Patent Publication Number: US-6220370-B1

Title: Circulating gun system

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/120,735, filed Feb. 18, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a tubing conveyed perforating gun system of the type used to perforate a well bore for the production of well bore fluids, and, specifically, to such a system with internal components designed to decrease firing debris and to allow reverse washing of fill encountered in the well bore, without tripping the system out of the well. 
     2. Description of the Prior Art 
     As oil and gas wells are being drilled, the integrity of the borehole is preserved by cementing a casing or liner in place in the borehole. The casing or liner is a metal cylindrical conduit which must be punctured or perforated over the desired production interval in order to produce well bore fluids once drilling is complete. A perforating gun which utilizes some form of fired projectile and an explosive charge is used to perforate the casing or liner to begin production from the well. 
     Prior perforating gun techniques have either utilized tools which were run on a wireline or cable or have utilized tubing conveyed devices which were run on a tubing string to a desired depth in a well bore. Tubing conveyed devices have certain advantages over wireline methods. For example, tubing conveyed devices allow safe, immediate release of formation pressure at maximum pressure differentials into the tubing string. With tubing conveyed perforating systems, the tubing can be run into position, a packer set to seal off the well bore, and the surface wellhead equipment can be installed. The packer setting can be checked by circulating fluid under pressure through the well annulus or through the well tubing string. Once the surface work is completed and tested for safety, the perforating gun can be fired to bring in the well. Tubing Conveyed Perforating (TCP) systems provide rig time savings, higher shot density, greater gun length and the ability to perforate “under balanced” so that perforations are cleansed through formation fluid backflow. Since perforating guns can be run below the production tubing they enable the well to be perforated and completed, i.e., put into production, in one operation. 
     Occasionally, sand fill has infiltrated into the well and causes problems with gravel packing or other well bore operations. It is thus desirable to provide an apparatus having the capability of reverse circulating the fill out of the well. Obviously, it is desirable to accomplish the reverse circulation of the fill out of the well without having to pull the work string, gravel packing and/or perforating apparatus. 
     In wells utilizing a sump packer below the zone to be perforated, it is necessary for the perforating string to have its lower end sealingly engaged with a bore of the sump packer prior to performing the desired well bore operation. With the prior art systems, if sand fill was encountered on top of the sump packer, it was generally necessary to trip the perforating apparatus and its associated tool string out of the well. A work string was then run into the well to reverse circulate the sand fill away from the sump packer. The work string was then required to be tripped out of the well so that the perforating tool string could again be run into the well. Often times, as many as three trips in and out of the well were required before the entire operation could be accomplished. 
     The present invention has as one object to provide a tubing conveyed perforating apparatus with means for reducing the accumulation of firing debris within the well bore at the conclusion of the firing operation. 
     Another object of the invention is to provide such an apparatus which allows for the reverse circulation of sand fill encountered within the well bore, such as sand fill encountered directly on top of a sump packer located within the well bore. 
     Another object of the invention is to provide a tubing conveyed perforating apparatus which allows the plug in a sump packer to be placed and released, perforation of the well casing, reverse circulation of fill and/or debris from the top of the sump packer, and subsequent retrieval of the plug from the sump packer. 
     Another object of the invention is to provide such an apparatus which is relatively simple in design and economical to manufacture. 
     SUMMARY OF THE INVENTION 
     The tubing conveyed perforating apparatus of the invention is used in perforating a surrounding well bore. The apparatus comprises a tubular assembly made up of a plurality of tubular sections. The tubular sections present a generally cylindrical exterior and a concentric interior bore. The tubular assembly has an upper connecting end for connection in tubing string extending to the well surface and a lower end. At least one of the selected tubular sections comprises a tubular firing section having a plurality of explosive charges carried therein. Each of the explosive charges is initially aligned with a region of reduced wall area provided within the tubular firing section surrounding the charges. A piston sleeve is mounted on the exterior of the tubular firing section. The piston sleeve has a plurality of apertures therein which are initially aligned with the regions of reduced wall area in the tubular firing section and thus with the explosive charges. A firing means is located within the tubular assembly for detonating the explosive charges to perforating the surrounding well bore. The piston sleeve includes a piston area which communicates by means of an internal port with the interior bore of the tubular firing section. Detonation of the firing means applies a force to the piston area to shift the piston sleeve, thereby moving the piston sleeve apertures out of alignment with openings formed in the tubular firing section due to detonation of the explosive charges. This action serves to trap any resulting explosive debris within the interior bore of the tubular firing section. 
     In addition to utilizing the force of explosive gases to shift the piston sleeve, well hydrostatic pressure can be utilized to apply a force to the piston area to shift the piston sleeve, the well hydrostatic pressure being communicated to the interior bore of the tubular firing section upon detonation of the explosive charges. Detonation of the explosive charges creates openings in the tubular firing section at the regions of reduced wall area, thereby forming a temporary flow path to the interior bore of the tubular firing section. 
     Preferably, a plurality of tubular firing sections are connected end-to-end in the tubular assembly, the firing sections being connected by ignition means for detonation by the firing means. 
     The lower end of the tubular assembly can carry a sealing plug which is designed to seat within a mating bore of a sump packer located within the well bore. The sealing plug is preferably connected to the lower end of the tubular assembly by a shear means, whereby setting weight on the tubing string shears the shear means to release the lower end of the tubular assembly from the sealing plug. A piston actuated retrieving assembly can be located within the lower end of the tubular assembly above the sealing plug. The piston actuated retrieving assembly has a reactive piston area which is exposed to forces applied by the firing of the explosive charges and/or well hydrostatic pressure to shift the retrieving assembly downwardly within the lower end of the tubular assembly. The lower end of the tubular assembly can also be provided with one or more bottom circulation ports for ultimately communicating the interior bore of the tubular assembly with the surrounding well annulus. Movement of the piston actuated retrieving assembly downwardly within the tubular assembly serves to uncover the bottom circulation ports. 
     The piston actuated retrieving assembly preferably includes a fishing head at a lower extent thereof which includes a colleted opening for engaging a mating surface provided on the sealing plug for retrieving the sealing plug from the bore of the sump packer. The piston actuated retrieving assembly includes an intermediate length between the reactive piston area and the fishing head, the intermediate length being provided with a latch means for locking the retrieving assembly in a lower, shifted position. 
     In the method of the invention, a perforating apparatus is run on a tubing string into a well bore having a sump packer located at a selected subterranean location. The sump packer has a packer bore therethrough. The perforating apparatus carried by the tubing string includes a plurality of tubular sections having generally cylindrical exteriors and concentric interior bores, at least one of the tubular sections comprising a tubular firing section having a plurality of explosive charges therein. The lower end of the tubular assembly is provided with a sealing plug which is designed to seat within the bore of the sump packer located within the well bore. 
     The sealing plug is connected to the lower end of the tubular assembly by a shear means, whereby setting weight on the tubing string shears the shear means to release the lower end of the tubular assembly from the sealing plug. The assembly is also provided with the piston actuated retrieving assembly and bottom circulation port, as previously described, which are used after the perforating operation. 
     The well tubing string is lowered downwardly within the well bore until the sealing plug is received within the sump packer bore. By continuing to apply downward weight on the tubing string, the shear means is sheared to release the lower end of the tubular assembly from the sealing plug. The tubing string is then typically picked up a few feet and the explosive charges are detonated to perforating the desired production interval and simultaneously shift the piston actuated retrieving assembly downward within the lower end of the tubular assembly. Downward movement of the retrieving assembly serves to uncover the bottom circulation port. 
     The assembly can then be lowered downwardly while washing any accumulated debris or sand from off the sump packer by reverse circulating fluid down the well annulus, through the bottom circulation port and up the interior bore of the assembly and tubing string to the well surface. 
     The assembly can be lowered further downwardly until the fishing head of the retrieving assembly engages the sealing plug. Pulling the assembly upwardly pulls the engaged sealing plug upwardly out of the packer bore. 
     Additional objects, features and advantages will be apparent in the written description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side, cross-sectional view of the upper end of the tubing conveyed perforating apparatus of the invention showing a portion of the firing head thereof in the running-in position within a well bore; 
     FIG. 1A is a side, cross-sectional view of the apparatus of FIG. 1 after detonation of the firing head; 
     FIG. 2 is a downward continuation of FIG. 1 depicting the lower end of the firing head of the apparatus and the upper end of the tubular firing section thereof; 
     FIG. 2A is a side, cross-sectional view, similar to FIG. 2 showing the position of the apparatus after firing; 
     FIG. 3 is a downward continuation of FIG. 2 primarily showing the tubular firing section of the apparatus including the shaped charges and shape charge holder thereof; 
     FIG. 3A is a view similar to FIG. 3 showing the apparatus after firing of the shaped explosive charges; 
     FIG. 4 is a downward continuation of FIG. 3 showing the lower end of the apparatus with the sealing plug thereof engaged within the bore of a sump packer located within the well bore; and 
     FIG. 4A is a view similar to FIG. 4 but showing the retrieving operation in which the retrieving assembly is shown engaging a mating surface of the sealing plug. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-4 illustrate a tubing conveyed perforating apparatus of the invention, designated generally as  11 . Each of the downward continuing sequence of views illustrates the respective components of the apparatus in the running-in position, prior to firing the explosive charges. The apparatus  11  includes a tubular assembly made up of a plurality of tubular sections  13 ,  15 ,  17 ,  19 . Each tubular section has a generally cylindrical exterior  21  and a generally concentric interior bore  23 . The tubular assembly has an upper connecting end  25  for connection in the tubing string (not shown) leading to the well surface and the assembly has a lower end ( 27  in FIG.  4 ). 
     With reference to FIG. 3, at least one selected tubular section  17  comprises a tubular firing section having an elongate charge holder  29  located between an upper connector  31  and a lower connector  33  thereof. A plurality of explosive charges, e.g., charges  35 ,  37 ,  39 ,  41 , are mounted on the charge holder  29 . The charges are arranged in a selected pattern and orientation for producing the desired perforating pattern upon detonation. 
     While the explosive charges  35 ,  37 ,  39 ,  41  are shown mounted in tubular charge holder, it will be understood that other means can be utilized for supporting or mounting the charges within the tubular firing section. For example, U.S. Pat. Nos. 5,638,901 and 5,662,178, both assigned to the assignee of the present invention, show “spiral strips” for supporting explosive charges within a surrounding tubular firing section. U.S. Pat. No. 5,829,538, also assigned to the assignee of the present invention, shows an explosive charge arrangement in which the support means is comprised of disintegratable materials. Other arrangements will be familiar to those skilled in the relevant arts. 
     The tubular firing section  17  which surrounds the charge holder  29  is provided with regions of reduced wall area or cross sectional thickness  43 ,  45 ,  47 ,  49 . These regions are initially aligned with the explosive charges mounted on the charge holder  29 . The regions of reduced wall area will be penetrated by the explosive charges upon detonation by the firing means, as will be discussed below. The thickness of the regions of reduced wall area is selected to initially seal off the interior of the tubular firing section and maintain the integrity thereof, while also being puncturable by the explosive charges without leaving a “burr” which would interfere with subsequent movement of the piston sleeve  51 . 
     As shown in FIGS. 3 and 3A, piston sleeve  51  is mounted on the exterior of the tubular firing section  17 . The piston sleeve  51  has a plurality of apertures  53 ,  55 ,  57 ,  59  which are initially aligned with the regions of reduced wall area  43 ,  45 ,  47 ,  49  in the tubular firing section and thus with the explosive charges. 
     While only one tubular firing section is illustrated, it will be understood that a plurality of such tubular sections can be connected end-to-end, in the tubular assembly. The firing sections are connected by any suitable ignition means for detonation by an associated firing means. In the example of FIG. 3, bi-directional boosters  61 ,  63  can be used to ballistically connect the various sections of the assembly. The booster sections  61 ,  63  include end caps having a central bore for receiving a det cord  65  for actuating the depending explosive charges. The boosters are commercially available from Owen Oil Tools, Inc., of Ft. Worth, Tex., and will be familiar to those skilled in the art. In the embodiment of the invention illustrated, the booster sections, e.g., section  61 , are provided with vertical bores  62  (FIGS. 3 and 3A) which allow fluids to travel upwardly within the internal bore of the tubular firing section after detonation of the device. 
     With reference to FIG. 2, the upper connector  31  has an externally threaded upper extent for engaging the mating internally threaded surface  67  of the tubular firing section  17 . The lower connector  33  also has an external profile  69  (FIG. 3) which receives the lower most extent of the tubular firing section  17 , thereby rigidly fixing the firing section in position. 
     As shown in FIG. 2, the upper connector  31  has a region of stepped external diameter  69  which forms a ledge for receiving piston area  71  (FIG. 2A) of a piston actuator  73  which engages and supports the downwardly extending piston sleeve  51 . An internal port  75  communicates the interior bore  77  of the tubular firing section  17  with the piston area  71 , whereby detonation of the firing means and/or well bore hydrostatic pressure during and after detonation, applies a force to the piston area  71  to shift the piston sleeve  51  (see FIG.  2 A). Firing of the exposive charges causes the regions of reduced wall area to be punctured, forming openings in the tubular firing section  17 . Upon firing, the piston sleeve apertures  53 ,  55 ,  57 ,  59  shift out of alignment with the now formed openings  43 ,  45 ,  47 ,  49  in the tubular firing section  17  to trap any resulting explosive debris within the interior bore of the tubular firing section (see FIGS.  3  and  3 A). 
     FIG.  1  and the top portion of FIG. 2 depict a TCP firing head which generally utilizes conventional components and will be familiar to those skilled in the art. The firing head  79  includes an outer tubular body  81  with an internal bore  83  which contains a length of det cord. Appropriately located O-ring seals  85 ,  87 ,  89 ,  91  isolate the internal bore  83 . The det cord located within bore  83  can be ignited by a conventional firing means so that the downwardly continuing det cord  65  is, in turn, ignited, thereby actuating the depending shaped charges carried by the charge holder  29 . 
     Any convenient means can be utilized for firing the guns in the TCP apparatus. Typical techniques include drop-bar or “go-devil” systems, electrical firing systems or hydraulic systems. In FIGS. 1 and 1A, a conventional firing apparatus  93  is utilized to actuate the detonator  95  which ignites the various associated lengths of det cord. 
     In the particular embodiment of the invention illustrated, the firing head  79  includes a tubular sub  95  (FIG. 1) having upper circulating ports  97  located therein at one selected circumferential location. The upper circulating ports  97 , as shown in FIG. 1, are initially closed off by means of the piston sub  99  located within the tubular sub  95 . As shown in FIG. 1A, firing of the explosive charges generates explosive gases in the bore  101  which gases act upon the piston area  103  to drive the piston sub  99  upwardly, thereby uncovering the upper circulating ports  97 . The piston sub  99  forms a sealing engagement with the surrounding tubular sub by means of appropriate O-ring seals such as seals  105 ,  107 . 
     As will be apparent to those skilled in the relevant art, operation of all moving parts within the apparatus can be effected as a result of forces generated by the explosive gases generated by the explosive charges or as a result of well hydrostatic pressure communicated to the interior bore of the device. Thus, as an example, well bore hydrostatic pressure present during and after the firing of the explosive charges could be utilized to drive the piston sub  99  upwardly. 
     FIGS. 3 and 4 illustrate the lower tubular section  19  of the apparatus and the internal components thereof. With reference to FIG. 4, the lower end  27  of the tubular section carries a sealing plug  109  having a stinger  111  which is designed to seat within a mating bore  113  of a sump packer  115 . The sealing plug  109  is connected to the lower end  27  of the tubular assembly by an appropriate shearable connection such as shear pins  117 ,  119 . In this manner, setting weight on the tubing string from the well surface shears the shear pins to release the lower end of the tubular assembly from the sealing plug  109 . 
     With reference to FIG. 3, the upper extent of tubular section  19  has an internally threaded surface  118  which carries a bull plug  119 . The bull plug  119  has an externally threaded surface which engages the downwardly extending sleeve  121 . Sleeve  121 , has an internal bore  123  which, in turn, receives a piston actuated retrieving head  125  (FIG.  4 ). The retrieving head  125  has a reactive piston area  127  which comprises the end surface of an upper piston element  129 . Piston element  129  has cylindrical external sidewalls  131  which, in the running-in position illustrated in FIG. 4, initially cover bottom circulation ports  133 . The reactive piston area  127  is exposed to forces applied by the firing of the explosive charges and/or by exposure to well bore hydrostatic pressure, to shift the retrieving head downwardly within the sleeve  121 , as shown in FIGS. 4 and 4A. 
     Sleeve  121  also has a bottom sub  135  threadedly engaged thereto. The bottom sub  135  has an internal bore  137  which slidingly receives the external cylindrical surface of the intermediate length  139  of the retrieving assembly. In addition to external O-ring seals  141 , intermediate length  139  carries a latch ring  143  in a circumferential groove located on the external cylindrical surface thereof. As illustrated in FIG. 4A, downward movement of the intermediate length  139  allows the latch ring to expand outwardly, thereby locking the retrieving assembly in a lower, shifted position. 
     A fishing head  145  is carried at a lower extent of the intermediate length  139  of the retrieving assembly. Preferably, the fishing head  145  is attached to the intermediate length  139  by means of a shear stub  147 . Collet fingers  149  extend downwardly from the fishing head and define a fishing opening  150  which is adapted to matingly engaging a nipple  151  provided on the sealing plug. 
     The operation of the device will now be described. The apparatus, as generally illustrated in FIGS. 1-4 is run into position within the well bore suspended from a tubing string extending to the well surface. The stinger  111  of the sealing plug  109  is inserted within the mating bore  113  of the sump packer (FIG. 4) previously set within the well bore. Weight is then applied via the tubing string, causing the shear pins  117  to sever, thereby freeing the tubular section  19  from the sealing plug, leaving the sealing plug in place within the sump packer. The tubing string is then lifted upwardly, usually a few feet, into the vicinity of the production interval and an upper packer in the tubing string (not shown) is set. The firing means is then actuated to detonate the explosive charges and fire the guns. The firing action and/or well hydrostatic pressure uncovers the upper circulating ports  97  in the upper end of the firing head. The firing action (and/or well hydrostatic pressure) also simultaneously shifts the piston sleeve  51  upwardly on the tubular firing section of the apparatus, thereby covering the openings which have been formed in the regions of reduced wall area provided in the tubular section  17  so that firing debris is trapped within the interior bore of the assembly (see FIGS.  3  and  3 A). The explosive gases from the charges (and/or well hydrostatic pressure) also act upon the reactive piston area  127  of piston  129  (FIG. 4) to shift piston  129  and the retrieving assembly downwardly within the tubular section  19 . This action exposes the bottom circulation ports  133  and locks the retrieving assembly in the extended position by means of the latch ring  143 . 
     After perforating and stabilizing the well, the tubing string is continuously lowered, allowing sand to be circulated off the sealing plug. This is accomplished by circulating well bore fluids down the well annulus, up the lower end  27 , through the bottom circulating ports  133  through the interior bore of the device and out the upper circulating ports  97  and up the tubing string to the well surface. Once any sand or debris has been removed from the upper surface of the sealing plug and sump packer, the work string can be lowered downwardly, thereby allowing the collet fingers of the retrieving head  145  to engage the nipple  151  of the sealing plug, as shown in FIG.  4 A. By lifting the tubing string from the well surface, the sealing plug  109  can now be pulled out of engagement with the sump packer  115 . If, for some reason, the plug  109  cannot be pulled from the packer, the shear stud  147  will sever, thereby allowing the system to be retrieved to the well surface. 
     An invention has been provided with several advantages. The combination perforating and circulating gun system saves time and effort, providing a one trip operation which replaces as many as three trips required in the prior art. The piston sleeve provided about the tubular firing section provides a convenient means for trapping any firing debris associated with the perforating operation. By providing a circulating system, sand or other debris can be reverse circulated out of the well to remove obstructions of sand or other contaminants located above a sump packer in a well bore. The reverse circulation operation can be accomplished without the necessity of tripping the work string from the well bore or requiring the presence of additional equipment. Reverse flow can also be utilized to remove other types of obstructions encountered in the well bore. 
     While the invention has been shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.