Patent Application
20140000907
1. Field of Invention
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.
2. Description of Prior Art
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.
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.
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.
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.
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.
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.
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:
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.
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.
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.
Shown in
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
In
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.
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.
Still referring to
Referring now to
Further illustrated in
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 (
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.
