Patent Publication Number: US-2022220812-A1

Title: Keyhole threads with inductive coupler for drill pipe

Description:
RELATED APPLICATIONS 
     This application presents a modification of U. S. Pat. No. 11,204,115, to Mitchell, entitled Threaded Connection for Tubular Members, issued Dec. 21, 2021, and is incorporated herein by this reference for all that it teaches. The prior art figures and related text are taken from said patent. The teachings of said patent apply to this application except for the modifications disclosed herein. 
     U.S. patent application Ser. No. 17/543,655, to Fox, entitled Inductive Data Transmission System for Drill Pipe, filed Dec. 6, 2021, is incorporated herein by this reference for all that it teaches. 
    
    
     BACKGROUND 
     This disclosure relates to releasable connections between tubular members or bodies. In some aspects, this disclosure relates to connections between downhole tubulars, such as drill pipe joints, as are employed in drilling systems. For instance, in some rotary drilling applications, a drill bit is attached to the lower end of a drill string composed of lengths of tubular drill pipe and other components joined together by tool joints with rotary shouldered threaded connections (RSTCs). In this disclosure, the term “drill string” is used herein to include all arrangements in which pipes or other tubulars are threaded together end-to-end, including pipelines, risers and all downhole tubular strings such as drill strings and work strings. For clarity, the term is not limited only to tubular strings used in drilling a borehole. Furthermore, the tubular members that make up a drill string may also be substituted with other rods, shafts, or other cylindrical members that may be used at the surface and which may require a releasable connection. In some applications, the drill string includes threads that are engaged by right hand and/or left hand rotation. The threaded connections are generally configured to sustain the weight of the drill string, withstand the strain of repeated make-up and break-out, resist fatigue, resist additional make-up during drilling, provide a leak proof seal, and/or not loosen during normal operations. For example, the rotary drilling process may subject the drill string to significant dynamic tensile stresses, dynamic bending stresses and/or dynamic rotational stresses. Additionally, the tool joints or pipe connections in the drill string include appropriate shoulder area, thread pitch, shear area and friction to transmit the required drilling torque. In some applications, a minimum make-up torque is applied to the tool joint during make-up of the tool joint, the minimum make-up torque corresponding to the minimum amount of torque necessary to develop a desired tensile stress in the external thread or compressive stress in the internal thread of the tool joint, where the desired stress level is sufficient in most conditions to prevent downhole separation or break-up and to prevent shoulder separation arising from bending loads. 
     SUMMARY OF THE DISCLOSURE 
     This application presents an inductively coupled drillstring, that may comprise a drillstring tool such as a drill pipe and other tools associated with a bottom hole assembly. The drillstring tool may comprise pin end and box end tool joints for attachment within the drillstring. The pin end tool joints may comprise external female helical threads, comprising a stem wall, and comprising a bulbous thread root. The box end tool joints may comprise internal male helical threads, comprising a stem wall, and comprising a bulbous thread crest. The male bulbous helical threads may be complementary with the female bulbous helical threads so that the respective threads may be suitable for coupling engagement when the respective tool joints may be made up into a drill string. The respective male and female bulbous threads may comprise a generally keyhole cross section. 
     At least a portion of the female bulbous helical thread root may comprise at least a portion of a first helical inductive coupler, and at least a portion of the male bulbous helical thread crest may comprise at least a portion of a second helical inductive coupler. When the respective male and female threads may be fully engaged at least a portion of the respective first and second helical inductive couplers may be opposed to each other within the drillstring. The opposed first and second helical couplers may enable inductive data transmission coupling across the pin end and box end threads and data transmission between drillstring tools. 
     The first helical inductive coupler may be disposed within the bulbous root of the female helical threads, and the second helical inductive coupler may be disposed within the bulbous crest of the male helical threads. Also, the respective first and second inductive couplers may be disposed at other locations on the respective male and female threads. At least a portion of two or more adjacent female bulbous helical thread roots may comprise at least a portion of the first helical inductive coupler. And at least a portion of two or more adjacent male bulbous helical thread crests may comprise at least a portion of the second helical inductive coupler. Due to the helical angular nature of the respective threads, a single inductive coupler may be viewed as part of two adjacent thread roots as well as two adjacent thread crests. 
     The respective helical couplers may comprise a magnetically conductive electrically insulating (MCEI) helical trough. The MCEI material may be ferrite. A ferrite composition comprising oxygen, iron, and manganese elements may be suitable for use in the inductive troughs. The MCEI helical trough may also comprise a polymer that may comprise a substantial volume of ferrite fibers. For example, polymer that may comprise up to  73  percent by volume of ferrite fibers may be a suitable MCEI trough material. The MCEI helical trough may be housed within a helical groove within female thread root and the male thread crest. The MCEI helical trough may also be housed within a metal channel disposed within the helical groove. Another housing for the MCEI trough may be a polymeric block. The MCEI trough may be molded within the polymeric block prior to insertion into the helical groove. The polymeric block may comprise a substantial volume of MCEI fibers of up to  73  percent by volume. The presence of the substantial volume of ferrite fibers in the composition of the polymeric block may aid in preventing leakage of the transmitted signal between the respective couplers. The ferrite fibers also may be instrumental in protecting the transmitted signal from outside electromagnet interference between the respective inductive couplers. 
     The respective helical inductive couplers may comprise an electrically conductive wire coil disposed within the MCEI helical trough. The coil may be a single wire, a twisted pair of wires, or a collection of wire strands. The wire coil may be magnetically and or electrically insulated, or both. The respective helical inductive couplers may comprise an electrically insulated wire coil. On the other hand, the wire may comprise insulation comprising a non-MCEI fibrous portion and a portion comprising a substantial volume of MCEI fibers. The portion of the wire insulation comprising the MCEI fibers may be oriented toward the opposed inductive coupler, while the non-MCEI fibrous portion may be oriented away from the opposed inductive coupler. The wire coil may be bare of insulation. The MCEI trough may be filled with a nonelectrically conductive polymer in order fix the wire coil within the MCEI trough and protect the inductive components from contamination in actual use. The wire coil may be connected to a cable within the drillstring tool. The cable may lead to electronic components within the drillstring tool and to a similarly constructed inductive conductor assembly at the opposite end of the drillstring tool. 
     The respective MCEI helical troughs may be a solid continuous trough. Or the MCEI trough may be a trough made up of MCEI segments intimately arranged end to end. The solid MCEI trough may comprise one or more perforations providing a passageway for the wire coil to exit the trough to connect to a ground and to a cable within the drillstring tool. Likewise, one or more of the MCEI trough segments may be perforated to provide a passageway for the exit of the coil wire. The perforated segments permit a gap free MCEI trough within the inductive couplers. 
     The hardness of the respective helical threads may be greater on the Rockwell C scale than the hardness of the material of the drillstring tool and respective pin and box ends adjacent the threads. The higher hardness of the respective male and female threads or at least a portion of the threads may aid in strengthening the threads in the presence of the groove housing the respective inductive couplers. However, the higher hardness may only apply to the threads comprising the groove housing the respective inductive couplers, or it may apply to the entire thread form within the respective tool joint. It may be desirable that the walls of the respective grooves comprise a hardness greater than the hardness of the respective thread roots and thread crests. The hardness of the walls of the inductive coupler grooves may be achieved through a process such as peening, including shot peening and laser peening, or brinelling. The hardness may extend into the thread material a distance sufficient to allow the grooved threads to resist the stresses of a working drillstring. 
     The diameter of the female bulbous helical thread may diminish proximate the box end&#39;s internal shoulder. Likewise, the diameter of the complementary male bulbous helical thread may diminish proximate pin end&#39;s internal shoulder. The diminishing respective thread diameters may aid the resilience of the made up tool joint. The following portion of the summary is taken from the &#39;115 reference and applies to this disclosure except for the modifications described herein. 
     An embodiment of a tubular member for threadably engaging another tubular member to form a tubular string comprises a first end comprising a helical female thread formed in an outer surface of the tubular member, wherein the female thread comprises a slot extending radially inwards from the outer surface, and a root extending radially inwards from the slot, wherein the root has a maximum width that is greater than a maximum width of the slot, a second end opposite the first end and comprising a helical male thread formed on an inner surface of the tubular member, wherein the male thread comprises a shank extending radially outwards from the inner surface, and a notch extending radially outwards from the shank, wherein the notch has a maximum width that is greater than a maximum width of the shank. In some embodiments, the first end comprises a pin end and the second end comprises a box end. In some embodiments, the maximum width of the notch of the male thread is greater than the maximum width of the slot of the female thread. In certain embodiments, the first end comprises a plurality of the female threads and the second end comprises a plurality of the male threads. In certain embodiments, the root of the female thread is defined by a concave inner surface and the notch of the male thread is defined by a convex outer surface. In some embodiments, the interface between the slot and the root of the female thread forms a pair of convex shoulders, and the interface between the shank and the notch of the male thread forms a pair of concave recesses. In some embodiments, the first end comprises an annular shoulder and an annular sealing surface positioned axially between the female thread and the shoulder, and wherein the shoulder is disposed at an acute angle relative to a central axis of the tubular member and configured to provide a radially directed force against the sealing surface in response to coupling the tubular member with an adjacent tubular member. In certain embodiments, the male thread and the female thread each comprise a dovetail shaped cross-sectional profile. 
     An embodiment of a tubular member for threadably engaging another tubular member to form a tubular string comprises a first end comprising a helical female thread formed in an outer surface of the tubular member, wherein the female thread comprises a slot extending radially inwards from the outer surface, a root extending radially inwards from the slot, wherein the root is defined by a concave inner surface, and a pair of convex curved shoulders extending between the slot and the root, a second end opposite the first end and comprising a helical male thread formed on an inner surface of the tubular member, wherein the male thread comprises a shank extending radially outwards from the inner surface, a notch extending radially outwards from the shank, wherein the notch is defined by a convex outer surface, and a pair of concave curved shoulders extending between the shank and the notch. In some embodiments, the slot of the female thread is defined by a pair of opposing first planar surfaces and the shank of the male thread is defined by a pair of opposing second planar surfaces. In some embodiments, the root of the female thread has a maximum width that is greater than a maximum width of the slot of the female thread, and the notch of the male thread has a maximum width that is greater than a maximum width of the shank of the male thread. In certain embodiments, the first end comprises a plurality of the female threads and the second end comprises a plurality of the male threads. In certain embodiments, the first end comprises an annular shoulder and an annular sealing surface positioned axially between the female thread and the shoulder, and wherein the shoulder is disposed at an acute angle relative to a central axis of the tubular member to provide a radially directed force against the sealing surface in response to coupling the tubular member with an adjacent tubular member. In some embodiments, the first end comprises a pin end and the second end comprises a box end. 
     An embodiment of a tubular member for threadably engaging another tubular member to form a tubular string comprises a first end comprising an annular first shoulder, a first helical thread, and an annular first sealing surface positioned axially between the first helical thread and the first shoulder, wherein the first shoulder is disposed at an acute angle relative to a central axis of the tubular member to provide a radially directed force against the first sealing surface in response to coupling the tubular member with an adjacent tubular member. In some embodiments, the first end further comprises an annular second sealing surface axially spaced from the first sealing surface and an annular second shoulder axially spaced from the first shoulder, and wherein the second sealing surface is positioned axially between the first helical thread and the second shoulder, and the second shoulder is disposed at an acute angle relative to the central axis of the tubular member to provide a radially directed force against the second sealing surface in response to coupling the tubular member with an adjacent tubular member. In some embodiments, the first helical thread comprises a slot extending radially inwards from the outer surface, and a root extending radially inwards from the slot, and wherein the root has a maximum width that is greater than a maximum width of the slot. In certain embodiments, the first helical thread comprises a pair of convex curved shoulders extending between the slot and the root, wherein the root of the first helical thread is defined by a concave inner surface. In certain embodiments, the tubular member further comprises a second end opposite the first end that comprises an annular second shoulder, a second helical thread, and an annular second sealing surface positioned axially between the second helical thread and the second shoulder, wherein the second shoulder is disposed at an acute angle relative to the central axis of the tubular member to provide a radially directed force against the second sealing surface in response to coupling the tubular member with an adjacent tubular member. In some embodiments, the second helical thread comprises a shank extending radially outwards from the inner surface, and a notch extending radially outwards from the shank, and wherein the notch has a maximum width that is greater than a maximum width of the shank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the exemplary embodiments of the disclosure that are presented herein, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a diagram of a portion of (Prior Art)  FIG. 4  representing the keyhole thread form comprising an inductive coupler. 
       (Prior Art)  FIG. 2  is a schematic view of an embodiment of a drilling system in accordance with the principles described herein; 
       (Prior Art)  FIG. 3  is a schematic, side cross-sectional view of a portion of an embodiment of a drill string of the drilling system of (Prior Art)  FIG. 2  in accordance with principles disclosed herein; 
       (Prior Art)  FIG. 4  is a side cross-sectional view of an embodiment of a tool joint formed between a pair of drill pipes in accordance with principles disclosed herein; 
       (Prior Art)  FIG. 5  is a side cross-sectional view of a box end of one of the drill pipes of (Prior Art)  FIG. 4 ; 
       (Prior Art)  FIG. 6  is a side cross-sectional view of a pin end of one of the drill pipes of (Prior Art)  FIG. 4 ; 
       (Prior Art)  FIG. 7  is a side cross-sectional view of an embodiment of a female thread form of the drill pipes of (Prior Art)  FIG. 4  in accordance with principles disclosed herein; 
       (Prior Art)  FIG. 8  is a side cross-sectional view of an embodiment of a male thread form of the drill pipes of (Prior Art)  FIG. 4  in accordance with principles disclosed herein; 
       (Prior Art)  FIG. 9  is an enlarged, cross-sectional view of the thread forms of (Prior Art)  FIGS. 7, 8  engaged with one another; 
       (Prior Art)  FIG. 10  is a side cross-sectional view of an embodiment of an annular seal of the tool joint of (Prior Art)  FIG. 4  in accordance with principles disclosed herein; and 
       (Prior Art)  FIG. 11  is a side cross-sectional view of another embodiment of an annular seal in accordance with principles disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following portion of the detailed description is taken from the &#39;117 reference and applies to this disclosure except for the modification described herein. 
     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. 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. Further, “couple” or “couples” may refer to coupling via welding or via other means, such as releasable connections using a connector, pin, key or latch. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a given axis (e.g., given axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the given axis. For instance, an axial distance refers to a distance measured along or parallel to the given axis, and a radial distance means a distance measured perpendicular to the given axis. 
     With regards to  FIG. 1 , this application presents an inductively coupled drillstring, that may comprise a drillstring tool such as a drill pipe and other tools associated with a bottom hole assembly. The drillstring tool may comprise pin end and box end tool joints  400  for attachment within the drillstring. The pin end  425  tool joints may comprise external female helical threads  410 , comprising a stem wall  465 , and comprising a bulbous thread root  445 . The box end  405  tool joints may comprise internal male helical threads  415 , comprising a stem wall  460 , and comprising a bulbous thread crest  450 . The male bulbous helical threads  415 / 450  may be complementary with the female bulbous helical threads  410 / 445  so that the respective threads may be suitable for coupling engagement when the respective tool joints may be made up into a drill string. The respective male  450  and female  445  bulbous threads may comprise a generally keyhole cross section  475 . 
     At least a portion of the female bulbous helical thread root  445  may comprise at least a portion of a first helical inductive coupler  470 , and at least a portion of the male bulbous helical thread crest  450  may comprise at least a portion of a second helical inductive coupler  420 . When the respective male  415  and female  410  threads may be fully engaged at least a portion of the respective first  470  and second  420  helical inductive couplers may be opposed to each other within the drillstring. The opposed first  470  and second  420  helical couplers may enable inductive data transmission coupling across the pin end  425  and box end  405  threads and data transmission between drillstring tools. 
     The first helical inductive coupler  470  may be disposed within the bulbous root  445  of the female helical threads  410 , and the second helical inductive coupler  420  may be disposed within the bulbous crest  450  of the male helical threads  415 . Also, the respective first  470  and second  420  inductive couplers may be disposed at other locations on the respective male  415  and female  410  threads. At least a portion of two or more adjacent female bulbous helical thread roots  445  may comprise at least a portion of the first helical inductive coupler  470 . And at least a portion of two or more adjacent male bulbous helical thread crests  450  may comprise at least a portion of the second helical inductive coupler  420 . Due to the helical angular nature of the respective threads, a single inductive coupler may be viewed as part of two adjacent thread roots  445  as well as two adjacent thread crests  450 . 
     The respective helical couplers may comprise a magnetically conductive electrically insulating (MCEI) helical trough  435 . The MCEI material may be ferrite. A ferrite composition comprising oxygen, iron, and manganese elements may be suitable for use in the inductive troughs  435 . The MCEI helical trough  435  may also comprise a polymer that may comprise a substantial volume of ferrite fibers. For example, polymer that may comprise up to 73 percent by volume of ferrite fibers may be a suitable MCEI trough  435  material. The MCEI helical trough  435  may be housed within a helical groove within female thread root  440  and the male thread crest  480 . The MCEI helical trough  435  may also be housed within a metal channel disposed within the helical groove  440 / 480 . Another housing for the MCEI trough  435  may be a polymeric block. The MCEI trough  435  may be molded within the polymeric block prior to insertion into the helical groove  440 / 480 . The polymeric block may comprise a substantial volume of MCEI fibers of up to 73 percent by volume. See the &#39;115 reference. The presence of the substantial volume of ferrite fibers in the composition of the polymeric block may aid in preventing leakage of the transmitted signal between the respective couplers  420 / 470 . The ferrite fibers also may be instrumental in protecting the transmitted signal from outside electromagnet interference between the respective inductive couplers  420 / 470 . 
     The respective helical inductive couplers  420 / 470  may comprise an electrically conductive wire coil  430  disposed within the MCEI helical trough  435 . The coil  430  may be a single wire, a twisted pair of wires, or a collection of wire strands. The wire coil  430  may be magnetically and or electrically insulated, or both. The respective helical inductive couplers  420 / 470  may comprise an electrically insulated wire coil  430 . On the other hand, the wire  430  may comprise insulation  455  comprising a non-MCEI fibrous portion and a portion comprising a substantial volume of MCEI fibers. The portion of the wire insulation  455  comprising the MCEI fibers may be oriented toward the opposed inductive coupler, while the non-MCEI fibrous portion may be oriented away from the opposed inductive coupler. The wire coil  430  may be bare of insulation  455 . The MCEI trough  435  may be filled with a nonelectrically conductive polymer in order fix the wire coil  430  within the MCEI trough  435  and protect the inductive components from contamination in actual use. The wire coil  430  may be connected to a cable within the drillstring tool. The cable may lead to electronic components within the drillstring tool and to a similarly constructed inductive conductor assembly at the opposite end of the drillstring tool. 
     The respective MCEI helical troughs  435  may be a solid continuous trough. Or the MCEI trough  435  may be a trough  435  made up of MCEI segments intimately arranged end to end. The solid MCEI trough  435  may comprise one or more perforations providing a passageway for the wire coil  430  to exit the trough  435  to connect to a ground and to a cable within the drillstring tool. Likewise, one or more of the MCEI trough  435  segments may be perforated to provide a passageway for the exit of the coil wire. The perforated segments permit a gap free MCEI trough  435  within the inductive couplers  420 / 470 . 
     The hardness of the respective helical threads  410 / 415  may be greater on the Rockwell C scale than the hardness of the material of the drillstring tool and respective pin  425  and box  405  ends adjacent the threads  410 / 415 . The higher hardness of the respective male  415  and female  410  threads or at least a portion of the threads may aid in strengthening the threads in the presence of the groove  440 / 480  housing the respective inductive couplers  420 / 470 . However, the higher hardness may only apply to the threads  445 / 450  comprising the groove  440 / 480  housing the respective inductive couplers, or it may apply to the entire thread form within the respective tool joint. It may be desirable that the walls of the respective grooves  440 / 480  comprise a hardness greater than the hardness of the respective thread roots  445  and thread crests  450 . The hardness of the walls of the inductive coupler grooves  440 / 480  may be achieved through a process such as peening, including shot peening and laser peening, or brinelling. The hardness may extend into the thread material a distance sufficient to allow the grooved threads to resist the stresses of a working drillstring. 
     The diameter of the female bulbous helical thread  410 / 445  may diminish proximate the box end&#39;s internal shoulder  202 . Likewise, the diameter of the complementary male bulbous helical thread  415 / 450  may diminish proximate pin end&#39;s internal shoulder  102 . The diminishing respective thread diameters may aid the resilience of the made up tool joint. Referring to (Prior Art)  FIG. 2 , an embodiment of a well or drilling system  10  is schematically shown. In this embodiment, drilling system  10  includes a drilling rig  20  positioned over a borehole  11  penetrating a subsurface formation  12  and a drill string  30  suspended in borehole  11  from a derrick  21  of rig  20 . Elongate drill string  30  has a central or longitudinal axis  35 , a first or upper end  30   a , and a second or lower end  30   b  opposite end  30   a . In addition, drill string  30  includes a drill bit  32  at lower end  30   b , a bottomhole assembly (BHA)  33  axially adjacent bit  32 , and a plurality of interconnected tubular members or drill pipe joints  50  extending between BHA  33  and upper end  30   a . BHA  33  and drill pipes  50  are coupled together end-to-end at tool joints or connections  70 . As will be discussed further herein, in this embodiment, connections  70  comprise double shouldered RSTCs. In general, BHA  33  can include drill collars, drilling stabilizers, a mud motor, directional drilling equipment, a power generation turbine, as well as capabilities for measuring, processing, and storing information, and communicating with the surface (e.g., MWD/LWD tools, telemetry hardware, etc.). 
     In this embodiment, drill bit  32  is rotated by rotation of drill string  30  at the surface. In particular, drill string  30  is rotated by a rotary table  22 , which engages a kelly  23  coupled to upper end  30   a . Kelly  23 , and hence drill string  30 , is suspended from a hook  24  attached to a traveling block (not shown) with a rotary swivel  25  which permits rotation of drill string  30  relative to hook  24 . Although drill bit  32  is rotated from the surface with drill string  30  in this embodiment, in general, the drill bit (e.g., drill bit  32 ) can be rotated via a rotary table and/or a top drive, rotated by downhole mud motor disposed in the BHA (e.g., BHA  33 ), or by combinations thereof (e.g., rotated by both rotary table via the drill string and the mud motor, rotated by a top drive and the mud motor, etc.). Thus, it should be appreciated that the various aspects disclosed herein are adapted for employment in each of these drilling configurations and are not limited to conventional rotary drilling operations. 
     Referring to (Prior Art)  FIGS. 3-10 , an embodiment of a plurality of drill pipe joints  50  of which the drill string  30  of drilling system  10  of (Prior Art)  FIG. 2  is shown in (Prior Art)  FIGS. 3-10 . In the embodiment of (Prior Art)  FIGS. 3-10 , each drill pipe joint  50  has a central or longitudinal axis  55  and generally includes a terminal first end  50 A, a terminal second end  50 B opposite first end  50 A, a central bore or passage  52  defined by a generally cylindrical inner surface  53  extending between ends  50 A,  50 B, and a generally cylindrical outer surface  54  extending between ends  50 A,  50 B. Additionally, each drill pipe joint  50  includes a pin or pin end  100  extending from first end  50 A and a box or box end  200  extending from second end  50 B. As will be described further herein, the pin end  100  of a first drill pipe joint  50  is insertable into the box end  200  of an adjacent second drill pipe joint  50  to form or define a connection  70  therebetween (pin ends  100  are shown partially inserted into adjacent box ends  200  in (Prior Art)  FIG. 3 ). 
     In this embodiment of (Prior Art)  FIGS. 3-10 , the pin end  100  of each drill pipe joint  50  comprises an axial portion of the drill pipe joint  50  extending between a primary or radially inner shoulder  102  that defines the first end  50 A of the drill pipe joint  50 , and a secondary or radially outer shoulder  120  that is axially spaced from first end  50 A. As will be described further herein, pin end  100  also includes a generally annular pin thread form  140  and an annular sealing surface  180  positioned axially between inner shoulder  102  and pin thread form  140 . In this embodiment, the box end  200  of each drill pipe joint  50  comprises an axial portion of the drill pipe joint  50  extending between a primary or radially inner shoulder  202  that is spaced from second end  50 B, and a secondary or radially outer shoulder  220  that defines the second end  50 B of the drill pipe joint  50 . As will be described further herein, box end  200  also includes a generally annular box thread form  240  and an annular sealing surface  280  positioned axially between outer shoulder  220  and box thread form  240 . 
     As shown particularly in (Prior Art)  FIG. 7 , the pin thread form  140  of pin end  100  comprises a plurality of female helical threads or grooves  142  formed in the outer surface  54  of drill pipe joint  50 . In this embodiment, pin thread form  140  comprises a “triple-start thread” including three separate helical threads  142 ; however, in other embodiments, pin thread form  140  may include different numbers of helical threads  142  formed in outer surface  54 , including a “single-start thread” including only a single helical thread  142 . Each helical thread  142  is formed entirely within, and thus, does not project radially outwards from (relative to central axis  55 ) the cylindrical outer surface  54  of drill pipe joint  50 . Additionally, each helical thread  142  has a dovetail-shaped cross-sectional profile including a slot  144  extending from outer surface  54  and a rounded or circular root  146  that defines a radially inner terminal end  148  of the helical thread  142 . In this arrangement, a radially outer end of the slot  144  defines the major diameter of each helical thread  142  while the inner terminal end  148  of root  146  defines the minor diameter of each helical thread  142 . 
     In the embodiment of (Prior Art)  FIGS. 3-10 , the slot  144  of each helical thread  142  has a rectangular cross-sectional profile defined by a pair of planar surfaces or edges  145  while the root  146  of each helical thread  142  has a circular cross-sectional profile defined by a concave curved surface  147 . In other embodiments, the edges  145  defining slot  144  may be nonplanar, comprising curved surfaces, for instance. Additionally, in other embodiments, the root  146  of each helical thread  142  may comprise different cross-sectional profiles (e.g., rectangular, triangular, etc.) while still providing helical thread  142  with a dovetail shape. The slot  144  of each helical thread  142  has a maximum width  144 W extending between edges  145  while root  146  has a maximum width  146 W extending across curved surface  147 , where maximum width  146 W of root  146  is greater than the maximum width  144 W of slot  144 . The interface between slot  144  and root  146  of each helical thread  142  forms a pair of convex curved shoulders  150  as the width of helical thread  142  decreases moving radially outwards from root  146  towards slot  144 . 
     As shown particularly in (Prior Art)  FIG. 8 , the box thread form  240  of box end  200  comprises a plurality of male helical threads  242  extending radially inwards from the inner surface  53  of drill pipe joint  50 . In this embodiment, box thread form  240  comprises a “triple-start thread” including three separate helical threads  242 ; however, in other embodiments, box thread form  240  may include different numbers of helical threads  242  formed on inner surface  53 , including a “single-start thread” including only a single helical thread  242 . Each helical thread  242  is dovetail-shaped including a shank  244  extending from inner surface  53  and a rounded or circular notch  246  that defines a radially inner terminal end or crest  248  of the helical thread  242 . In this arrangement, a radially outer end or root  250  of the shank  244  defines the major diameter of each helical thread  242  while the crest  248  of notch  246  defines the minor diameter of each helical thread  242 . 
     In this embodiment, the shank  244  of each helical thread  242  has a rectangular cross-sectional profile defined by a pair of planar surfaces or edges  245  while the notch  246  of each helical thread  242  has a circular cross-sectional profile defined by a convex curved surface  247 . In other embodiments, the edges  245  defining shank  244  may be nonplanar, comprising convex curved surfaces, for instance. Additionally, in other embodiments, the notch  246  of each helical thread  242  may comprise different cross-sectional profiles (e.g., rectangular, triangular, etc.) while still providing helical thread  242  with a dovetail shape. The shank  244  of each helical thread  242  has a maximum width  244 W extending between edges  245  while notch  246  has a maximum width  246 W extending across curved surface  247 , where maximum width  246 W of notch  246  is greater than the maximum width  244 W of shank  244 . The interface between shank  244  and notch  246  of each helical thread  242  forms a pair of curved or concave recesses  252  as the width of helical thread  242  decreases moving radially outwards from notch  246  towards shank  244 . 
     As shown particularly in (Prior Art)  FIG. 9 , when the pin end  100  and the box end  200  of adjacent drill pipe joints  50  are threadably connected to form connection  70 , helical threads  142  of the pin end  140  of a first drill pipe joint  50  are interlockingly received within the corresponding helical threads  242  of the box end  200  of a second drill pipe joint  50 . Particularly, the notch  246  of helical threads  242  are slidingly received in corresponding roots  146  of helical threads  142  while shanks  244  of helical threads  242  are slidingly received in the slots  144  of helical threads  142 . In this embodiment, the maximum width  246 W of each notch  246  is slightly larger than the maximum width  146 W of each corresponding root  146  while the maximum width  244 W of each shank  244  is slightly larger than the maximum width  144 W of each corresponding slot  144 . In this embodiment, the radius of curvature of the curved surface  147  of root  146  and of the curved surface  247  of notch  246  is approximately between 0.15″ and 0.22″; however, in other embodiments, the radius of curvature of each surface  147  and  247  may vary. Additionally, the radially extending length of each slot  144  and each shank  244  is approximately between 0.08″ and 0.12″; however, in other embodiments, the radially extending length of each slot  144  and shank  244  may vary. In this embodiment, the pin thread form  140  of pin end  100  and the box thread form  240  of box end  200  each has a pitch of approximately 0.3 threads per inch and a thread taper of approximately between 0. degree. and 3.7. degree. taper per foot; however, in other embodiments, the pitch and taper of thread forms  140  and  240  may vary. In some embodiments, crest  248  of the notch  246  of each helical thread  242  may be truncated to provide a space between crest  248  and the inner terminal end  148  of the root  146  in which the notch  246  is received to permit the communication or transport of materials (e.g., drill pipe joint lubricant, etc.) therethrough. In some embodiments, crest  248  may be truncated approximately between 0.010″ and 0.015″; however, in other embodiments, the amount of truncation of crest  248  may vary. 
     During operation of the drilling system  10  shown in (Prior Art)  FIG. 2 , an excessive degree of torque may be applied to adjacent drill pipe joints  50  during their makeup to form a connection  70  therebetween. The “overtorquing” of the adjacent drill pipe joints  50  may result in radially directed or bending forces (e.g., buckling) being applied to the corresponding pin end  100  and box end  200  of the adjacent drill pipe joints  50  in response to excessively forcible contact between the inner shoulder  102  of pin end  100  and inner shoulder  202  of box end  200  (shoulders  102  and  202  forming the primary load shoulder of the connection  70 ), and between the outer shoulder  120  of pin end  100  and the outer shoulder  220  of box end  200  (shoulders  120  and  220  forming the secondary load shoulder of the connection  70 ). In response to the application of bending forces to pin end  100  and box end  200  resulting from overtorquing of the connection  70 , outer surface  247  of the notch  246  of each helical thread  242  engages or contacts the shoulders  150  of each corresponding helical thread  142 , thereby preventing helical threads  242  from disengaging from the corresponding helical threads  142 . By preventing helical thread  242  from disengaging from helical threads  142 , stress is more evenly distributed across pin thread form  140  and box thread form  240 , thereby increasing the strength of the connection  70 . Moreover, the interlocking engagement between threads  142 ,  242  draws the sealing surfaces  180 ,  280  of pin end  100  and box end  200  together to increase the sealing integrity formed between ends  100 ,  200 . 
     As shown particularly in (Prior Art)  FIG. 10 , a metal-to-metal annular seal  185  is provided between the annular sealing surface  180  of pin end  100  and the annular sealing surface  280  of box end  200 , where annular seal  185  has an axially extending width  185 W. Particularly, annular sealing surface  180  of pin end  100  curves radially outwards away from central axis  55  of the drill pipe joint  50 . In this embodiment, curved sealing surface  180  has a radius of curvature approximately between 8″ to 12″; however, in other embodiments, the radius of curvature of sealing surface  180  may vary. The curvature of annular sealing surface  180  reduces the width  185 W of annular seal  185 , thereby increasing the contact pressure between surfaces  180  and  280  and the seal integrity of the annular seal  185  formed therebetween. 
     Annular seal  185  serves to restrict fluid communication between the central passages  52  of adjoined drill pipe joints  50  and the environment surrounding drill pipe joints  50 . In this embodiment, annular seal  185  comprises a gas tight seal. Additionally, annular sealing surface  280  of box end  200  is inclined (frustoconical) relative to central axis  55  such that the axial end of sealing surface  280  proximal inner shoulder  202  has a diameter that is greater than the diameter of the axial end of sealing surface  280  distal inner shoulder  202 . In this embodiment, sealing surface  280  of box end  200  is disposed at an angle of approximately 1. degree. to 2. degree. relative to central axis  55 ; however, in other embodiments, the angle of sealing surface  280  may vary, including an angle of 0. degree. relative to central axis  55 . In still other embodiments, sealing surface  280  of box end  200  may comprise a convex curved surface similar in geometry as the sealing surface  180  of pin end  100 . 
     In the embodiment shown in (Prior Art)  FIGS. 3-10 , the inner shoulder  102  of pin end  100  and the inner shoulder  202  of box end  200  are each angled relative to the central axis  55  of drill pipe joint  50 . Particularly, inner shoulder  102  of pin end  100  and the inner shoulder  202  of box end  200  radially extend at a non-zero angle .theta. relative to an axis extending orthogonally from central axis  55 . In other words, inner shoulder  102  and inner shoulder  202  are each disposed at the angle .theta. from orthogonal of central axis  55 . Thus, inner shoulder  102  of pin end  100  and inner shoulder  202  are disposed at an acute or obtuse angle relative to the central axis  55  of their respective drill pipe joints  50 . In this embodiment, angle .theta. is approximately 4. degree. to 7. degree.; however, in other embodiments, the angle .theta. at which inner shoulders  102  and  202  are disposed may vary. With inner shoulder  102  of pin end  100  and inner shoulder  202  of box end  200  each disposed at angle .theta., an angled or frustoconical interface  110  is formed at the interface between inner shoulders  102  and  202  when the pin end  100  and box end  200  of adjacent drill pipe joints  50  are threadably coupled to form connection  70 , as shown in (Prior Art)  FIG. 10 . 
     Upon forming the connection  70  between adjacent drill pipe joints  50 , opposing axial forces are applied to pin end  100  and box end  200  at least partly as a result of forcible contact between inner shoulder  102  of pin end  100  and inner shoulder  202  of box end  200 . Further, the angled interface  110  formed between inner shoulder  102  of pin end  100  and inner shoulder  202  of box end  200  translates a portion of the axially directed force applied to pin end  100  at inner shoulder  102  into a radially outwards directed force (indicated by arrow  112  in (Prior Art)  FIG. 10 ). The radially outwards directed force  112  is directed towards the sealing surface  280  of box end  200 , thereby increasing the contact pressure between sealing surface  280  of box end  200  and sealing surface  180  of pin end  100 , and thus, the seal integrity of the annular seal  185  formed between sealing surfaces  180  and  280 . 
     Referring to (Prior Art)  FIG. 11 , another embodiment of a drill pipe joint  300  for forming tool joints or connections  305  therebetween. Drill pipe joint  300  includes features in common with drill pipe joint  50  shown in (Prior Art)  FIGS. 3-10 , and shared features are labeled similarly. In the embodiment of (Prior Art)  FIG. 11 , drill pipe joint  300  includes box end  200  and a pin end  310 . Pin end  310  is similar to pin end  100  shown in (Prior Art)  FIG. 5  except that pin end  310  includes an annular second or outer sealing surface  312  disposed adjacent outer shoulder  120  of pin end  310 . Thus, in this embodiment, sealing surface  180  of pin end  310  comprises a first or inner sealing surface  180 . Outer sealing surface  312  of pin end  310  is formed on a radially outwards extending annular shoulder  314  of pin end  310  and sealingly engages the inner surface  53  of the box end  200  of a corresponding drill pipe joint  300 . In this arrangement, a second or outer metal-to-metal annular seal  315  is provided between the outer sealing surface  312  of pin end  310  and the inner surface  53  of box end  200 . In this embodiment, outer seal  315  compliments the first or inner seal  185  formed between the annular sealing surface  180  of pin end  310  and the annular sealing surface  280  of box end  200 , thereby providing a pair of annular seals  185 ,  315  that seal the central passages  52  of adjacent drill pipe joints  300  from the surrounding environment. 
     Additionally, in this embodiment the outer shoulder  120  of pin end  310  and the outer shoulder  220  of box end  200  are each angled relative to the central axis  55  of drill pipe joint  300 . Particularly, outer shoulder  120  of pin end  310  and the outer shoulder  220  of box end  200  radially extend at a non-zero angle .alpha. relative to an axis extending orthogonally from central axis  55 . Thus, outer shoulder  120  of pin end  310  and outer shoulder  220  of box end  200  are disposed at an acute or obtuse angle relative to the central axis  55  of their respective drill pipe joints  50 . In this embodiment, angle .alpha. is approximately  4 .degree. to  7 .degree.; however, in other embodiments, the angle .theta. at which inner shoulders  102  and  202  are disposed may vary. With outer shoulder  120  of pin end  310  and outer shoulder  220  of box end  200  each disposed at angle .alpha., an angled or frustoconical interface  318  is formed at the interface between outer shoulders  120 ,  220  when the pin end  310  and box end  200  of adjacent drill pipe joints  300  are threadably coupled to form connection  305 . The angled interface  318  translates a portion of the axially directed force applied to pin end  310  at outer shoulder  120  into a radially inwards directed force (indicated by arrow  320  in (Prior Art)  FIG. 11 ). The radially inwards directed force  320  is directed against the outer sealing surface  312  of pin end  310 , thereby increasing the contact pressure and seal integrity between sealing surface  312  and the inner surface  53  of box end  200 . 
     While 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. 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.