Patent Publication Number: US-7213655-B2

Title: System for connecting downhole tools

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/536,674, filed Jan. 15, 2004. 

   TECHNICAL FIELD 
   The present invention relates generally to connecting tools used in downhole applications, and more particularly to a connection system for fastening perforating guns together to form a tool string for use in a well. 
   BACKGROUND 
   After a well has been drilled and casing has been cemented in the well, one or more sections of the casing may be perforated using a string of perforating guns. After the perforating string is lowered into the well to a desired depth, the guns in the string are fired to create openings in the casing and to extend perforations into the surrounding formation. Production fluids in the perforated formation can then flow through the perforations and the casing openings into the wellbore. 
   In deploying a perforating string in a wellbore, the tools are usually assembled into a relatively long and heavy string, with the string suspended over and run into the wellbore. The perforating string includes a number of perforating guns coupled or fastened together in series, along with other components. The perforating guns are generally aligned in a predetermined pattern as a function of the desired perforation of the well formation. 
   Present fastening practices typically involve assembling the string manually at the surface before running into the wellbore. Such practices may be subject to human error, inefficiencies, and potential safety hazards. Accordingly, a need exists for a system to couple downhole tools together in series to form a tool string that may be automated and that yields a more reliable connection. The present invention is directed at providing such a system. 
   SUMMARY 
   In general, according to one embodiment of the present invention, a system for use in connecting downhole tools together in series to form a tool string is provided. 
   In general, according to another embodiment of the present invention, a system for connecting downhole tools together in series comprises an upper tool, a lower tool, and a sleeve arranged between the upper and lower tools for locking the tools together. 
   In general, according to yet another embodiment of the present invention, a system for connecting perforating guns together to form a perforating string comprises an upper gun assembly, a lower gun assembly having an axial bore therethrough for receiving the upper gun assembly, and a locking sleeve arranged between the gun assemblies for orienting the upper gun with respect to the lower gun and for locking the gun assemblies together. 
   Other or alternative features will be apparent from the following description, from the drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The manner in which these objectives and other desirable characteristics can be obtained is explained in the following description and attached drawings in which: 
       FIG. 1  is an elevation view of an embodiment of the connection system of the present invention illustrating the formation of a perforation string for use in a wireline-conveyed well completion operation on land. 
       FIG. 2A  is a schematic view of an embodiment of the present invention illustrating an upper perforating gun assembly, a lower perforating gun assembly and a locking sleeve. 
       FIG. 2B  is a cross-sectional view taken along line  2 B— 2 B of  FIG. 2A . 
       FIG. 3  is a perspective view of an embodiment of an upper perforating gun assembly in accordance with the present invention. 
       FIG. 4  is a perspective view of an embodiment of a locking sleeve accordance with the present invention. 
       FIG. 5  is a perspective view of an embodiment of a lower perforating gun assembly in accordance with the present invention. 
       FIG. 6  is a cross-sectional view of an embodiment of the connection system of the present invention illustrating the upper perforating gun assembly coupled with the lower perforating gun assembly. 
       FIG. 7A  is a profile view of an embodiment of the connection system of the present invention illustrating an upper perforating gun assembly and locking sleeve suspended over a lower perforating gun assembly. 
       FIG. 7B  is a cross-sectional view taken along line  7 B— 7 B of  FIG. 7A . 
       FIG. 8A  is a profile view of an embodiment of the connection system of the present invention illustrating the upper perforating gun assembly and locking sleeve being lowered into engagement with the lower perforating gun assembly. 
       FIGS. 8B ,  9 B and  10 B are enlarged views of portions of  FIGS. 8A ,  9 A and  10 A, respectively. 
       FIG. 8C  is a cross-sectional view taken along line  8 C— 8 C of  FIG. 8A . 
       FIG. 9A  is a profile view of an embodiment of the connection system of the present invention illustrating the locking sleeve being compressed against the lower perforating gun assembly by the upper perforating gun assembly such that the upper gun assembly can be threaded into engagement with the lower gun assembly. 
       FIG. 9C  is a cross-sectional view taken along line  9 C— 9 C of  FIG. 9A . 
       FIG. 10A  is a profile view of an embodiment of the connection system of the present invention illustrating the upper perforating gun assembly being rotated into threaded engagement with the lower perforating gun assembly such that the lugs of the locking sleeve align with the notched recesses of the lower gun assembly thus allowing the locking sleeve to decompress and lock the upper gun assembly to the lower gun assembly. 
       FIG. 10C  is a cross-sectional view taken along line  10 C— 10 C of  FIG. 10A . 
       FIG. 11  is a perspective view of an embodiment of the present invention illustrating the locking sleeve used in a rib and groove-type connection. 
   

   It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
   DETAILED DESCRIPTION 
   In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
   In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate. 
   While embodiments of the present invention are described with respect to connecting perforating guns to form a perforating string, in further embodiments other types of downhole tools, devices, and/or elements are connected together using the connection system of the present invention. For example, the system of the present invention may be used to connect valves, packers, sand screens, expandable tubing, diverter tools, drilling tools, float equipment, hangers, casing/liner running tools, well evaluation or logging tools, measurement while drilling tools, hydraulic lines, hoses, and other completion, drilling, or servicing equipment. In addition, the system of the present invention may be used to connect perforating guns and other items such as those listed above in an enclosed chamber such as pressure control equipment that is mounted above a pressurized wellbore. 
   In downhole oilfield operations, a variety of tools are often coupled together to form a tool string to perform particular tasks in a well. As these tools are often times heavy, cumbersome, and/or difficult to align, a “hands-free” or non-manual connection is desirable. An embodiment of the present invention provides a hands-free connection system to facilitate connecting and aligning (vertically and/or radially) two downhole tools together for use in well operations. Moreover, an embodiment of the connection system of the present invention may be used as a component in an automated tool handling operation. For example, robotic pipe handlers may be used to convey two tools to the well site, suspend the tools over the well, and couple, align, and lock the tools together using the hands-free connection system. 
   With reference to  FIG. 1 , according to one embodiment of the present invention, a perforating string  10  is positioned above a wellbore  20  which may be lined with casing  22 . In this illustrated embodiment, the perforating string  10  is suspended by a wireline  30  from a derrick  40  above the wellbore  20  in wireline-conveyed operations. However, in other embodiments, the perforating string may be suspended by tubing (e.g., coiled or jointed tubing) in tubing-conveyed operations, by rig handling equipment, drill pipe, or by any other conveying mechanism. Moreover, while this illustrated embodiment is used in land-based well operations, other embodiments of the connection system of the present invention may be used in offshore well operations. 
   Generally, according to an embodiment of the present invention, the gun string  10  includes an upper gun assembly  12  and a lower gun assembly  14  coupled together by a locking device  16 . Each gun assembly  12 ,  14  includes a carrier  12 A,  14 A for housing charges and a detonating cord and an adapter  12 B,  14 B for coupling guns in series. Additional guns may be included in the perforating string  10 , with additional locking devices  16  coupling the guns. The perforating string  10  may be formed by lowering and rotating the upper gun  12  into threaded engagement with the lower gun  14 . The locking device  16 , upon actuation, functions to lock the upper gun  12  and lower gun  14  together in a precise predetermined alignment. 
   More particularly, referring to  FIGS. 2A–5 , a connection system according to one embodiment of the present invention includes an upper perforating gun assembly  100 , a lower perforating gun assembly  200 , and a locking sleeve  300 . Note, for illustration purposes, only the adapters of the gun assemblies are shown and not the carriers. It is understood by those skilled in the art that other embodiments of the present invention include gun carriers with integral adapters and gun carriers that connect directly together in series without an adapter. 
   The upper perforating gun assembly  100  is generally cylindrical in shape and includes a carrier (see  FIG. 1 ), a shank  120 , and a threaded portion  130 . In one embodiment, the carrier may include a plurality of loading tubes for containing shaped charges. Alternatively, in another embodiment, the carrier may include a plurality of strips onto which capsule shaped charges are mounted. 
   The shank  120  of the upper perforating gun assembly  100  has a protruding ring  112  formed thereon having a plurality of tapered recesses  116  formed therein for engagement with the locking sleeve  300 . The shank  120  further includes a threaded hole  118  for receiving a through-bolt for attaching the locking sleeve  300  to the upper perforating gun assembly  100 . 
   The threaded portion  130  of the upper perforating gun assembly  100  includes a plurality of horizontal (i.e., non-spiral) threads  132 ,  133  protruding radially outward. The threads  132 ,  133  are arranged in columns having a selected width such that axial gaps  136  are formed between the columns. Moreover, the threaded portion includes a distinguishing feature that prevents engagement until proper vertical alignment is achieved. For example, in one embodiment, the bottom-most thread  133  in each column has a width greater than that of the other threads  132 . In other embodiments, the wider thread  133  may be located at the top or in the middle of the other threads. 
   The threaded portion  130  of the upper perforating gun assembly  100  further includes a distinguishing feature that prevents the upper gun from over engaging the lower gun  200 . For example, in one embodiment, a stop ring  134  is formed in the upper gun  100  above the threads  132 . The stop ring  134  protrudes radially outward and is continuous such that it circumscribes the total perimeter of the threaded portion  130 . 
   The threaded portion  130  of the upper perforating gun assembly  100  still further includes a set of two cylindrical keys  138  formed on the lower end of the upper perforating gun assembly  100  and protruding axially downward. The keys are positioned substantially equidistant from the central axis of the upper perforating gun assembly  100  and are spaced approximately 180 degrees apart. The number and position of the keys may vary. For example, by varying the number and/or position of the key, the keys may be used to ensure proper assembly (e.g., proper order of assembly). Moreover, the number and/or positioning of the keys may also be used to match tools that are to be connected to facilitate tool inventory control. 
   The lower perforating gun assembly  200  is also generally cylindrical in shape and includes a carrier (see  FIG. 1 ), a clamping section  220 , and a threaded housing  230 . In one embodiment, the carrier may include a plurality of loading tubes for containing shaped charges. Alternatively, in another embodiment, the carrier may include a plurality of strips onto which capsule shaped charges are mounted. 
   The clamping section  220  of the lower perforating gun assembly  200  is formed to receive a clamping tool to prevent the lower perforating gun assembly from rotating during engagement with the upper perforating gun assembly  100 . In further embodiments, instead of a clamping tool, other types of elements or mechanisms may be used to constrain axial rotation of the lower perforating gun assembly  200 . 
   The threaded housing  230  of the lower perforating gun assembly  200  is tubular in shape and has an open top end  230 A, a closed bottom end  230 B (see  FIG. 2B ), and a threaded axial bore  230 C formed therethrough. The open top end  230 A has a plurality of tapered recesses  232  formed therein for engagement with the locking sleeve  300 . 
   The threaded axial bore  230 C of the lower perforating gun assembly  200  includes a plurality of horizontal (i.e., non-spiral) receiving threads  236 ,  237  formed therein. The receiving threads are formed radially inward to receive the threads  132 ,  133  of the upper perforating gun assembly  100 . As with the threads  132 ,  133  of the upper perforating gun assembly  100 , the receiving threads  236 ,  237  are arranged in columns having a selected width such that axial gaps  239  are formed between the columns. The threads  236 ,  237  of the lower perforating gun assembly  200  are arranged such that threads  132 ,  133  of the upper perforating gun assembly  100  can slide axially downward through the axial gaps  239  when aligned. Furthermore, the bottom-most thread  237  of the lower perforating gun assembly  200  has a width greater than that of the other threads  236  for receiving the bottom-most thread  133  of the upper perforating gun assembly  100 . This insures that the upper perforating gun assembly  100  is fully engaged (vertically aligned) with the housing  230  of the lower perforating gun assembly  200  such that the upper assembly may be rotated. As with wider thread  133  of the upper gun  100 , the wider receiving thread  237  may be located at the top or middle of the threads to facilitate vertical alignment of the perforating guns  100 ,  200 . 
   Still furthermore, the receiving threads  236  prevent the upper perforating gun assembly  100  from over engaging the lower perforating gun assembly  200 . For example, in one embodiment, the top-most thread  238  of the receiving threads  236  serves as a shoulder to engage the stop ring  134  and thereby halt further downward axial translation of the upper perforating gun assembly  100  within the housing  230 . This insures that the upper perforating gun assembly is not overly engaged with the housing  230  of the lower perforating gun assembly  200  before the upper perforating gun assembly is rotated. However, other embodiments may include other mechanisms for preventing over engagement of the upper gun  100  and lower gun  200 . 
   The closed bottom end  230 B of the housing  230  has a set of two locking grooves  234  formed therein for receiving the set of keys  138  of the upper perforating gun assembly  100  (see also  FIG. 6 ). Each locking groove  234  (for a two key system) forms an arc ranging from 30 to 90 degrees. In this illustrated embodiment, each locking groove  234  forms an arc of approximately 60 degrees. The locking grooves  234  limit the rotation of the upper perforating gun assembly  100  within the housing  230  of the lower perforating gun assembly  200 . In further embodiments, the upper perforating gun assembly may include a different number and arrangement of cylindrical keys and locking grooves such that the degree of arc of each locking groove is different than 60 degrees. 
   The locking sleeve  300  is generally tubular in shape and may be fabricated from a suitable metal such as steel or a steel alloy. The locking sleeve  300  includes a top end  300 A, a bottom end  300 B, and a compressible body  300 C with an axial bore formed therethrough. 
   The top end  300 A of the locking sleeve  300  includes a plurality of tapered lugs  310  for engagement with the tapered recesses  116  of the upper perforating gun assembly  100 . 
   The bottom end  300 B of the locking sleeve  300  also includes a plurality of tapered lugs  320  for engaging the tapered recesses  232  of the lower perforating gun assembly  200 . 
   The compressible body  300 C of the locking sleeve  300  includes a bolt hole  330  formed therein for receiving a through-bolt for attachment of the locking sleeve to the upper perforating gun assembly  100 . In other embodiments, instead of a through-bolt connection, other types of elements may be used to connect the locking sleeve  300  to the upper perforating gun assembly  100  including, inter alia, pins, screws, c-rings or other fasteners. The body  300 C further includes a plurality of transverse slots  340  formed therein. The transverse slots  340  permit the locking sleeve  300  to compress like a spring in response to an external force to achieve a desired axial deflection. Furthermore, once the compressive force is removed, the locking sleeve  300  returns to its original state. The size and arrangement of the transverse slots  340  are selected to achieve the required deflection to permit the upper perforating gun assembly  100  to engage the lower perforating gun assembly  200 . 
   In another embodiment of the present invention, instead of being connected to the upper perforating gun assembly  100 , the locking sleeve  300  is integral with the upper gun. 
   With reference to  FIG. 6 , an embodiment of the present invention includes a perforating string  400  having an upper gun  100  and a lower gun  200  coupled together by a locking device  300  to form an axial bore  405  through the string. The axial bore  405  houses a detonating cord  410  and detonation transfer components. Once the perforating string is coupled and run downhole to a target depth, the detonating cord  405  is initiated to fire the shaped charges carried by the upper gun  100  and lower gun  200 . 
   In operation, with respect to  FIGS. 7A–10C , a perforating string is assembled at the surface with one or more sleeves  300  used to connect successive gun assemblies. As shown in  FIGS. 7A and 7B , to connect two perforating gun assemblies  100 ,  200  together, the lower perforating gun assembly  200  is first suspended in place above the wellbore and is restrained at the clamping section  220  by a clamping tool to prevent the gun assembly from falling into the wellbore and/or rotating. The locking sleeve  300  is attached to the upper perforating gun assembly  100  such that the tapered lugs  310  of the locking sleeve mate with the tapered recesses  116  of the upper perforating gun assembly respectively. The upper perforating gun assembly  100  is then moved by pipe handling equipment to be suspended over the lower perforating gun assembly  200 . Once suspended, the upper perforating gun assembly  100  is rotated above the lower perforating gun assembly  200  until the threads  132 ,  133  of the upper assembly are aligned with the axial gaps  239  formed in the axial bore  230 C of the lower assembly and the receiving threads  236 ,  237  of the lower assembly are aligned with the axial gaps  136  formed on the threaded portion  130  of the upper assembly. 
   As shown in  FIGS. 8A ,  8 B and  8 C, the upper perforating gun assembly  100  is lowered into the threaded axial bore  230 C of the lower perforating gun assembly  200 . The threads  132  (see  FIG. 8B , which depicts an enlarged view of the tool section  231  of  FIG. 8A ),  133  of the upper perforating gun assembly  100  slide through the axial gaps  239  formed in the axial bore  230 C of the lower perforating gun assembly  200  and the axial gaps  136  formed on the threaded portion  130  of the upper assembly slide across the receiving threads  236 ,  237  of the lower assembly. The upper perforating gun assembly  100  translates axially downward through the axial bore  230 C of the lower perforating gun assembly  200  until the tapered lugs  320  of the locking sleeve  300  contact the upper end  230 A of the lower assembly. 
   As shown in  FIGS. 9A ,  9 B and  9 C, a predetermined external force is then applied to the upper perforating gun assembly  100  to compress the transverse slots  340  of the locking sleeve  300  such that the locking sleeve deflects axially downward. The deflection is halted once the stop ring  134  (see  FIG. 9B , which depicts enlarged view of the tool section  231  of  FIG. 9A ) contacts the top-most thread  238  of the receiving threads  236 . At this point, the threads  132  are laterally aligned with the receiving threads  236 , the wide thread  133  is aligned with the wide receiving thread  237 , and the cylindrical keys  138  of the upper perforating gun assembly  100  are engaging the locking grooves  234  of the lower perforating gun assembly  200  such that the upper assembly is free to rotate within the axial bore  230 C of the lower assembly. 
   As shown in  FIGS. 10A ,  10 B and  10 C, the upper perforating gun assembly  100  is rotated approximately 60 degrees until the cylindrical keys  138  (see  FIG. 10C ) of the upper perforating gun assembly  100  reach the end of the locking grooves  234  of the lower perforating gun assembly  200 . At this point, the threads  132  (see  FIG. 10B , which depicts an enlarged view of the tool section  231  of  FIG. 10A ) are engaging the receiving threads  236  and the wide thread  133  is engaging the wide receiving thread  237 . Moreover, as the tapered lugs  320  of the locking sleeve  300  are aligned with the tapered recesses  232  of the lower perforating gun assembly  200 , the sleeve decompresses axially and lengthens to lock the upper perforating gun assembly  100  into threaded engagement with the lower perforating gun assembly  200 . In this way, a more reliably aligned perforating string may be formed. 
   In the event that the upper perforating gun assembly  100  is to be disconnected from the lower perforating gun assembly  200 , a predetermined torquing force is needed to shift the lugs  320  out of the recesses  232  and simultaneously compress the locking sleeve  300 . Once this is accomplished, the threads  132 ,  133  of the upper perforating gun assembly  100  are shifted back into the axial gaps  239  of the lower perforating gun assembly  200  and the upper assembly may be lifted out of the axial bore  230 C of the lower assembly. It will be understood by those skilled in the art that the torquing force required to disconnect the upper assembly  100  from the lower assembly  200  is a function of the slope of the tapered lugs  320  and recesses  232  and the spring constant of the locking sleeve  300 . 
   In other embodiments of the present invention, other mechanisms may be employed (besides the horizontal thread embodiments described above) to axially align two downhole tools such that locking sleeve can lock the two tools together in radial alignment. For example, the rib and groove connection illustrated in  FIG. 11  provides a mechanism to axially align two downhole tools. This connection is similar to that disclosed in U.S. Pat. No. 6,257,792, issued Jul. 10, 2001, which is incorporated herein by reference. This embodiment includes: (1) an upper tool assembly  500 , (2) a lower tool assembly  600 , and (3) a locking sleeve  700 . The upper tool assembly  500  includes an axial bore  511  formed therethrough, a first end  512 , and a second end  513 . At the first end  512  of the upper tool assembly  500 , the longitudinal bore  511  includes a plurality of ribs  514  that are preferably evenly spaced about the circumference of the longitudinal bore  511 , and a plurality of grooves  515  defined between the ribs  514 . Each rib  514  includes a recess  516  disposed between a first leg  517  and second leg  518 . The first leg  517  includes a distal end  519  and the second leg  518  includes a distal end  520 . The distal end  520  of the second leg  518  is located closer to the first end  512  of the upper tool assembly  500  than is the distal end  519  of the first leg  517 . The first end  512  includes one or more tapered recesses  550  formed therein. 
   Still with reference to  FIG. 11 , the lower tool assembly  600  includes a shoulder  631  adjacent to a main body portion  632  and a pin member  633 . The pin member  633  includes a plurality of lugs  634  for mating with the recesses  516  in the ribs  514  on the upper tool assembly  500 . The shoulder  631  includes one or more tapered recesses  650  formed therein. 
   The locking sleeve  700  may be similar to that described above with respect to the horizontal thread embodiments. The locking sleeve  700  includes a top end, a bottom end, and a compressible body with an axial bore formed therethrough. The top end of the locking sleeve  700  includes one or more tapered lugs  710  for engagement with the tapered recesses  550  of the upper tool assembly  500 . The bottom end of the locking sleeve  700  includes one or more tapered lugs  720  for engaging the tapered recesses  650  of the lower tool assembly  600 . The compressible body of the locking sleeve  700  includes a mechanism (as described more fully above with respect to the horizontal thread embodiments) to connect the locking sleeve to the upper tool assembly  500 . The body also includes transverse slots  340  to facilitate axial deflection. 
   To operate this embodiment of the hands-free connection system of the present invention, the upper tool assembly  500  is lowered into engagement with the lower tool assembly  600  such that the lugs  634  on the pin  633  slide into the grooves  515  of the bore  511  until the shoulder  631  on the lower assembly abuts against the lower end of the locking sleeve  700 . The sleeve  700  is compressed such that the lugs  534  extend past the distal ends  520  of the second legs  518  of the ribs  514  (but not past the distal ends  519  of the second legs  517 ). The upper tool assembly  500  is rotated a fraction of a full 360 degree turn until the lugs  634  contact the first legs  517  on the ribs  514  and are positioned adjacent their corresponding recesses  516 . At this point, the lugs  720  of the sleeve  700  are aligned with the corresponding recesses  650  of the lower assembly  600  and the sleeve is free to decompress axially downward to slide the lugs  634  of the lower assembly into the corresponding recesses  516  of the upper assembly  500 . Thus, an axially and radially aligned coupling of the upper tool assembly  500  and lower tool assembly  600  is achieved. 
   Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.