Patent Publication Number: US-6708761-B2

Title: Apparatus for absorbing a shock and method for use of same

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates, in general, to absorbing a shock between two tubular members and, in particular, to an apparatus for absorbing a shock between two tubular members using a plurality of layers of energy absorbing members that are sequentially deformed. 
     BACKGROUND OF THE INVENTION 
     Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation using shaped charge perforating guns, as an example. 
     After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation. 
     Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, numerous charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or the like. Once the charge carriers are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the carrier, creates a hydraulic opening through the casing and cement and then penetrates the formation forming a perforation therein. 
     It has been found, however, that a shock wave may be generated that travels upwardly through the tools of the tool string when the shaped charge perforating guns are fired. This shock wave may damage certain tools in the tool string. In addition, it has been found that the firing bar used to contact the firing head of the perforating guns may be forced back uphole after the shaped charge perforating guns are fired. The firing bar may then damage equipment in the wellhead. Further, it has been found that once the perforating process is complete and the shaped charge perforating guns are released, they may damage the temporary plug that is commonly located within the casing below the formation that was perforated. 
     A need has therefore arisen for an apparatus that can be installed within the tool string that can absorb the shock wave generated by firing the shaped charge perforating guns. A need has also arisen for such an apparatus that can absorb the shock of the firing bar contacting wellhead equipment if the firing bar is forced back uphole after the shaped charge perforating guns are fired. Further, a need has arisen for such an apparatus that can absorb the shock of the shaped charge perforating guns contacting the temporary plug after the shaped charge perforating guns are released. 
     SUMMARY OF THE INVENTION 
     The present invention disclosed herein comprises a shock absorber that can be installed within a tool string to prevent damage to other downhole equipment caused by shocks. For example, the shock absorber of the present invention may be installed within the tool string to absorb the shock wave generated by firing shaped charge perforating guns. Likewise, the shock absorber of the present invention may be installed within the tool string to absorb the shock of the shaped charge perforating guns contacting the temporary plug after the shaped charge perforating guns are released. The shock absorber of the present invention may also be installed at the wellhead to absorb the shock of the firing bar if it is forced back uphole after the shaped charge perforating guns are fired. Additionally, the shock absorber of the present invention, may be used between virtually any downhole tools or between any two devices that may encounter significant one time shocks. 
     The shock absorber of the present invention comprises first and second tubular members that are slidably positioned relative to one another. A plurality of layers of energy absorbing members extends radially from the second tubular member such that movement of the second tubular member in a first direction relative to the first tubular member sequentially deforms the layers of energy absorbing members, thereby absorbing the shock. 
     In one embodiment of the shock absorber of the present invention, the second tubular member is positioned interiorly of the first tubular member. In another embodiment, the second tubular member is positioned exteriorly of the first tubular member. In one embodiment of the shock absorber of the present invention, the energy absorbing members are positioned between the first and second tubular members. The energy absorbing members may extend radially outwardly from the second tubular member or may extend radially inwardly from the second tubular member. 
     In one embodiment of the shock absorber of the present invention, each layer of energy absorbing members includes a plurality of shear pins. In another embodiment, each layer of energy absorbing members is a shear ring. In either embodiment, a subsequent layer of energy absorbing members may begin to deform before a previous layer of energy absorbing members is completely deformed when the second tubular member moves in the first direction relative to the first tubular member to allow for a smooth shock absorption. 
     In one embodiment of the shock absorber of the present invention, when the second tubular member moves in either longitudinal direction relative to the first tubular member, the energy absorbing members in adjacent layers are sequentially deformed. In this embodiment, first and second pluralities of layers of energy absorbing members extend radially from the second tubular member such that movement of the second tubular member in a first direction relative to the first tubular member sequentially deforms the layers of energy absorbing members of the first plurality of layers of energy absorbing members. Likewise, movement of the second tubular member in a second direction relative to the first tubular member sequentially deforms the layers of energy absorbing members of the second plurality of layers of energy absorbing members, thereby absorbing a shock in either direction. 
     The method of the present invention involves slidably positioning a first tubular member relative to a second tubular member, radially extending a plurality of layers of energy absorbing members from the second tubular member and sequentially deforming the layers of energy absorbing members as the second tubular member is moved in a first direction relative to the first tubular member, thereby absorbing the shock. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
     FIG. 1 is a schematic illustration of an offshore oil and gas platform operating a pair of apparatuses for absorbing a shock of the present invention; 
     FIG. 2 is a half sectional view of an apparatus for absorbing a shock of the present invention prior to absorbing a shock; 
     FIG. 3 is a half sectional view of an apparatus for absorbing a shock of the present invention after a portion of a shock has been absorbed; 
     FIG. 4 is a half sectional view of an apparatus for absorbing a shock of the present invention after a shock has been absorbed; 
     FIG. 5 is a half sectional view of an apparatus for absorbing a shock of the present invention after a shock has been absorbed; 
     FIG. 6 is a half sectional view of another embodiment of an apparatus for absorbing a shock of the present invention before a shock has been absorbed; and 
     FIG. 7 is a half sectional view of another embodiment of an apparatus for absorbing a shock of the present invention before a shock has been absorbed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention. 
     Referring initially to FIG. 1, a pair of shock absorbers of the present invention operating from an offshore oil and gas platform is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including subsea blow-out preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work sting  30 . 
     A wellbore  32  extends through the various earth strata including formation  14 . A casing  34  is cemented within wellbore  32  by cement  36 . Work string  30  includes various tools such as shaped charge perforating guns  38 ,  40 ,  42 , a packer  44  and shock absorbers  46 ,  48 . When it is desired to perforate formation  14 , work string  30  is lowered through casing  34  until shaped charge perforating guns  38 ,  40 ,  42  are positioned adjacent to formation  14 . Thereafter, shaped charge perforating guns  38 ,  40 ,  42  are sequentially fired such that the shaped charges are detonated. Upon detonation, the liners of the shaped charges form jets that create a spaced series of perforations  50  extending outwardly through casing  34 , cement  36  and into formation  14 . 
     When the shaped charge perforating guns  38 ,  40 ,  42  are fired, a shock wave may be generated that travels upwardly through the tools of work string  30  which may damage certain tools in work string  30 . In the illustrated embodiment, shock absorber  48  absorbs this shock to prevent such damage. In addition, once the perforating process is complete, shaped charge perforating guns  38 ,  40 ,  42  may be released and allowed to fall down wellbore  32 . Commonly there is a temporary plug (not pictured) located within casing  34  below formation  14 . When shaped charge perforating guns  38 ,  40 ,  42  encounter the temporary plug, shaped charge perforating guns  38 ,  40 ,  42  may damage the temporary plug. In the illustrated embodiment, shock absorber  46  absorbs this shock to prevent such damage. 
     Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the shock absorbers of the present invention are equally well-suited for use in deviated wells, inclined wells or horizontal wells. Also, even though FIG. 1 depicts an offshore operation, it should be noted by one skilled in the art that the shock absorbers of the present invention are equally well-suited for use in onshore operations. In addition, even though the shock absorbers of the present invention have been described with reference to absorbing shock during and following a perforating operation, those skilled in the art should recognize that the shock absorbers of the present invention are equally-well suited for absorbing shock between virtually any downhole tools or between any two devices that may encounter significant one time shocks. 
     Now referring to FIG. 2, therein is depicted a shock absorber of the present invention that is generally designated  60 . Shock absorber  60  includes an axially extending, generally tubular outer housing  62 . Outer housing  62  includes an upper connector  64  that is threadably attachable to another tool (not pictured). Outer housing  62  also includes a primary housing section  66  that is threadably coupled to upper connector  64 . Threadably attached to the lower end of primary housing section  66  is an end cap  68 . A longitudinal bore is defined within outer housing  62 . Specifically, upper connector  64  defines upper bore  70 , primary housing section  66  defines primary bore  72  and end cap  68  defines lower bore  74 . Upper bore  70  and lower bore  74  have radially reduced inner diameters compared with primary bore  72 . At the lower end of upper connector  64  is a shoulder  76  that separates upper bore  70  and primary bore  72 . Likewise, at the upper end of end cap  68  is a shoulder  78  that separates lower bore  74  from primary bore  72 . 
     It should be apparent to those skilled in the art that the use of directional terms such as top, bottom, above, below, upper, lower, upward, downward, etc. are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. As such, it is to be understood that the downhole components described herein may be operated in vertical, horizontal, inverted or inclined orientations without deviating from the principles of the present invention. 
     Slidably positioned within outer housing  62  is an axially extending, generally tubular mandrel  80 . Mandrel  80  includes an upper section  82  that is slidably received within upper bore  70  of outer housing  62 . Mandrel  80  also includes an intermediate section  84  that is slidably received within primary bore  72  of outer housing  62 . Mandrel  80  further includes a lower section  86  that is slidably received within lower bore  74  of outer housing  62  and is threadably attachable to another tool (not pictured). Extending radially outwardly from upper section  82  of mandrel  80  is a plurality of energy absorbing members  88 . In the illustrated embodiment, each energy absorbing member  88  includes one or more shearable members  90  and one or more corresponding outer rings  92 . For example, shearable members  90  may be a plurality of shear pins such that two or more of such shear pins are spaced circumferentially around upper section  82  of mandrel  80  in which case each shear pin includes its own outer ring  92 . Alternatively, shearable members  90  may be shear rings, each of which circumferentially extends around upper section  82  of mandrel  80  and each of which has a corresponding outer ring  92 . It should be noted by those skilled in the art that even through energy absorbing members  88  have been depicted as including two parts, shearable members  90  and outer rings  92 , energy absorbing members  88  could alternatively be a single part wherein, for example, shearable members  90  and outer rings  92  are integral with one another. 
     Energy absorbing members  88  are positioned longitudinally along upper section  82  of mandrel  80  in a layer arrangement including layers  94 - 104 . Accordingly, each layer  94 - 104  may include a plurality of shearable members or a single shearable member. Even though FIG. 2 has been depicted as having six layers  94 - 104 , it should be understood by those skilled in the art that any number of layers of energy absorbing members  88  could alternatively be utilized those numbers being either greater than or less than six. 
     Extending radially outwardly from lower section  86  of mandrel  80  are additional energy absorbing members  106  that may be identical to energy absorbing members  88 . Specifically, energy absorbing members  106  include shearable members  108  that may be shear pins or shear rings and outer rings  110 . Energy absorbing members  106  are oriented longitudinally along lower section  86  of mandrel  80  in layers  112 ,  114 . 
     In operation, when a shock is applied between outer housing  62  and mandrel  80  causing mandrel  80  to move upwardly relative to outer housing  62 , outer rings  92  of layer  94  of energy absorbing members  88  contact shoulder  76 . As mandrel  80  continues its upward movement relative to outer housing  62 , shearable members  90  of layer  94  begin to deform and absorb some of the shock applied between mandrel  80  and outer housing  62 . 
     As best seen in FIG. 3, before shearable members  90  of layer  94  of energy absorbing members  88  is completely deformed, outer rings  92  of layer  94  contact outer rings  92  of layer  96 . The contact between adjacent layers of energy absorbing members  88  before respective shearable members  90  are completely deformed allows shock absorber  60  of the present invention to absorb the shock applied between mandrel  80  and outer housing  62  in a smooth manner without creating sequential impacts between outer housing  62  and mandrel  80 . It should be noted, however, that the distance between the layers of energy absorbing members  88  could alternatively allow complete deformation of shearable members  90  of one layer of energy absorbing members  88  before shearable members  90  of a subsequent layer of energy absorbing members  88  begin to deform. In either case, energy absorbing members  88  are sequentially deformed beginning at layer  94  and progressing through subsequent layers  96 - 104  of energy absorbing members  88  until the entire shock between housing  62  and mandrel  80  is absorbed. As best seen in FIG. 4, the maximum amount of shock that can be absorbed by shock absorber  60  has been absorbed and all shearable members  90  in the various layers  94 - 104  of energy absorbing members  88  have been sheared. Importantly, it should be noted that the number of layers of energy absorbing members  88  as well as the strength of shearable members  90  may be selected based upon the expected shock to be absorbed by shock absorber  60  such that the entire expected shock may be absorbed without shearing all shearable members  90 . 
     In certain applications of shock absorber  60 , after shock absorber  60  has absorbed the initial shock, mandrel  80  may travel downwardly relative to housing  62 , for example, to carry the weight of the tool string below shock absorber  60 . In this case, to avoid significant impact between mandrel  80  and outer housing  62  during this downward movement, energy absorbing members  106  are used. Specifically, when mandrel  80  moves downwardly relative to housing  62  such that outer rings  110  of layer  112  of energy absorbing members  106  contact shoulder  78 , shearable members  108  begin to deform thereby absorbing this shock. Before shearable members  108  of layer  112  are completely deformed, outer rings  110  of layer  112  contact outer rings  110  of layer  114  allowing for a smooth energy absorbing process. Energy absorbing members  106  continue to absorb the shock up to the maximum travel of mandrel  80  relative to housing  62  as best seen in FIG.  5 . Again, it should be noted by those skilled in the art that the number of energy absorbing members  106  as well as the number and strength of shearable members  108  may be selected based upon the expected shock to be absorbed. Further, it should be noted that housing  62  and mandrel  80  may be allowed to rotate relative to one another or such rotation may be prevented using an anti-rotation lock or the like. 
     While FIGS. 2-5 have depicted a shock absorber of the present invention that is intended to take a major shock in one direction, mandrel  80  moving upwardly relative to housing  62 , and a minor shock in the other direction, mandrel  80  moving downwardly relative to housing  62 , it should be understood by those skilled in the art that the shock absorber of the present invention could alternatively be configured to take a major shock regardless of the relative longitudinal direction of movement between mandrel  80  and housing  62 . 
     For example, and now referring to FIG. 6, therein is depicted a shock absorber of the present invention that is generally designated  160 . Shock absorber  160  includes an axially extending, generally tubular outer housing  162 . Outer housing  162  includes an upper connector  164  that is threadably attachable to another tool (not pictured). Outer housing  162  also includes a primary housing section  166  that is threadably coupled to upper connector  164 . Threadably attached to the lower end of primary housing section  166  is an end cap  168 . A longitudinal bore is defined within outer housing  162 . Specifically, upper connector  164  defines upper bore  170 , primary housing section  166  defines primary bore  172  and end cap  168  defines lower bore  174 . Upper bore  170  and lower bore  174  have radially reduced inner diameters compared with primary bore  172 . At the lower end of upper connector  164  is a shoulder  176  that separates upper bore  170  and primary bore  172 . Likewise, at the upper end of end cap  168  is a shoulder  178  that separates lower bore  174  from primary bore  172 . 
     Slidably positioned within outer housing  162  is an axially extending, generally tubular mandrel  180 . Mandrel  180  includes an upper section  182  that is slidably received within upper bore  170  of outer housing  162 . Mandrel  180  also includes an intermediate section  184  that is slidably received within primary bore  172  of outer housing  162 . Mandrel  180  further includes a lower section  186  that is slidably received within lower bore  174  of outer housing  162  and may be threadably attached to another tool (not pictured). Extending radially outwardly from upper section  182  of mandrel  180  is a plurality of energy absorbing members  188  that include shearable members  190  and outer rings  192 . 
     Energy absorbing members  188  are positioned longitudinally along upper section  182  of mandrel  180  in a layer arrangement including layers  194 - 204 . Accordingly, each layer  194 - 204  may include a plurality of shearable members or a single shearable member. Even though FIG. 6 has been depicted as having six layers  194 - 204 , it should be understood by those skilled in the art that any number of layers of energy absorbing members  188  could alternatively be utilized those numbers being either greater than or less than six. 
     Extending radially outwardly from lower section  186  of mandrel  180  are additional energy absorbing members  206  that may be identical to energy absorbing members  188 . Specifically, energy absorbing members  206  include shearable members  208  that may be shear pins or shear rings and outer rings  210 . Energy absorbing members  206  are oriented longitudinally along lower section  186  of mandrel  180  in layers  212 - 222 . Again, it should be noted by those skilled in the art that any number of layers of energy absorbing members  206  could alternatively be utilized those numbers being either greater than or less than six. 
     Shock absorber  160  is configured to absorb a major shock regardless of the relative longitudinal direction of movement between mandrel  180  and housing  162 . Assuming the rating of shearable members  190  and shearable members  208  is the same, shock absorber  160  can absorb the same shock whether mandrel  180  moves upwardly relative to housing  162  or downwardly relative to housing  162 . It should be understood by those skilled in the art, however, that shearable members  190  may have different ratings than shearable members  208  and there may be a different number of layers of energy absorbing members  188  as compare to energy absorbing members  206 , as seen above in FIGS. 2-5. 
     In some shock absorbing applications, it is important to have access through a shock absorber. Accordingly, as best seen in FIG. 7, therein is depicted a shock absorber of the present invention having a full bore that is generally designated  260 . Shock absorber  260  includes an axially extending, generally tubular housing  262 . Housing  262  includes an upper connector  264  that is threadably attachable to another tool (not pictured). Housing  262  also includes a primary housing section  266  that is threadably coupled to upper connector  264 . Threadably attached to the lower end of primary housing section  266  is an end cap  268 . A longitudinal bore  270  is defined within housing  262  that allows other tools to pass therethrough. A radially reduced outer diameter  272  is defined along primary housing section  266  between shoulder  276  of upper connector  264  and shoulder  278  of end cap  268 . 
     Slidably positioned about housing  262  is an axially extending, generally tubular sleeve  280 . Sleeve  280  includes an upper section  282  that is slidable around upper connector  264  of housing  262 . Sleeve  280  also includes an intermediate section  284  that is slidably positioned around primary housing section  266  of housing  262 . Sleeve  280  further includes a lower section  286  that is slidable around end cap  268  of housing  262  and is threadably attachable to another tool (not pictured). Extending radially inwardly from upper section  282  of sleeve  280  is a plurality of energy absorbing members  288  that include shearable members  290  and outer rings  292 . 
     Energy absorbing members  288  are positioned longitudinally along upper section  282  of sleeve  280  in a layer arrangement including layers  294 - 304 . Accordingly, each layer  294 - 304  may include a plurality of shearable members or a single shearable member. Likewise, extending radially inwardly from lower section  286  of sleeve  280  are additional energy absorbing members  306  that may be identical to energy absorbing members  288 . Specifically, energy absorbing members  306  include shearable members  308  that may be shear pins or shear rings and outer rings  310 . Energy absorbing members  306  are oriented longitudinally along lower section  286  of sleeve  280  in layers  312 ,  314 . According, using shock absorber  260  of the present invention, other tools or equipment may pass through longitudinal bore  270 . Also, it should be noted that housing  262  and sleeve  280  may be allowed to rotate relative to one another or such rotation may be prevented using an anti-rotation lock or the like if desired. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.