Abstract:
A check valve for gas lift applications can be attached externally to a side pocket mandrel or can be a gas lift valve used in the mandrel. The valve has a seat with a non-elastomeric element and a metal element. A biasing element resiliently biases the non-elastomeric element to provide resiliency to the seal produced. A metal dart moves in the bore relative to the seat and allows or prevents flow through the valve body. When exposed to a first differential pressure, the dart engages the non-elastomeric element resiliently biased by the biasing element. When exposed to a greater differential pressure, the dart engages the metal element, which can be part of the valve in the bore. In one arrangement, the non-elastomeric element can be a thermoplatistic component with a metal spring energized seal as the biasing element. Alternatively, the non-elastomeric element can be the jacket of metal spring energized seal with a coil spring as the biasing element.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The subject matter of the present disclosure is directed to a gas lift check valve, and more particularly to a seal arrangement for improved well integrity in gas lift completions. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Operators use gas lift valves in side pocket mandrels to lift produced fluids in a well to the surface. Ideally, the gas lift valves allow gas from the tubing annulus to enter the tubing through the valve, but prevent flow from the tubing to the annulus. A typical gas lift completion  10  illustrated in  FIG. 1  has a wellhead  12  atop a casing  14  that passes through a formation. Tubing  20  positioned in the casing  14  has a number of side pocket mandrels  30  and a production packer  22 . To conduct a gas lift operation, operators install gas lift valves  40  by slickline into the side pocket mandrels  30 . One suitable example of a gas lift valve is the McMurry-Macco® gas lift valve available from Weatherford—the Assignee of the present disclosure. (McMURRY-MACCO is a registered trademark of Weatherford/Lamb, Inc.) 
         [0003]    With the valves  40  installed, compressed gas G from the wellhead  12  is injected into the annulus  16  between the production tubing  20  and the casing  14 . In the side pocket mandrels  30 , the gas lift valves  40  then act as one-way valves by allowing gas flow from the annulus  16  to the tubing string  20  and preventing gas flow from the tubing  20  to the annulus  16 . Downhole, the production packer  22  forces produced fluid entering casing perforations  15  from the formation to travel up through the tubing  20 . Additionally, the packer  22  keeps the gas flow in the annulus  16  from entering the tubing  20 . 
         [0004]    The injected gas G passes down the annulus  16  until it reaches the side pocket mandrels  30 . Entering the mandrel&#39;s ports  35 , the gas G must first pass through the gas lift valve  40  before it can pass into the tubing string  20 . Once in the tubing  20 , the gas G can then rise to the surface, lifting produced fluid in the tubing  20  in the process. 
         [0005]    As noted above, the installed gas lift valves  40  regulate the flow of gas from the annulus  16  to the tubing  20 . To prevent fluid in the tubing  20  from passing out the valve  40  to the annulus  16 , the gas lift valve  40  can use a check valve that restricts backflow. 
         [0006]    One type of side pocket mandrel  30  is shown in more detail in  FIGS. 2A-2B . This mandrel  30  is similar to a Double-Valved external (DVX) gas-lift mandrel, such as disclosed in U.S. Pat. No. 7,228,909 incorporated herein by reference in its entirety. The mandrel  30  has a side pocket  32  in an offset bulge from the mandrel&#39;s main passage  31 . This pocket  32  holds the gas lift valve  40  as shown in  FIG. 2B . The pocket&#39;s upper end has a seating profile  33  for engaging a locking mechanism of the gas lift valve  40 , while the pocket&#39;s other end has an opening  34  to the mandrel&#39;s main passage  31 . 
         [0007]    Lower ports  36  in the mandrel&#39;s pocket  32  communicate with the surrounding annulus ( 16 ) and allow for fluid communication during gas lift operations. As shown in  FIGS. 2A-2B , these ports  36  communicate along side passages  37  on either side of the pocket  32 . When these passages  37  reach a seating area  39  of the pocket  32 , these passages  37  communicate with the pocket  32  via transverse ports  38 . In this way, fluid entering the ports  36  can flow along the side passage  37  to the transverse ports  38  and into the seating area  39  of the pocket  32  where portion of the gas lift valve  40  positions. As shown in  FIG. 2B , the gas lift valve  40  has packings  43  that straddle and packoff the exit of the ports  38  in the mandrel&#39;s seating area  39 . This is where inlets  42  of the gas lift valve  40  position to receive the flow of gas. 
         [0008]    In the current arrangement, the ports  36  on the mandrel  30  can receive external check valves  50  that dispose in the ports  36 . The check valves  50  allow gas G flow from the annulus ( 16 ) into the mandrel&#39;s ports  36 , but prevent fluid flow in the reverse direction to the annulus ( 16 ). In general, the check valve  50  has a tubular body having two or more tubular members  52 ,  54  threadably connected to one another and having an O-ring seal  53  therebetween. 
         [0009]    The upper end of the valve  50  threads into the mandrel&#39;s port  36 , while the lower end can have female threads for attaching other components thereto. Internally, a compression spring  58  or the like biases a check dart  55  in the valve&#39;s bore against a seat  56 . To open the one-way valve  50 , pressure from the annulus ( 16 ) moves the check dart  55  away from the seat  56  against the bias of the spring  58 . If backflow occurs, the dart  55  can seal against the seat  56  to prevent fluid flow out the check valve  50 . 
         [0010]    During gas lift, for example, the injected gas G can flow through the check valves  50 , continue through separate flow paths in the ports  36  and passage  37 , and then flow from the transverse ports  38  toward the inlets  42  of the gas lift valve  40 . In turn, the gas lift valve  40  allows the gas G to flow downward within the valve  40 , through a check valve  45 , and eventually flow out through outlets  44  and into the side pocket  32 . From there, the gas G flows out through the slot  34  in the mandrel  30  and into the production tubing ( 20 ) connected to the mandrel&#39;s main passage  31 . 
         [0011]    Because the gas lift valve  40  and the separate check valves  50  both prevent fluid flow from the tubing  20  into the annulus  16 , they can act as redundant backups to one another. Moreover, the check valves  50  allow the gas lift valve  40  to be removed from the mandrel  30  for repair or replacement, while still preventing flow from the tubing  20  to the annulus  16 . This can improve gas lift operations by eliminating the time and cost required to unload production fluid from the annulus  16  as typically encountered when gas lift valves are removed and replaced in conventional mandrels. 
         [0012]    Various types of check valves can be used with gas lift valves or with other downhole components. For example,  FIGS. 3A-3C  illustrates types of prior art check valves for use with gas lift valves and mandrels. In particular,  FIGS. 3A and 3B  respectively show a CV-1 check valve  60 A and a CV-2 check valve  60 B from Weatherford&#39;s McMurry-Macco®CV series of reverse-flow check valves. These check valves  60 A-B can attach to the bottom of a gas lift valve, to ports of a side pocket mandrel, or other flow-control device. 
         [0013]    As shown, the check valves  60 A-B each have an upper housing  62  threadably coupled to a lower housing  64  with an  0 -ring seal  63  therebetween. Disposed in the bore of the valves  60 A-B, a dart  66  is biased by a spring  68  toward a seat  70 . As shown in  FIGS. 3A-3B , the seat  70  has an elastomeric component  72  and a retainer  74 . 
         [0014]    Another example of a check valve  60 C is shown in  FIG. 3C . This check valve  60 C is similar to the DVX check valve available from Weatherford. This particular check valve  60 C is well suited for a Double-Valved External (DVX) gas-lift mandrel described previously with reference to  FIGS. 2A-2B . As shown, this check valve  60 C includes an upper body  62  coupled to a lower body  64  by a port housing  65  and O-rings  63 . As before, the check dart  66  can move in the port housing  65  against the bias of a spring  68  relative to a seat  70 . Here, the seat  70  has a check seal  72  typically composed of elastomer (i.e., elastic polymer), such as nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, fluorocarbon rubber, tetra-fluoro-ethylene-propylene, and perfluoroelastomers. 
         [0015]    During a gas lift operation, upstream pressure typically from the surrounding annulus acts against the check valve  60 A-C and is higher than the downstream pressure from the tubing. The pressure differential depresses the spring-loaded dart  66  in the valve  60 A-C, allowing injection gas to flow through the check valve  60 A-C and into the production tubing. If the downstream pressure is greater than the upstream pressure, flow across the check dart  66  forces the dart  66  against the seat  17 , which prevents backflow. In the seating process, an elastomeric seal is first established between the dart  66  and elastomeric component  72 . As the differential pressure increases, a metal-to-metal seal is then formed for additional protection between the dart  66  and portion of the lower housing  64  forming part of the seat  70 . 
         [0016]    As seen in  FIGS. 3A-3C , check valves  60 A-C for gas lift valves use elastomeric resilient seals  72  to provide a secondary seal to the metal-to-metal seal between the check dart  66  and the seat  70 . As expected, such a dual seal protects against backflow, prevents casing from damage, and avoids costly workover operations. Unfortunately, the elastomeric seal  72  can be prone to explosive decompression during use. 
         [0017]    In explosive decompression, the seal  72  is exposed to gas laden fluid at high pressure, and the compressed gas enters the interstices of the seal&#39;s elastomer. As long as operating pressures remain high, the seal  72  remains intact. Whenever the pressure falls, however, the gas in the elastomer of the seal  72  expands and can cause the seal  72  to rupture. 
         [0018]    Explosive decompression has been a recognized problem in valve seals, and two solutions have been developed for handling it. In a first solution, specific types of elastomers have been developed that are more resistant than others to explosive decompression. An example of such an elastomer is FKM XploR V9T20, which is available from Trelleborg Sealing Solutions. Although these types of elastomers may be useful, even seals with such elastomers can still have issues with explosive decompression in check valves used for gas lift operations. 
         [0019]    Another solution developed in the art has been to use only metal-to-metal sealing with no resilient seal in check valves. An example of such a check valve with only metal-to-metal sealing is the 15K Severe Service MTM Check Valve available from Halliburton. Although exclusive metal sealing may solve problems related to explosive decompression, a check valve utilizing only a metal-to-metal seal can be less reliable in sealing, especially if there is any debris present in the injection fluid. Moreover, the exclusive metal-to-metal seal can be costly to manufacture and maintain. 
         [0020]    The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
       SUMMARY 
       [0021]    A check valve apparatus for a gas lift application can be used as an external check valve attached to the outside of a side pocket mandrel that holds a gas lift valve therein. Alternatively, the check valve apparatus can actually be part of a gas lift valve or any other type of valve. 
         [0022]    The apparatus has a valve body with a seat and dart disposed in the valve&#39;s bore. The seat has a first seal element composed of a non-elastomeric material and has a second seal element composed of a metal material. Being non-elastomeric material, the first seal element can be composed of a thermoplastic, such as polytetrafluoroethylene (PTFE), a moly-filed PTFE, or polyetheretherketone (PEEK). A biasing element, such as a spring, resiliently biases this first (non-elastomeric) seal element of the seat to provide resiliency to the seal produced. 
         [0023]    When the dart composed of a metal material moves in the valve&#39;s bore relative to the seat, the dart allows or prevents flow through the valve body by engaging or disengaging the seat. When exposed to proper flow from the annulus to the mandrel, the dart moves against the bias of the dart&#39;s spring away from the seat. When exposed to a first differential pressure from backflow, however, the dart engages the first (non-elastomeric) seal element resiliently biased by the biasing element. When exposed to a greater differential pressure, the dart further engages the second (metal) seal element, which can include portion of the valve body in the bore. 
         [0024]    In one arrangement, the biasing element is an energized seal disposed in a face seal configuration that biases the first seal element axially along the bore. This energized seal can be a metal spring energized seal having a jacket with a metal finger spring disposed therein. In another arrangement, the first seal element can be a jacket of an energized seal, while the biasing element is a spring of the energized seal disposed in the jacket. The energized seal in this arrangement can be a metal spring energized seal disposed in a rod and piston seal configuration and can bias transversely to the bore. The spring can use a coil spring for this energized seal. 
         [0025]    The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  illustrates a typical gas lift completion. 
           [0027]      FIG. 2A  illustrates a side pocket mandrel according to the prior art for use with dual external check valves. 
           [0028]      FIG. 2B  illustrates portion of a gas lift valve positioned in the side pocket mandrel of  FIG. 2A  with an external check valve disposed thereon. 
           [0029]      FIGS. 3A-3C  illustrate prior art check valves. 
           [0030]      FIG. 4  illustrates a cross-section of a check valve with one seat arrangement according to certain teachings of the present disclosure. 
           [0031]      FIG. 5A  illustrates a detail of the seat arrangement for the check valve of  FIG. 4 . 
           [0032]      FIG. 5B  illustrates a cross-sectional detail of the spring loaded cup seal for the disclosed seat arrangement. 
           [0033]      FIG. 6  illustrates a cross-section of a check valve with another seat arrangement according to certain teachings of the present disclosure. 
           [0034]      FIG. 7A  illustrates a detail of the seat arrangement for the check valve of  FIG. 6 . 
           [0035]      FIG. 7B  illustrates another configuration for the seat arrangement of  FIG. 6 . 
           [0036]      FIG. 7C  illustrates various energized seals for use in the seat arrangements of the present disclosure. 
           [0037]      FIG. 8  illustrates a side pocket mandrel with an external check valve having the disclosed seat arrangement. 
           [0038]      FIG. 9  illustrates a gas lift valve having the disclosed seat arrangement. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    A gas lift check valve  80  illustrated in  FIG. 4  has a seat arrangement  100  according to the present disclosure. As before, the check valve  80  includes an upper body  82  coupled to a lower body  84  by a port housing  85  and O-rings  83 . A check dart  86  can move in the port housing  85  against the bias of a spring  88  relative to the seat arrangement  100 . 
         [0040]    This valve  80  is well suited for the Double-Valved external (DVX) gas-lift mandrel, such as described previously with reference to  FIGS. 2A-2B  and disclosed in the incorporated U.S. Pat. No. 7,228,909. However, the check valve  80  with its seat arrangement  100  can be used in other implementations and can be attached directly to a gas lift valve or other flow control device that either has or does not have its own one-way valve. Moreover, multiple check valves  80  can be screwed together to create multiple check barriers for additional protection against backflow. 
         [0041]    As shown in  FIG. 5A , the seat arrangement  100  includes a check seal  110  and a spring loaded cup seal  130  arranged between the port housing  85  and the lower body  84 . The check seal  110  is composed of non-elastomeric material, such as polytetrafluoroethylene (PTFE) or moly-filed PTFE polytetrafluoroethylene, molybdenum sulfide (MoS 2 ) Filled, which is also known as Teflon®). (TEFLON is a registered trademark of E. I. Du Pont De Nemours and Company Corporation.) Other suitable materials that are non-elastomeric include other thermoplastic polymers. 
         [0042]    Because the check seal  110  is non-elastomeric, it lacks the resiliency typically provided for check valve seals using elastomer. For this reason, the spring loaded cup seal  130  is used to provide resiliency to the seat arrangement  100 . The cup seal  130  is arranged in a face seal configuration and biases the check seal  110  relative to the lower housing  84 . As shown in the cross-sectional detail of  FIG. 5B , the spring loaded cup seal  130  has a jacket  132  in which a spring element  134  is disposed. The jacket  132  is composed of non-elastomeric material, such as PTFE or the like, while the spring element  134  is composed of non-corrosive metal or other suitable material. 
         [0043]    As shown in  FIGS. 4 and 5A , the resiliency of the cup seal  130  acts axially along the valve  80  and acts against the seating direction of the dart  86 . As fluid pressure in the valve  80  builds and/or the bias of the spring  88  acts to seat the dart  86  on the seat arrangement  100 , the check dart  66  engages the seat arrangement  100  to prevent backflow. In the seating process, the non-elastomeric seal from the check seal  110  is first established with the dart  66 , and the resiliency for this seal is provided by the bias of the cup seal  130 . As the differential pressure increases, a metal-to-metal seal is then formed for additional protection, as the dart  66  engages an inside metal area  140  ( FIG. 5A ) of the lower housing  84  around the valve&#39;s seat arrangement  100 . 
         [0044]    Another seat arrangement  150  for the check valve  80  illustrated in  FIG. 6  has a spring loaded cup seal  160  and a retaining element  180 .  FIG. 7A  illustrates a detail of the check seal  160  for the check valve of  FIG. 6 , while  FIG. 7B  illustrates the spring loaded cup seal  160  in greater detail relative to the check dart  86  and other valve components. In FIGS.  6  and  7 A- 7 B, components of the valve  80  are similar to those described previously so the same reference numerals are used. 
         [0045]    As before, the seat arrangement  150  uses a non-elastomeric material and a spring mechanism for the check seal  160 . This seat arrangement  150  differs somewhat from the previous arrangement  100  in that the bias or resiliency of the check seal  160  is orthogonal to the axis of the check valve  80 . Rather than a face configuration, for example, the check seal  160  is disposed in a rod and piston seal configuration. As shown in  FIGS. 7A-7B , the resiliency of the check seal  160  therefore acts transversely to the valve  80 &#39;s longitudinal axis. In this way, the check seal  160  presses outward into the valve&#39;s bore and acts orthogonally to the seating direction of the dart  86  as shown in  FIG. 7B . 
         [0046]    As shown in  FIG. 6 , the retaining element  180  can be composed of non-elastomeric material, such as PTFE or metal. Disposed between the mated housings  84  and  85 , the retaining element  180  helps retain or hold the check seal  160  and may facilitate assembly. As an alternative shown in  FIG. 7B , the seat arrangement  150  can lack a retaining element ( 180 ). Instead, the lower housing portion  84  is configured to directly retain the check seal  160  as well as provide the metal area for the metal-to-metal seal with the check dart  86 . As will be appreciated, these and other suitable configurations can be used to retain the check seal  160  in the valve  80 . 
         [0047]    As best shown in  FIGS. 7A-7B , the check seal  160  has a jacket  162 , a coil spring  164 , and a hat ring  164 . The jacket  162  and hat ring  164  are both preferably composed on non-elastomeric materials. For example, the jacket  162  can be composed of PTFE, such as Avalon® 56 or the like, while the hat ring  164  can be composed of polyetheretherketone (PEEK), such as Arlon® 1000 or the like. (AVALON and ARLON are registered trademarks of Green, Tweed &amp; Co. of Kulpsville, Pa.) The coil spring  164  is preferably composed of corrosive resistant metal, such as Elgiloy® 58% Cr or the like. (ELGILOY is a registered trademark of Elgiloy Company.) 
         [0048]    As shown in FIGS.  6  and  7 A- 7 B, fluid pressure in the valve  80  builds and/or the bias of the spring  88  acts to seat the dart  86  on the seat arrangement  150  so the check dart  66  engages the seat arrangement  150  to prevent backflow. In the seating process, the non-elastomeric seal from check seal  160  is first established with the dart  66 , and the resiliency for this seal is provided transversely by the biasing element of the check seal  160 . As the differential pressure increases, a metal-to-metal seal is then formed for additional protection, as the dart  66  engages an inside metal area  184  around the valve&#39;s seat arrangement  150 . 
         [0049]    As evidenced by the present disclosure, the disclosed seat arrangements (i.e.,  100  and  150 ) can overcome issues typically encountered in check valves. By using the non-elastomeric material for the resilient seal, for example, issues with explosive decompression can be avoided completely, yet the seal can still provide high sealing integrity even if debris is present. The biasing elements (e.g., cup seal  130  or spring loaded check seal  160 ) give resiliency to the seat arrangements  100 ,  150  even though the non-elastomeric materials of the seat arrangements  100 ,  150  do not have any elasticity. This resiliency by the biasing elements can actually provide a boost to the resilient seal and help it seal even more reliably as an unexpected benefit. In this way, the more pressure present on the check valve actually produces more force between the resilient seal and the check valve  80  and further enhances the seal produced. 
         [0050]    The seating arrangements  100 ,  150  disclosed herein can use an energized seal. For example, any of the various metal spring energized seals (i.e., an MSE® seal) known in the art can be used in face or piston and rod seal configurations depending on the arrangement. (MSE is a registered trademark of Green, Tweed &amp; Co. of Kulpsville, Pa.)  FIG. 7C  shows various energized seals  190 A-C that can be used as a resiliency element (as in  FIG. 5A ), a check seal element (as in  FIG. 6 ), or both. 
         [0051]    In general, the energized seals  190 A-C have a ring-shaped jacket  191  composed of non-elastomeric polymer, such as PTFE, and have a biasing element  192 ,  194 , or  196  that energizes the polymer jacket  191 . When seated in the jacket  191 , the biasing element  192 ,  194 , or  196  is under compression and applies force against the jacket&#39;s sides. For example, the energized seals  190 A-C can use biasing elements, including a finger spring  192 , a coil spring  194 , and a double coil spring  196 , each of which is preferably composed of metal. By contrast, seal  190 D uses an O-ring  198  in the jacket  191  and may be suitable for some applications. 
         [0052]    As noted herein, the check valve  80  of  FIG. 6  can attach to the port of a side pocket mandrel. For example,  FIG. 8  shows the check valve  80  having the disclosed seat arrangement  100 , 150  attached to the external port  36  of the side pocket mandrel  30 . (Similar reference numbers are used for like components discussed previously.) The valve  80  can thread into the external port  36  or attach in any other suitable manner. In this way, the valve  80  can act as a redundant check valve to prevent backflow and can operate as the one-way valve when the gas lift valve  40  is removed from the side pocket  32  for repair or replacement. 
         [0053]    Although discussed in relation to an external check valve, the disclosed seat arrangements  100 , 150  may actually be used with any poppet-type sealing device that requires a gas tight seal. As one example, even a gas lift valve  40  as shown in  FIG. 9  can use the seat arrangement  100 , 150  of the present disclosure in conjunction with its internal check dart  48 . (Similar reference numbers are used for like components discussed previously.) 
         [0054]    As shown, the retrievable, one-way check valve in the gas lift valve  40  disposing in a side pocket mandrel may use the disclosed seat arrangement  100 , 150 . In this way, the seat arrangement  100 , 150  operates in conjunction with the gas lift valve&#39;s dart  48  to allow flow through the valve&#39;s internal passage  46  from the inlets  42  to the outlets  44  and prevent backflow in the reverse direction. 
         [0055]    The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. Various types of materials have been discussed herein. For the sake of understanding and without limitation to the claims and available materials, elastomer refers to polymers that are elastic (i.e., NBR, HNBR, FKM, TFE/P, FFKM, and the like), while thermoplastic refers to polymers that are not elastic and do not recover upon deformation (i.e., PTFE, PEEK, PPS, PAI, PA, EDPM+PP, PVDF, ECTFE, and the like). 
         [0056]    In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.