Abstract:
A shear ram assembly including upper and lower ram blocks having blades positioned on opposing sides of pipe and other, more ductile items, and arranged to close around and shear the pipe and the more ductile items. The shear ram assembly includes pipe guide arms attached to the upper ram block and configured to guide pipe and other items into the path of the blades, and to be received by recesses in the lower ram block. Also included are wear plates mounted on top of the pipe guide arms and positioned to force the lower ram block to rise as the arms enter the recesses, thereby causing the gap between the blades to decrease so that the blades can better shear the more ductile items.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This technology relates generally to well drilling. In particular, this technology relates to a shear ram assembly for a blowout preventer (“BOP”) that has wear plates designed to adjust the relative position of ram blocks so that blades of the ram blocks can better shear ductile items, such as wireline, coiled tubings, etc. 
         [0003]    2. Brief Description of Related Art 
         [0004]    Offshore drilling rigs typically employ a riser to connect the subsea wellhead with the drilling rig. A BOP is located at a lower end of the riser. Land rigs also use BOPs. A BOP is a large assembly having many features for closing around a drill pipe and/or casing in the event that high pressure in the wellbore begins pushing the drilling mud upward. Those features include an annular assembly that seals around the pipe, regardless of the diameter. In addition, the BOP has pipe shear ram assemblies that will shear a drill pipe string or a production tubing string in the event of an emergency. 
         [0005]    Pipe shear ram assemblies typically have two rams, each of which has a blade mounted to it. Pistons move the rams toward each other to shear pipe and other items extending through the BOP. Generally, one blade is located at a higher elevation than the other, and the higher blade slides over the lower blade when the shear rams close. This difference in elevation creates a gap between the blades. 
         [0006]    One problem with known shear ram assemblies is that the blades may not shear everything in the well bore. For example, because there is a gap between the blades, items that are ductile or flexible may simply bend between the blades, rather than cut. Thus, even after the ram blocks are closed and the blades have deployed, ductile items like wiring or flexible tubing may still be intact. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed herein is a pipe shear ram assembly for use in a BOP that in one example includes upper and lower ram blocks having blades. The ram blocks are designed to be positioned on opposite sides of a well bore so that the pipe string, and other more ductile items, such as wiring, pass between the blades of the ram blocks. In the event of an emergency, the ram blocks close by moving toward one another so that the blades pass over one another. As the blades pass over one another, they shear the pipe string and other items in the wellbore, and then seal the wellbore. Generally, as the blades of the upper and lower ram blocks pass over one another, there is a vertical gap between the blades. 
         [0008]    In an example embodiment, the pipe shear ram assembly disclosed herein includes a pair of pipe guide arms that are mounted to the upper ram block and are positioned to enter corresponding recesses in the lower ram block as the ram blocks close. In this example, the pipe shear arms are located in an outboard position relative to the blades and have a wedge-shaped inboard profile. One purpose of the pipe guide arms is to direct piping or other items located on the edges of the wellbore into the path of the blades to be cut. 
         [0009]    Wear plates may be attached to the upper surfaces of the pipe guide arms. The wear plates are positioned so that their top surfaces are higher than the tops of the recesses on the lower ram block. As the rams blocks close, therefore, and the pipe guide arms, along with the wear plates, enter the recesses, the lower ram block is forced to rise so that the recesses can accept the wear plates. As the lower ram block rises, so does the blade attached to the lower ram block. Thus, the gap between the blades of the upper and lower ram blades is reduced. The edges of either the recesses or the wear plates may be chamfered to allow entry of the wear plates into the recesses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will be better understood on reading the following detailed description of nonlimiting embodiments thereof and on examining the accompanying drawings, in which: 
           [0011]      FIG. 1  is a perspective view of the ram blocks of a shear ram assembly in accordance with this disclosure; 
           [0012]      FIG. 1A  is a perspective view of the ram blocks of  FIG. 1 , with the ram blocks substantially dosed around pipe and ductile items; 
           [0013]      FIG. 2  is a side view of the ram blocks of  FIG. 1 ; 
           [0014]      FIG. 3  is a bottom perspective view of the ram blocks of  FIG. 1 ; 
           [0015]      FIG. 4  is a front view of the upper ram Hock of  FIG. 1 ; 
           [0016]      FIG. 5  is a top view of the upper ram block of  FIG. 1 ; and 
           [0017]      FIG. 6  is a perspective view of the ram blocks of  FIG. 1  installed within a subsea BOP assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    The foregoing aspects, features, and advantages of the present invention will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the invention illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0019]    Referring to  FIG. 1 , shear rams  10  are shown removed from the housing or bonnet (not shown) in which they are located. Shear rams  10  are part of a ram BOP assembly that is part of a stack assembly. In the case of offshore drilling, the stack assembly is located at the lower end of a riser extending downward from a drilling vessel. The lower end of the BOP stack assembly will normally also contain pipe rams, variable bore rams, and a quick disconnect mechanism for disconnecting from the riser in an emergency. When actuated, shear rams  10  will close the through bore and also shear pipe and other items in the well, such as, for example, drill pipe, tubing, casing, or wiring. 
         [0020]    In the example of  FIG. 1 , shear rams  10  include a generally planar upper ram block  12  having a lateral surface that defines a face or forward end  14 . A semicircular groove  16  is located on the upper side of upper ram block  12  for receiving a portion of an elastomeric seal. An upper shearing blade  18  mounts to forward end  14 , by any appropriate means, such as, for example, by fasteners  74 . Upper blade  18  has a forward face  20  with an upper edge  22  and a lower edge  24 . For purposes of this disclosure, the term forward, with reference to the ram blocks and associated components, shall mean in a lateral direction from face  20  and away from end  14 . In the example of  FIG. 1 , the lower edge  24  extends farther forward from forward end  18  than upper edge  22 , resulting in face  20  inclining relative to forward end  14 . Face  20  is also generally concave or converging, resulting in the center of face  20  between its outboard ends  26  being recessed relative to the more forward portions of face  20  at outboard ends  26 . A variety of different shapes for upper blade  18  may be employed. 
         [0021]    Pipe guide arms  28  are elongate members shown located on the outboard sides of upper ram block forward end  14  and projecting generally forward away from end  14 . In one embodiment; the pipe guide arms  28  are similar to those disclosed in U.S. patent application Ser. No. 13/339,519, which is hereby incorporated herein by reference. Each arm  28  can be formed integrally with upper ram block  12 , or can be otherwise attached, such as by welding or fasteners. Each arm  28  has a vertically oriented inboard side  30  extending forward from a base  32  of each arm  28 . Base  32  is where arm  28  joins forward end  14 . Each arm  28  also has a wedge surface  34  that extends from a junction with a forward end of inboard side  30  to a tip  38 , and an upper surface  36 . The wedge surface  34  depends laterally inward with distance away from the tip  38 . As shown in  FIG. 2 , upper surface  36  is spaced at a lower elevation on upper ram block forward end  14  than upper blade lower edge  24 . Upper surface  36  is not located directly under upper blade  18  in this example because inboard side  30  of each arm  28  is approximately the same outboard distance as one of the upper blade outboard ends  26 , as shown, e.g., in  FIG. 5 . Also,  FIGS. 2 and 5  illustrate that tip  38  extends forwardly more than upper blade  18  from forward end  14 . The junction of inboard side  30  with wedge surface  34  is approximately in vertical alignment with the junction of upper shear blade upper edge  22  and outboard end  26 . One purpose of the arms  28  is to guide a pipe (not shown) and other, more ductile items, in an inboard direction toward the blades. A wear plate  52  is optionally attached to the top surface of each arm  28 , as discussed in greater detail below. 
         [0022]    Referring again to  FIG. 1 , a substantially planar lower ram block  40  is illustrated in horizontal alignment with upper ram block  12 . Lower ram block  40  has a forward end  42  that is parallel to forward end  14  of upper ram block  12 . A top seal groove  44  in the upper side of lower ram block  40  receives an elastomeric seal and aligns with seal groove  16  to form a continuous seal when ram blocks  12 ,  40  are in abutment with each other. The seal is not necessarily circular. On its upper surface, lower ram block  40  has a sheared pipe end recess  46  for receiving the lower end of well pipe and ductile items after shearing. Sheared pipe end recess  46  has a curved rear wall portion  48  that blends with two straight side wall portions  50 . Other shapes are feasible. 
         [0023]    A lower blade  54  is attached to forward end  42  of lower ram block  40 . Lower blade  54  is at a lower elevation than upper blade  18 , as illustrated in  FIG. 2 . Lower blade  54  slides under upper blade  18  when shearing. An upper edge  56  of lower blade  54  is at a slightly lower elevation than lower edge  24  of upper blade  18 . Lower blade  54  has a lower edge  58  that is closer to lower block forward end  42  than the upper edge  56 . A face  60  extends between lower edge  58  and upper edge  56  and is thus inclined relative to forward end  42 . As illustrated in  FIG. 2 , in this example, the inclination of lower blade face  60  is the same as the inclination of upper blade face  20 . Lower blade face  60  also recesses or converges to a central area that is closer to lower block forward end  42  that the outboard ends  62  of lower blade  54 , as shown in  FIG. 1 . The length of lower blade  54  from one outboard end  62  to the other is the same as the length of upper blade  18  from one outboard end  26  to the other. 
         [0024]    Referring to  FIG. 3 , which shows the bottom of shear rams  10 , a recess  64  is located on lower shear block  40  along each outboard side outward and rearward from lower blade outboard ends  62 . Each recess  64  has a space or clearance provided along an outboard side to receive one of the arms  28  when ram blocks  12 ,  40  are closed. Each recess  64  is defined by a downward-facing upper side wall  66  and an inboard sidewall  68 , sidewalk  66  and  68  being flat and perpendicular in this example. Each recess  64  is aligned with one of the arms  28  to receive the arm when in the dosed, or sheared position. Each recess  64  has a greater longitudinal length than the length of each arm  28 . Also, upper side wall  66  has a greater width than that of each arm  28 , and inboard side wall  68  has a greater height than the height of each arm  28 . Recess  64  need not be a closed cavity, and in the example shown has no outboard side wall or bottom side wall. 
         [0025]    Referring to  FIGS. 1 and 2 , the wear plates  52  may be attached to the arms  28  in any appropriate manner, such as, for example, by welding, adhesive, or mechanical fasteners. In an alternative embodiment, the wear plates  52  may be formed integral with the arms  28 . Each wear plate  52  has a thickness sufficient that the top  70  of each wear plate  52  is slightly higher than the upper side wall  66  of the recesses  64  when the ram blocks  12 ,  40  are open. Thus, when the ram blocks  12 ,  40  close, the wear plate  52  comes into contact with the upper side wall  66  of the recess  64  and forces the lower ram block  40  to raise. As the lower ram block  40  raises, the lower blade  54  raises relative to the upper blade  18 , so that the vertical gap between the blades  18 ,  54  is reduced. A forward edge  72  of the recess  64  is chamfered (as shown in  FIGS. 2 and 3 ) to enable the wear plate  52  to slide into recess  64  as the ram blocks  12 ,  40  close. Alternatively, the forward edge of the wear plate may be chamfered for the same purpose. In yet another embodiment, the arms  28  may be positioned so that the upper surface  36  of the arms  28  themselves contact the upper side wall  66  of the recess  64 , thereby forcing the ram block  40  to raise. In such an embodiment, wear plates  52  may not be necessary. 
         [0026]      FIG. 1A  shows the upper and lower ram blocks  12 ,  40  in a substantially closed position around pipe  100  and ductile items  102 , such as, for example, flexible tubing or wiring. Arms  28 , including wear plates  52 , are shown partially engaged with recess  64 . As can be seen, upper and lower blades  18 ,  54  have substantially passed over, each other, shearing both the pipe  100  and the ductile items  102 . 
         [0027]    One advantage to the use of wear plates  52  to narrow the gap between the upper and lower blades  18 ,  54  is that, as shown in  FIG. 1A , the rams  12 ,  40  are able to better shear ductile items. For example, in embodiments that do not include the wear plates  52 , the vertical offset between the upper end  56  of the lower blade  54  and the lower end  24  of the upper blade  20  may be great enough that ductile items will not sever, but will merely bend, or flex, in the gap between the blades as the blades close. However, with the wear plates  52  in place, such as shown in  FIG. 1A , the gap between the blades is substantially decreased so that even ductile items will be severed, having no room to bend. In one example embodiment, the vertical distance between the upper end  56  of the lower blade  54  and the lower end  24  of the upper blade  20  when the wear plates  52  are not in place is about 0.020 inch. Conversely, in embodiments with the wear plates  52 , the vertical offset between the blades is reduced to a range of less than about 0.020 inch, and in the range of about 0.003 inch or less to about 0.008 inch. 
         [0028]      FIG. 4  is a front view of the upper ram  12  according to an embodiment of the present technology. In particular,  FIG. 4  shows wear plates  52  attached to the upper surface  36  of each arm  28 .  FIG. 5  similarly shows a top view of the upper ram  12  having wear plates  52  attached to the arms  28 ,  FIGS. 4 and 5  also show the position of the arms  28  relative to the blade  18  of the upper ram  12 . For example,  FIGS. 4 and 5  show that the wear plates  52  are positioned lateral to the upper ram blade  18  so that they do not interfere with the path of the blade  18  as the rams  12 ,  40  close. Although the wear plates  52  are shown to be rectangular in shape, they may alternatively be a different shape, as long as the top  70  of each wear plate  52  is configured to contact the upper side wall  66  of the recess  64  and raise the lower ram block  40  relative to the upper ram block  12 , as described above. 
         [0029]    Referring to  FIG. 6 , shear rams  10  are shown installed in a typical subsea BOP assembly. The BOP assembly has a BOP stack  76  that includes a frame  78  with a wellhead connector  80  at the lower end for connecting to a subsea wellhead assembly (not shown). Shear rams  10  are normally located above pipe rams, which in this example include pipe rams  82 ,  84 , and  86 . Each pipe ram  82 ,  84 , and  86  has rams with semi-cylindrical recesses on the mating faces for closing around a different size range of pipe. When closed, shear rams  10  will seal off the bore and if pipe and/or other items are present, will shear the pipe and other items. 
         [0030]    A lower marine riser package (LMRP)  88  connects to the upper end of BOP stack  76 . An annular BOP  90  may be located at the lower end of LMRP  88 . Annular BOP  90  will close around any size of pipe and seal the annulus between the pipe and the side wall of the bore. Annular BOP  90  will also seal fully even if a pipe is not present. A flex joint  92  is located at the upper end of LMRP  88  to allow flexing of a lower end of a riser string  94  connected to flex joint  92 . Choke and kill lines  96  extend from below annular blowout preventer  90  to alongside riser  94  for pumping fluid into the well. In the event of an emergency, LMRP  88  and riser  94  can be detached from BOP stack  76 . Redundant control pods  98  mount LMRP  88  and contain hydraulic and electrical circuitry for controlling movement of the various rams  10 ,  82 ,  84 ,  86 , the annular BOP  90 , and other equipment. Control pods  98  are retrievable from LMRP  88  and are connected to an umbilical (not shown) leading to the drilling vessel at the surface. 
         [0031]    While the technology has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the technology. Furthermore, it is to be understood that the above disclosed embodiments are merely illustrative of the principles and applications of the present technology. Accordingly, numerous modifications may be made to the illustrative embodiments and other arrangements may be devised without departing from the spirit and scope of the present technology as defined by the appended claims.