U.S. patent application number 14/426637 was filed with the patent office on 2015-08-20 for gas lift valve.
The applicant listed for this patent is SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Yushan Li, Weng Keong Tiong, Chao Wang.
Application Number | 20150233220 14/426637 |
Document ID | / |
Family ID | 50237614 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150233220 |
Kind Code |
A1 |
Tiong; Weng Keong ; et
al. |
August 20, 2015 |
GAS LIFT VALVE
Abstract
A gas lift valve is provided with increased longevity and
reliability for preventing backflow. A wide cylindrical sliding
member stabilizes axial movement of a valve element in the gas lift
valve. A wide spring around the sliding member biases the valve
element toward closure during back flow. The spring is physically
supported and guided by the sliding member and protected from gas
flow injection by the same sliding member. A one-piece poppet
version of the valve element provides a consistent closing seal,
and the sliding member protects the valve seat and poppet from full
force of an injected gas. A dart version of the valve element
includes a hexagonal race for movement of the sliding member, which
prevents rotational wear of components and provides a straight flow
path for the injection gas with no sharp transitions to wear and no
sharp angles to erode.
Inventors: |
Tiong; Weng Keong;
(Singapore, SG) ; Wang; Chao; (Missouri City,
TX) ; Li; Yushan; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHLUMBERGER TECHNOLOGY CORPORATION |
Sugar Land |
TX |
US |
|
|
Family ID: |
50237614 |
Appl. No.: |
14/426637 |
Filed: |
September 6, 2013 |
PCT Filed: |
September 6, 2013 |
PCT NO: |
PCT/US2013/058364 |
371 Date: |
March 6, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61698629 |
Sep 8, 2012 |
|
|
|
61698627 |
Sep 8, 2012 |
|
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Current U.S.
Class: |
166/319 ;
29/890.12 |
Current CPC
Class: |
Y10T 29/49405 20150115;
B21K 1/20 20130101; E21B 34/10 20130101; E21B 43/123 20130101 |
International
Class: |
E21B 43/12 20060101
E21B043/12; E21B 34/10 20060101 E21B034/10; B21K 1/20 20060101
B21K001/20 |
Claims
1. A gas lift valve, comprising: a first port for receiving a gas
from a well annulus; a second port for transferring the gas to a
well production tube; a valve seat; a poppet valve element for
allowing a one-way flow of the gas past the valve seat and for
preventing a back flow of the gas; a sliding barrel attached to the
poppet valve element to maintain a sealing surface of the poppet
valve element in alignment with a sealing surface of the valve
seat; and a spring coiled around the outside diameter of the
sliding barrel to bias the poppet valve element in a closed
position against the valve seat.
2. The gas lift valve of claim 1, wherein the sliding barrel and
the spring have a wide cross-sectional diameter substantially the
same as a diameter of the poppet valve element to maintain a
sealing interface of the poppet valve element and the valve seat in
parallel-planar alignment with each other.
3. The gas lift valve of claim 1, wherein the poppet valve element
comprises a one-piece member for alignment of a sealing surface of
the poppet valve element with a sealing surface of the valve
seat.
4. The gas lift valve of claim 1, wherein the spring is protected
from a main flow of the gas by the barrel.
5. The gas lift valve of claim 1, wherein a sealing interface
between the poppet valve element and the valve seat is protected
from a direct high speed flow of the gas by at least one valve
component.
6. The gas lift valve of claim 1, wherein a maximum open state of
the poppet valve element is determined by the poppet valve element
contacting an end housing of the gas lift valve.
7. A gas lift valve, comprising: a first port for receiving a gas
from a well annulus; a second port for transferring the gas to a
well production tube; a valve seat; a dart valve element for
allowing a one-way flow of the gas past the valve seat and for
preventing a back flow of the gas; a sliding barrel attached to the
dart valve element to maintain a sealing surface of the dart valve
element in alignment with a sealing surface of the valve seat; a
spring coiled around the outside perimeter of the sliding barrel to
bias the poppet valve element in a closed position against the
valve seat; and a race of hexagonal cross-section for a movement of
the sliding barrel.
8. The gas lift valve of claim 7, further comprising a flow path
for gas substantially free from sharp angular transitions.
9. The gas lift valve of claim 7, wherein a hex dart configuration
counteracts erosion at sharp corners.
10. The gas lift valve of claim 7, wherein the spring is
fully-guided on an inside diameter (ID) of the spring for
stability.
11. The gas lift valve of claim 7, wherein a hex dart configuration
prevents a rotation of a valve component caused by high velocity
gas flow.
12. The gas lift valve of claim 7, wherein the sliding barrel and
the spring have a wide cross-sectional diameter substantially the
same as a diameter of the dart valve element to maintain a sealing
interface of the dart valve element and the valve seat in
parallel-planar alignment with each other.
13. The gas lift valve of claim 7, wherein the spring is protected
from a main flow of the gas by the barrel.
14. The gas lift valve of claim 7, wherein a sealing interface
between the dart valve element and the valve seat is protected from
a direct high speed flow of the gas by at least one valve
component.
15. A method, comprising: constructing a gas lift valve with a wide
cylindrical sliding member to reliably seat a valve element; and
biasing the valve element toward a closed state with a wide spring
around the wide cylindrical sliding member.
16. The method of claim 15, wherein the wide cylindrical sliding
member and the spring have a cross-sectional diameter substantially
the same as a largest diameter of the valve element to maintain a
sealing interface of the valve element and a valve seat in a
parallel-planar alignment with each other; and wherein the wide
cylindrical sliding member protects the valve element and a valve
seat from a full force of a gas injection flow.
17. The method of claim 15, wherein the spring is protected from a
main flow of an injection gas by the wise cylindrical sliding
member.
18. The method of claim 15, further comprising attaching a
one-piece poppet-shaped valve element to the wide cylindrical
sliding member to reliably close the gas lift valve during a back
flow condition.
19. The method of claim 15, further comprising: incorporating a
dart valve element in the gas lift valve to prevent a back flow
condition; and incorporating a hexagonal race for the wide
cylindrical sliding member in the gas lift valve to prevent a
rotation of the valve components caused by a high velocity gas
flow.
20. The method of claim 19, wherein the hexagonal race provides a
flow path for a gas substantially free from sharp angular
transitions; and wherein the hexagonal race counteracts erosion at
sharp corners.
Description
BACKGROUND
[0001] Gas lift is a process in which a gas is injected from the
annulus of a well into the production tubing of the well, to lower
the density of oil being recovered, making the fluid easier to
lift. "Annulus" as applied to a well casing refers to the space,
lumen, or void around the outside of a central pipe within a larger
pipe, tubing, or casing that immediately surrounds the central
pipe. An annulus is the space between pipes when one pipe is
inserted into another pipe. The injected gas aerates to lighten the
well fluid for flow to the surface. Gas lift valves control the
flow of gas during either an intermittent or continuous-flow gas
lift operation. A principle of gas lift operation is differential
pressure control with a variable orifice size to further constrain
the maximum flow rate of gas. By incorporating a hydrostatic
pressure chamber that can be charged with different pressures,
injection pressure-operated gas lift valves and unloading valves
can be configured so that an upper valve in the production string
opens before a lower valve opens, even though both valves receive
the injection gas from the same annulus. A gas lift valve is either
fully open or fully closed, there is no intermediate valve state.
Gas lift valves are often retrievable using a kick-off tool in the
well. Back check is a critical component for gas lift valves to
prevent the well fluid from recirculating back to the annulus of
the casing.
SUMMARY
[0002] An example gas lift valve includes a first port for
receiving a gas from a well annulus, a second port for transferring
the gas to a well production tube, a valve seat, a poppet valve
element for allowing a one-way flow of the gas past the valve seat
and for preventing a back flow of the gas, a sliding barrel
attached to the poppet valve element to maintain a sealing surface
of the poppet valve element in alignment with a sealing surface of
the valve seat, and a spring coiled around the outside diameter of
the sliding barrel to bias the poppet valve element in a closed
position against the valve seat. A one-piece poppet version of the
valve element provides a consistent closing seal. A dart version of
the valve element includes a hexagonal race to prevent rotational
wear of components and a straight flow path for the injection gas
with no sharp transitions and angles to wear and erode. An example
method includes constructing a gas lift valve with a wide
cylindrical sliding member to reliably seat a valve element and
biasing the valve element toward a closed state with a wide spring
around the wide cylindrical sliding member. This summary section is
not intended to give a full description of the example gas lift
valves. A detailed description with example embodiments
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a diagram of an example gas lift operation using
improved gas lift valves.
[0004] FIG. 2 is a diagram of an example gas lift valve
assembly.
[0005] FIG. 3 is a diagram of a first embodiment of an example gas
lift valve.
[0006] FIG. 4 is a diagram of a second embodiment of an example gas
lift valve.
[0007] FIG. 5 is a diagram showing a cross-sectional view of the
example gas lift valve of FIG. 4.
[0008] FIG. 6 is a flow diagram of an example method of
constructing a gas lift valve.
DETAILED DESCRIPTION
[0009] This disclosure describes gas lift valves with improved
features. For context, FIG. 1 depicts a gas lift system 100 that
includes a production tubing 140 that extends into a wellbore. For
purposes of gas injection, the system 100 includes a gas compressor
120 that is located at the surface of the well to pressurize gas to
be communicated to an annulus 150 of the well. To control the
communication of gas between the annulus 150 and a central
passageway 170 of the production tubing 140, the system 100 may
include several side pocket gas lift mandrels 160 (example gas lift
mandrels 160a, 160b and 160c). Each of the gas lift mandrels 160
includes an associated gas lift valve 180 (such as example gas lift
valves 180a, 180b and 180c) for establishing one-way fluid
communication from the annulus 150 to the central passageway 170.
Near the surface of the well, one or more of the gas lift valves
180 may be unloading valves. An unloading gas lift valve opens when
the annulus pressure exceeds the production tubing pressure by a
certain threshold, a feature that aids in pressurizing the annulus
below the valve before the valve opens. Other gas lift valves 180
are located farther below the surface of the well and may not have
an opening pressure threshold.
[0010] Each gas lift valve 180 may contain a check valve element
that opens to allow fluid flow (gas) from the annulus 150 into the
production tubing 140 and closes when the fluid would otherwise
back flow in the opposite direction. For example, the production
tubing 140 may be pressurized for purposes of setting a packer,
actuating a tool, performing a pressure test, and so forth. Thus,
when the pressure in the production tubing 140 exceeds the annulus
pressure, the valve element is closed to ideally form a seal to
prevent flow from the tubing 140 to the annulus 150. However, it is
possible that this seal may leak, and if leakage does occur, well
operations that rely on production tubing pressure may not be able
to be completed or performed. The leakage may require an
intervention, which is costly, especially for a subsea well.
[0011] FIG. 2 shows a gas lift valve assembly 200 in accordance
with some embodiments of the example gas lift valves. In general,
the gas lift valve assembly 200 includes an example gas lift valve
180 that includes a valve element (described further below) to
control fluid communication between the annulus 150 of the well and
the central passageway 170 of the production tubing 140. The
example gas lift valve 180 resides inside a longitudinal passageway
204 of a mandrel 206. In addition to the longitudinal passageway
204, the mandrel 206 includes a separate longitudinal passageway
208 that has a larger cross-section than passageway 204, is
eccentric to passageway 204, and forms part of the production
tubing string (140). As depicted in FIG. 2, the longitudinal
passageways 204 and 208 are generally parallel to each other. The
mandrel 206 includes at least one radial port 210 to establish
communication between the longitudinal passageways 204 and 208 and
also includes at least one radial port 212 to establish fluid
communication between the longitudinal passageway 204 and the
annulus 150 of the well that surrounds the mandrel 206.
[0012] In general, the gas lift valve 180 is configured to control
fluid communication between the longitudinal passageway 208 and the
annulus 150 of the well. In this regard, the gas lift valve 180
includes an upper seal 214 and a lower 216 seal (for example,
o-ring seals, v-ring seals, or a combination) that circumscribe the
outer surface housing of the example gas lift valve 180 to form a
sealed region that contains radial ports 218 of the example gas
lift valve 180 and the radial ports 212 of the mandrel 206. One or
more lower ports 220 (located near a lower end 222 of the
longitudinal passageway 204) of the gas lift valve 180 are located
below the lower seal 216 and are in fluid communication with the
radial ports 210 near the lower end 222. The longitudinal
passageway 204 is sealed off (not shown) to complete a pocket to
receive the example gas lift valve 180. In this arrangement, the
example gas lift valve 180 is positioned to control fluid
communication between the radial ports 210 (i.e., the central
passageway of the production tubing string 140) and radial ports
212 (of the mandrel 206, in fluid communication with the annulus
150). During operation, the example gas lift valve 180 establishes
a one-way communication path from the annulus 150 to the central
passageway 170 of the production tubing 140. Thus, when enabled,
the gas lift valve 180 permits gas flow from the annulus 150 to the
production tubing 140 and ideally prevents flow in the opposite
direction.
[0013] The gas lift valve 180 may be installed or removed by a
wireline operation in the well. Thus, in accordance with some
embodiments, the example gas lift valve assembly 200 may include a
latch 224 (located near an upper end 226 of the mandrel 206) that
may be engaged with a wireline tool (not shown) for installing the
example gas lift valve 180 in the mandrel 206 or removing the
example gas lift valve 180 from the mandrel 206.
[0014] The example gas lift valve assembly 200 may be used in a
subterranean well or in a subsea well, depending on a particular
embodiment.
[0015] In an implementation, the example gas lift valve 180 has a
general design that is depicted in FIG. 3. Radial ports 218 of the
example gas lift valve 180 may be formed in a tubular housing 302
of the example gas lift valve 180. The tubular housing 302 may be
connected to an upper concentric housing section 304 of the gas
lift valve 180 that extends to the latch 224 (not shown in FIG.
3).
[0016] The housing 302 includes an interior space 305 for receiving
gas that flows in from the radial ports 218. Injection gas that
enters the radial ports 218 flows into the interior space 305 and
through an orifice 306, which may be connected to the lower end of
the housing 70. The orifice 306 may by cylindrical, square-edged,
or streamlined for venture effects, for example. The housing around
the orifice 306 may be partially circumscribed by the lower end of
the housing 302 and may be sealed to the housing 302 with one or
more seals 308, such as o-rings, for example. The housing of the
orifice 306 may extend inside an upper end of a lower housing 310
that is concentric with the housing 302 and extends further
downhole. The housings 310 and 302 may be sealed together via one
or more seals 312, such as o-rings. As also depicted in FIG. 3, the
lower seal 216 (formed from one or more v-type seals, o-rings,
etc.) may circumscribe the outer surface of the housing 310 in some
embodiments. The orifice 306 is in communication with a lower
passageway 314 that extends through the housing 310.
[0017] Poppet Back Check Valve Embodiment
[0018] In an implementation, the lower end of the housing 310 forms
a valve seat 316, a seat that is opened and closed (for purposes of
controlling the one-way flow through the gas lift valve 180) via a
valve element 322 of a check valve assembly 318. The check valve
assembly 318 may be spring-loaded using, for example, spring 320 in
a guided spring assembly. The check valve assembly 318 may be
anchored or secured via a socket-type connection to a movable,
sliding, hollow cylindrical member, such as a piston or barrel 324
surrounded by the inside diameter of coils of the spring 320. The
check valve assembly 318 moves as a unit depending on the injected
gas pressure, allowing pressurized gas to flow through the valve
end of the barrel 324 in a controlled manner.
[0019] In an implementation, a poppet-shaped version of the valve
element 322 ("poppet valve element" 322) allows gas flow, or closes
off gas flow as the case may be, controlling fluid communication
through the valve seat 316. The check valve assembly 318 exerts an
"upward" bias force (towards the surface, i.e., toward closure of
the example gas lift valve 180 against back pressure) on the valve
element 322 for biasing the valve element 322 to close off fluid
communication through the valve seat 316.
[0020] The particular mushroom-like geometry of a poppet-shaped
disk, when used as the valve element 322, provides a concerted
valve closure all the way around the sealing perimeter of the
poppet valve element 322 when the poppet valve element 322 shuts
during pressure scenarios that would cause backflow. In an
implementation, a one-piece poppet valve element 322 ensures
alignment of the seal surface when it closes.
[0021] Besides this consistent evenness of the closing seal due to
the poppet geometry, the poppet valve element 322 also provides
reliability in the seal that is created between the poppet valve
element 322 and the valve seat 316. The poppet-shaped valve element
322, as guided by the piston or barrel 324 that supports the spring
320, moves smoothly and reliably in one axial direction for opening
and closing. The relatively large bore of the barrel 412 located
just inside the coils of the spring 406 provides strength and
smoothness to the axial movement of the dart valve element 404, and
removes unnecessary play, as compared with conventional back check
valves that use a spindly support member for movement of a
conventional valve element.
[0022] In an implementation, the cross-sectional diameter of the
barrel 324 may be substantially the same diameter as that of the
poppet valve element 322 to maintain a sealing surface of the
poppet valve element 322 in good or perfect parallel-planar
alignment with a sealing surface of the valve seat 316. Thus, the
geometry of the check valve assembly 318 affords the poppet valve
element 322 reliable and smooth movement, so that the poppet valve
element 322 makes a consistent leak-proof seal. Thus, the poppet
valve element 322 snaps shut against the valve seat 316 in
consistent alignment making a quick and reliable seal when the
pressure in the production tubing 140 becomes greater than the
pressure in the annulus 150.
[0023] When, however, the annulus pressure is sufficient (relative
to the production tubing pressure) to exert a force on the poppet
valve element 322 to overcome the bias of the spring 320, then the
poppet valve element 322 retracts (opens downward) to permit gas
fluid to flow from the annulus 150 into the production tubing 140
to effect gas lift.
[0024] The lower end of the lower housing 310 may be sealed via an
o-ring 328 for example, to a nose housing or end housing 326 that
extends further downward toward the lower port(s) 220 of the
example gas lift valve 180. An interior space 330 inside the end
housing 326 is in communication with the production tubing side
(140 and 170) of the example gas lift valve 180 and receives the
injected gas via the annulus 150 that opens the check valve
assembly 318 and flows through the valve seat 316.
[0025] An example gas lift valve 180 that includes the poppet valve
element 322 provides several other advantages. A wide spring 320
can be used and the inside diameter (ID) of the spring 320 can be
disposed around and guided by the piston or barrel 324, as shown.
This arrangement provides steady and reliable movement of the
poppet valve element 322 as compared with conventional
spring-loaded valve elements that either rely on an unsupported
spring or rely on a narrow spring that imparts too much play in the
side-to-side movement of a conventional valve element. In FIG. 3,
the spring 320 is also protected from the flow stream, adding to
longevity and reliable function of the spring 320. The design and
geometry of the example gas lift valve 180 also avoids direct high
speed flow past the sealing surface, which can provide a valve
closure for preventing backflow that is more sensitive to smaller
backflow pressures. In an implementation, the movement of the open
poppet valve element 322 is stopped by the poppet valve element 322
itself contacting the nose housing or end housing 326 of the
example gas lift valve 180, as compared with conventional
techniques of having movement limited by other components attached
to a valve element, which could cause the valve element to stick at
an open position.
[0026] Ideally, fluid cannot flow from the production tubing side
of the check valve assembly 318 to the annulus side, because of the
poppet valve element 322 closing and making a seal against the
valve seat 316.
[0027] Hex Dart Back Check Valve Embodiment
[0028] FIG. 4 shows an example hex dart gas lift valve 402, which
includes an example valve race 502 (FIG. 5) that has a hexagonal
cross-section, and includes a dart style back check valve element
404 ("dart valve element" 404). This example embodiment of a gas
lift valve 402 provides several advantages, including a gas flow
path that is relatively free from sharp angular transitions, to
reduce wear and increase longevity. The hexagonal geometry of the
hex dart gas lift valve 402 counteracts erosion at sharp corners,
especially when some impurities or abrasives also flow through the
valve components with the injected gas. The hex dart gas lift valve
402 uses a spring 406 that is fully guided on its inside diameter
(ID) for stability. The hex-shaped race 502 (FIG. 5) of the hex
dart gas lift valve 402 can also prevent rotation of the dart valve
element 404 and connected components (and thus prevent valve
sticking) caused by high velocity gas flow.
[0029] In FIG. 4, a lower housing 408 of the example gas lift valve
402 provides the structure for a valve seat 410. The valve seat 410
opens or closes for controlling one-way flow through the example
gas lift valve 402 via the dart valve element 404. A piston, hollow
cylindrical member, or barrel 412 may be spring-loaded using, for
example, spring 406 around the outside diameter of the barrel 412
in a guided spring assembly. The dart valve element 404 may be
anchored or secured via a socket-type connection 414 to the piston
or barrel 412 that is surrounded by the inside diameter of the
spring 406.
[0030] The dart valve element 404, connector 414, and barrel 412
move as a unit to open against the expansive bias of the spring
406, which is set to keep the valve closed, opening when injected
gas pressure overcomes the force of the spring 406. Orifice
openings near the connector 414 may allow control of the amount of
pressurized gas that can flow through the valve seat 410 at a given
time, thereby adding control and sensitivity to the valve.
[0031] The dart valve element 404 is guided in its movement by the
barrel 412 that stabilizes and guides the spring 406. The
relatively large bore of the barrel 412 located just inside the
coils of the spring 406 provides strength and smoothness to the
axial movement of the dart valve element 404, and removes
unnecessary play, as compared with conventional back check valves
that use a spindly support member for movement of a conventional
valve element. In an implementation, the diameter of the barrel 412
may be substantially the same diameter as that of the dart valve
element 404. The relatively wide spring 406 and the geometry of the
hex race 502 and wide barrel 412 member affords the dart valve
element 404 reliable and smooth movement, so that the dart valve
element 404 makes a consistent leak-proof seal. The dart valve
element 404 shuts against the valve seat 410 in consistent
alignment making a reliable seal when the pressure in the
production tubing 140 becomes greater than the pressure in the
annulus 150, resulting in a potential back flow condition.
[0032] When the annulus pressure is sufficient (relative to the
production tubing pressure) to exert a force on the dart valve
element 404 to overcome the bias of the spring 406, then the dart
valve element 404 is pushed back (opens downward) to permit gas
fluid to flow from the annulus 150 into the production tubing 140
to effect gas lift.
[0033] The lower end of the lower housing 408 may be sealed via an
o-ring 416 for example, to a nose housing or end housing 418 that
extends further downward toward the lower port(s) 420 of the
example hex dart gas lift valve 402. An interior space 422 inside
the end housing 418 is in communication with the production tubing
side (140 and 170) of the example hex dart gas lift valve 402 and
receives the injected gas via the annulus 150 that opens the dart
valve element 404 and flows through the valve seat 410.
[0034] FIG. 5 shows an example cross-section of a hexagonal race
502 of the hex dart gas lift valve 402, as viewed from the plane in
FIG. 4 designated (in 2D) by line C-C. Depending on implementation,
part of the barrel 412 may be hexagonal and ride in the hexagonal
race 502, or in some implementations the entire barrel 412 may have
a hexagonal outside sliding surface, or in still other
implementations, the entire valve element assembly, including the
dart valve element 404 may have hexagonal outer presentations. The
hexagonal race 502 prevents rotation of the dart valve element 404
and associated components, and thus prevents extra surface wear and
potential valve sticking that can be caused by high velocity gas
flow.
EXAMPLE METHOD
[0035] FIG. 6 is a flow diagram of an example method 600 of
constructing a gas lift valve. In the flow diagram the individual
operations are shown as blocks.
[0036] At block 602, a gas lift valve is constructed to include a
wide cylindrical sliding member to reliably seat a valve element.
The wide cylindrical sliding member, or barrel, is attached to the
valve element. Because the barrel moves within a large bore, the
barrel has very stable movement in an axial direction with very
little play in other movement directions. This assures a strong and
correctly aligned seal mating between the valve element and the
valve seat.
[0037] At block 604, the valve element is biased toward a closed
state with a wide spring around the wide cylindrical sliding
member. The wide spring is both supported by the wide cylindrical
sliding member and protected from the gas being injected by the
wide cylindrical sliding member.
[0038] The wide cylindrical sliding member and the spring may have
a cross-sectional diameter substantially the same as a largest
diameter of the valve element in order to maintain a sealing
interface of the valve element and a valve seat in a
parallel-planar alignment with each other with very little
deviation to a side. The wide cylindrical sliding member can also
protect the valve element and a valve seat from full force of a gas
injection flow.
[0039] A poppet valve element connected to the wide cylindrical
sliding member reliably closes the gas lift valve during a back
flow condition. Alternatively, a dart valve element in the gas lift
valve prevents a back flow condition and when used with a hexagonal
race or bore for the wide cylindrical sliding member, rotational
wear of the valve components caused by a high velocity gas flow can
be prevented. The hexagonal race also provides a flow path for the
injected gas that is free from sharp angular transitions
counteracts erosion at sharp corners.
[0040] Conclusion
[0041] Although only a few example embodiments have been described
in detail above, those skilled in the art will readily appreciate
that many modifications are possible in the example embodiments
without materially departing from the subject matter. Accordingly,
all such modifications are intended to be included within the scope
of this disclosure as defined in the following claims. In the
claims, means-plus-function clauses are intended to cover the
structures described herein as performing the recited function and
not only structural equivalents, but also equivalent structures. It
is the express intention of the applicant not to invoke 35 U.S.C.
.sctn.112, paragraph 6 for any limitations of any of the claims
herein, except for those in which the claim expressly uses the
words `means for` together with an associated function.
* * * * *