Patent Publication Number: US-11639643-B2

Title: Kinetic ram having pressure relief device

Description:
Continuation of International Application No. PCT/US2019/044084 filed on Jul. 30, 2019. Priority is claimed from U.S. Provisional Application No. 62/712,774 filed on Jul. 31, 2018. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable. 
     BACKGROUND 
     This disclosure relates to the field of well pressure control apparatus such as blowout preventers (“BOPs”). More particularly the disclosure relates to pyrotechnically generated, gas pressure operated valves (“rams”) used in BOPs. BOPs for oil and gas wells are used, among certain reasons, to prevent potentially catastrophic events known as blowouts, where high well fluid pressures and uncontrolled fluid flow from a subsurface formation into the well can expel tubing (e.g., drill pipe and well casing), tools and drilling fluid out of a well. Blowouts present a serious safety hazard to drilling crew, the drilling rig and the environment and can be extremely costly. Typically BOPs have “rams” that are opened and closed by actuators. The most common type of actuator is operated hydraulically to push closure elements into or across a through bore in a BOP housing (itself sealingly coupled to the well) to close the well. In some cases, the rams have hardened steel shears to cut through a drill string or other tools or devices which may be in the well and thus in the through bore at the time it is necessary to close the BOP. 
     A limitation of hydraulically actuated rams is that they require a large amount of hydraulic force to move the rams against the pressure inside the wellbore (and thus in the through bore) and in the case of shear rams subsequently to cut through objects in the through bore. 
     An additional limitation of hydraulically actuated rams is that the hydraulic force is typically generated at a location away from the BOP (necessitating a hydraulic line from the pressure source to the rams), making the BOP susceptible to failure to close if the hydraulic line conveying the hydraulic force is damaged. Other problems associated with hydraulically actuated rams may include erosion of cutting and sealing surfaces on the rams due to the relatively slow closing of the rams in a flowing wellbore. Cutting through tool joints, drill collars, large diameter tubulars and off-center pipe strings under heavy compression may also present problems for hydraulically actuated rams. 
     Pyrotechnic gas pressure operated BOP rams have been proposed which address some of the limitations of hydraulically actuated BOPs. An example of such a pyrotechnic gas pressure operated BOP is described in International Application Publication No. WO 2016/176725 filed by Kinetic Pressure Control Limited. A limitation of pyrotechnic based BOPs such as disclosed in the foregoing publication is that in the event the ram becomes stuck in its passageway, pressure in the pyrotechnic firing chamber can build to a point where the pressure vessel would fail. Such failure risk is based on the fact that such BOP rams rely on the progression of a piston used to move the ram to increase the volume in the firing chamber as the pyrotechnic charge generates gas. 
     SUMMARY 
     A kinetic ram for a blowout preventer according to one aspect of the disclosure includes a pressure chamber having a piston movably disposed therein. A gas generating charge disposed at one end of the pressure chamber. A ram is coupled to the piston on a side of the piston opposed to the gas generating charge. The ram is arranged to move across a through bore in a blowout preventer housing disposed at an opposed end of the pressure chamber. An initial volume in the pressure chamber between the one end and the piston is chosen to limit a maximum pressure caused by actuating the gas generating charge to a predetermined maximum pressure, and/or the pressure chamber comprises a pressure relief device arranged to vent pressure in the pressure chamber above the maximum pressure. 
     In some embodiments, the maximum pressure is at most three times an operating pressure to accelerate the piston to a selected velocity. 
     In some embodiments, the maximum pressure is at most one- and one-half times an operating pressure to accelerate the piston to a selected velocity. 
     In some embodiments, the maximum pressure is at most five times an operating pressure to accelerate the piston to a selected velocity. 
     In some embodiments the initial volume is chosen by providing a selected initial distance between the gas generating charge and the piston. 
     In some embodiments, the initial volume is chosen by providing at least one pressure relief hole in at least one of the pistons and an interior wall of the pressure chamber. 
     In some embodiments, the at least one pressure relief hole is covered by a burst disk. 
     Some embodiments further comprise a restraint coupled to the piston and arranged to hold the piston against pressure in the pressure chamber until the pressure in the pressure chamber exceeds a selected amount. 
     In some embodiments, the restraint comprises at least one shear pin. 
     In some embodiments, the restraint comprises an integral attachment forming part of the gas generating charge. 
     Some embodiments comprise a second pressure chamber having a second piston movably disposed therein, a second gas generating charge disposed at one end of the second pressure chamber, a second ram coupled to the second piston on a side of the second piston opposed to the second gas generating charge, the second ram arranged to move across the through bore or a through bore in a second blowout preventer housing disposed at an opposed end of the second pressure chamber and wherein at least one of, an initial volume in the second pressure chamber between the one end and the second piston is chosen to limit a maximum pressure caused by actuating the second gas generating charge to a predetermined maximum pressure, and the second pressure chamber comprises a pressure relief device arranged to vent pressure in the pressure chamber above the maximum pressure. Such embodiments may have the ram and the second ram moving in opposed directions with reference to the first through bore. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a side view of a pyrotechnic gas operated BOP known in the art prior to the present disclosure. 
         FIG.  2    shows a plan view of the BOP shown in  FIG.  1   . 
         FIGS.  3 ,  4  and  5    show, respectively a side view and plan views of an example embodiment of a BOP according to the present disclosure. 
         FIGS.  6  and  7    show another example embodiment of a BOP according to the present disclosure. 
         FIGS.  8  and  9    show another example embodiment of a BOP according to the present disclosure. 
         FIG.  10    shows another example embodiment similar in principle to the embodiment shown in  FIGS.  8  and  9   . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, like components common the several drawings are identified with like reference numerals.  FIG.  1    and  FIG.  2    show, respectively, a side view and a plan view of a pyrotechnic gas operated BOP known in the art prior to the present disclosure. A non-limiting example of such a BOP is described in International Application Publication No. WO 2016/176725 filed by Kinetic Pressure Control Limited. 
     A pyrotechnic gas pressure operated BOP  10 , which may also be referred to as a “kinetic BOP” comprises a housing  12  having a through bore  14 . The housing  12  may be coupled to a wellhead, another BOP or a similar structure so that such similar structure may be closed to flow by operating the kinetic BOP  10 . A passageway  34  may be formed in a receiving cover  32  coupled to one side of the housing  12 . The housing  12  may comprise a part  34 A of the passageway adjacent to the passageway  34  in the receiving cover  32 . A further part  34 B of the passageway may be formed in a pressure chamber  16  coupled to an opposed side of the housing  12 . The passageway  34  and its parts  34 A,  34 B provide a travel path for a ram  20 . The travel path enables the ram  20  to attain sufficient velocity resulting from actuation of a pyrotechnic charge  24  and subsequent gas expansion against a piston  18  such that kinetic energy in the ram  20  may be sufficient to sever any device disposed in the through bore  14  and to enable the ram  20  to extend into the passageway  34  across the through bore  14 . A ring cutter  28  is disposed in the passageway coincident with the through bore  14 . A seal  30  may provide effective flow closure between the through bore  14  and the ram  20  when the ram  20  is moved into the through bore  14  such that fluid pressure in the through bore  14  is excluded from the passageway  34  and parts  34 A,  34 B thereof. When the ram  20  is disposed across the through bore  14  after actuation of the pyrotechnic charge  24 , the through bore  14  is thereby effectively closed to flow across the ram  20 . The piston  18  may be decelerated by a brake  26  such as a crush sleeve or similar device such that the piston  18  does not strike the housing  12  so as to damage the housing  12 . The pyrotechnic charge  24  may be actuated by an initiator  22  of types well known in the art. 
     As may be determined with reference to the &#39;725 publication cited above, upon initial actuation of the pyrotechnic charge  24 , there is a relatively small volume between the charge and the piston  18  before the piston  18  has begun to move. Such volume may be referred to as the “initial volume.” There is also typically an amount of free volume inside the charge  24  itself because the propellant in the charge  24  is typically supplied as a granular substance. 
     The relatively small initial volume is needed for proper function of the BOP  10  as such initial volume enables a high gas pressure to be generated rapidly on actuation of the charge  24 , which provides a motive force to accelerate the piston  18  and consequently the ram  20 . In addition, propellants used in such BOPs, such as a nitrocellulose- and/or nitroglycerin-based propellants, the rate of combustion of the propellant is related to the maximum gas pressure induced within a gas chamber  24 A disposed between the charge  24  and the piston  18 . Without the high pressure being generated, the piston  18  would not be accelerated to its required velocity. For purposes of defining the scope of the present disclosure it should be understood that a separate ram and piston are equivalent structures to an integral piston and ram, wherein such structures are functionally similar. 
     A drawback of having a small initial volume occurs in a “jamming event.” If the piston  18  and/or the ram  20  becomes jammed during actuation, and the initial volume does not increase as a result of piston  18  movement, the pressure developed within the pressure chamber  16  behind the piston  18  could be substantially greater than the normal or desired BOP actuating pressure. Depending on where in the passage the piston  18  and/or the ram  20  becomes jammed, the pressure in the pressure chamber  16  may become many times the normal or desired actuating pressure. Such elevated pressure may result in failure of the pressure chamber  16 . It would be possible to design a pressure chamber capable of withstanding pressure that is multiples of the desired BOP actuating pressure, but it may be reasonably expected that such a pressure chamber would be bulky, expensive, and therefore impractical. 
     According to the present disclosure, the initial volume may be chosen and/or actuatable features may be provided so that the minimum chamber volume is at least an amount chosen to limit the maximum pressure in the pressure chamber  16  in a jamming event to a predetermined limit pressure. In some embodiments, and referring to  FIG.  3   , the initial volume may be chosen using one or more various structures including, for example, increasing an initial distance  11  between the charge  24  and the piston  18 , milling relief holes  13  into the piston  18 , and/or milling relief holes (not shown) into the interior wall of the chamber  16 . 
     In some embodiments, the initial distance  11  and/or volume of relief holes  13  may be chosen such that the total volume limits gas pressure in the pressure chamber  16  in the event of piston or ram jamming to at most 1.5 times the desired actuating pressure. 
     In some embodiments, the initial distance  11  and/or volume of relief holes  13  may be chosen such that the total volume limits gas pressure in the pressure chamber  16  in the event of piston or ram jamming to at most 3 times the desired actuating pressure. 
     In some embodiments, the initial distance  11  and/or volume of relief holes  13  may be chosen such that the total volume limits gas pressure in the pressure chamber  16  in the event of piston or ram jamming to at most 5 times the desired actuating pressure. 
     In order to maintain the performance of the BOP and to successfully accelerate the piston  18  at the desired rate, and referring to  FIG.  4   , in some embodiments, hold back shear pins  15  may be used to hold the piston  18  initially at a selected initial distance  11 . The initial distance  11  in some embodiments may be chosen such that the initial volume limits the maximum pressure in the pressure chamber  16  as explained above. The shear pins  15  have a chosen breaking strength to hold the piston  18  in place until the desired pressure (which maximum pressure may be limited as explained above) is reached, thus allowing the piston  18  to accelerate to a higher velocity over a shorter distance. In addition, by allowing pressure to build in the pressure chamber  16 , a faster combustion of the charge  24  may take place.  FIG.  5    shows the shear pins  15  having been ruptured when the pressure in the chamber  16  causes force on the piston  18  to exceed the breaking strength of the shear pins  15 , thus accelerating the piston  18  and the ram  20 . 
       FIG.  6    shows another embodiment comprising relief holes  17  in the piston each terminated by a burst disk  19 . In order to minimize the amount of initial free volume but still maintain a safe device where the pressure chamber  16  will not fail in a jamming event a burst disk  19  or similar pressure relief valve may in installed in a corresponding hole  17  the piston  18 . In the event the pressure in the chamber  16  rises to a predetermined level above the desired actuating pressure the burst disk(s)  19  will fail, whereby pressure is relieved to the opposite side of the piston  18 . This relief of pressure may prevent the failure of the chamber  16 . 
       FIG.  7    shows another embodiment corresponding to the example embodiment shown in  FIG.  6   , wherein relief holes  13  in the piston  18  do not extend all the way through the face of the piston  18 . Such relief holes  13  may be similar to those explained with reference to  FIG.  3   . In the present embodiment, the relief hole(s)  13  may be closed by a respective burst disk  19 . In the event the pressure chamber  16  pressure rises to a predetermined level above the desired actuating pressure, the burst disk(s)  19  will fail, and the volume in the pressure chamber  16  is then increased by the volume of the relief hole(s)  13 . 
     In some embodiments, the additional volume introduced by failure of the burst disk(s)  19  is enough to limit pressure rise in a jamming event to no more than 3 times the desired firing pressure. In some embodiments, the additional volume introduced by failure of the burst disk(s)  19  is enough to limit pressure rise in a jamming event to no more than 5 times the desired firing pressure. 
     In some embodiments, the additional volume introduced by failure of the burst disk(s)  19  is enough to limit pressure rise in a jamming event to no more than 1.5 times the desired firing pressure. 
     In some instances, shear pins such as may be used in the example embodiments explained with reference to  FIGS.  4  and  5    may be undesirable because they can provide significant and uneven stress increases on the pressure chamber  16 . It is therefore more desirable to centrally locate a restraint or “hold back” device similar in function to shear pins, but this is difficult to obtain in practice because the charge  24  is located so as to be in the way. In some embodiments, the charge  24  itself or its housing can also act as a hold back device. In such embodiments, the charge  24  may comprise integral attachments  24 A to couple the charge  24  to the piston  18 . The charge  24  itself can now also perform the same function as the shear pins ( 15  in  FIG.  4   ) by restraining the piston  18  until a desired chamber pressure is reached. Such restraint enables the piston  18  to accelerate to a higher velocity over a shorter distance. In addition, by allowing pressure to build in the pressure chamber  16  a faster combustion of the charge  24  may be obtained. The embodiment shown in  FIG.  8    may comprise relief holes  13  in the piston  18  as explained with reference to  FIG.  7    and may further comprise burst disks to close such relief holes  13  also as explained with reference to  FIG.  7   .  FIG.  9    shows the embodiment of  FIG.  8    after initiation of the charge  24  and subsequent rupture of the integral attachments  24 A.  FIG.  9    shows the piston  18  without relief holes  13  and burst disks  15  as in  FIG.  8    only to illustrate that such embodiment is possible. Another example embodiment which may use a similar principle to the embodiment shown in  FIGS.  8  and  9    is shown in  FIG.  10   , in which the charge  24  may be coupled to the piston  18  using a shear bolt  23  or similar attachment that is designed to fail at a selected force, e.g., tension, above a predetermined threshold. In  FIG.  10    the shear bolt  23  has been ruptured after initiation of the charge  24  and development of the requisite gas pressure. 
     In some embodiments, any of the structures shown in  FIGS.  3  through  10    may be used to provide two gas pressure operated rams substantially as shown in any of the foregoing figures arranged on one housing as shown in the figures or two separate housings coupled longitudinally. In some embodiments, the two rams may be disposed on a same side of the one or two housings. In some embodiment, the two rams may be disposed on opposed sides of the through bore  14  in either a single housing or in two housings such that two rams operated in opposed directions. 
     Although only a few examples have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the examples. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.