Abstract:
Blowout preventer (BOP) and method for sealing a well. The BOP includes a body having first and second conduits, the first conduit being substantially perpendicular on the second conduit; a piston extending through the first conduit and being configured to reciprocate inside the first conduit, the piston having a body portion, a neck portion and a head portion in this order; a ram block disposed on the piston and configured to move with the piston inside the first conduit for closing the second conduit; and a shim configured to fill a gap between a back region of the ram block and the body portion of the piston.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for reducing a gap between components of a ram blowout preventer (BOP). 
       BACKGROUND 
       [0002]    One apparatus for sealing a well is the BOP. The BOP is a safety mechanism that is used at a wellhead of an oil or gas well. The BOP may be used for offshore drilling and also for land-based drilling. The BOP is configured to shut the flow from the well when certain events occur. One such event may be the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure generated by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent and/or control it, the well and/or the associated equipment may be damaged. 
         [0003]    The BOP may be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. One type of BOP, an annular BOP, is conventionally implemented as a valve to release the pressure either in the annular space between a casing and a drill pipe or in the open hole (i.e., hole with no casing) during drilling or completion operations. Another type of BOP, a ram BOP, can be located below the annular BOP and above the wellhead. These ram BOPs can generally be broken down into a few categories: (1) blind rams for sealing an open hole, (2) pipe rams for sealing a hole with drill pipe in use, (3) shear rams for sealing the hole and cutting the drill pipe, etc. 
         [0004]      FIG. 1  shows a well  10  located in an offshore environment. A wellhead  12  of the well  10  may be fixed to the seabed  14 . A ram BOP  16  is secured to the wellhead  12 .  FIG. 1  shows, for clarity, the BOP  16  detached from the wellhead  12 . However, the BOP  16  is attached to the wellhead  12  or another part of the well  10 . A drill pipe  18  is shown traversing the ram BOP  16  and entering the well  10 . The ram BOP  16  may have two ram blocks  20  attached to corresponding pistons  22 . The pistons move integrally with the ram blocks  20  along directions A and B to close the well. 
         [0005]    A cut view of the ram BOP  16  that shows the ram blocks  20  is shown in  FIG. 2 . The ram blocks  20  are shown closed inside a cavity  24 . The cavity  24  may be bordered, at one end, by a top seat  26  and a wear plate  28 . The ram blocks  20  may include a packer  30  (which may be an elastomer) and a top seal  31 , which seals the well  10  when the ram blocks  20  are closed. 
         [0006]    In situations when the ram BOP is a pipe ram BOP used for shearing the drill pipe or other tools in the hole when sealing the well, having the desired shear strength and shared load through the desired load bearing surfaces is desired. This can be complicated by variable forces acting upon the system, such as, the reaction force produced by the drill line when asymmetrically disposed relative to the shear surface of the ram block  20 , and force produced by variable upward pressure from the kick or additional items inside of the drill pipe that also need to be sheared off to seal the well, e.g., a cable attached to a down hole piece of equipment, to name just a few examples. 
         [0007]    In addition, piston  22  may neck down into a piston rod portion  302  which includes a neck section  304  and head section  306  as shown in  FIG. 3 . In  FIG. 3 , a portion of the piston rod  302  is shown as dashed lines representing the portion of the piston rod  302  which is covered by the ram block  20  when looking from the top down. The piston rod head section  306  has a face  308  which is in contact with the ram block  20 . This contact surface of the face  308  is where the force is applied from the piston  22  to the ram block  20  when closing the BOP to shear, for example, a load  314 . Also shown is a gap  310  which exists between the piston rod  302  and the ram block  20  when the ram block  20  is installed. Since there is a gap  310 , shoulders  312  of the piston rod  302  are not applying force from the piston rod  302  to the ram block  20 . Additionally, this gap may allow undesirable twisting forces to be exerted upon the piston rod neck  304 . For example, if the load  314  is asymmetrically distributed relative to the ram block  20 , as shown in  FIG. 3 , a non-uniform force would act on head section  306 , which in turn will try to bend the neck section  304  along direction A. 
         [0008]    Accordingly, it would be desirable to provide systems and methods that can achieve the sealing of a well and shear materials in the well but also avoid the additional challenges described above. 
       SUMMARY 
       [0009]    According to an exemplary embodiment there is a ram BOP for sealing a well. The ram BOP includes a body having first and second conduits, the first conduit being substantially perpendicular on the second conduit; a piston extending through the first conduit and being configured to reciprocate inside the first conduit, the piston having a body portion, a neck portion and a head portion in this order; a ram block disposed on the piston and configured to move with the piston inside the first conduit for closing the second conduit, where the ram block has a recess in a back region configured to receive the neck portion and the head portion of the piston such that a gap is formed between the back region of the ram block and the body portion of the piston across a part of the neck region of the piston; and a shim configured to fill the gap between the back region of the ram block and the body portion of the piston. 
         [0010]    According to another exemplary embodiment, there is a method of assembling a ram block to a piston for use in a ram BOP. The method includes: extending the piston to a partially open position along an axis; placing a ram block on a piston rod of the piston such that a face of a head end of the piston rod is contacting the ram block; measuring, in a direction substantially parallel to the axis of the piston rod, a gap between the ram block and the piston rod; removing the ram block; adding material to the ram block such that when the ram block is reinstalled the gap is reduced; and reinstalling the ram block. 
         [0011]    According to another exemplary embodiment, there is a method of shearing material in a well by a ram BOP. The method includes: engaging with a piston rod, attached to a piston, a ram block on two substantially parallel surfaces of the ram block, where a first parallel surface is between a shoulder of the piston rod and a shim attached to the ram block and a second parallel surface is between a face of the piston rod and the ram block; applying a force to the piston in a first direction such that axial forces on each of the two substantially parallel surfaces are substantially equivalent; and moving the piston rod along the first direction towards the well hole for shearing the tool. 
         [0012]    According to another exemplary embodiment, there is a shim for filling a gap between a ram block and a piston. The shim includes a stock thickness no greater that a thickness of the gap. A shape of the shim is such that outer edges of the shim substantially match a shape of a back face of the ram block and inner edges of the shim are dimensioned to fit around a necked portion of the piston, and the shim is attachable to the ram block. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings illustrate exemplary embodiments, wherein: 
           [0014]      FIG. 1  is a schematic diagram illustrating a ram blowout preventer (BOP) disposed on top of the well; 
           [0015]      FIG. 2  is a schematic diagram of a conventional ram BOP; 
           [0016]      FIG. 3  shows a relationship between a piston rod and a ram block; 
           [0017]      FIG. 4  shows a cut away section of a ram BOP according to exemplary embodiments; 
           [0018]      FIG. 5  shows a relationship between a piston rod, a ram block and applied forces associated with shearing an off-centered object in a well according to exemplary embodiments; 
           [0019]      FIG. 6  illustrates a shim according to exemplary embodiments; 
           [0020]      FIG. 7  depicts a shim attached to a ram block according to exemplary embodiments; 
           [0021]      FIG. 8  shows relative surface areas of the piston rod face, the piston rod neck and the shim according to exemplary embodiments; 
           [0022]      FIG. 9  depicts a partially opened BOP according to exemplary embodiments; 
           [0023]      FIG. 10  shows a side view of a piston rod, bonnet and ram block prior to removing the ram block according to exemplary embodiments; 
           [0024]      FIG. 11  shows a piston, attached piston rod and a detached ram block according to exemplary embodiments; 
           [0025]      FIG. 12  illustrates a method flowchart for assembly of a ram block according to exemplary embodiments; and 
           [0026]      FIG. 13  shows method flowchart for shearing a tool in a well according to exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
         [0028]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0029]    Systems and methods according to exemplary embodiments can improve load sharing on the end of the piston rod in a ram BOP and reduce the associated stress of a given load. In order to provide context for this discussion, an exemplary grouping of components within a ram BOP  400 , which can take advantage of exemplary embodiments described herein, will now be described with respect to  FIGS. 4 and 5 . 
         [0030]      FIG. 4  shows a cut away section of a ram BOP  400  and  FIG. 5  shows the relationship, when looking down, between the piston rod  404  and the ram block  408  when the ram block  408  is installed. Ram BOP  400  includes a piston  402  which has a piston rod section  404  which includes a neck section  514 , a head section  512  and a slot  406  (also a second slot, shown in  FIG. 5 , of a similar shape and size is on the opposite side of piston rod  404 ). A ram block  408  used for shearing material in the well, e.g., drill pipe, cable, tools and the like, can be moved when force is applied to the piston  402  in either direction along an X axis  410 . When enough force is applied to the piston  402 , it can be moved along the X axis  410  to either open or close the ram block  408 . 
         [0031]    The ram BOP  400  also has a bonnet  412  which can be unbolted and swung open on the hinge  414 . In one application, the bonnet  412  is unscrewed or slides away from the ram BOP  400 . This allows access to the ram block  408  for removal, replacement and maintenance of the ram block  408  as desired. According to an exemplary embodiment shown in  FIGS. 4 and 5 , the ram block  408  is placed over a top of the piston rod  404  in order to be attached to the piston  402 . The ram block  408  will remain attached to the piston  402  due to the large weight of the ram block  408  (between 100 and 400 kg). When the ram block  408  is placed over the top of the piston rod  404 , e.g., the piston rod receives a cavity  516  of the ram block  408 , a portion of the ram block  408  fits in the slots  406  of the piston rod  404 . When the piston rod  404  is moved back and forth, the piston rod  404  physically engages the ram block  408 , e.g., the surface  520  at an edge of the cavity  516 , and the ram block  408  moves together with the piston  402 . 
         [0032]    However, as shown in  FIG. 5 , when the ram block  408  is placed on the piston rod  404  a gap  502  exists between the ram block  408  and piston rod  404 . This gap  502  has a thickness which is measurable along the X axis  410 . The dashed line portion of the piston rod  404  generally represents its location within the ram block  408 . According to purely illustrative embodiments, the thickness of the gap  502  may be less than half an inch (1.27 cm), e.g., 0.125 in. (0.3175 cm), and the slot(s)  406  can be in the range of 1-10 inches (2.54-25.4 cm), e.g., 3.25 in. (8.255 cm), however other dimensions can be used. This gap  502  is present because heavy and large components can be difficult to machine precisely, etc. 
         [0033]    In general operation, the piston  402 , piston rod  404  and ram block  408  can be moved along the X axis  410  to either open or close the ram block  408 . To close the ram block  408 , a force is exerted on the piston  402  to move the ram block  408 . However, since the piston rod  404  is necked down, combined with the gap  502  between the ram block  408  and the piston rod  404 , no force is transferred from the piston rod shoulders  504  to the ram block  408  since they are not in contact with the ram block  408 . In the case where the ram block  408  closes to shear something in the well, e.g., a cable  506 , and the cable  506  is off-center of the hole, unequal forces are applied to the head portion  512  of the piston rod  404 . These unequal forces are shown by a force F  508  and a force f 510 . Since one tab of the piston rod head  512  is closer to the contact point(s) between the ram block  408  and the cable  506 , force F  508  is greater than force f 510 . This difference in force can create an undesirable twisting to the necked portion  514  of the piston rod  404 . 
         [0034]    According to exemplary embodiments, various systems and methods can be used to fill the gap  502  between the ram block  408  and the piston rod  404  such that the axial load initially exerted on the piston  402  is transferred across the shoulders  504  of the piston rod  404  to the ram block  408 . Additionally, the removal of the gap  502  reduces the potential twisting applied to the piston rod neck  514 . According to one exemplary embodiment, the shim can be shaped to fit substantially around the neck portion of the piston rod  404  and the shim has a radius along the outer edge of the shim which is greater than or equal to a radius of a face of the head portion of the piston rod  404 . For example, according to exemplary embodiments, a shim  602  as shown in  FIG. 6  can be used to fill the gap  502 . Shim  602  is shown here as a “horseshoe” shaped shim that can be attached to the ram block  408 . In an exemplary embodiment, the shim  602  may be bolted to the ram block  408  (bolt holes not shown). However, other attachment options such as adhesives or welding could be used. When attached to the ram block  408 , the face of the shim  602  is substantially parallel to the face  518  of the piston rod head  512  and the contact points on the shim  602 , e.g., the shoulders  504  of the piston rod  404  and the ram block  408 . The size and shape of shim  602  is a function of the thickness of the gap  502 , the size and shape of the piston rod head  512  and the size and shape of the piston rod neck  514 . While a horseshoe shaped shim  602  is shown in  FIGS. 6 and 7 , other shapes may be used as desired, e.g., two crescent shaped shims. According to exemplary embodiments, shim  602  has yield strength equal to, or greater than that of the piston rod  404 , e.g., in the neighborhood of 135K psi (930.8 KPa). Additionally, according to one exemplary embodiment shim  602  may be constructed from 4340 alloy steel which is then heat treated to attain the desired strength. 
         [0035]    The shim  602  is configured to fit closely around the piston rod neck  514  without completely surrounding it as shown by the open portion  604  of the shim  602 . The outer portion  606  of the shim  602  is dimensioned to approximate the shape of the piston rod head  512  such that when the shim  602  is in place around the piston rod neck  514  the resultant form is similar to the form of the piston rod head  512 . In one exemplary embodiment, the desired thickness of the shim  602  is achieved by grinding or machining off stock from the shim  602  until the shim  602  is roughly the thickness of the gap, e.g., one or two thousandths of an inch (0.01 mm or 0.0508 mm) thinner than the gap  502 , or to have a thickness in the range of 2.54 cm to 25.4 cm, or when possible driving the thickness of the gap to zero, e.g., 0.01 mm or less. This allows close contact of the piston rod  404 , shim  602  and ram block  408  which results in increased load sharing along the X axis  410 . Also, according to other exemplary embodiments, other shapes and configurations of shim  602  can be used as desired. An example of shim  602  attached to ram block  408  is shown in  FIG. 7  which achieves this purpose, i.e., shim  602  substantially fills the gap  502 . Additionally, according to one exemplary embodiment, shim  602  has holes  702  for allowing shim  602  to be bolted (or screwed into) to ram block  408 , however, according to other exemplary embodiments, shim  602  may not have holes and may be attached to ram block  408  by other means. 
         [0036]    The amount of load sharing from the piston  402  to the ram block  408  in a conventional ram BOP is limited by the surface area of the piston rod neck  514  along a plane YZ perpendicular to the X direction  410 . According to exemplary embodiments, when using the desired shim  602  (or other method of filling the gap  502 ), the load can be shared across the new larger surface area described by the surface area of the piston rod neck  514  along the YZ plane and the surface area of the shim  602 , which approaches the surface area of the piston rod head  512 . For example, as illustrated in  FIG. 8 , the surface area of the piston rod neck  514  is shown as surface A 1   802 , the surface area of the shim  602  is shown as A 2   804  and the surface area of the face  518  of the piston rod  404  is shown as surface A 3   806 . All these surfaces are substantially parallel (within manufacturing tolerances) to the YZ plane. Combining the surface area A 1   802  with the surface area A 2   804  results in a total surface area which can, according to an exemplary embodiment, substantially equal the surface area A 3   806 . It should be understood by those of ordinary skill in the art that the shim  602  may be a single shim, e.g., a horseshoe shaped shim of the desired thickness, multiple shims, e.g., two crescent shaped shims of the desired thickness, or stacks of shims and combinations thereof. 
         [0037]    According to exemplary embodiments as described above, the gap  502  can be measured between the ram block  408  and the piston rod  404  as will be discussed next. As shown in  FIGS. 9-11  the ram BOP  400  can be opened up to allow for easy measurement of the gap  502  and the removal and installation of the ram block  408 . After the bonnet  412  of the ram BOP  400  is opened, the ram block  408  is moved with the piston road  402  to a partially open position, which allows clearance for removal of the ram block  408 . The bonnet  412  is unbolted from the ram BOP  400  and swung open on the hinge  414  as shown in  FIG. 9 . The ram block  408  is mainly supported by the bonnet  414  and a base piece  902  attached to the bonnet  412 . A side view is shown in  FIG. 10 , which shows the piston  402  going through the bonnet  412  with the piston rod  404  entering the ram block  408 . Additionally, the base piece  902  and the gap  502  are shown here. At this point, the gap  502  between the piston rod shoulders  312  and the ram block  408  is measured. Then, the ram block  408  can be lifted off from the piston rod  404  along direction B, as shown in  FIGS. 10 and 11 .  FIG. 11  shows a view looking down from above onto the piston  402  and piston rod  404  as well as a view looking down from above onto the ram block  408 , removed from the piston rod  404 . A dashed line section which shows a cavity  1102  where the piston rod  404  lies within/below the ram block  408  is also shown. As can be seen from  FIG. 11 , the ram block  408  may need to be lifted vertically (along direction B) at least until it clears the piston rod head  512  for removal. However, according to other exemplary embodiments, different configurations for ram BOP  400  can be used such that the ram block  408  is removed in a horizontal manner. Additionally,  FIG. 11  shows which surfaces are in contact when the piston rod  404  engages the ram block  408  for movement to either open or close the ram block  408 . Based on the measurement gap  502 , an appropriate shim  602  is machined to correct dimensions and attached to a back portion of the ram block  408  as shown in  FIG. 7 . Then, the ram block  408  is positioned back on the piston rod  404 . 
         [0038]    According to an exemplary embodiment, a shim for filling a gap between a ram block and a piston in a blowout preventer may include a stock having a thickness no greater that a thickness of the gap. The shape of the shim is such that outer edges of the shim substantially match a shape of a back face of the ram block and inner edges of the shim are dimensioned to fit around a necked portion of the piston, and the shim is attachable to the ram block. 
         [0039]    As described above, the gap  502  can be filled to allow contact between the piston rod  404  and the ram block  408  in this location, i.e., increase a contact area between the piston rod  404  and the ram block  408 . According to exemplary embodiments, a method for assembly of a ram block  408 , which fills this gap will now be described with respect to the flowchart of  FIG. 12 . The method of assembling a ram block  408  to a piston  402  for use in a ram BOP  400  includes: extending the piston  402  to a partially open position along an axis in step  1202 ; placing a ram block  408  on a piston rod  404  of the piston  402  such that a face of a head end  512  of the piston rod  404  is contacting the ram block  408  in step  1204 ; measuring, in a direction substantially parallel to the axis of the piston rod  404 , a gap  502  between the ram block  408  and the piston rod  404  in step  1206 ; removing the ram block  408  in step  1208 ; adding material to the ram block  408  such that when the ram block  408  is reinstalled the gap  502  is reduced in step  1210 ; and reinstalling the ram block  408  in step  1212 . 
         [0040]    While the exemplary embodiments described above may use a shim  602  or the like for filling the gap  502  other exemplary methods can be used. According to one exemplary embodiment the ram block  408  can be made to a certain size such that no gap  502  (or just enough gap  502  to allow installation) exists. The ram block  408  can then, as needed, be machined or ground down to the desired size for installation which still allows the desired axial load sharing capabilities described above to occur. Alternatively, material can be deposited upon the desired surface of the ram block  408  to build it up to the desired size to remove the gap  502 . This deposited material can also be machined off or ground down if too much is deposited. Additionally, the mating surfaces of the piston rod  404  and/or the ram block  408  can be ground or polished to a desired surface characteristic, e.g., surface finish, parallelism between features and the like, to both aid in installation to result in the desired axial load sharing capabilities. 
         [0041]    It is noted that ram blocks  408  are generally interchangeable parts for a ram BOP  400 . That is, the ram blocks  408  may be removed and replaced on an existing ram BOP  400  at desired intervals. In addition, one particular type of ram block  408  may be adapted to fit into more than one ram BOP  400 . For example, it is common to install multiple BOPs in a BOP stack. By using similar ram BOPs  400 , it enables a ram block  408  to be used in more than one ram BOP  400 . Thus, it is likely that a gap  502  is present between the ram block  408  and the piston rod  404  irrespective of how accurately these parts are machined and the method described above corrects this problem. 
         [0042]    According to another exemplary embodiment, a method of shearing a tool in a well will now be described with respect to the flowchart shown in  FIG. 13 . A method of shearing the tool in a well by a ram BOP  400  includes: engaging with a piston rod  404 , attached to a piston  402 , a ram block  408  on two substantially parallel surfaces of the ram block  408 , where a first parallel surface is between a shoulder of the piston rod  404  and a shim  602  attached to the ram block  408  and a second parallel surface is between a face of the piston rod  404  and the ram block  408  in step  1302 ; applying a force to the piston  402  in a first direction such that axial forces on each of the two substantially parallel surfaces are substantially equivalent in step  1304 ; and moving the piston in the first direction towards the well hole for shearing the tool in step  1306 . 
         [0043]    The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus, the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. For example, exemplary embodiments described above allow for resisting the twisting and compression of a neck portion  514  of the piston rod  404  when acting on a tool by having the shim  602  fill in the gap. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. 
         [0044]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other example are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements within the literal languages of the claims.