Abstract:
A shaped charge carrier tool is provided that has particular utility for perforating well casing as a preparation for cement placement. A plurality, four or more elongated shaped charge carrier ribs having a high bending modulus are secured for radially expanded displacement around a central framing tube or rod. Radius rods link the ends of the carrier ribs to top and bottom hinge carriers. The hinge carriers encircle the framing tube and are free for axial translation along the framing tube. Articulating hinges connect the radius rods to the carrier ribs and to the hinge carriers. Opposed compressed coil springs provide a resilient bias on the hinge carriers to translate the carrier ribs radially outward against the interior surface of a well casing as the tool passes from a riser tube into a larger inside diameter well casing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Not applicable 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to the industrial art of earth-boring and well drilling for the recovery of fluid minerals. More particularly, the invention relates to a carrier for a multiplicity of shaped explosive charges to penetrate well casing with multiple apertures. 
         [0004]    Description of Related Art 
         [0005]    In the oil and gas industry, well plugging operations are often performed to seal wellbores in order to abandon the wells. Eventually, all wells exhaust their purpose and are abandoned. Either the well is a “dry hole”, having no economically viable production, or has depleted the production strata. In either case, a non-productive well is or should be permanently “plugged”. “Plug and abandonment” procedures are required under various state and federal laws and regulations. Plug and abandonment operations performed upon a cased wellbore require that at least a section of the wellbore be filled with cement to prevent the upward movement of fluids toward the surface of the well. To seal the wellbore, a bridge plug is typically placed at a predetermined depth in the wellbore and thereafter, cement is injected into the wellbore to form a column of cement high enough to ensure the wellbore is permanently plugged. 
         [0006]    In addition to simply sealing the interior of a wellbore, plug and abandonment regulations additionally require that an area outside of the wellbore be sufficiently blocked to prevent any fluids from migrating towards the surface of the well along the outside of the casing. Migration of fluid outside of the casing is more likely to arise after a fluid path inside the wellbore has been blocked. Additionally, where multiple strings of casing line a wellbore, the annular area between concentric casing strings can form a fluid path in spite of being cemented into place when the well was completed. Inadequate cement jobs and deterioration of cement over time can lead to flow paths being opened through an otherwise solid cement barrier. 
         [0007]    There are several reasons to line a well borehole with two or more substantially concentric casings. As one example, two or more mineral strata may be produced from the same borehole. In this example, a smaller diameter casing is set within a larger diameter casing. A first mineral stratum of oil, gas or both, may be produced along the flow annulus between the two casings. A second, usually deeper mineral stratum is produced along the flow bore of the smaller or innermost casing. This sequence may be repeated for multiple pay strata and multiple concentric casings. 
         [0008]    Another example of multiple concentric casings is that of extremely deep borings that require a tapered casing string to line an unstable raw borehole along a greater depth than normally expected of a surface casing. In this context, a “tapered” casing string means one in which an inner casing of smaller OD than the ID of an outer casing is secured to the end of the outer casing. Although the surface casing may not penetrate a mineral bearing stratum, the annulus between two concentric casings may carry a flow of gas that has escaped an inner flow bore. 
         [0009]    Many off-shore, deep water wells have extremely large surface casings; in the order of 24″ ID. These large surface casings are set to a bottom hole depth of 3,000′ to 5,000′ below the seafloor. The seafloor may be under an ocean depth of 1,000′ to 5,000′ below a drilling rig floor. 
         [0010]    When a well is abandoned, all of the productive flow channels must be filled with cement to a designated depth below the surface or seafloor. In the case of multiple casings, there are two possible approaches available for sealing all of the annuli present. In one approach, as represented by U.S. Pat. No. 5,472,052 to P. F. Head, all of the upper ends of casings that are interior of the outermost casing are milled away down to the designated depth. Thereafter, a solid core of cement is placed to fill the interior volume of the outermost casing. The annulus between the outermost casing OD and the raw borehole ID is filled with cement when originally set. 
         [0011]    An alternative well plugging procedure is to set a bridge plug within the innermost casing and perforate the inner casing wall above the plug. Cement is pumped down the inner casing and forced out into the annulus between the inner and outer casings. For multiple annuli, this process is repeated by the selective use of shaped charges that will perforate only the desired number of casing walls but not the outermost casing. 
         [0012]    Of the two procedures available for plugging an abandoned well, the latter procedure of casing wall perforation and filling the one or more annuli with cement is more economical by several orders of magnitude. However, deep water offshore wells present unique difficulties for this alternative procedure. When originally drilled, a large drilling platform or drill ship was used to support the immense weights and forces necessary to drill such wells. A “riser” of greater diameter than the largest casing to be set in a particular well links the surface casing to the drilling rig to protect the borehole from invading seawater and as a conduit for the return flow of drilling fluid. When the drilling and well preparation is complete the drilling platform is removed along with the large riser. Smaller and lighter drill ships capable of supporting considerably smaller risers, in the order of 6⅝″, are used for well maintenance. By the time of well abandonment, platforms such as was used for the original drilling, are not economically available. In many deep water wells, however, even the smallest or innermost casing is larger than the riser capacity of most maintenance ships. 
         [0013]    Casing perforations utilized in a cement “squeezing” operation are typically formed with a perforating assembly that includes a number of shaped charges. An apparatus representative of this concept includes resiliently biased members that remain in contact with the casing wall as the apparatus is lowered into the well. The shaped charges are mounted on the inside surface of bars that are resiliently biased to maintain physical contact with the interior casing wall. The shaped charges are secured at a predetermined distance from the inside bar surface as determined by the casing wall thickness and/or the number of casing walls to be penetrated. An example of such a resiliently biased perforating gun is disclosed in U.S. Pat. No. 5,295,544 to D. V. Umphries. However, the radial expansion distance of a prior art resilient bar is insufficient to accommodate the radial difference between a 6⅝″ maintenance ship riser and a 24″ casing. 
       SUMMARY OF THE INVENTION 
       [0014]    The present perforating tool provides a variable diameter carrier for multiple perforation charges having the functional capacity of descending along a small inside diameter riser pipe into a larger inside diameter casing. As the carrier enters the larger diameter casing, a bias force on shaped charge carrier ribs expands the ribs into contact with the inside wall surfaces of the larger casing. 
         [0015]    The carrier comprises an axially aligned central tube or rod that may be supported at the end of a wire line, tubing or pipe string. Secured to the central rod are two framing discs. Geometric planes respective to the framing discs are typically normal to the central rod axis and are separated by a distance determined by the length of shaped charge carrier ribs. 
         [0016]    Along the central rod length on opposite sides of the framing discs are hinge carriers that are confined to the central tube for axial translation along the tube length. Coil springs confined around the central tube bear upon the hinge carriers to resiliently bias the hinge carriers toward each other. 
         [0017]    One end of a plurality of radius rods has an articulated connection to the hinge carriers. The opposite end of each radius rod is hinged to a respective end of a shaped charge carrier rib. The opposing bias of the coil springs acting upon the hinge carriers and radius rods imposes resilient radial bias on the shaped charge carrier ribs. The shaped charge carrier ribs are shaped to a substantially rigid section modulus to oppose mid-length bending between the hinges. An outer face of each shaped charge carrier rib is substantially straight between the hinges to physically engage the inside surface of the intended casing. A line of shaped charges is secured along the inside length of the charge carrier ribs at predetermined distances inwardly from the rib outside surface as dictated by the perforation mission. 
         [0018]    The shaped charge carrier ribs of an assembled tool are radially compressed against the bias of the coil springs at both ends for transit along the riser bore. As the tool enters a larger ID casing, the coil spring bias expands the charge carrier ribs into contact with the inside casing surface for final placement and discharge of the shaped charges. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is hereafter described in detail and with reference to the drawings wherein like reference characters designate like or similar elements throughout the several figures and views that collectively comprise the drawings. Respective to each drawing figure: 
           [0020]      FIG. 1  is a pictorial view of a prior art apparatus. 
           [0021]      FIG. 2  is a partial section view of the invention in a collapsed assembly mode. 
           [0022]      FIG. 3  is a partial section view of the invention in an expanded assembly mode. 
           [0023]      FIG. 4  is a section view of the invention along cutting plane IV-IV of  FIG. 2 . 
           [0024]      FIG. 5  is a section view of the invention along cutting plane V-V of  FIG. 3 . 
           [0025]      FIG. 6  is a sectioned detail of a shaped charge carrier rib. 
           [0026]      FIG. 7  is a profile view of a particular utility of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    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. Moreover, in the specification and appended claims, the terms “pipe”, “tube”, “tubular”, “rod”, “casing”, “liner” and/or “other tubular goods” are to be interpreted and defined generically to mean any and all of such elements without limitation of industry usage. 
         [0028]    In describing a preferred embodiment of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
         [0029]    With reference to  FIG. 1 , an example of a prior art casing perforator is shown to comprise six rows of shaped charge carrier ribs  12 . Each charge carrier rib may support six shaped charges  14 , for example. The six shaped charge carrier ribs  12  are supported between upper and lower framing discs,  16  and  17  A framing rod  19  passes centrally through the framing discs  16  and  17 . The framing discs  16  and  17  are secured to upper and lower collars  20  and  21 , respectively, by upper and lower legs  23  and  24 . The upper and lower collars  20  and  21  ring the framing rod  19 . A rigid assembly of collars  20  and  21 , the legs  23  and  24 , the framing discs  16  and  17  and shaped charge carriers  12  is confined along the length of framing rod  19  between upper and lower compression nuts  26  and  27 . 
         [0030]    Distinctive of this prior art tool represented by  FIG. 1  is provision for compression load against the shaped charge carriers  12 . Such compression loading is imposed by preloading nuts  29  (only the upper nut  29  is shown) turned against the respective framing discs  16  and  17 . Compression load at opposite ends of the shaped charge carriers  12  effects a resiliently arced position to the carriers thereby forcing a bias on the shaped charges  14  against the inside surface of a surrounding casing. 
         [0031]    Although the prior art tool described by  FIG. 1  is effective for use with a casing of known size having direct accessibility, compliance to casing size variation is extremely limited; a limitation the present invention is intended to overcome. 
         [0032]    Referring to the partial sections of  FIGS. 2 and 4 , the present invention is shown in a radially constricted mode as configured to traverse the length of a small diameter riser pipe  50 . Central to the tool construction is a framing rod or tube  30  preferably having a hollow bore to carry detonation cord  31 . A bail  36  may secured to the upper end of the framing tube for attachment of a suspension wireline  38 . In a mid-section of the framing tube, upper and lower framing discs,  32  and  33  respectively, are secured at selected axial positions along the framing tube  30  length. The outer perimeter of the framing discs  32  and  33  set constrictive limit stops for a plurality of shaped charge carrier ribs  40 . 
         [0033]    The shaped charge carrier ribs  40  are secured to the central framing tube  30  by a translational linkage that will maintain a substantial parallelism between the ribs  40  as the are translated from a first constricted circumference to greater circumference in abutted engagement with the inner walls of a larger ID casing. Although only two shaped charge carrier ribs  40  are illustrated by  FIGS. 2 and 3  as a diametric pair, it should be understood the tool will normally be provided with four to eight such shaped charge carrier ribs. Consequently, the axial separation between the framing discs  32  and  33  should be no greater than the length of the shaped charge carrier ribs  40  but may be somewhat less. 
         [0034]    A preferred embodiment of a suitable translating linkage mechanism may include an articulated joint or hinge  44  secured at opposite distal ends of each shaped charge carrier rib  40 . One distal end of a tie rod  42  is secured to a carrier rib  40  by an articulated joint or hinge  44  and the opposite distal end of the tie rod  42  is secured to an upper or lower hinge carrier  48  or  49  by an articulated joint or hinge  46 . The hinge carriers  49  are radially confined around the framing tube  30  but are freely translated along the tube length. Upper and lower coil springs  52  and  53 , respectively, are compressed between the hinge carriers  48  and  49  and upper and lower base rings  55  and  56  for a passively resilient displacement force on the rib  40  articulation linkage. 
         [0035]    Viewing  FIGS. 2 and 3  comparatively, it may be seen that when the tool passes from the smaller diameter bore of the riser  50  into a casing  60  of greater diameter, the expanding bias of springs  52  and  53  displace hinge carriers  48  and  49  along the framing tube  30  in mutually opposite directions. Hinge carrier displacement is transferred to the tie rod hinges  46  which are confined to a fixed radial separation distance from the framing tube  30 . Consequently, the interior ends of the fixed length tie rods  42 , hinged to the shaped charge carrier ribs  40 , displace the shaped charge carrier ribs from contact with the framing discs  32  and  33  and radially out against the inside surface of the greater diameter casing  60 . 
         [0036]    The enlarged detail of  FIG. 6  illustrates a representative shaped charge  41  secured within the inside arc of a shaped charge carrier rib  40  having a cross-sectional shape configured to high bending modulus. An aperture  42  is formed in the apex of-the carrier in line with the discharge axis of the shaped charge  41 . The spring driven bias on the shaped charge carrier rib  40  presses the rib apex line into tangent contact with the inside surface of the casing  60 . Shaped charge penetration depth may be adjusted by a controlled separation distance between the contact face of the carrier rib and the discharge face of the shaped charge. 
         [0037]    Those of ordinary skill in the art will also understand that section shapes having a high bending modulus other than the half cylinder arc of carrier rib  40  may also be used. A channel section rib is an example. Box sections, rectangular sections and 90° angle sections may also be used. 
         [0038]    It is important that the casing perforations opened by the present tool are limited to the one or more intended interior casings and exclusive of the outermost well casing. Skilled selection of shaped charge penetration depth, capacity and configuration considers the casing wall thickness and annulus separation between the walls. This selection process is assisted by a controlled separation distance of a shaped charge discharge face from the inside surface of the casing. The present invention facilitates such controlled separation distance. 
         [0039]    Among relevant tool design criteria is the length of the tie rods  42  as it affects the expanded angle of the rods. After discharge, the tool is usually withdrawn from the wellbore back through the riser  50 . As the tool passes through the transition point between the casing and riser, the shaped charge carrier rib ends attached to the upper tie rods  42  are forced inwardly toward the framing tube  30 . Consequently, the upper hinge carrier  48  translates upwardly against the bias of upper spring  52 . Such compressive force on the spring  52  translates to the tensile force drawn on the wireline  38 . 
         [0040]    In a different application, two of the present perforating tools  64  and  66  may be secured at the end of a suspension pipe or tubing string  61  with a bore packer  65  attached between the two as illustrated by  FIG. 7  to verify the seal integrity of cement annulus around a casing. A bridge plug  62  is set to seal the bore of a subject casing  60  to be tested for integrity of a cement annulus seal around the subject casing  60 . The  FIG. 7  tool assembly is positioned above the bridge plug  62 . The packer  65  is expanded to seal the annulus  69  between the casing  60  ID and the suspension tube  61  OD. The lowermost perforating tool  66  is now confined in a pressure retention zone  68  between the bridge plug  62  and the packer  65 . 
         [0041]    Discharge of the two perforating tools  64  and  66  opens apertures through the casing  60  into the surrounding cement sealing collar. From the surface, fluid is pumped through the suspension tube  61  into the pressure retention zone  68 . Simultaneously, pressure within the annulus  69  between the casing  60  ID and the suspension tube  61  OD above the packer  65  is monitored. An increase in annulus fluid pressure above the packer  65  is an indication of leakage and fluid migration past the cement sealing collar around the subject casing  60  OD, 
         [0042]    Those of ordinary skill will also quickly appreciate a wheeled adaption of the invention for use in deviated or horizontal well bore directions. Such wheeled embodiments may be by directly attached axles or fore and aft accessory carriages. 
         [0043]    The foregoing description of the invention represents a fundamental, self-actuating embodiment having a standing resilient expansion bias on the charge carrier ribs imposed by a pair of identical coil springs  52  and  53 . Hence, the tool has no dependency on remote controls or power sources to engage and disengage inside diameter surfaces of larger casings. However, numerous alternative mechanisms are also well known to the prior art. 
         [0044]    Non-illustrated examples of mechanisms that are generally equivalent to the coil springs  52  and  53  may include pneumatic, oleo-pneumatic and hydraulic piston/cylinder devices operating as direct substitutes for the coil springs  52  and  53 . 
         [0045]    Charge carrier ribs  40  may be expanded by numerous translational mechanisms other than the radius rods  42  described herein. For example, an opposed scissors mechanism similar to a lifting jack may be particularly useful in certain applications to translate the charge carrier ribs radially against a casing ID. 
         [0046]    Another example of the invention may position the radius rods and hinge carriers between the charge carrier ribs and the central tube with a resilient force such as springs between the hinge carriers. 
         [0047]    Although the invention disclosed herein has been described in terms of specified and presently preferred embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.