator  36  via wellbore  32  and/or work string  30 , such as by increasing the pressure in a compressible or substantially incompressible fluid. When the pressure signal reaches a predetermined threshold, the actuation sequence commences by breaking one or more shear pins within firing head actuator  36 . This mechanical response to the pressure event by firing head actuator  36  triggers an electronic timer mechanism within firing head actuator  36  that delays further response by firing head actuator  36  such that the desired pressure balance may be established in wellbore  32  prior to the perforation event. When the electronic timer mechanism times out, an electronic signal is sent to a trigger mechanism of firing head actuator  36 , which causes a pressure actuated impact piston to be mechanically released. The pressure actuated impact piston then contacts an initiator that starts the detonation sequence causing shaped charges within perforating gun tandem  38  to form high speed jets that penetrate casing  34  and a depth into formation  14  forming perforations therein. 
     Even though  FIG. 1  depicts the present invention in a vertical wellbore, it should be understood by those skilled in the art that the present invention is equally well suited for use in wellbores having other directional configurations including horizontal wellbores, deviated wellbores, slanted wellbores, lateral wellbores and the like. Accordingly, it should be understood by those skilled in the art that the use of directional terms such as above, below, upper, lower, upward, downward, uphole, downhole and the like 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, the uphole direction being toward the surface of the well and the downhole direction being toward the toe of the well. Also, even though  FIG. 1  depicts the present invention in an offshore operation, it should be understood by those skilled in the art that the present invention is equally well suited for use in onshore operations. 
     Referring now to  FIGS. 2A-2C , a firing head actuator for a well perforating system is depicted and generally designated  100 . The firing head actuator  100  includes an actuator housing assembly  102  that is operable to be coupled within a tubular string as described above. In the illustrated embodiment, actuator housing assembly  102  includes a upper impact piston housing member  104 , timer housing member  106  that is threadably coupled to the lower end of upper impact piston housing member  104 , a fluid chamber housing member  108  that is threadably coupled to the lower end of timer housing member  106 , a release piston housing member  110  that is threadably coupled to the lower end of fluid chamber housing member  108 , a lower impact piston housing member  112  that is threadably coupled to the lower end of release piston housing member  110  and an end cap housing member  114  that is threadably coupled to the lower end of lower impact piston housing member  112 . Even though actuator housing assembly  102  has been depicted and described as having a particular number and a particular arrangement of housing member, those skilled in the art will recognize that an actuator housing assembly could alternatively have a different arrangement of a different number of housing members without departing from the principles of the present invention. 
     An upper impact piston  116  is disposed within upper impact piston housing member  104 . Upper impact piston  116  has an outer O-ring  118  that seals within an upper bore  120  of upper impact piston housing member  104 . Upper impact piston  116  also has outer O-rings  122 ,  124  that seal within a lower bore  126  of upper impact piston housing member  104 . Upper impact piston  116  is initially secured to upper impact piston housing member  104  by a plurality of shear pins  128 . A pin retainer sleeve  130  is disposed about upper impact piston housing member  104 . Upper impact piston  116  carries a actuation pin  132  on its lower end. 
     A time delay actuation assembly  134  is disposed within timer housing member  106 . Time delay actuation assembly  134  includes a barrier assembly  136  that includes a barrier  138  and a support assembly  140  having a fluid passageway  142  defined therethrough. Barrier  138  initially prevents fluid  144  disposed within chamber  146  of fluid chamber housing member  108  from entering a chamber  148  of timer housing member  106 . Time delay actuation assembly  134  also includes an electronic time delay assembly depicted as control system  150  that includes a signal detector, a control circuit, a power supply, an electronic timing device and an electric signal output generator. Time delay actuation assembly  134  further includes a piercing assembly  152  includes a chemical element or energetic material  154 , an ignition agent  156  and a piercing element  158  slidably disposed within a cylinder  160 . Chemical element  154  is preferably a combustible element such as a propellant that has the capacity for extremely rapid but controlled combustion that produces a combustion event including the production of a large volume of gas at high temperature and pressure. 
     In an exemplary embodiment, chemical element  154  may comprises a solid propellant such as nitrocellulose plasticized with nitroglycerin or various phthalates and inorganic salts suspended in a plastic or synthetic rubber and containing a finely divided metal. Chemical element  154  may comprise inorganic oxidizers such as ammonium and potassium nitrates and perchlorates such as potassium perchlorate. It should be appreciated, however, that substances other than propellants may be utilized without departing from the principles of the present invention, including other explosives, pyrotechnics, flammable solids or the like. In the illustrated embodiment, ignition agent  156  is connected to the control circuit via an electrical cable  162  so that, when the predetermined time period of the electronic timing device has expired, the control circuit supplies an electric signal in the form of an electrical current to ignition agent  156 . In the illustrated embodiment, the signal detector of control system  150  is operably associated with a sensor depicted as percussion element  164 . 
     At its lower end, time delay actuation assembly  134  includes a release piston  166  is partially is disposed within release piston housing member  110 . Release piston  166  has an outer O-ring  168  that seals within chamber  146  of fluid chamber housing member  108 . Release piston  166  also has outer an O-ring  170  that seals within bore  172  of release piston housing member  110 . Release piston housing member  110  has one or more ports  174  that provide fluid communication between the wellbore and a lower piston area of release piston  166 . Together, release piston  166 , barrier assembly  136  and piercing assembly  152  may be referred to as a trigger assembly. 
     A lower impact piston  176  is disposed within lower impact piston housing member  112 . Lower impact piston  176  has outer O-rings  178 ,  180  that seal within a bore  182  of lower impact piston housing member  112 . Lower impact piston  176  is initially secured within lower impact piston housing member  112  by the interaction of release piston  166  supporting retainer elements  184  within detents or a radial groove  186  of lower impact piston  176 . Lower impact piston  176  carries a firing pin  188  on its lower end. A percussion type initiator  190  is disposed between lower impact piston housing member  112  and end cap housing member  114 . An upper portion of a detonation cord  192  is disposed within end cap housing member  114 . Detonation cord  192  is the first element of the detonation train the initiates shaped charges within the perforating guns operably associated with firing head actuator  100 . 
     The operation of firing head actuator  100  will now be described with reference to  FIGS. 2A-2C  and  3 A- 3 C. When it is desired to perforate the wellbore, a pressure signal is sent from the surface to firing head actuator  100  via the wellbore and the work string conveying the well perforating system as described above. For example, this may be achieved by increasing the pressure in a compressible or substantially incompressible fluid in the wellbore that is communicated to firing head actuator  100  via one or more ports in the work string. This pressure signal is applied to an upper piston area of upper impact piston  116 . When the pressure signal reaches a predetermined threshold, the downward force on upper impact piston  116  causes shear pins  128  to break. This allows upper impact piston  116  to move downwardly relative to upper impact piston housing member  104  and causes actuation pin  132  to contact sensor  164 , as best seen in  FIG. 3A . The mechanical interaction or contact between actuation pin  132  and sensor  164  provides an input signal to the signal detector of control system  150 . The control circuit of control system  150  processes the input signal and starts a clock within the electronic timing device of control system  150 . The well operator may now pressure balance the well as desired by bleeding off the required amount of pressure. 
     When the predetermined time period of the electronic timing device has elapsed, a clock output signal is processed by the control circuit. The control circuit then causes an electric signal, for example, an electrical current, to be supplied from the power supply to ignition agent  156 . Ignition agent  156  now initiates a chemical reaction in chemical element  154 . The chemical reaction creates pressure that acts on piercing element  158  causing downward movement of piecing barrier  138 , as best seen in  FIG. 3B . Fluid communication is thus established between chamber  146  and chamber  148  through opening  194  in barrier  138 , which allows fluid  144  to exit chamber  146  as release piston  166  is urged upwardly by pressure from the wellbore via ports  174 . The upward movement of release piston  166  releases retainer elements  184  from radial groove  186  of lower impact piston  176 , as best seen in  FIG. 3B . Wellbore pressure acting on lower impact piston  176  now urges lower impact piston  176  downwardly. The downward movement causes firing pin  188  to impact percussion initiator  190 , as best seen in  FIG. 3C . This impact starts the progression of the detonation event at detonation cord  192 , which continues through the perforating guns as discussed above. 
     Referring next to  FIGS. 4A-4C , a firing head actuator for a well perforating system is depicted and generally designated  200 . The firing head actuator  200  includes an actuator housing assembly  202  that is operable to be coupled within a tubular string as described above. In the illustrated embodiment, actuator housing assembly  202  includes a upper impact piston housing member  204 , timer housing member  206  that is threadably coupled to the lower end of upper impact piston housing member  204 , a release piston housing member  210  that is threadably coupled to the lower end of timer housing member  206 , a lower impact piston housing member  212  that is threadably coupled to the lower end of release piston housing member  210  and an end cap housing member  214  that is threadably coupled to the lower end of lower impact piston housing member  212 . Even though actuator housing assembly  202  has been depicted and described as having a particular number and a particular arrangement of housing member, those skilled in the art will recognize that an actuator housing assembly could alternatively have a different arrangement of a different number of housing members without departing from the principles of the present invention. 
     An upper impact piston  216  is disposed within upper impact piston housing member  204 . Upper impact piston  216  has an outer O-ring  218  that seals within an upper bore  220  of upper impact piston housing member  204 . Upper impact piston  216  also has outer O-rings  222 ,  224  that seal within a lower bore  226  of upper impact piston housing member  204 . Upper impact piston  216  is initially secured to upper impact piston housing member  204  by a plurality of shear pins  228 . A pin retainer sleeve  230  is disposed about upper impact piston housing member  204 . Upper impact piston  216  carries a actuation pin  232  on its lower end. 
     A time delay actuation assembly  234  is disposed within timer housing member  206 . Time delay actuation assembly  234  includes an electric motor  236 . Time delay actuation assembly  234  also includes an electronic time delay assembly depicted as a control system  250  that includes a signal detector, a control circuit, a power supply, an electronic timing device and an output signal generator. In the illustrated embodiment, the signal detector of control system  250  is operably associated with a sensor depicted as percussion element  264 . Time delay actuation assembly  234  also includes a release piston  266  that is partially disposed within release piston housing member  210  and has an upper end that is coupled to and received within electric motor  236 . Together, release piston  266  and electric motor  236  may be referred to as a trigger assembly. A lower impact piston  276  is disposed within lower impact piston housing member  212 . Lower impact piston  276  has outer O-rings  278 ,  280  that seal within a bore  282  of lower impact piston housing member  212 . Lower impact piston  276  is initially secured to lower impact piston housing member  212  by the interaction of release piston  266  supporting retainer elements  284  within detents or a radial groove  286  of lower impact piston  276 . Lower impact piston  276  carries a firing pin  288  on its lower end. A percussion type initiator  290  is disposed between lower impact piston housing member  212  and end cap housing member  214 . An upper portion of a detonation cord  292  is disposed within end cap housing member  214 . Detonation cord  292  is the first element of the detonation train that initiates shaped charges within the perforating guns operably associated with firing head actuator  200 . 
     The operation of firing head actuator  200  will now be described with reference to  FIGS. 4A-4C  and  5 A- 5 C. When it is desired to perforate the wellbore, a pressure signal is sent from the surface to firing head actuator  200  via the wellbore and the work string conveying the well perforating system as described above. The pressure signal is applied to an upper piston area of upper impact piston  216 . When the pressure signal reaches a predetermined threshold, the downward force on upper impact piston  216  causes shear pins  228  to break. This allows upper impact piston  216  to move downwardly relative to upper impact piston housing member  204  and causes actuation pin  232  to contact sensor  264 , as best seen in  FIG. 5A . The mechanical interaction or contact between actuation pin  232  and sensor  264  provides an input signal to the signal detector of control system  250 . The control circuit of control system  250  processes the input signal and starts a clock within the electronic timing device of control system  250 . The well operator may now pressure balance the well as desired by bleeding off the required amount of pressure. When the predetermined time period of the electronic timing device has elapsed, a clock output signal is processed by the control circuit. The control circuit then causes an electric signal, for example, an electrical voltage, to be supplied from the power supply to electric motor  236 . Operation of electric motor  236  retracts release piston  266  in the upward direction. The upward movement of release piston  266  releases retainer elements  284  from radial groove  286  of lower impact piston  276 , as best seen in  FIG. 5B . Wellbore pressure acting on lower impact piston  276  now urges lower impact piston  276  downwardly. The downward movement causes firing pin  288  to impact percussion initiator  290 , as best seen in  FIG. 5C . This impact starts the progression of the detonation event at detonation cord  292 , which continues through the perforating guns as discussed above. 
     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.