Patent Publication Number: US-9903185-B2

Title: Perforating gun with eccentric rotatable charge tube

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 61/938,886, filed Feb. 12, 2014 and from U.S. Provisional Application Ser. No. 62/021,494 filed on Jul. 7, 2014, the entire disclosures of which is incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to devices and method for perforating a subterranean formation. 
     BACKGROUND 
     Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. Perforations are usually made using a perforating gun that is generally comprised of a steel tube “carrier,” a charge tube riding on the inside of the carrier, and with shaped charges positioned in the charge tube. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent to the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string. 
     In certain instances, it may be desirable to have the shaped charges point in a particular direction after the perforating gun is positioned in the wellbore. The present disclosure addresses the need for perforating guns that can point or direct the shaped charges in a desired direction in such situations. 
     SUMMARY 
     In aspects, the present disclosure provides a perforating gun for perforating a formation. The perforating gun may include a carrier, an orienting device retained in the carrier, and a charge tube rotatably connected to the orienting device. The orienting device misaligns a center axis of the charge tube with a different second axis such that gravity can cause the charge tube to rotate about the different second axis. The charge tube does not rotate about the center axis of the charge tube while the charge tube rotates about the different second axis. In one arrangement, the orienting device includes a decentralizer having a mandrel connected to the charge tube and an end plate, the end plate being rotatably connected to the hub and retained in the carrier. The different second axis may be one of: (i) a center axis of the carrier, (ii) a center axis of the end plate, and (iii) a center axis of the hub. The orienting device may include a bearing rotatably connecting the end plate to the hub. 
     It should be understood that certain features of the invention have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will in some cases form the subject of the claims appended thereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For detailed understanding of the present disclosure, references should be made to the following detailed description taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
         FIG. 1  schematically illustrates a side sectional view of a perforating gun with an eccentric rotatable charge tube according to one embodiment of the present disclosure; 
         FIG. 2  schematically illustrates a sectional view of an orienting device according to one embodiment of the present disclosure; 
         FIG. 3  schematically illustrates a side sectional view of a perforating gun with an eccentric rotatable charge tube according to one embodiment of the present disclosure that has a predetermined misalignment between charge tube axis and an axis of the carrier tube; 
         FIG. 4  schematically illustrates an isometric end sectional view of an orienting device according to one embodiment of the present disclosure; 
         FIG. 5  schematically illustrates an end view of one embodiment of an orienting device according to the present invention; 
         FIG. 6  schematically illustrates a side view of an external orienting device according to one embodiment of the present disclosure; 
         FIG. 7  schematically illustrates an end view of the  FIG. 6  embodiment; 
         FIG. 8  schematically illustrates alternate embodiments of a perforating gun in accordance with the present disclosure; 
         FIG. 9  schematically illustrates a connector in accordance with one embodiment of the present disclosure; and 
         FIG. 10  schematically illustrates a well in which embodiments of the present disclosure may be deployed. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to devices and methods for perforating a formation intersected by a wellbore. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. 
     Referring now to  FIG. 1 , there is shown one embodiment of a perforating gun  100  in accordance with the present disclosure. For ease of discussion, devices such as shaped charges, boosters, electrical wiring, connectors, fasteners and detonating cords have been omitted. The perforating gun  100  may include a carrier  102  that is shaped to receive a charge tube  104 . The perforating gun  100  also includes orienting devices  106  that allows the charge tube  104  to orient itself relative to gravity when positioned in the wellbore. In embodiments, an orienting device  106  is positioned on each of the opposing ends of the charge tube  104 . While two orienting devices  106  are shown, it is contemplated that one orienting device  106  may also be used or that three or more orienting devices  106  may be used. 
     Referring now to  FIG. 2 , there is shown a section of the perforating gun  100  that includes one non-limiting embodiment of an orienting device  106  according to the present disclosure. In this embodiment, the orienting device  106  includes an end plate  108 , a bearing  110 , and a decentralizer  112 . The end plate  108  is retained in the carrier  102  and the decentralizer  112  is fixed to the charge tube  104 . The bearing  110  rotatably connects the decentralizer  112  to the end plate  108 . Thus, the decentralizer  112 , which is connected to the charge tube  104 , can rotate relative to the end plate  108 , which is connected to the carrier  102 . 
     The decentralizer  112  may be shaped and dimensioned to allow gravity to rotate the charge tube  104  relative to the carrier  102  when the perforating gun  100  is in a non-vertical alignment. In one embodiment, the decentralizer  112  has a hub  114  and a mandrel  116 , both of which may be cylindrical in shape. A center axis  118  of the hub  114  and a center axis  120  of the mandrel  116  are eccentrically aligned. Thus, the charge tube  104  rotates, or in a sense orbits, about the center axis  118  of the hub  114 . The charge tube  104  does not rotate about the center axis  120  of the mandrel  116 . The center axis  120  aligns with the center axis of the charge tube  104 . It should be appreciated that this axial misalignment shifts the center of gravity of the charge tube  104  a predetermined distance from the center axis  118 . Thus, when in the non-vertical alignment, gravity can rotate the charge tube  104  about the axis  118 . The center axis  118  may be the center axis of the carrier  102 , the end plate  108 , and/or the bearing  110  and the center axis  120  may be the center axis of the charge tube  104 . 
     Referring now to  FIG. 3 , there is sectionally shown the perforating gun  100 . The carrier  102  ( FIG. 1 ) has been omitted for clarity. It should be appreciated that the orienting assemblies  106  cause the center axis  120  of the charge tube  104  to be misaligned, or eccentric, with the center axis  118  of the hub  114 . Thus, a center of gravity of the charge tube  104  is shifted from concentric alignment with the center axis  118 . When in a non-vertical position, such as a horizontal position, gravity will act to cause a moment arm to rotate the center of gravity to the lowest position. The misalignment is selected to form a sufficient moment arm length to allow gravity to act on the weight of the charge tube  104  to rotate the charge tube  104 . Thus, the misalignment is specifically engineered to cause rotation of the charge tube  104  if the perforating gun  100  in a predetermined situation, e.g., the perforating gun is in a wellbore section that has a deviation from vertical greater than a specified value. The misalignment is not merely an artifact of conventional manufacturing and assembly. 
     Referring now to  FIG. 4 , there is isometrically shown the perforating gun  100 . The carrier  102  ( FIG. 1 ) has been omitted for clarity. As described above, an orienting device  106  is shown attached to each end of the charge tube  104 . The end plates  108  may be ring shaped members that have a bore  130  in which the bearings  110  are disposed. The bearings  110  may be any device that permits relative rotation between two connected parts. Typically, but not always, the bearings  110  may include friction reducing elements such as spherical elements or highly polished surfaces. The two surfaces may be concentrically arranged such that the bearing  110  is positioned between them. The decentralizer  112  may include a passage  132  through the hub  114  and the mandrel  116 . As shown, the passage  132  has two eccentrically aligned bores, each of which has a different size. However, the passage  132  may be of any desired configuration. 
     Referring now to  FIG. 5 , there is shown an end view of the orienting device  106  positioned inside a wellbore  10 . A wellbore high side or the twelve o&#39;clock position is shown with numeral  12  and a wellbore low side or the six o&#39;clock position is shown with numeral  14 . Relative to gravity, the twelve o&#39;clock position  12  is at a higher depth (true vertical depth) than the six o&#39;clock position  14 . The point  140  may be the center axis of the hub  114  ( FIG. 2 ) which may be concentric with the center axis of the end plate  108 . Point  142   a  may be the initial position of the center axis of the charge tube  104 . Due to the misalignment of the points  140  and  142   a , the center of gravity of the charge tube  104  is shifted. The distance between the location of the center of gravity of the charge tube  104  and the center axis of the hub  114  ( FIG. 2 ) provide a moment arm that gravity acts on to rotate charge tube  104  until the center of gravity of the charge tube  104  substantially aligns with the six o&#39;clock position  14 . For convenience, the position of the axis of rotation of the charge tube  104  after rotation is shown with point  142   b.    
     Referring back to  FIG. 4 , the charge tube  104  is generally configured to have a substantially uniformly distributed mass around the axis  120 . That is, the charge tube  104  does not have any mass or weights that are specifically added to create a weight imbalance that could cause rotation about the axis  120 . While a certain amount of weight variances may occur due to the distribution of shaped charges or other conventional components, such an imbalance does not induce a specified and predetermined rotation. Stated differently, the center of gravity of the charge tube  104  remains generally aligned with the center axis, or the axis of rotation, of the charge tube  104 . In yet a different aspect, the weight distribution is not affected by devices intimately related to the firing of the shaped charges (not shown). Thus, it should further be noted that the charge tube  104  does not rotate about its own center axis  120 . 
     The teachings of the present disclosure may also be used in other embodiments wherein eccentric axes are used for rotating entire gun systems. For example, an eccentric tandem sub that has external rollers may be used to orient the guns. 
     Referring  FIG. 6 , there is shown an embodiment of a perforating gun  100  that uses external rollers  180 . A coiled tubing string  50  ( FIG. 10 ) may be used to convey the perforating gun  100 . A swivel or other rotational decoupler  64  ( FIG. 10 ) may be used to allow the perforating gun  100  to rotate relative to the coiled tubing string  50  ( FIG. 8 ) or other conveyance device. Each external roller  180  includes opposing two pin connections  182  that project from a collar  186 . The pin connections  182  connect to box connections  188  of the carrier  190 . As used herein, a “pin” refers to a projection such as a tube, rod or cylinder and a “box” refers to a bore or cavity shaped to receive the “pin.” The collar  186  includes a plurality of roller elements  192  that are distributed on a circumferential face  194 . The roller elements  192  contact an inner surface  196  of a wellbore tubular (not shown), such as casing or tubing. The roller elements  192  may be balls, spherical elements, or any other friction reducing elements that allow relative rotational movement between the gun  100  and the inner surface  196 . The carrier  190  and the collar  186  are fixed to one another and rotate in unison. 
     The axis  200  of the carrier  190  is decentralized relative to the axis  202  of the collar  186  to cause an eccentricity  204  of sufficient distance to allow gravity to rotate the perforating gun  100  relative to the wellbore tubular  196  when the perforating gun  100  is in a non-vertical alignment. In one embodiment, the pin connections  182  are positioned eccentric relative to the axis  202  of the collar  186 . The eccentric relationship between the pin connections  182  and the collar  186  is shown in  FIG. 7 . Thus, the weight of the perforating gun  100  creates a moment arm around the axis  202  of the collar  186  and rotates the perforating gun  100  to align with wellbore low side. 
     Referring now to  FIG. 8 , there is sectionally shown another embodiment of a perforating gun  100  according to the present disclosure. As before, the carrier  102  ( FIG. 1 ) has been omitted for clarity. In this embodiment, the perforating gun  100  is configured to accommodate perforating guns of extended lengths (e.g., five feet or more). For example, weights  240  may be added to the charge tube  104  in order to assist rotation. The weights  240  have no other function than to increase the mass on which gravity can act. Also, in addition to the bearings  110  ( FIG. 2 ) in the orienting assemblies  106 , intermediate supports  242  may be distributed along the charge tube  104 . These supports  242  may be bearings, collars, centralizers, journals, polished surfaces, spherical elements, or any other elements that support weight and promote allow relative rotational movement between the gun  100  and the inner surface  196  ( FIG. 7 ). The weights  240  and/or supports  242  may be used separately or together to reduce undesirable effects such as sagging or increased frictional resistance due to increased weight and length of the perforating gun  100  ( FIG. 1 ). As in the previously discussed embodiments, the center of gravity of the charge tube  104  is shifted from concentric alignment with the center axis  118 . Thus, when in a non-vertical position, such as a horizontal position, gravity will act to cause a moment arm to rotate the center of gravity to the lowest position. 
     Referring now to  FIG. 9 , there is shown one embodiment of a connector assembly  250  that may be used to transfer energy and/or signals between a non-rotating carrier, such as coiled tubing or wireline, and the components of the perforating gun  100  ( FIG. 1 ) that rotate, such as the equipment housed in the charge tube  104  ( FIG. 2 ). In one arrangement, the connector assembly  250  includes an electrical contact assembly  252  that is enclosed within a housing  254 . The electrical contact assembly  252  includes a cavity  256  for receiving an electrical contact tube  258 . 
     The contact tube  258  is fixed to the rotating decentralizer  112  and may include electrically conductive bristles or brushes that physically contact the electrical contact assembly  252 . The electrical connections may be formed by a first single or multi-strand wire (not shown) connected to the electrical contact assembly  252  and a second single or multi-strand wire (not shown) connected to the electrical contact tube  258 . During operation, the electrical contact tube  258  rotates relative to the electrical contact assembly  252 . An electrical connection is maintained by the physical contact of the surfaces of these two components. 
     The connector assembly  250  can also provide a ballistic connection between a non-rotating carrier and the rotating sections of the perforating gun  100  ( FIG. 1 ). By “ballistic” connection, it is meant a connection that can detonate a energetic material using the energy released by a previously detonated energetic material, e.g., transferring a high-order detonation. As used herein, a high-order detonation is a detonation that produces high amplitude pressure waves (e.g., shock waves) and thermal energy. In one embodiment, a ballistic connection may be formed by positioning a first energetic component  260  in the housing  254  and positioning a second energetic component  262  inside the contact tube  258 . The first energetic component  260  may include a detonator cord, a detonator, a booster charge, and/or other energetic materials. The second energetic component  262  may include a detonator cord, a detonator, a booster charge, and/or other energetic material materials. Illustrative energetic materials may include, materials such as oxidizers, fuels (e.g., metals, organic material, etc.), propellant materials (e.g., sodium nitrate, ammonium nitrate, etc.), explosive materials (e.g., RDX, HMX and/or HNS, etc.), binders and/or other suitable materials. 
     For arrangements where a single gun is used, a single connector  250  may be used. For example, an electrical signal carried by a wireline may be transferred from the electrical contact assembly  252  to electrical contact tube  285 . The transferred signal may be used to detonate the second energetic component  262 . In another arrangement, a pressure activated firing head (not shown) may be activated by increasing wellbore pressure. The pressure activated firing head detonates the first energetic component  260 , which then detonates the second energetic component  262 . 
     For gun trains having two or more guns, two or more connectors  250  may be used. For example, a connector  250  may be used at each decentralizer  112  ( FIG. 3 ) across which an electrical signal or a detonation transfer is desired. In one arrangement, the first connector  250  initiates the firing of a first gun set using an electrical signal, and the remaining connectors  250  ballistically transfer the detonation between the gun sets. In another arrangement, two or more connector  250  initiates the firing of a first gun set using an electrical signal. 
     It should be appreciated that the connector  250  provides flexibility in how a perforating gun  100  may be run into a well. For coiled tubing run perforating guns  100 , a pressure activated firing head may be used. For wireline run perforating guns  100 , an electrically activated firing head may be used. 
     Referring initially to  FIG. 10 , there is shown a well construction and/or hydrocarbon production facility  30  positioned over subterranean formations of interest  32 . The facility  30  can be a land-based or offshore rig adapted to drill, complete, or service the wellbore  12 . The facility  30  can include known equipment and structures such as a platform  40  at the earth&#39;s surface  42 , a wellhead  44 , and casing  46 . A work string  48  suspended within the well bore  12  is used to convey tooling into and out of the wellbore  12 . The work string  48  can include coiled tubing  50  injected by a coiled tubing injector (not shown). Other work strings can include tubing, drill pipe, wire line, slick line, or any other known conveyance means. The work string  48  can include telemetry lines or other signal/power transmission mediums that establish one-way or two-way telemetric communication from the surface to a tool connected to an end of the work string  48 . A suitable telemetry system (not shown) can be known types as mud pulse, electrical signals, acoustic, or other suitable systems. A surface control unit (e.g., a power source and/or firing panel)  54  can be used to monitor and/or operate tooling connected to the work string  48 . 
     In one embodiment, a perforating tool such as a perforating gun train  60  is coupled to an end of the work string  48 . An exemplary gun train  60  includes one or more guns or gun sets, each of which includes perforating shaped charges  62 . In some embodiments, the work string  48  may include a swivel or rotational decoupler  64  that allows on or more sections of the perforating gun train  60  to rotate relative to the work string  48 . The gun train  60  is disposed in a non-vertical section  14  of the wellbore  12 . While the non-vertical section  14  is shown as horizontal, the non-vertical section  14  may have any angular deviation from a vertical datum. 
     Referring to  FIGS. 1 and 5 , in one illustrative method of use, when the gun train  60  is positioned in the non-vertical section  14 , the misalignment between the center axis of the hub  114  ( FIG. 2 ) and the center axis of the charge tube  104  allows gravity to act on a moment arm to rotate charge tube  104  until the center of gravity of the charge tube  104  substantially aligns with the six o&#39;clock position  14 . It should be appreciated that this rotation will allow the shaped charges (not shown) to be fired in any azimuthal direction relative to the wellbore high side. For example, the shaped charges (not shown) may be arranged to fire toward the wellbore high side, nine-degrees from wellbore high side, to the wellbore low side, etc. 
     In aspects, what has been described includes a perforating gun that includes a carrier and an orienting device connected to the carrier, wherein the orienting device misaligns a center axis of the carrier with a different second axis, and wherein gravity causes the charge tube to rotate about the different second axis while the carrier does not rotate about the center axis of the carrier. 
     From the above, it should be appreciated that what has been described includes a gravity oriented perforating gun. The perforating gun may include a charge tube disposed inside a carrier, a plurality of shaped charges positioned along the charge tube, and at least one orienting device positioned on each opposing end of the charge tube. Each orienting device may include an end plate retained in the carrier, a decentralizer fixed to the charge tube, and a bearing rotatably connecting the decentralizer to the end plate. The decentralizer includes a cylindrical hub and a cylindrical mandrel, a center axis of the hub and a center axis of the mandrel are eccentrically aligned, and the decentralizer rotates relative to the end plate. 
     This embodiment is susceptible to numerous variants. The charge tube may be fixed to the mandrel. A center axis of the charge tube may align with the center axis of the mandrel. The center axis of the hub may be a center axis of at least one of: (i) the carrier, (ii) the end plate, and (iii) the bearing, and the center axis of the mandrel may align with the center axis of the charge tube. The endplate may be a ring shaped member having a bore in which the bearing is received, and wherein the bearing has a bore in which the hub is received. The mandrel may be telescopically connected to the charge tube and a bore may extend through the mandrel and the hub. A connector assembly associated with the orienting device may include a housing, an electrical assembly fixed to the housing, and a contact tube rotatably connected to the electrical assembly and fixed to the decentralizer. The gun may include a first energetic component in the housing and a second energetic component in the contact tube. The first energetic component may include at least one of: (i) a detonator cord, (ii) a detonator, (iii) a booster charge, and (iv) an energetic material and the second energetic component may include at least one of: (i) a detonator cord, (ii) a detonator, (iii) a booster charge, and (iv) an energetic material. The gun may include (i) at least one weight positioned along the charge tube, and (ii) at least one support positioned along the charge tube. 
     Another perforating gun according to the present disclosure includes a carrier; and an orienting device connected to the carrier. The orienting device misaligns a center axis of the carrier with a different second axis. Gravity causes the charge tube to rotate about the different second axis while the carrier does not rotate about the center axis of the carrier. The orienting device may include at least one external roller. The gun may include a rotational decoupler connecting the carrier to a coiled tubing string. The external roller may include opposing pins that project from a collar, and wherein the carrier includes a box connecting to each pin. The collar may include a plurality of roller elements that are distributed on a circumferential face. The roller elements may be configured to contact an inner surface of a wellbore tubular. The carrier and the collar may be fixed to one another and rotate in unison. An axis of the carrier may be decentralized relative to the axis of the collar to cause an eccentricity of sufficient distance to allow gravity to rotate the carrier relative to the wellbore tubular when the carrier is in a non-vertical alignment. The pins may be positioned eccentric relative to an axis of the collar. 
     As used in this disclosure, the terms “aligned” means co-linear or concentric. Thus, axes that are aligned are concentric. Axes that are misaligned or eccentric are separated by a predetermined distance. As used in this disclosure, terms such as “substantially,” “about,” and “approximately” refer to the standard engineering tolerances that one skilled in the art of well tools would readily understand. 
     The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.