Abstract:
A polished rod BOP ram seal is formed with protrusions that are disposable in corresponding seal retention pockets formed in a seal-receiving groove in a BOP ram receiving the seal. The resultant mechanical interlock between the ram seal and the ram provides increased resistance to extrusion of the seal from the ram under high-pressure, high-velocity fluid flow conditions through the BOP.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure relates in general to blowout preventers (BOPs) for use in conjunction with producing oil wells, and relates in particular to seals for polished rod rams and blind rams incorporated into such BOPs. 
       BACKGROUND 
       [0002]    Polished rod blowout preventers (rod BOPs) have been in use for oil and gas wells for over fifty years. Known types of rod BOPs have incorporated a variety of different ram designs, but they have typically included a large elastomeric seal section with a small steel insert to support it. 
         [0003]    As working pressures at the wellhead increased, new rod BOP designs came into common use which had opposing rams made of steel, with each ram having a groove into which an elastomeric seal element could be installed. In such designs, the seal groove on each ram extends transversely across the inner end face of ram, axially along the side of the ram and then along a circular path around at least a portion of the circumference of the ram, thereby creating a seal between the rams and their respective bores, and also creating a seal between each set of opposing rams and the polished rod. The seals have a cross-section that is smaller than the grooves, thereby allowing them to be compressed into the grooves. This design provided enhanced sealing effectiveness at higher pressures, as compared with earlier polished rod BOP seal designs. One example of this type of ram seal for a rod BOP can be seen in Canadian Patent No. 2,716,430. 
         [0004]    In recent years, however, the process of hydraulic fracturing (commonly referred to as “fraccing”) has added a new consideration to design and performance criteria for polished rod BOPs. Wells are often situated in close proximity to each other, and during fraccing operations in subsurface formations penetrated by multiple and relatively closely-spaced wells, fluid communication between wells has become common. Due to such fluid communication, high operating pressures in one well can result in similarly high pressures undesirably developing in one or more adjacent wells, which may necessitate closure of the BOPs on those wells. 
         [0005]    However, for wells having prior art BOPs of the type described above, when the rams with narrow grooves are closed, a problem occurs: as the aperture between the polished rod and the opposing rams gets smaller, the velocity of the wellbore fluid passing through the BOP increases rapidly. The resultant high fluid velocity causes displacement or “extrusion” of the seals out of their grooves in the rams, resulting in failure of the BOP at exactly the time when well control is most required. 
         [0006]    For the foregoing reason, there is a need for improved polished rod blowout preventers that will function in conditions of concurrent high fluid pressure and high fluid velocity, while reducing or eliminating the risk of extrusion of the ram seals and resultant loss of BOP effectiveness. 
       BRIEF SUMMARY 
       [0007]    The present disclosure teaches embodiments of a ram seal for polished rod BOPs in which extrusion of the ram seal from an associated BOP ram under high-pressure, high-velocity fluid flow conditions is resisted by forming the seal element with anti-extrusion protrusions that are disposable in corresponding seal retention pockets formed in a seal-receiving groove in the ram. 
         [0008]    In a first aspect, the present disclosure teaches a seal element for use with a ram of a blowout preventer (BOP), with the seal element being made from a resilient material and comprising:
       a curved segment having first and second ends; and   a generally rectangular flat segment having two generally parallel flat surfaces extending between two generally parallel side edges; a first end contiguous with the first end of the curved segment; and a second end contiguous with the second end of the curved segment;
 
such that the seal element is configured in the general shape of a “D”, with the flat surfaces of the flat segment being parallel to the plane of the “D”, and wherein the seal element is formed with one or more flat surfaces, with one or more protrusions projecting from at least one of the one or more flat surfaces.
       
 
         [0011]    The curved segment of the seal element may be of semi-circular configuration. 
         [0012]    In certain embodiments, the flat segment of the seal element may be formed with a semi-circular recess, for receiving and sealing against the cylindrical surface of a polished rod. 
         [0013]    In certain embodiments, one or more of the one or more protrusions may be provided in the form of elongate protrusions parallel to the side edges of the flat  . segment. In such embodiments, the elongate protrusion(s) may be semi-circular in cross-section. 
         [0014]    In embodiments having protrusions projecting from both of the flat surfaces of the seal element, the position of at least one of the protrusions projecting from one flat surface may coincide with the position of a corresponding protrusion projecting from the other flat surface. 
         [0015]    In a second aspect, the present disclosure teaches BOP rams adapted to receive seal elements in accordance with the aforesaid first aspect of the present disclosure. In one embodiment of a BOP ram in accordance with the present disclosure, the BOP ram has a cylindrical outer surface and a flat end face, plus a seal groove configured to receive a seal element in accordance with the aforesaid first aspect of the disclosure, with the seal groove being characterized by:
       an end face segment extending across the flat end face of the ram;   axially-extending side segments extending along the cylindrical outer surface of the ram;   a curved segment extending circumferentially around the cylindrical outer surface of the ram between the ends of the side segments; and   one or more seal retention pockets, with each seal retention pocket being configured to receive one of the one or more protrusions projecting from the seal element.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Embodiments will now be described with reference to the accompanying Figures, in which numerical references denote like parts, and in which: 
           [0021]      FIG. 1  is an isometric view of a first prior art BOP ram seal for use with a polished rod BOP ram. 
           [0022]      FIG. 2  is an isometric view of a second prior art BOP ram seal for use with a polished rod BOP ram. 
           [0023]      FIG. 2A  is an isometric view of a prior art BOP ram adapted to receive a ram seal as in  FIG. 2 , 
           [0024]      FIG. 3  is an isometric view of a third prior art BOP ram seal similar to the ram seal in  FIG. 2  but configured for use with a BOP blind ram. 
           [0025]      FIG. 3A  is an isometric view of a prior art BOP blind ram adapted to receive a BOP blind ram seal as in  FIG. 3 . 
           [0026]      FIG. 4  is an isometric view of a first embodiment of a BOP ram seal in accordance with the present disclosure, configured for use with a polished rod BOP ram. 
           [0027]      FIG. 4A  is an isometric view of a rod BOP ram adapted to receive a rod BOP ram seal as in  FIG. 4 . 
           [0028]      FIG. 5  is an isometric view of a second embodiment of a BOP ram seal in accordance with the present disclosure, configured for use with a BOP blind ram. 
           [0029]      FIG. 5A  is an isometric view of a BOP blind ram adapted to receive a BOP blind ram seal as in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIGS. 1, 2, and 3  illustrate examples of prior art BOP ram seals. The prior art seal  10  in  FIG. 1  is substantially similar to, for example, the seal illustrated in Canadian Patent No. 2,716,430. The prior art seal  20  in  FIG. 2  and the prior art seal  30  in  FIG. 3  are configured, respectively, for use with a polished rod BOP ram  25  as shown in  FIG. 2A  and a BOP blind ram  35  as shown in  FIG. 3A . Prior art BOP rams as in  FIGS. 2A and 3A , respectively, have seal grooves  27  and  37  for receiving prior art ram seals  20  and  30  respectively. 
         [0031]    Prior art ram seals  20  and  30 , respectively, include button-like projections  22  and  32  receivable in mating pockets in seal grooves  27  and  37  in BOP rams  25  and  35 , respectively. These button-like projections are provided to counteract a tendency for seals  20  and  30  to “creep” out of seal grooves  27  and  37  in BOP rams  25  and  35  due to friction developing between the seals and their respective BOP ram bores, particularly when the seals are dry. These projections were found to be effective for that particular purpose, but not effective to prevent seal extrusion under high-pressure, high-velocity fluid flow conditions. 
         [0032]      FIG. 4  illustrates a first embodiment  100  of an “anti-extrusion” rod BOP ram seal element in accordance with the present disclosure, configured for use in conjunction with a polished rod BOP ram. Rod BOP ram seal  100  incorporates a curved (and typically semi-circular) segment  105  extending between the ends of a flat segment  110 , with flat segment  110  having opposed and generally parallel flat surfaces  112 , an inner side edge  114 , and an outer side edge  116 , with side edges  114  and  116  being generally parallel to each other. A semi-cylindrical rod recess  130  is formed into flat segment  110  along outer side edge  116  to facilitate sealing against a polished rod. 
         [0033]    In the illustrated embodiment, rod BOP ram seal  100  is formed with two “anti-extrusion” protrusions  120  projecting from each of the flat surfaces  112 , for inhibiting displacement of BOP ram seal  100  from a BOP ram in which it has been installed. Preferably, the positions of the protrusions  120  on one flat surface  112  will mirror the positions of the protrusions  120  on the other flat surface  112  as seen in  FIG. 4 . However, this is by way of preferred and non-limiting example only; alternative embodiments of rod BOP ram seal  100  may use different numbers and/or positional arrangements of protrusions  120  without departing from the scope of the present disclosure. 
         [0034]    Preferably, protrusions  120  are of elongate configuration and are oriented generally parallel to side edges  114  and  116 . However, protrusions  120  of other configurations or orientations may be used without departing from the intended scope of the present disclosure. 
         [0035]      FIG. 4A  illustrates a rod BOP ram  150  configured to receive a rod BOP ram seal  100  as illustrated in  FIG. 4 . Rod BOP ram  150  is generally cylindrical, with a cylindrical outer surface  154  and a flat end face  152  formed with a semi-cylindrical recess  180  for receiving a polished rod. Rod BOP ram  150  is formed with a continuous seal groove  160  comprising an end face groove segment  162  (extending across flat end face  152  and recess  180  therein), side groove segments  164  (extending in an axial direction along cylindrical outer surface  154 ), and a curved groove segment  166  (extending circumferentially around cylindrical outer surface  154  between the ends of side groove segments  164 ). When rod BOP ram seal  100  is installed on rod BOP ram  150 , flat segment  110  of ram seal  100  will be disposed within end face groove segment  162  of seal groove  160  in rod BOP ram  150 , and curved segment  105  will be disposed within side groove segments  164  and curved groove segment  166  of seal groove  160 . 
         [0036]    End face segment  162  of seal groove  160  has parallel flat groove surfaces  163  spaced to accommodate flat segment  110  of rod BOP ram seal  100 . Appropriately configured seal retention pockets  170  are formed into flat groove surfaces  163  to receive protrusions  120  on ram seal  100 . 
         [0037]      FIG. 5  illustrates a second embodiment  200  of an “anti-extrusion” BOP ram seal element in accordance with the present disclosure, configured for use in conjunction with a BOP blind ram. BOP blind ram seal  200  incorporates a curved segment  205  extending between the ends of a flat segment  210 , with flat segment  210  having opposed and generally parallel flat surfaces  212 , an inner side edge  214 , and an outer side edge  216 , with side edges  214  and  216  being generally parallel to each other. BOP blind ram seal  200  is preferably formed with two “anti-extrusion” protrusions  220  projecting from each of flat surfaces  212 , as in the embodiment illustrated in  FIG. 5 . 
         [0038]    BOP blind ram seal  200  is thus substantially similar to rod BOP ram seal  100  except that it does not have the rod recess  130  of rod BOP ram seal  100 . 
         [0039]      FIG. 5A  illustrates a BOP blind ram  250  configured to receive a BOP blind ram seal  200  as illustrated in  FIG. 5 . BOP blind ram  250  is generally cylindrical, with a cylindrical outer surface  254  and a flat end face  252 , and is formed with a continuous seal groove  260  comprising an end face groove segment  262 , side groove segments  264 , and a curved groove segment  266  extending circumferentially around cylindrical outer surface  254  between the ends of side groove segments  264 . When BOP blind ram seal  200  is installed on BOP blind ram  250 , flat segment  210  of ram seal  200  will be disposed within end face groove segment  262  of seal groove  260  in BOP blind ram  250 , and curved segment  205  will be disposed within side groove segments  264  and curved groove segment  266  of seal groove  260 . 
         [0040]    End face segment  262  of seal groove  260  has parallel flat groove surfaces  263  spaced to accommodate flat segment  210  of BOP blind ram seal  200 , with seal retention pockets  270  formed into flat groove surfaces  263  to receive protrusions  220  on ram seal  200 . 
         [0041]    BOP blind ram  250  is thus substantially similar to rod BOP ram  150  except that its end face  252  does not have the rod recess  180  of rod BOP ram  150 . 
         [0042]    It will be readily appreciated by those skilled in the art that various modifications to embodiments in accordance with the present disclosure may be devised without departing from the present teachings, including modifications which may use structures or materials later conceived or developed. It is to be especially understood that the scope of the claims appended hereto should not be limited by any particular embodiments described and illustrated herein, but should be given the broadest interpretation consistent with the disclosure as a whole. It is also to be understood that the substitution of a variant of a claimed element or feature, without any substantial resultant change in functionality, will not constitute a departure from the scope of the disclosure or claims. 
         [0043]    In this patent document, any form of the word “comprise” is intended to be understood in a non-limiting sense, meaning that any item following such word is included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one such element is present, unless the context clearly requires that there be one and only one such element. Any use of any form of any term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements in question, but may also extend to indirect interaction between the elements such as through secondary or intermediary structure, without departing from the scope of the disclosure. 
         [0044]    Relational or conformational terms such as but not limited to “circular”, “cylindrical”, “flat”, and “parallel” are not intended to denote or require absolute mathematical or geometrical precision. Accordingly, such terms are to be understood as denoting or requiring substantial precision only (e.g., “substantially circular” or “generally parallel”) unless the context clearly requires otherwise. 
         [0045]    Any use of any form of the term “typical” is to be interpreted in the sense of being representative of common usage or practice, and is not to be interpreted as implying essentiality or invariability.