Patent Publication Number: US-11047188-B2

Title: Power cartridges for setting tools

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of U.S. provisional patent application No. 62/641,741 filed Mar. 12, 2018, and entitled “Power Cartridges for Setting Tools” which is incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     After a wellbore has been drilled through a subterranean formation, the wellbore may be cased by inserting lengths of pipe (“casing sections”) connected end-to-end into the wellbore. Threaded exterior connectors known as casing collars may be used to connect adjacent ends of the casing sections at casing joints, providing a casing string including casing sections and connecting casing collars that extends from the surface towards the bottom of the wellbore. The casing string may then be cemented into place to secure the casing string within the wellbore. 
     In some applications, following the casing of the wellbore, a wireline tool string may be run into the wellbore as part of a “plug-n-perf” hydraulic fracturing operation. The wireline tool string may include a perforating gun for perforating the casing string at a desired location in the wellbore, a downhole plug that may be set to couple with the casing string at a desired location in the wellbore, and a setting tool for setting the downhole plug. In certain applications, once the casing string has been perforated by the perforating gun and the downhole plug has been set, a ball or dart may be pumped into the wellbore for landing against the set downhole plug, thereby isolating the portion of the wellbore extending uphole from the set downhole plug. With this uphole portion of the wellbore isolated, the formation extending about the perforated section of the casing string may be hydraulically fractured by fracturing fluid pumped into the wellbore. 
     SUMMARY OF THE DISCLOSURE 
     An embodiment of a tool string disposable in a wellbore comprises a plug configured to seal against an inner surface of a tubular string disposed in the wellbore, and a setting tool coupled to the plug, comprising a piston slidably disposed in a housing of the setting tool and comprising a central passage, and a combustible assembly disposed in the passage of the piston, wherein the combustible assembly comprises a housing and combustible material disposed in the housing, wherein, in response to a pressurization of the central passage of the piston of the setting tool, the setting tool is configured to actuate the plug to seal against the inner surface of the tubular string. In some embodiments, the combustible assembly housing comprises a plurality of the planar surfaces and wherein the planar surfaces are circumferentially spaced about the housing. In some embodiments, the housing of the setting tool is coupled to a housing of the plug, and the setting comprises a mandrel coupled to the piston, the mandrel of the setting tool being coupled to a mandrel of the plug, and wherein displacement of the mandrel of the setting tool results in displacement of the mandrel of the plug. In certain embodiments, the tool string further comprises a plug-shoot firing head coupled to the setting tool, and a wireline extending from the tool string to a surface of the wellbore, wherein the plug-shoot firing head comprises an ignitor ballistically coupled to the combustible assembly and is configured to ignite the combustible material of the combustible assembly in response to receiving a signal transmitted by the wireline. In certain embodiments, the combustible assembly comprises a power cartridge. In some embodiments, the combustible assembly housing comprises a rectangular cross-section having a maximum width and a minimum width that is less than the maximum width. In some embodiments, the combustible assembly housing comprises a hexagonal cross-section having a maximum width and a minimum width that is less than the maximum width. In certain embodiments, the setting tool comprises a first chamber and a second chamber are formed in the setting tool housing, wherein fluid communication between the first chamber and the second chamber is restricted when the piston is in a first position, and wherein fluid communication is permitted between the first chamber and the second chamber when the piston is in a second position. In certain embodiments, the setting tool comprises a mandrel slidably disposed in the setting tool housing and coupled to the piston, and an annular seal positioned between the mandrel and the setting tool housing, wherein the annular seal isolates the first chamber from the second chamber in the setting tool housing. In some embodiments, an opening is formed between an outer surface of the combustible assembly housing and an inner surface of the piston, and wherein the opening comprises a flowpath for providing fluid communication between a chamber formed in the combustible assembly housing and the first chamber. In some embodiments, the opening comprises an arcuate opening formed between a planar surface of the combustible assembly housing and the inner surface of the setting tool housing. 
     An embodiment of a setting tool for actuating a plug in a wellbore comprises a housing comprising a central passage, wherein a first chamber and a second chamber are formed in the setting tool housing, a piston slidably disposed in the setting tool housing and comprising a central passage, and a combustible assembly disposed in the passage of the piston, wherein the combustible assembly comprises a housing and combustible material disposed in the combustible assembly housing, wherein fluid communication between the first chamber and the second chamber is restricted when the piston is in a first position, and wherein fluid communication is permitted between the first chamber and the second chamber when the piston is in a second position, wherein, in response to a pressurization of the central passage of the piston, the setting tool is configured to displace the piston between the first position and the second position. In some embodiments, the setting tool further comprises a mandrel slidably disposed in the setting tool housing and coupled to the piston, and an annular seal positioned between the mandrel and the setting tool housing, wherein the annular seal isolates the first chamber from the second chamber in the setting tool housing. In some embodiments, an opening is formed between an outer surface of the combustible assembly housing and an inner surface of the piston, and wherein the opening comprises a flowpath for providing fluid communication between a chamber formed in the combustible assembly housing and the first chamber. In certain embodiments, the opening comprises an arcuate opening formed between a planar surface of the combustible assembly housing and the inner surface of the setting tool housing. In certain embodiments, an outer surface of the combustible assembly housing comprises a plurality of circumferentially spaced planar surfaces. In some embodiments, the combustible assembly housing comprises a rectangular cross-section having a maximum width and a minimum width that is less than the maximum width. In some embodiments, the combustible assembly housing comprises a hexagonal cross-section having a maximum width and a minimum width that is less than the maximum width. In certain embodiments, the combustible assembly comprises a power cartridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments of the disclosure, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a schematic, partial cross-sectional view of a system for completing a subterranean well including an embodiment of a setting tool in accordance with the principles disclosed herein; 
         FIG. 2  is a side view of an embodiment of the setting tool of  FIG. 1  in accordance with principles disclosed herein; 
         FIG. 3  is a cross-sectional view along lines  3 - 3  of  FIG. 2  of the setting tool of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view along lines  4 - 4  of  FIG. 3  of the setting tool of  FIG. 2 ; 
         FIG. 5  is a perspective view of an embodiment of a power cartridge of the setting tool of  FIG. 2  in accordance with principles disclosed herein; 
         FIG. 6  is a side cross-sectional view of another embodiment of the setting tool of  FIG. 1  in accordance with principles disclosed herein; 
         FIG. 7  is a cross-sectional view along lines  7 - 7  of  FIG. 6  of the setting tool of  FIG. 6 ; and 
         FIG. 8  is a perspective view of an embodiment of a power cartridge of the setting tool of  FIG. 6  in accordance with principles disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. Further, the term “fluid,” as used herein, is intended to encompass both fluids and gasses. 
     Referring now to  FIG. 1 , a system  10  for completing a wellbore  4  extending into a subterranean formation  6  is shown. In the embodiment of  FIG. 1 , wellbore  4  is a cased wellbore including a casing string  12  secured to an inner surface  8  of the wellbore  4  using cement (not shown). In some embodiments, casing string  12  generally includes a plurality of tubular segments coupled together via a plurality of casing collars. In this embodiment, completion system  10  includes a tool string  20  disposed within wellbore  4  and suspended from a wireline  22  that extends to the surface of wellbore  4 . Wireline  22  comprises an armored cable and includes at least one electrical conductor for transmitting power and electrical signals between tool string  20  and the surface. System  10  may further include suitable surface equipment for drilling, completing, and/or operating completion system  10  and may include, in some embodiments, derricks, structures, pumps, electrical/mechanical well control components, etc. Tool string  20  is generally configured to perforate casing string  12  to provide for fluid communication between formation  6  and wellbore  4  at predetermined locations to allow for the subsequent hydraulic fracturing of formation  6  at the predetermined locations. 
     In this embodiment, tool string  20  generally includes a cable head  24 , a casing collar locator (CCL)  26 , a direct connect sub  28 , a plurality of perforating guns  30 , a switch sub  32 , a plug-shoot firing head  34 , a setting tool  100 , and a downhole or frac plug  36  (shown schematically in  FIG. 1 ). Cable head  24  is the uppermost component of tool string  20  and includes an electrical connector for providing electrical signal and power communication between the wireline  22  and the other components (CCL  26 , perforating guns  30 , setting tool  100 , etc.) of tool string  20 . CCL  26  is coupled to a lower end of the cable head  24  and is generally configured to transmit an electrical signal to the surface via wireline  22  when CCL  26  passes through a casing collar, where the transmitted signal may be recorded at the surface as a collar kick to determine the position of tool string  20  within wellbore  4  by correlating the recorded collar kick with an open hole log. The direct connect sub  28  is coupled to a lower end of CCL  26  and is generally configured to provide a connection between the CCL  26  and the portion of tool string  20  including the perforating guns  30  and associated tools, such as the setting tool  100  and downhole plug  36 . 
     Perforating guns  30  of tool string  20  are coupled to direct connect sub  28  and are generally configured to perforate casing string  12  and provide for fluid communication between formation  6  and wellbore  4 . Particularly, perforating guns  30  include a plurality of shaped charges that may be detonated by a signal conveyed by the wireline  22  to produce an explosive jet directed against casing string  12 . Perforating guns  30  may be any suitable perforation gun known in the art while still complying with the principles disclosed herein. For example, in some embodiments, perforating guns  30  may comprise a hollow steel carrier (HSC) type perforating gun, a scalloped perforating gun, or a retrievable tubing gun (RTG) type perforating gun. In addition, gun  30  may comprise a wide variety of sizes such as, for example, 2¾″, 3⅛″, or 3⅜″, wherein the above listed size designations correspond to an outer diameter of perforating guns  30 . 
     Switch sub  32  of tool string  20  is coupled between the pair of perforating guns  30  and includes an electrical conductor and switch generally configured to allow for the passage of an electrical signal to the lowermost perforating gun  30  of tool string  20 . Tool string  20  further includes plug-shoot firing head  34  coupled to a lower end of the lowermost perforating gun  30 . Plug-shoot firing head  34  couples the perforating guns  30  of the tool string  20  to the setting tool  100  and downhole plug  36 , and is generally configured to pass a signal from the wireline  22  to the setting tool  100  of tool string  20 . Plug-shoot firing head  34  may also include mechanical and/or electrical components to fire the setting tool  100 . 
     In this embodiment, tool string  20  further includes setting tool  100  and downhole plug  36 , where setting tool  100  is coupled to a lower end of plug-shoot firing head  34  and is generally configured to set or install downhole plug  36  within casing string  12  to isolate desired segments of the wellbore  4 , as will be discussed further herein. Once downhole plug  36  has been set by setting tool  100 , an outer surface of downhole plug  36  seals against an inner surface of casing string  12  to restrict fluid communication through wellbore  4  across downhole plug  36 . Downhole plug  36  of tool string  20  may be any suitable downhole or frac plug known in the art while still complying with the principles disclosed herein. Additionally, although setting tool  100  is shown in  FIG. 1  as incorporated in tool string  20 , setting tool  100  may be used in other tool strings comprising components differing from the components comprising tool string  20 . 
     Referring to  FIGS. 1-5 , an embodiment of the setting tool  100  of the tool string  20  of  FIG. 1  is shown in  FIGS. 2-5 . In the embodiment of  FIGS. 2-5 , setting tool  100  has a central or longitudinal axis  105  and generally includes an outer housing  102 , a piston  140  slidably disposed at least partially in housing  102 , and a mandrel  160  slidably disposed at least partially in housing  102 . In some embodiments, piston  140  comprises a firing head adapter  140  for coupling setting tool  100  with plug-shoot firing head  34 . Housing  102  of setting tool  100  has a first end  104 , a second end  106  axially spaced from first end  104 , a central bore or passage  108  defined by a generally cylindrical inner surface  110  extending between ends  104 ,  106 , and a generally cylindrical outer surface  112  extending between ends  104 ,  106 . In this embodiment, housing  102  comprises a plurality of tubular segments  102 A and  1026  coupled together via releasable or threaded connectors  114 ; however, in other embodiments, housing  102  of setting tool  100  may comprise a single, unitary member. Additionally, an annular seal  116  is positioned radially between tubular segments  102 A and  102 B of housing  102  to seal the connection formed therebetween from the environment surrounding setting tool  100  (e.g., wellbore  4 ). 
     In this embodiment, housing  102  includes at least one shear pin  118  that extends radially into central passage  108  from inner surface  110  and is frangibly connected to piston  140 . As will be discussed further herein, shear pin  118  restricts relative axial movement between piston  140  and housing  102  prior to the actuation of setting tool  100 . Additionally, in this embodiment, the inner surface  110  of housing  102  includes a radially inwards extending shoulder or flange  120  located proximal second end  106 . The inner surface  112  of flange  120  includes a pair of axially spaced annular seals  122  that sealingly engage mandrel  160  of setting tool  100 . Housing  102  also includes at least one vent port  124  axially located between flange  120  and second end  106 , where vent port  124  extends radially between inner surface  110  and outer surface  112  of housing  102 . In this configuration, vent port  124  provides fluid communication between at least a portion of central passage  108  of housing  102  and the environment surrounding setting tool  100 . In this embodiment, the outer surface  112  of housing  102  further includes a releasable or threaded connector  126  at second end  106  for threadably connecting with a corresponding connector of downhole plug  36  (not shown in  FIGS. 2-5 ). 
     Piston  140  of setting tool  100  has a first end  142 , a second end  144  axially spaced from first end  142 , a central bore or passage  146  defined by a generally cylindrical inner surface  148  extending between ends  142 ,  144 , and a generally cylindrical outer surface  150  extending between ends  142 ,  144 . In this embodiment, piston  140  comprises a plurality of tubular segments  140 A,  140 B coupled together via a releasable or threaded connector  152 ; however, in other embodiments, piston  140  of setting tool  100  may comprise a single, unitary member. Additionally, a pair of annular seals  154  are positioned radially between tubular segments  140 A,  140 B of piston  140  to seal the connection formed therebetween from central passage  108  of housing  102  and the environment surrounding setting tool  100  (e.g., wellbore  4 ). Further, an annular seal  155  is positioned adjacent to connector  152  to sealingly engage the inner surface  110  of housing  102 . 
     In this embodiment, the inner surface  148  of piston  140  includes a releasable or threaded connector  156  located at second end  144  for releasably connecting to a corresponding connector of mandrel  160 . Although in this embodiment piston  140  and mandrel  160  comprise distinct, releasably connectable members, in other embodiments, piston  140  and mandrel  160  may comprise a single, unitary member. In this embodiment, piston  140  includes one or more circumferentially spaced ports  158  that extend at an angle relative to central axis  105  of setting tool  100 . Particularly, each port  158  includes a first end formed at the inner surface  148  and a second end formed at the second end  144  of piston  140 . In this configuration, the second end of each port  158  is disposed circumferentially about and radially spaced from central passage  146 . Further, piston  140  includes a pair of annular seals  159  disposed on outer surface  150  and located proximal second end  144 . Seals  159  of piston  140  sealingly engage the inner surface  110  of housing  102 . 
     Mandrel  160  of setting tool  100  has a first end  162 , a second end  164  axially spaced from first end  162 , and a generally cylindrical outer surface  166  extending between ends  162 ,  164 . In this embodiment, the outer surface  166  of mandrel  160  includes a first releasable or threaded connector  168  located at first end  162  and a second releasable or threaded connector  170  located at second end  164 . First releasable connector  168  of mandrel  160  threadably connects to the releasable connector  156  of piston  140  to thereby releasably connect piston  140  with mandrel  160 . Second releasable connector  170  of mandrel  160  releasably or threadably connects with a corresponding connector of a mandrel of downhole plug  36  (not shown in  FIGS. 2-5 ). In some embodiments, the outer surface  166  of mandrel  160  may includes a radially outwards extending annular shoulder located proximal releasable connector  170 . The outwards extending annular shoulder may have a larger diameter than an inner diameter of the flange  120  of housing  102 , thereby preventing the outwards extending annular shoulder from passing through flange  120 . 
     Setting tool  100  includes a combustible assembly or power cartridge  180  that is received in the passage  146  of piston  140 . As will be described further herein, at least a portion of power cartridge  180  is configured to ignite or combust to thereby set or actuate setting tool  100 . In some embodiments, power cartridge  180  is ballistically connected to an ignitor (not shown) that is in signal communication with wireline  22 . In some embodiments, the ignitor may be disposed in plug-shoot firing head  34 ; however, in other embodiments, it may be disposed in setting tool  100 . In this manner, a firing signal may be communicated to the ignitor disposed in setting tool  100  from the surface of wellbore  4  via wireline  22  to ignite power cartridge  180 . 
     Power cartridge  180  of setting tool  100  has a central or longitudinal axis disposed coaxial with central axis  105 , a first or upper end  180 A, a second or lower end  1806  opposite upper end  180 A, and generally includes a tubular outer housing  182  and ignitable or combustible material  198  housed therein. Housing  182  of power cartridge  180  includes a central chamber or passage  184 , a first or open end  186  located at upper end  180 A of power cartridge  180 , a second or enclosed end comprising a cap  188  located at the lower end  180 B of power cartridge  180 , and an outer surface  190  extending between the open end  186  and cap  188 . Cap  188  of housing  182  is positioned directly adjacent or contacts the first end  162  of mandrel  160 . In this embodiment, cap  188  is permanently coupled (e.g., welded, formed, molded, etc.) with the tubular portion of housing  182 ; however, in other embodiments, cap  188  may be releasably coupled with the tubular portion of housing  182 . In this embodiment, housing  182  of power cartridge comprises a metallic material (e.g., steel, aluminum, etc.); however, in other embodiments, housing  182  may comprise various materials, such as cardboard, plastic, etc. In this embodiment, combustible material  198  is received in the chamber  184  of housing  182  and extends substantially between open end  186  and cap  188 . In this embodiment, combustible material  198  comprises a pyrotechnic compound; however, in other embodiments, combustible material  198  may comprise other ignitable, flammable, and/or combustible materials. 
     As shown particularly in  FIGS. 4 and 5 , in this embodiment, housing  182  of power cartridge  180  has a rectangular cross-sectional profile  191  with the outer surface  190  of housing  182  including a plurality of axially aligned and circumferentially spaced planar or uncurved surfaces  192  extending between open end  186  and cap  188 . Rectangular cross-sectional profile  191  formed by planar surfaces  192  of housing  182  has a maximum width  192 A and a minimum width  192 B. As will be discussed further herein, the maximum width  192 A of the rectangular cross-sectional profile  191  is similar or substantially equal to an inner diameter  148 D (shown in  FIG. 3 ) of the inner surface  148  of piston  140  while minimum width  192 B of the rectangular cross-sectional profile  191  is less than the inner diameter  148 D of inner surface  148 . 
     As described above, setting tool  100  is pumped downhole though wellbore  4  along with the other components of tool string  20 . As tool string  20  is pumped through wellbore  4 , the position of tool string  20  in wellbore  4  is monitored at the surface via signals generated from CCL  26  and transmitted to the surface using wireline  22 . Once tool string  20  is disposed in a desired location in wellbore  4 , setting tool  100  may be fired or actuated from the run-in position shown in  FIG. 2  to the full-stroke position (not shown) to thereby set the downhole plug  36  of tool string  20 , and one or more of perforating guns  30  may subsequently be fired to perforate casing  12  at the desired location. 
     Particularly, when setting tool  100  is run through wellbore  4  along with tool string  20 , housing  102  is connected to an outer housing (not shown) of downhole plug  36  via releasable connector  126  and mandrel  160  of setting tool  100  is connected to a mandrel (not shown) of downhole plug  36  via releasable connector  170 . In this arrangement, relative axial movement between mandrel  160  and housing  102  of setting tool  100  may provide relative axial movement between the mandrel and outer housing of downhole plug  36  to thereby set downhole plug  36  such that downhole plug  36  seals against an inner surface of casing string  12 . Once tool string  20  is disposed in a predetermined or desired position in wellbore  4 , setting tool  100  may be set or actuated by igniting or combusting power cartridge  180 . In some embodiments, power cartridge  180  is ballistically connected to an ignitor (not shown) that is in signal communication with wireline  22 . In some embodiments, the ignitor may be disposed in plug-shoot firing head  34 ; however, in other embodiments, it may be disposed in setting tool  100 . In this manner, a firing signal may be communicated to the ignitor disposed in setting tool  100  from the surface of wellbore  4  via wireline  22  to ignite power cartridge  180 . 
     Fluid pressure begins to build in the central passage  146  of piston  140  following the ignition of the combustible material  198  housed within housing  182  of power cartridge  180 , the fluid pressure in passage  146  being communicated to an annular pressure chamber  200  disposed about mandrel  160  and extending axially between seals  159  of piston  140  and seals  122  of the flange  120  of housing  102 . As shown particularly in  FIG. 4 , a plurality of arcuate gaps or openings  194  are formed between planar surfaces  192  of the housing  182  of power cartridge  180  and the inner surface  148  of piston  140 . Thus, fluid pressure formed in the chamber  184  of housing  182  created by the ignition of the combustible material  190  of power charge  180  is permitted to flow out into passage  146  via open end  186 , and through passage  146  into pressure chamber  200  via arcuate gaps  194  and ports  158  of piston  140 . 
     In this manner, arcuate gaps  194  reduce the restriction to the communication of fluid flow and/or pressure between open end  186  of the housing  182  of power cartridge  180  and pressure chamber  200 . The reduction in the restriction of flow and/or pressure communication along a flowpath extending through passage  146  of piston  140  provided by arcuate gaps  194  prevents excessive fluid pressure from building in the chamber  184  of housing  182  and/or passage  146  of piston  140 , thereby reducing the likelihood of either housing  182  and/or piston  140  failing or otherwise being damaged during the actuation of setting tool  100 . Although in this embodiment arcuate gaps  194  are formed via planar surfaces  192  of the housing  182  of power cartridge  180 , in other embodiments, one or more radial openings or gaps may be formed between housing  182  and piston  140  via other features located on the outer surface  190  of housing  182 , such as axially extending grooves formed in the outer surface  190  of housing  182 , or other features permitting fluid flow between housing  182  and piston  140 . 
     Fluid pressure building in pressure chamber  200  acts against the second end  144  of piston  140 , applying an axially directed upward force (e.g., in the direction of plug-shoot firing head  34 ) against piston  140 . The axially directed force applied against piston  140  from fluid pressure in pressure chamber  200  shears the shear pin  118 , allowing piston  140  and mandrel  160  to travel or stroke upwards in the direction of plug-shoot firing head  34 . As mandrel  160  strokes upwards in concert with piston  140 , mandrel  160  actuates or pulls the mandrel of downhole plug  36 , thereby displacing the mandrel of downhole plug  36  relative to the outer housing of plug  36 . Fluid pressure in pressure chamber  200  continues to force piston  140  and mandrel  160  axially upwards, causing an annular groove  172  formed in the outer surface  166  of mandrel  160  to pass and enter into axial alignment with flange  120  of the housing  102  of setting tool  100 . An annular passage formed between the inner surface of flange  120  and annular groove  172  of the outer surface  166  of mandrel  160  permits fluid pressure in pressure chamber  200  to vent to an annular vent chamber  202  disposed about mandrel  160  and extending axially between seals  122  of flange  120  and the second end  106  of housing  102 . Additionally, fluid vented to vent chamber  202  from pressure chamber  200  is vented from setting tool  100  to wellbore  4  via the vent port  124  formed in housing  102 . In other embodiments, housing  102  may not include vent port  124  and pressure within pressure chamber  200  may be vented through other means. 
     Referring to  FIGS. 1 and 6-8 , another embodiment of a setting tool  250  of the tool string  20  of  FIG. 1  is shown in  FIGS. 6-8 . Setting tool  250  includes features in common with the setting tool  100  shown in  FIGS. 2-5 , and shared features are labeled similarly. In the embodiment of  FIGS. 6-8 , setting tool  250  has a central or longitudinal axis  255  and generally includes outer housing  102 , piston  140 , mandrel  160 , and a power cartridge  260  received in the passage  146  of piston  140 . In this embodiment, power cartridge  260  has a central or longitudinal axis disposed coaxial with central axis  255  of setting tool  250 , a first or upper end  260 A, a second or lower end  260 B opposite upper end  260 A, and generally includes a tubular outer housing  262  and combustible material  198  housed therein. Housing  262  of power cartridge  260  includes a central chamber or passage  264 , a first or open end  266  located at upper end  260 A, a second or enclosed end comprising a cap  268  located at lower end  260 B, and an outer surface  270  extending between the open end  266  and cap  268 . 
     As shown particularly in  FIGS. 7 and 8 , unlike power cartridge  180  shown in  FIGS. 3-5  which includes rectangular cross-sectional profile  191 , housing  262  of power cartridge  260  has a hexagonal cross-sectional profile  271  with the outer surface  270  of housing  262  including a plurality of axially aligned and circumferentially spaced planar or uncurved surfaces  272  extending between open end  266  and cap  268 . Hexagonal cross-sectional profile  271  formed by planar surfaces  272  of housing  262  has a maximum width  272 A and a minimum width  272 B. In this embodiment, the difference between maximum width  272 A and minimum width  272 B of hexagonal cross-sectional profile  271  may be less than the difference between maximum width  192 A and minimum width  192 B of the rectangular cross-sectional profile  191  of housing  182  shown in  FIGS. 3-5 . However, in this embodiment, a greater number of arcuate gaps or openings  274  are formed between planar surfaces  272  of the housing  262  of power cartridge  260  and the inner surface  148  of piston  140  than the number of arcuate gaps  194  formed between the planar surfaces  192  (shown in  FIG. 4 ) of the housing  182  of power cartridge  180  and the inner surface  148  of piston  140 . 
     In this manner, sufficient cross-sectional area may be provided between the planar surfaces  272  of housing  262  and the inner surface  148  of piston  140  to permit the necessary communication of pressure and/or fluid flow through passage of piston  140  during the actuation of setting tool  250  to prevent damage occurring (e.g., due to over pressurization) to housing  262  and/or piston  140 , as well as other components of setting tool  250 . Further, although in this embodiment housing  262  of power cartridge  260  includes a hexagonal cross-sectional profile  271 , in other embodiments, the outer surface  270  of housing  262  may comprise varying cross-sectional profiles configured to provide gaps or spaces (e.g., annular, arcuate, etc.) between outer surface  270  and the inner surface  148  of piston  140 . 
     While exemplary embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure presented herein. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.