Abstract:
A valve assembly for use in regulating a fracturing fluid that includes an actuating stem for actuating a gate, a balancing stem, and a backseat on the stem that defines a backseat seal when urged against a profile in the valve assembly. The backseat seal is energized by applying a force to an end of the balancing stem. An end of the balancing stem is enclosed within a plenum, so that the force on an end of the balancing stem can be applied by pressurizing the plenum. The assembly can be on an opposite side of the valve body/bonnet to create a backseat seal on a balancing stem/bonnet to allow changing the stem packing on the balance stem side while maintaining pressure integrity.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention relates generally to a valve assembly. More specifically, the invention relates to a method and device for backseating a gate valve assembly having a balanced stem by applying a force to a balanced stem. 
         [0003]    2. Description of Prior Art 
         [0004]    Fracturing subterranean formations adjacent to a well typically involves connecting an adapter to the upper end of a wellhead member and pumping high pressure liquid into the well. Isolating the pressure at designated locations in the well creates fractures in the formation. Beads or other proppant material is generally included in the fracturing fluid to enter the cracks to keep them open after the high pressure is removed. This type of operation is particularly useful for earth formations that have low permeability but adequate porosity and contain hydrocarbons, as the hydrocarbons can flow more easily through the fractures created in the earth formation. 
         [0005]    The pressure employed during fracturing may be many times the natural earth formation pressure that ordinarily would exist. For example during fracturing, pressure in the wellhead can be 8,000 to 9,000 psi; whereas wellhead pressure might otherwise be at a few hundred to a few thousand psi. Because of this, valves employed for regulating the flow of fracturing fluid to a wellhead may require higher forces for their opening and closing. Sometimes, these high pressure valves may utilize balancing stems to compensate for pressure differentials that can impede valve operation. 
         [0006]    Gate valves sometimes include a backseat feature for sealing between a valve stem and valve bonnet so that packing in the valve assembly can be changed. Backseats are typically made up of complimentary profiled surfaces in the stem and valve bonnet that when urged together isolate pressure communication along the stem. Backseats are generally energized by the pressure in the flow through the valve exerting a force on a bottom surface of the valve stem and urging together the profiled surfaces in the stem and bonnet. 
       SUMMARY OF THE INVENTION 
       [0007]    Provided herein is an example of a gate valve assembly that includes a body and a passage through the body. A source of fracturing fluid used for fracturing a subterranean formation communicates with the passage. Also included is a gate that can slide within the body and having a bore that selectively registers with the passage. An actuating stem is coupled to an end of the gate and projects into a channel in the body. A backseat seal is on an outer surface of the actuating stem that can selectively engage a profile in the channel. A balancing stem couples to an end of the gate distal from the actuating stem and a plenum is included that encloses an end of the balancing stem opposite from the gate valve, so that when the plenum is pressurized, a force is applied to the end of the balancing stem distal from the gate valve to urge the backseat seal into sealing engagement with the profile in the channel. A piston may optionally be included that is on the end of the balancing stem distal from the gate valve; where the piston has an outer periphery in sealing contact with an inner surface of the plenum. Optionally included is a pressure source in pressure communication with the plenum. In an example embodiment, the backseat seal projects radially outward from an outer surface of the actuating stem and has a wedge shaped cross section. The profile can have a shape that is complementary to the backseat seal and is defined where an inner diameter of the channel transitions radially inward. Optionally included is an upper bonnet having a chamber in which the end of the actuating stem coupled to the gate is disposed, and a lower bonnet having a chamber in which the end of the balancing stem coupled to the gate is disposed, wherein the chambers in the upper and lower bonnets are in pressure communication with the passage. An axial actuator may be included that is coupled to an end of the actuating stem distal from the gate for axially moving the stem. 
         [0008]    Also provided herein is a method of regulating flow to a wellhead assembly. In one example embodiment the method includes providing a gate valve assembly that has a body, a gate moveable in the body, an actuating stem coupled to an end of the gate, a backseat seal on the actuating stem, and a balancing stem coupled to an end of the gate distal from the actuating stem. Fluid is communicated to the gate valve assembly so that pressure in the fluid is applied to ends of the actuating stem and balancing stem coupled to the gate and generates substantially equal forces that are applied to the gate in opposite directions. A force is applied to urge the balancing stem against the gate in a direction that displaces the actuating stem so that the backseat seal engages a profile in the body to form a seal around a portion of the actuating stem. Optionally, the step of forcing the balancing stem includes pressurizing an area around an end of the balancing stem distal from the gate. In one example, the area is pressurized by providing a plenum around the end of the balancing stem distal from the gate and flowing pressurized fluid to the plenum. Alternatively, packing is provided in an annulus between the actuating stem and the body that is isolated from pressure of the fluid by the backseat seal. In another example, the applied force is removed. 
         [0009]    An example of a wellhead assembly mounted over a wellbore is described herein that includes a production tree, a valve block on the production tree in fluid communication with a source of fracturing fluid, and a valve assembly on the valve block. The valve assembly is made up of a valve body having a passage in fluid communication with the fracturing fluid, a gate in the body, an actuating stem having a lower end that is mounted on an upper end of the gate and that is in pressure communication with the passage, a backseat seal circumscribing a portion of the actuating stem, a balancing stem having an upper end mounted on a lower end of the gate and that is in pressure communication with the passage, and a means for selectively forcing the balancing stem upward and against the gate and to seat the backseat seal against a profile in the body to form a seal. Optionally, the means for selectively forcing the balancing stem upward includes a plenum mounted on a lower end of the valve body that is in communication with a source of pressurized fluid. Alternatively, the plenum has an inner diameter sized to be in selective sealing contact with an outer surface of the balancing stem. In one example, a piston on a lower end of the balancing stem is included. In an example embodiment, included is a hand wheel on the valve assembly for moving the gate. 
     
    
     
       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 partial sectional view of an example embodiment of a wellhead assembly having a frac valve assembly in accordance with the present invention. 
           [0012]      FIG. 2  is a side sectional view of an example of a frac valve assembly of  FIG. 1  and having a backseating feature in accordance with the present disclosure. 
           [0013]      FIG. 3  is a side partial sectional view of an embodiment of a portion of the frac valve assembly of  FIG. 2  in accordance with the present invention. 
           [0014]      FIGS. 4A and 4B  are side sectional views of a backseat seal being formed along a stem of the frac valve assembly of  FIG. 2  in accordance with the present invention. 
           [0015]      FIGS. 5 and 6  are a side partial sectional views of alternate embodiments of a portion of the frac valve assembly of  FIG. 2  in accordance with the present invention. 
       
    
    
       [0016]    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 
       [0017]    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. 
         [0018]    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. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
         [0019]    Shown in  FIG. 1  is an example of a wellhead assembly  20  illustrated in a side partial sectional view where the wellhead assembly  20  includes a production tree  22  mounted over a wellbore  24 . The wellhead assembly  20  includes a wellhead housing  26  shown depending downward from the production tree  22  into the wellbore  24  and in which a string of casing  28  is coaxially disposed therein. The production tree  22  includes an axial main bore  30  shown intersected by a production line  32  that extends laterally through the production tree  22 . A wing valve  34  is in the production line  32  and provided for controlling flow through the production line  32 , and a swab valve  36  is shown set in an upper end of the main bore  30 . An auxiliary line  38  may optionally be included onto the production tree  22 . 
         [0020]    An example embodiment of a valve block  40  is shown set on an upper end of the production tree  22 . A bore  42  axially traverses the valve block  40  and has a lower end in fluid communication with the upper end of the main bore  30 . Optionally, an access valve  44  is provided in an upper end of the bore  42 . Also optionally, is an auxiliary line  46  that intersects the bore  42  and shown having a portion projecting outward past an edge of the body of the valve block  40 . On a side opposite the auxiliary line  46  is an inlet line  48  that also extends laterally through the valve block  40  and intersects the bore  42 . A valve assembly  50  is shown set in the inlet line  48 , and in the example of  FIG. 1 , can be used for regulating fluids, such as a fracturing fluid, that are designated for entry into the valve block  40 . A flow line  52  connects to an upstream side of the valve assembly  50 , where the flow line  52  delivers fluid from a fluid supply  54  to the valve assembly  50 . As indicated above, fracturing fluid may be delivered through the line  52 , and as such, one example of the fluid supply  54  can be a series of high pressure pumps for pressurizing fracturing fluid. 
         [0021]    In  FIG. 2  is an example embodiment of the valve assembly  50  and is shown in a side sectional view. The valve assembly  50  of  FIG. 2  includes a valve body  56  that is shown intersected by a passage  58  that extends laterally through the width of the body  56 . A gate  60  is shown axially disposed within the body  56  and having a portion set within the passage  58 . The gate  60  includes a bore  62  laterally oriented and shown registered with the passage  58 . By axially traversing the gate  60  within the body  56 , flow through the passage  58  may be regulated through the valve assembly  50 . An actuating stem  64  is shown coupled onto an upper end of the gate  60  and is used to transmit a force for vertical movement of the gate  60  within the body  56 . 
         [0022]    A threaded rod  66  is shown set on an upper end of the actuating stem  64  and is circumscribed by a sleeve  68 . The sleeve  68  is mounted into a hand wheel  70  and rotatable by rotation of the hand wheel  70 . Threads are provided on an inner surface of the sleeve  68  that engage threads on an outer surface of the threaded rod  66 . The sleeve  68  is shown mounted within a housing  72  and is rotatable with respect to the housing  72 . The housing  72  is a generally annular member coupled on an upper end of the valve body  56 . Although rotatable, the sleeve  68  is not vertically moveable with respect to the housing  72 . A bearing assembly  74  shown set in an annular space between the sleeve  68  and stem housing  72  provides a reduction of friction, thereby allowing ease of movement of the sleeve  68  to reduce frictional forces associated with actuation of the gate  60 . 
         [0023]    As is known, pressure within the passage  58  can migrate past the face of the gate  60  and onto a lower-most surface of the actuating stem  64 . This results in an upward force on the actuating stem  64  that resists downward movement of the gate  60 . To compensate for the upward force, a balancing stem  76  is shown coupled on a lower end of the gate  60 . The upper end of the balancing stem  76 , which is shown having a substantially same cross-sectional area as the actuating stem  64 , is also in pressure communication with the passage  58 . Thus, a downward force is exerted on the upper end of the balancing stem  76  that transfers to the gate  60  and cancels the upward force on the actuating stem  64 . The valve assembly  50  includes an upper bonnet  78  that is shown mounted on an upper end of the valve body  56 . An opening within the bonnet  78  defines a chamber  79  in which is an upper end of the gate  60 . The chamber  79  has a pressure substantially the same as that of the passage  58 . As will be described in more detail below, backseating functions can be compromised by introduction of a balancing stem. 
         [0024]    Still referring to  FIG. 2 , a balancing stem plenum  80  is shown mounted onto a neck portion  81  of a lower bonnet  82 . The lower bonnet  82 , which is substantially the same as the upper bonnet  78 , mounts on a lower end of the valve body  56 . In the example of  FIG. 2 , the plenum  80  is a tubular-shaped member having an upper end configured for attachment onto the neck  81 . The plenum  80  is open on its upper end and substantially closed on its lower end. Optionally, provided with the valve assembly  50  is a valve stand  84  that is made up of a disc-like base  86  that is set in a plane transverse to an axis of the balancing stem  76 . Wedge-shaped legs  88  have lower ends that mount on an upper side of the base  86  and are arranged to have edges parallel to an axis of the balancing stem  76 . The edges of the legs  88  are set apart so that a tubular-like sleeve  90  can be inserted in between the legs  88 . A flange on an upper end of the sleeve  90  projects radially outward, thereby forming a lip for supporting the sleeve  90  within the legs  88 . In the example of  FIG. 2 , the plenum  80  is shown inserted within the sleeve  90 . 
         [0025]    Referring now to  FIG. 3 , a side partial sectional view of a detail of the plenum  80  is shown. In the example of  FIG. 3 , a gland packing  92  is provided in an annulus between the neck  81  and balancing stem  76 . The packing  92  is retained in place by a packing collar  93  that has an outer diameter close to an outer diameter of the neck  81 . Radially inward from its outer periphery, the collar  93  projects axially upward and in a direction substantially normal from its outer portion. The axial projecting section of the collar  93  is shown contacting a lower end of the packing  92 . Still referring to  FIG. 3 , the plenum  80  has an open upper end and side walls that project radially outward proximate to its upper end, thereby defining a radial ledge  94  that is shown set up against a lower surface of the packing collar  93 . Upward and past the radial ledge  94 , side walls of the plenum  80  extend axially upward and circumscribe an outer surface of the neck  81 . Threads  96  are formed on an inner surface of the upper end of the plenum  80  and outer surface of the neck  81  that allow for coupling of the plenum  80  onto the bonnet  82 . 
         [0026]    Further illustrated in  FIG. 3  is that the open inner space of the plenum can be pressurized via connection to a line  98  for delivering pressurized fluid from a pressure source  100  into the plenum  80 . A valve  102  is optionally shown for regulating flow of fluid through the line  98 . As indicated by the arrows directed against a lower end of the balancing stem  76 , the presence of pressurized fluid within the plenum  81  exerts an upward force on the balancing stem  76  to urge it against the gate  60 . 
         [0027]      FIG. 4A  illustrates in a side sectional view an example of how the upward force applied to the balancing stem  76  can counteract its compensating force to overcome backseating issues. More specifically, a backseat  104  is shown set on an outer periphery of the actuating stem  64  and in a location proximate where the actuating stem  64  projects through a bore  106  formed through the bonnet  78 . In the example of  FIG. 4A , the backseat  104  has a triangular-shaped cross-section and has an increasing radius with distance towards the gate  60 . In one example, the backseat  104  is referred to as a backseat seal. Also shown in  FIG. 4A  is a profile  108  that is formed in the bonnet  78  and at an opening of the bore  106 .  FIG. 4B  illustrates an example where a backseat seal is formed, thereby isolating pressure above the bonnet  78  from the chamber  79 . More specifically, the actuating stem  64  has moved upward in the direction of the arrow so that the backseat  104  has sealingly engaged the profile  108 , thereby forming a pressure barrier axially along the stem  64 . As such, by forming a backseating procedure, any packing  109  ( FIG. 2 ) set within the annulus between the actuating stem  64  and bonnet  78 , above the backseat  104 , may be accessed and replaced without exposing personnel to the pressures within the passage  58 . 
         [0028]      FIG. 5  illustrates an alternate embodiment of a plenum  80 A, wherein the plenum has an internal diameter (ID) substantially the same as an outer diameter of the balancing stem  76 . As such, sealing contact may take place between the balancing stem  76  and inner diameter of the annulus  80 A. Thus, when pressurizing fluid from the source  100  and through the line  98  enters within the plenum  80 A, a smaller amount of fluid may be required in order to move the balancing stem  76  upward. Referring now to  FIG. 6 , yet another example embodiment of the plenum  80  is illustrated, wherein a piston  110  is shown set within the plenum  80  and having an upward end in contact with a lower end of the balancing stem  76 . Optional O-ring seals  112  may be provided on an outer periphery of the piston  110  to provide a seal between the piston  110  and inner surfaces of the plenum  80 . 
         [0029]    In one example of operation, fluid from the fluid supply  54  is being delivered to the wellhead assembly  20 . Over a period of time, the packing  109  may require replacement and to safely provide access to within the stem housing  72 , the actuating stem  64  is urged upward so that the backseat  104  is in sealing engagement with the profile  108  ( FIG. 4B ). During this time, the packing  109  can be accessed and pressure within the passage  58  is isolated from above the backseat  104 , although pressure in the chamber  79  may remain substantially the same as that of the passage  58 . After successfully replacing the packing  109  the force provided on the lower end of the balancing stem  76  can be removed, thereby disengaging the backseat  104  from the profile  108 . 
         [0030]    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.