Abstract:
A lock open device for use with a valve in a hydraulic fracturing system, which maintains the valve in an open position. The lock open device includes a plate with beveled edges and spring loaded ball bearings strategically disposed to contact the edges and interfere with axial movement of the plate. The plate couples to a gate member in the valve, so that the interference between the plate and the ball bearings maintains the valve in a designated open or closed position. The angle of the bevel regulates how much force is required to urge the plate past the ball bearings to thereby open/close the valve.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention relates generally to production of oil and gas. More specifically, the invention relates to a locking assembly for use with a valve of a hydraulic fracing system. 
         [0003]    2. Description of Prior Art 
         [0004]    Hydrocarbon producing wellbores are sometimes stimulated to increase the production of hydrocarbons. Hydraulic fracturing, or fracing, is one example of stimulation, which involves pressurizing all or a portion of the wellbore to improve communication between the surrounding formation and the wellbore. Generally, a fracing fluid is pressurized at surface by a pump, which then enters a line having an end downhole. As the fluid exits the line it builds pressure in the wellbore that in turn produces, or further propagates, fractures in the formation. Subterranean fractures occur when the pressure exerted by the pumped fluid exceeds the fracture gradient of the formation strata. Typically, the fluid used for fracing includes one or more of water, acids, bauxite, carbon dioxide, nitrogen, and additives. 
         [0005]    The high pressures formed during fracing, along with the impulses that occur when fractures are formed, create vibrations in the piping system that carries the fracing fluid. Vibrations of sufficient magnitude, and/or duration, can cause valves in the piping system to either inadvertently open or close. 
       SUMMARY OF THE INVENTION 
       [0006]    An example of a hydraulic fracturing system is described herein that includes a pump, a discharge line attached to the pump that can be put in a wellbore. Also included is a valve assembly in the line; the valve assembly includes a body, a passage, a gate, and a bore in the gate that selectively registers with the passage. The system also includes a valve lock assembly that is made up of a cam disk, a balance stem connecting the cam disk and the gate and a retention element that is urged into a path of the cam disk by a resilient member. When a force is applied to the gate to urge the cam disk against the retention element that is less than a designated amount, the retention element is retained in the path of the cam disk by the resilient member. Optionally, when a force is applied to the gate to urge the cam disk against the retention element that exceeds the designated amount, a force is exerted by the cam disk onto the retention element to overcome a force applied by the resilient member and the retention element is moved out of the path of the cam disk. In one example, the cam disk includes a beveled outer edge that contacts the retention element. In an example embodiment, a thrust force is defined by the force applied to the gate to urge the cam disk against the retention element, and wherein upper and lower portions of the outer edge are beveled at angles with respect to an axis of the cam disk so that the thrust force necessary to urge the cam disk past the retention element is greater in one axial direction than in an opposite axial direction. The retention element can be made up of a ball bearing and the resilient member may be made of a spring. In one example, the system includes a plurality of ball bearings and springs and a housing that circumscribes the balance stem having bores radially formed through a sidewall of the housing for retaining the ball bearings and springs. A valve actuator may be coupled to the gate. 
         [0007]    Also disclosed herein is a balancing system for use with a hydraulic fracturing valve. In one example the balancing system includes a generally planar cam member in selective coupling engagement with a valve gate. The cam member is subject to a thrust force from the valve gate in response to a force applied to the valve gate. A latching assembly is included that is made up of a latching element that is maintained in interfering contact with the cam member by a resilient member. The interfering contact takes place when the thrust force produces a resultant force against the latching element that is less than a designated amount. In one example, the latching element is urged out of interfering contact and out of a path of the cam member when the thrust force produces a resultant force against the latching element that exceeds the designated amount. The cam member can have an outer periphery with an upper section profiled at an angle with respect to an upper surface of the cam member and a lower section profiled at an angle with respect to a lower surface of the cam member. In an example embodiment, the upper and lower surfaces are substantially parallel, and wherein the upper and lower sections are profiled at different angles, so that an amount of the thrust force that produces a resultant force against the latching element that exceeds the designated amount is greater when the cam member is axially urged in one direction than when the cam member is axially urged in an opposite direction. The gate may be subjected to forces from vibrations that produce resultant forces that are less than the designated amount. 
         [0008]    A valve assembly is provided herein that can be used in a hydraulic fracing system. In one example embodiment the valve assembly includes a valve body having a passage, a gate having a bore that is in selective registration with the passage, an actuator coupled with the gate, and a means for retaining the gate in a designated position within the valve body. The gate can be unlocked from the designated position by applying a force that exceeds a force used to lock the gate. Optionally, the means for retaining the gate are a cam disk coupled to the gate and a latch that retains the cam disk in place when the lock force is applied to the gate and releases the gate when an unlock force is applied to the gate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    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: 
           [0010]      FIG. 1  is a side partial sectional view of an example embodiment of a hydraulic fracturing system in accordance with the present invention. 
           [0011]      FIG. 2  is a side sectional view of a detailed portion of a balance stem of the embodiment of  FIG. 1  shown in a locking configuration. 
           [0012]      FIG. 3  is a side sectional view of a detailed portion of a balance stem of the embodiment of  FIG. 1  shown in an unlocking configuration. 
       
    
    
       [0013]    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 
       [0014]    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. 
         [0015]    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. 
         [0016]      FIG. 1  is a partial side sectional view of an example embodiment of a hydraulic fracturing system  10  used in creating fractures  12  within a subterranean formation  14  by pressurizing a space within the wellbore  16 . The system  10  includes a pump  18  that pressurizes a fracturing fluid and a line  20  connected to a discharge of the pump  18 . The line  20  is shown fed through an optional wellhead assembly  22  and has an exit disposed in the wellbore  16 . Optionally, a packer  24  may be provided in an annular space between the line  20  and inner walls of the wellbore  16  to isolate a zone of the wellbore  16  for the step of fracturing. In the example of  FIG. 1 , the wellbore  16  is lined with a string of casing  26  that is cemented in place in the formation with cement  28 . 
         [0017]    A valve assembly  30  is shown in the line  20  downstream of the pump  18  and upstream of the wellhead assembly  22 . The valve assembly  30  of  FIG. 1  includes a valve body  32  and a passage  34  that laterally extends through the body  32  and is in fluid communication with the line  20 . A gate  36  is shown axially inserted within the valve body  32 , wherein the gate  36  includes a bore  38  that selectively registers with the passage  34  for regulating the flow of fluid through the valve assembly  30 . A valve actuator  40  is shown coupled with the gate  36  via a valve stem  42 . Due to the high pressures and flow rates associated with the hydraulic fracturing process, substantial vibrations may be imparted onto the valve gate  36  that may move the gate  36  out of a designated position within the valve body  32 . To retain the valve gate  36  in the desired position, a valve lock assembly  44  is shown coupled to an end of the gate  36  by a balance stem  46 . 
         [0018]    Referring now to  FIG. 2 , one example embodiment of the valve lock assembly  44  is shown in detail in a side sectional view. In this example, the valve lock assembly  44  is shown further including a generally planar-shaped cam disk  48  that mounts on a lower terminal end of the balance stem  46 . In the example of  FIG. 2 , a threaded fastener  50  bolts the cam disk  48  in place on the stem  46 . Further illustrated in  FIG. 2  is a housing  52 , that in one example is a substantially annular member having a cylindrical outer circumference. The cam disk  48  is shown having upper and lower surfaces  54 ,  56  that in the example of  FIG. 2  are largely parallel with one another and transverse to an axis A X  of the balance stem  46 . The cam disk  48  also has an outer periphery  58  profiled to have an upper portion  60 ; as shown the upper portion  60  is coincident with a plane P U  that intersects the axis A X  above the cam disk  48  at an oblique angle. Similarly, a lower portion  62  is formed on the outer periphery  58  below the upper portion  60  that lies in a plane P L  that intersects the axis A X  at an oblique angle but below the cam disk  48 . In the example of  FIG. 2 , the angle at which plane P U  intersects the axis A X  is different from the angle that P L  intersects the axis A X . 
         [0019]    Further shown in  FIG. 2  are retention assemblies  64  that are provided within bores  66  formed through a side wall of the housing  52 . The bores  66  are shown having a radially inwardly directed taper  68  proximate to an inner wall of the housing  52 . Ball bearings  70  are inserted within the bores  66  and have a diameter less than the diameter of the bore  66  but greater than that of the taper  68  so that a portion of the ball bearing  70  projects through the bore  66  to inside of the housing  52 , but prevented from fully entering into the housing  52 . A spring  72  is biases the ball bearing  70  against the taper  68  and is held in place against by bolts  74  that threadingly insert into the bores  66  from the outer surface of the housing  52 . The inward biasing of the springs  72  positions a portion of the ball bearings  70  into interfering contact with an axial path of the cam disk  48 . More specifically, in the example of  FIG. 2 , a force diagram is shown that is based on an angle α of the lower portion  62 . In this example, a force Fα in the force diagram depicts an amount of force required to urge the ball bearings  70  radially outward against the springs  72  so that the cam disk  48  may move axially downward past its current location. 
         [0020]    Similarly, in  FIG. 3 , cam disk  48  is illustrated below the ball bearings  70  so that its upper portion  60  is engaging the bearings  70  and a force diagram is provided that illustrates a force necessary to push the ball bearings  70  radially outward and allow the cam disk  40  to move upward within the housing  52 . In the example of  FIG. 3 , the angle β of the upper portion  60  as shown relative to the axis A X  of the balance stem  46 . As the angle a is greater than the angle β, the thrust force F β  required for upward movement of the cam disk  48  as shown in  FIG. 3  exceeds the force Fα for downward movement of the cam disk past the ball bearings  70 . Thus, in one example of use, the valve gate  36  may be urged into its desired location and the cam disk  48  and retention assemblies  64  strategically located so that the cam disk  48  is in the configuration of  FIG. 3 , thereby requiring a greater force to “unlock” the valve then would be required for moving the valve into a locking position, i.e., in the configuration of  FIG. 2  into the configuration of  FIG. 3 . 
         [0021]    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.