Abstract:
A blowout preventer having a body, a main bore in the body, and rams that project into the main bore. The rams can be shear rams for shearing a tubular in the main bore, pipe rains for sealing around a tubular in the main bore, or sealing rams that seal across the main bore. The rams are in cavities formed in the body, the cavities are formed such that more than two rams can be disposed at the same elevation in the body thereby reducing the overall height of the blowout preventer stack.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/881,737, filed Sep. 24, 2013, the full disclosure of which is hereby incorporated by reference herein for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present disclosure relates in general to production of hydrocarbon from a subterranean wellbore, and in particular to a blowout preventer (BOP) having adjacent cavities. 
         [0004]    2. Description of Prior Art 
         [0005]    Drilling a wellbore for production of oil and/or gas typically involves inserting a drilling string having a drill bit on its lower end through a wellhead assembly mounted over hydrocarbon bearing strata. Blowout preventers are often mounted onto the wellhead assembly for shearing or sealing around the drill string, and sealing in the wellbore. Offshore drilling rigs normally employ a riser to connect the subsea wellhead with the drilling rig, where the blowout preventer is located at a lower end of the riser. Generally, blowout preventers are assembled into a stack and include shear rams for shearing the drill string or tubular, and pipe rams sized to close and seal around pipe strings of certain diameters. 
         [0006]    Typically each elevational section in the stack includes a cavity in which rams are disposed. Each cavity will contain a pair of either shear rams or pipe rams, where the rams are on opposite sides of a main bore that extends through the stack. The rams face one another, so that when activated are urged towards one another and into the main bore, either to shear or seal against the tubular in the main bore. Thus blowout preventers having a number of elevational sections may be large and occupy a large amount of space, and can thus be heavy thereby adding to the difficulties of transportation and installation. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed herein are examples of a blowout preventer. In one example, a blowout preventer for use with a wellhead assembly includes a body having an axis, a main bore in the body that is substantially parallel with the axis, at least three cavities in the body at substantially the same axial location in the body and that intersect the main bore, and a ram in each of the cavities. One of the rams can be a pipe ram and one of the rams can be a shear ram. Each ram may optionally include a block having a forward side facing the main bore, a rearward side distal from the forward side, lateral sides extending between the forward and rearward sides and that are in a plane that is generally parallel with the axis. The ram block can further have an upper side that extends between upper terminal ends of the forward and rearward sides. A seal can be provided on the ram block that extends along the upper side and the forward side. In an example, the axial location is a first axial location, wherein the cavities make up a first set of cavities, and wherein a second set of cavities are formed in the body at a second axial location that is spaced axially away from the first axial location. Rams may be further included that are in the second set of cavities. Four cavities can optionally be provided in the body at the same axial location, and wherein rams in two of the cavities are shear rams and rams in two of the cavities are pipe rams. An upper connection can optionally be included that selectively couples to a riser; a lower connection can also be included that selectively couples to a wellhead housing. 
         [0008]    Another example of a blowout preventer for use with a wellhead assembly includes a body having an axis and a main bore aligned with the axis, cavities in the body that extend radially outward from the main bore and along paths that range up to about 90° from one another, and a ram assembly in each of the cavities. The cavities can be at about the same axial location along the axis. Each ram assembly can be made up of a block and a forward portion that selectively extends into the main bore. Each ram assembly can further include a forward side on which the forward portion is attached, a rearward side opposite the forward side, and lateral sides that extend between the forward and rearward sides, wherein the lateral sides are substantially fiat. An actuator can optionally be included for urging each rain assembly from the cavity towards the main bore. 
         [0009]    An example of blowout preventer stack, which is selectively coupled with a wellhead assembly, is made up of an axis in the stack, a plurality of blowout preventers stacked on one another and each having a body, a main bore projecting axially through each of the bodies and that is substantially parallel with the axis, cavities in each body at substantially the same axial location in the body and that intersect the main bore and that extend along paths that range up to about 90° from one another, and rams in the cavities. Each ram can include a block having a forward side facing the main bore, a rearward side distal from the forward side, lateral sides extending between the forward and rearward sides and that are in a plane that is generally parallel with the axis. Cavities in each body can be about the same axial location along the axis. In one example four cavities are provided in each body at the same axial location, and wherein rams in two of the cavities comprise shear rams and rams in two of the cavities comprise pipe rams. An upper connection can selectively couple to a riser and a lower connection can selectively couple to a wellhead housing. In one example, each ram includes a block and a forward portion that selectively extends into the main bore. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0011]      FIG. 1  is a side sectional view of an example of a blowout preventer on a wellhead assembly and in accordance with an embodiment of the present invention. 
           [0012]      FIG. 2  is an axial sectional view of the blowout preventer of  FIG. 1  and taken along lines  2 - 2  and in accordance with the present invention. 
           [0013]      FIG. 3  is a partial sectional view of the blowout preventer of  FIG. 1  and taken along lines  2 - 2  with a portion of the chamber housing removed, and in accordance with the present invention. 
           [0014]      FIG. 4  is a perspective view of an example of a ram assembly for use with the blowout preventer of  FIG. 1  and in accordance with the present invention. 
       
    
    
       [0015]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0016]    The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. 
         [0017]    It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
         [0018]      FIG. 1  shows a partial side sectional view of one example of a blowout preventer  10  mounted on top of a wellhead assembly  11 , where a housing  12  of the wellhead assembly  11  is anchored on the sea floor  14 . A clamp connection  16  couples the blowout preventer  10  onto housing. Housing  12  and blowout preventer  10  are mounted over a wellbore  18 , where wellbore  18  is shown being formed by a drill string  20  that extends axially through blowout preventer  10 . Additionally, a length of conductor pipe  22  projects downward into wellbore  18  and on which the wellhead housing  12  is connected. The example of the blowout preventer  10  of  FIG. 1  is for use subsea, and as such a riser  24  attaches to an upper end of blowout preventer  10  via flanged connection  26 . Further included with blowout preventer  10  are actuators  28   1 ,  28   2 ,  28   3  and actuators  30   1 ,  30   2 ,  30   3 . In the illustrated example, actuators  28   1-3  are set at a distance axially lower than actuators  30   1-3 . 
         [0019]    An axial sectional view of the blowout preventer  10  is provided in  FIG. 2  and taken along lines  2 - 2  of  FIG. 1 . In this example, four actuator assemblies  30   1 ,  30   2 ,  30   3 ,  30   4  are shown mounted on a body  32  of blowout preventer  10 . Adjacent actuators  30   1 ,  30   2 ,  30   3 ,  30   4  are set at an angle from one another that is about 90°. However, other angles are envisioned that can be less than or greater than 90°. Example angles are 30°, 45°, 60°, 120° and any value between these specific values. To accommodate the placement of the actuators  30   1-4 , connections  34  for choke and kill lines (not shown.) are provided along corner sections and in between adjacent actuators  30   1-4 . A main bore  36  is shown extending axially through the blowout preventer  10  and intersecting the chamber housing  38  that covers the blowout preventer  10 . 
         [0020]    Referring now to  FIG. 3 , axial section view of blowout preventer  10  is shown taken along lines  3 - 3  of  FIG. 1 . In this example, the upper portion of chamber housing  38  has been removed thereby making visible ram chamber  40  in which rams  42  are housed. Also visible in this example is ram chamber  43  in Which rams  44  are housed. More specifically, chamber  40  projects radially from main bore  36  and through body and terminating adjacent actuators  30   2 ,  30   4 . In the illustrated example, rams  42  are shear rams for shearing a tubular, such as drill string  20  ( FIG. 1 ) that may be projecting through blowout preventer  10 . Optionally, rams  44  may be pipe rams that when projected radially inward and adjacent main bore  36  may seal around a. tubular that is coaxially disposed within main bore  36 . In the example of  FIG. 3 , actuators  30   1 ,  30   3  are associated with the pipe rams  44 . Thus, operating actuators  30   2 ,  30   4  can project the shear rams  42  radially inward and into the main bore  36 . Similarly, operating actuators  30   1 ,  30   3  can actuate pipe rams  44  so that pipe rams  44  project radially inward to main bore  36 . 
         [0021]    An advantage of the present system, as realized in  FIG. 1 , is that more than 2 ram assemblies can be set in the blowout preventer  10  at a single axial location, or elevation, within blowout preventer  10 . Thus, the overall length of the blowout preventer  10  can be less than that of other known blowout preventers. The shorter stack of the blowout preventer  10  therefore results in one that is easier o transport, and install due to its dimensions, and it also has a lower weight thereby increasing safety of transportation in an installation. 
         [0022]    An example of a shear ram  42  is provided in a perspective view in  FIG. 4 . In this example, shear ram  42  includes a substantially solid ram block, which resembles a rectangular member having generally planar surfaces. A seal  48  is shown imbedded within the rain block  46  and has surfaces that extend upward from an upper surface  50  of ram block  46 . To accommodate the multiple ram assemblies at a single elevation, lateral sides  52  of the ram  42  are flat and have a generally planar outer surface. A shear blade  54  is shown mounted on a forward. side  56  of ram block  46 . On a side opposite forward side  56  is rearward side  58 , which can receive an urging force to urge the shear ram  42  into main bore  36  ( FIG. 3 ). Optionally, the actuators  28   1-4 ,  30   1-4  can be operated hydraulically, such as by the hydraulic supply  60  ( FIG. 1 ) shown connected on an outer surface of actuators  28   1 ,  28   3 . In this example, a piston  62  (shown in dashed outline) couples via a rod to rearward side  58  of ram  42  so that by urging hydraulic fluid under pressure into actuators, ram  42  can be selectively urged radially inward into bore  36 . 
         [0023]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.