Abstract:
A tubing drain valve in a production tubing string, positioned above a pump, is operated to open drain ports in the housing for draining produced fluids from the production tubing when the pump is shut off. The drain valve incorporates a check valve assembly which is freely moveable within the drain valve to shift a sleeve to open and close the drain ports. An uphole end of the check valve assembly is above the sleeve and seals to the top of a sleeve to shift the sleeve downhole and open the drain ports. A downhole end of the check valve is positioned below the sleeve in the valve. When the pump is turned on, the downhole end of the check valve assembly moves uphole to seal to the sleeve, creating a positive force to lift the sleeve to block the drain ports. The produced fluids flow through the valve and the production tubing to surface. The positive force minimizes the effect of fouling of the valve due to debris above the valve which might otherwise result in failure to shift the sleeve uphole, leaving the drain ports open.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application claiming priority of U.S. Provisional Patent application Ser. No. 61/176,980 filed May 11, 2009, the entirety of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Embodiments of the invention are related to valves used in production tubing fluidly connected to submersible pumping assemblies and more particularly, to valves positioned above the submersible pumping assembly to drain fluid from the production tubing to the annulus when the pumping assembly is shutdown. 
       BACKGROUND OF THE INVENTION 
       [0003]    Submersible pumping assemblies such as progressive cavity pumps and centrifugal pumps are suspended downhole in a wellbore by a string of production tubing. During pumping, fluid is discharged up the production tubing by the pump. When the pump stops, either intentionally or as a result of a failure of the pumping assembly, fluid in the production tubing string may flow back down into the pump causing the pump to reverse and potentially causing debris in the fluid to enter the pump. The debris remains in the pumping assembly and, when the pump is restarted, may cause damage to the pumping assembly. 
         [0004]    Alternatively, in the case where an operator wishes to pull the pump and the production tubing from the wellbore, such as for servicing of the pumping assembly, the pump and production tubing may pack off resulting in fluid remaining in the production tubing. In order to reduce the weight of the loaded production tubing for extraction from the wellbore, a bailing operation may be required which is both costly and time consuming. 
         [0005]    It is known to provide a valve above the discharge of an electrical submersible pump for draining the tubing above the pump when the pump shuts down. U.S. Pat. No. 6,289,990 to Baker Hughes Incorporated teaches a tubing shunt valve which is pressure actuated between a sealed position, wherein fluid communication between the production tubing and an annulus thereabout via shunt ports is prevented, and a drain position, wherein fluid is drained from the production tubing above the pump through shunt ports into the annulus. The Baker Hughes valve utilizes a single diameter valve cage having a seal interface which shifts across the shunt ports when moving between the sealed and drain positions. The Baker Hughes valve utilizes a spring biased valve head and shaft forming a piston which is confined within a bore in the valve cage. The valve head seals against a valve seat formed in the valve cage in the drain position. The valve seat is in fluid communication with the discharge of the pump therebelow. The shifting of the sleeve to the sealed or production position is reliant upon a friction resistance to shifting of the valve cage being less than a fluid force required to open the valve head when biased to the drain position. Applicant believes that any additional resistance due to fouling could prevent shifting of the valve cage to seal the shunt ports even though the pump may have overcome the biasing spring to cause the valve head to unseat and fluid to pass through the valve seat and the plurality of axial passages in the valve cage. 
         [0006]    Further, the spring which biases the valve head must be matched to the depth of the well as a result of increasing hydrostatic pressure and therefore many iterations of the valve are required for use in wells of different depths. 
         [0007]    There is a need for a drain valve which reliably seals the shunt ports through repeated movement of the valve between the sealed and drain positions and which is reliably and rapidly actuated between the sealed production position and the drain position when required. 
       SUMMARY OF THE INVENTION 
       [0008]    A tubing drain valve utilizes a first check valve positioned below a sleeve which is axially moveable in a housing, to form a downhole piston face. Pumped fluid, acting at the downhole piston face, result in a significant positive force to lift the sleeve to block one or more drain ports in the housing, in a production position. Thus, the valve does not rely upon overcoming a biasing force to permit fluid communication with the formation and is less prone to fouling. The valve therefore minimizes failures to shift the sleeve to block the one or more drain ports in the production position. 
         [0009]    A second check valve is positioned above the sleeve for forming an uphole piston face when sealed against the sleeve. Produced fluid in the production tubing, upon stopping the pump, acts at the uphole piston face for shifting the sleeve downhole to open the one or more drain ports. The fluids are drained through the one or more drain ports to the annulus. 
         [0010]    In one broad aspect therefore, a tubing drain valve for incorporation between a production tubing string and a pump, the tubing drain valve comprising: a housing having an uphole end for connection to the production tubing string above the pump and a downhole end for connection to the pump, downhole of the housing, the housing having a valve bore in communication with fluid in the tubing string and the pump; one or more drain ports in the housing communicating with the valve bore; a sleeve fit to the valve bore and being axially moveable in a reciprocating action in the valve bore, the sleeve having a central bore therethrough; a first check valve positioned downhole of the sleeve for sealing the central bore at a downhole end of the sleeve for forming a downhole piston face, fluid from the pump acting thereat to lift the sleeve uphole to block the one or more drain ports in a production position; and unsealing from the central bore for permitting fluid to flow therethrough in the production position; a second check valve positioned above the sleeve for unsealing from the central bore at an uphole end of the sleeve for permitting fluid to flow therethrough in the production position; and sealing the central bore for forming an uphole piston face, fluid in the production tubing string thereabove acting thereat to move the sleeve downhole to open the one or more drain ports in a drain position for draining fluid from the production tubing string therethrough. 
         [0011]    The first and second check valves are spaced by a valve stem for forming a check valve assembly which is freely, axially moveable in the sleeve. Spacing of a stop and an uphole shoulder in the housing permits the check valve assembly&#39;s axial, uphole movement to be stopped at the stop before the sleeve&#39;s axial, uphole movement is stopped by the uphole shoulder. This causes the first and second check valves to be unsealed from the sleeve for permitting uphole flow of fluids thereby in the production position. 
         [0012]    In another broad aspect of the invention, a method for operating a tubing drain valve, positioned between a production tubing string and a pump, for blocking one or more drain ports in a valve housing in a production position for producing fluid through a valve bore in the housing when the pump is operating and opening the one or more drain ports in a drain position for draining fluid from the production tubing when the pump is stopped, the method comprising: receiving fluid from the pump when operating the pump to flow fluid uphole; shifting a first check valve axially uphole to seal a central bore of a sleeve housed in the valve bore at a downhole end of the sleeve, for forming a downhole piston face; the fluid acting at the downhole piston face; lifting the sleeve to move axially uphole within the valve bore to block the one or more drain ports in the production position, arresting the uphole movement of the first check valve; and lifting the sleeve to unseal at least the first check valve from the central bore to permit the fluid to flow therethough receiving fluid from the production tubing when the pump is stopped for ceasing the flow of fluid uphole; moving a second check valve downhole to seal the central bore at an uphole end of the sleeve and for forming an uphole piston face, fluid in the production tubing thereabove acting at the uphole piston face; and shifting the sleeve downhole to open the one or more drain ports in the drain position. 
         [0013]    Advantageously, providing a seal which remains above the drain ports and a seal which remains below the drain ports extends the life of the seals as damage due to engagement of the seals with the drain ports is avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1A-1C  are longitudinal sectional views of a prior art drain valve illustrating the sequential action of the valve, more specifically, 
           [0015]      FIG. 1A  illustrates a valve cage shifted downhole sufficient to open shunt ports in a production tubing string and a piston therein biased to a downhole position for sealing a valve seat in the valve cage fluidly connected to a formation therebelow, fluid from the production tubing being drained through the shunt ports to an annulus; 
           [0016]      FIG. 1B  illustrates the valve cage shifted to an uphole position for closing the shunt ports and the valve head remaining biased to the downhole position for preventing flow therethrough from the formation below; and 
           [0017]      FIG. 1C  illustrates the valve cage in the uphole position for closing the shunt ports and the valve head shifted to a uphole production position by pressure from the pump therebelow for opening the valve seat to permit fluid flow to the production tubing string thereabove; 
           [0018]      FIG. 2A  is a longitudinal sectional view of a drain valve according to an embodiment of the invention, the valve being shown in a production position; 
           [0019]      FIG. 2B  is a longitudinal sectional view of a drain valve according to another embodiment of the invention, the first check valve being shown blocking a bore of the housing; 
           [0020]      FIG. 3  is an exploded perspective view of the drain valve according to  FIG. 2A   
           [0021]      FIG. 4  is a side view of a free floating check valve assembly axially moveable within the drain valve according to  FIG. 2A ; 
           [0022]      FIG. 5  is a perspective plan view of a sleeve axially moveable within a housing of the drain valve according to  FIG. 2A  illustrating a central support through which the free floating check valve assembly is mounted and a plurality of ports thereabout through which fluid is permitted to flow in a production position; 
           [0023]      FIG. 6  is a plan view of the sleeve of  FIG. 5 ; 
           [0024]      FIG. 7  is a side view of the free floating check valve assembly of  FIG. 4  in the sleeve of  FIG. 5 ; 
           [0025]      FIG. 8  is a side view of a lower housing section of the drain valve of  FIG. 2A , illustrating a plurality of drain ports formed thereabout; 
           [0026]      FIG. 9  is a side view of an upper housing section of the drain valve of  FIG. 2A  illustrating a opening for mounting a tag bar thereacross to stop upward travel of the check valve assembly therein; and 
           [0027]      FIGS. 10A-10F  are cross-sectional views of the drain valve according to  FIG. 2A  in operation and illustrating axial movement of the free floating check valve assembly and the sleeve therein as a result of pressure differentials between the pump discharge therebelow and the hydrostatic head in a production tubing string thereabove; more particularly 
           [0028]      FIG. 10A  illustrates the free floating check valve assembly, after pumping has stopped, having been moved axially downhole by pressure in the tubing string, to seat an uphole end of the check valve assembly to an uphole end of the sleeve for forming an uphole piston face; 
           [0029]      FIG. 10B  illustrates the drain valve in a drain position, the uphole piston face having been acted on by the pressure of the fluids in the tubing to move the check valve assembly and sleeve downhole to a maximum extent within the housing for opening the drain ports to the annulus; 
           [0030]      FIG. 10C  illustrates the drain valve when pumping is started, the check valve assembly being shifted axially uphole to seat the downhole end at a downhole end of the sleeve for forming a downhole piston face, the downhole end of the check valve assembly preventing fluid flow from the pump discharge therethrough; 
           [0031]      FIG. 10D  illustrates the pump discharge pressure acting on the downhole piston face for shifting the free floating check valve assembly and sleeve axially uphole to close the drain ports; 
           [0032]      FIG. 10E  illustrates the pump discharge pressure continuing to act on the downhole piston face for shifting the free floating check valve assembly axially to a maximum extent for sealing the sleeve to the housing above the drain ports and thereafter engaging an uphole end with a tag bar in the housing, the downhole end of the check valve assembly preventing fluid flow from the formation therethrough; and 
           [0033]      FIG. 10F  illustrates the drain valve in a production position, the sleeve shifted axially to a maximum extent, an uphole end of the sleeve engaging a shoulder in the housing and the downhole end of the check valve assembly being spaced below the downhole end of the sleeve for permitting fluid flow therethrough from the formation to the production tubing string. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Drain valves according to embodiments of the invention provide a positive force for shifting a sleeve to close drain ports in a housing when the drain valve is shifted from a drain position to a production position. Thus, the drain valve more reliably closes the drain ports even when there is debris positioned above the sleeve which typically contributes to fouling of prior art valves. 
         [0035]    In order to understand the unique and distinctive aspects of embodiments of the invention, a more detailed description of the general principles of a known prior art drain valve are first set forth. Embodiments of the present invention are described thereafter. 
       PRIOR ART 
       [0036]    As noted in the Background of the Invention herein, U.S. Pat. No. 6,289,990 to Baker Hughes Incorporated teaches a tubing shunt valve  10 . 
         [0037]    In operation, as shown in  FIGS. 1A-1C , when a pump (not shown) connected to a production tubing string S below the shunt valve  10  begins to operate ( FIG. 1B ), fluid pressure P generated by the pump closes shunt ports  12  in a body  13  of the tubing shunt valve  10 . A valve cage  14 , having a consistent hydrodynamic diameter, is forced upwards. The pressure P, downhole from the valve  10 , acts against a piston  16 , formed by the combination of a lower end  18  of the valve cage  14  and a spring-biased valve member  20  having a valve head  22 , housed therein. The valve head  22  initially closes a valve seat  24  ( FIG. 1B ) in the valve cage  14 . Produced fluid does not initially pass uphole through valve cage  14  because the valve head  22  is biased into sealing engagement with the valve seat  24  by a spring  26 . 
         [0038]    The valve cage  14  moves upwards until an upper end  28  abuts an upper interior rim  30  formed on an upper collar  32  in the valve body  13 . A seal  36  positioned below the shunt ports  12  is slid over the shunt ports  12  as the valve cage  14  slides over the shunt ports  12 . A lower seal  37  positioned at a downhole end of the valve cage  14  remains below the shunt ports, thus sealing the shunt ports  12 . 
         [0039]    The valve cage  14  abutting the upper interior rim  30  is no longer capable of further upward motion. Continued fluid pressure P from the pump therebelow overcomes the spring  26  ( FIG. 1C ) forcing the valve member  20  and valve head  22  to move upward out of sealing engagement with the valve seat  22  in a production position. Well fluid then passes through the valve seat  24  and upwards through passages  34  in the valve cage  14  and through the production tubing S thereabove. When the valve cage  14  is in the production position, the shunt ports  12  in the valve body  13  are closed by the valve cage  14 . The resulting closed shunt valve  10  prevents communication between the production tubing and an annulus between the production tubing S and casing in the wellbore. 
         [0040]    When the pump is shut down, a static column of produced fluid F is within the tubing above the shunt valve  10 . As the pump is shut down, fluid pressure P no longer acts upwards against the valve head  22 . The spring  26  biases the valve head  22  downward until the valve head  22  is in sealing engagement with the valve seat  24 , once again forming the piston  16 . The static column of produced fluid F opens the shunt valve  10  by forcing the valve cage  14  downward until the lower end  18  of valve cage  14  engages a lower interior rim  38  in the valve body  13  ( FIG. 1A ). When the valve cage  14  is in this lower, drain position, openings  40  in the valve cage  14  are in alignment with the shunt ports  12 . Produced fluid F is allowed to drain through the aligned ports  12 ,  40  to empty into the annulus. The produced fluid F will continue to flow out of the shunt ports  12  into the well annulus until pressure within the tubing string S and the annular area are equalized. 
         [0041]    Applicant believes that it is apparent that if there is any resistance to movement of the valve cage  14 , due to debris in the produced fluid, the spring biased valve head  22  will open before the valve cage  14  moves and blocks the shunt ports  12 , thus rendering the shunt valve  10  inoperative. 
       Embodiments of the Invention 
       [0042]    In a drain valve, according to embodiments of the invention, the valve cage of the prior art is replaced by a tubular piston or sleeve which is axially moveable within a housing. The biased valve member of the prior art is replaced by a first check valve and a second check valve which engage downhole and uphole ends of the sleeve, respectively, for forming downhole and uphole piston faces for moving the sleeve axially within the housing to block and open drain ports in the housing, as described herein. 
         [0043]    In greater detail and having references to  FIGS. 2A-9 , the valve  100  comprises, a housing  110  having a valve bore  112  therethrough. The valve bore  112  is in fluid communication with a string of production tubing thereabove and with a pump positioned therebelow. The production tubing and the pump are not illustrated but are well known. A tubular sleeve  114  is housed within the housing  110  and has a central bore  116  formed therethrough. The sleeve  114  is axially moveable in a reciprocating action within the housing  110 . The sleeve  114  moves uphole to block one or more drain ports  118  in the housing  110  in the production position when the pump is operating and moves downhole to open the one or more drain ports  118  in a drain position to drain produced fluid F from the production tubing. When the pump is stopped, the fluid F flows through the one or more drain ports  118  to an annulus between the production tubing and wellbore casing. 
         [0044]    As shown in  FIGS. 2A-4  and  FIGS. 10A-10F , a first check valve  120  is positioned below a downhole end  122  of the sleeve  114 . The first check valve  120  is axially moveable in the valve&#39;s bore  112  below the sleeve  114 . When the first check valve  120  is caused to move uphole to engage the sleeve&#39;s downhole end  122 , a downhole piston face DH is formed and the central bore  116  of the sleeve  114  is sealed. Discharge of fluid from the pump acts at the downhole piston face DH, creating a force to move the sleeve  114  uphole to block the one or more drain ports  118 . Uphole movement of the first check valve  120  is arrested and the sleeve  114  is caused to move further uphole to unseal from the first check valve  120  for opening the central bore  116  of the sleeve  114 , permitting fluids to flow thereby into the production tubing thereabove, in the production position. 
         [0045]    A second check valve  124  is positioned above the sleeve  114  and is unsealed from the sleeve  114  in the production position to permit fluids to flow thereby. When the pump is stopped, the second check valve  124  falls through gravity or is caused to move downhole to engage an uphole end  126  of the sleeve  114 , forming an uphole piston face UH. The central bore  116  of the sleeve  114  and the housing  110  therebelow are sealed by the uphole piston face UH, preventing fluid to flow thereby to the pump below. The hydraulic head of the fluid F in the production tubing acts at the uphole piston face UH, creating a force to move the sleeve  114  axially downhole, opening the one or more drain ports  118  in the drain position. The fluid F drains out of the valve bore  112  through the one or more drain ports  118  to the annulus. 
         [0046]    Having reference again to  FIGS. 2A-4 , and in an embodiment of the invention, the first and second check valves  120 , 124  are connected and spaced apart by a valve stem  128  for forming a free floating check valve assembly  130 . The valve stem  128  has a length longer in a length of the sleeve  114  so as to space the first check valve  120  from the second check valve  124  and permit both first and second check valves  120 ,  124  to be unsealed from the sleeve  114  in the production position. 
         [0047]    As shown in  FIGS. 5-7 , the sleeve  114  further comprises a tubular sleeve body  115  having a central bore  116  and a central support  132 , supported in the central bore  116  for guiding the axially, freely-moveable valve stem  128  therein. A flow passage  134  is formed circumferentially about the sleeve&#39;s central support  132 . The flow passage  134 , which may be a plurality of flow ports, permits pumped fluids to flow through the sleeve  114  when the drain valve  100  is in the production position. 
         [0048]    As seen in  FIG. 2A , and in one embodiment, a downhole portion of the valve&#39;s bore  112  has a reduced diameter  136  and the first check valve  120  is sized to seal therein for forming a check valve piston  138  in the drain position. Discharge from the pump acts on the check valve piston  138  to drive the check valve piston  138  uphole out of the reduced diameter  136  to engage the downhole end  122  of the sleeve  114  for forming the downhole piston face DH. 
         [0049]    Having reference to  FIGS. 2A ,  2 B,  3 ,  8  and  9 , the housing  110  comprises an uphole shoulder  140  spaced from a downhole shoulder  142  for limiting the maximal extent of the axial reciprocating movement of the sleeve  114  between the production position and the drain position. 
         [0050]    The housing  110  further comprises a stop  144  positioned above the uphole shoulder  140 . The stop  144  engages the second check valve  124  of the check valve assembly  130  for arresting the uphole movement of the first check valve  120  connected thereto, before the sleeve  114  reaches the uphole shoulder  140 . This results in the sleeve  114  being able to continue to move uphole and unseal from the first check valve  120  in the production position for permitting flow of fluids thereby. The position of the stop  144  and the uphole shoulder  140  the spacing of the first and second check valves  120 ,  124  and the spacing of the uphole and downhole ends  126 , 122  of the sleeve  114  co-operate to enable: the first check valve  120  to seal at the downhole end  126  of the sleeve  144  or the second check valve  124  to seal at the uphole end  122  of the sleeve  114  and for neither the uphole end  126  or the downhole end  122  of the sleeve  114  to be sealed to the check valve assembly  130  in the production position. 
         [0051]    Having reference to  FIG. 3 , the stop  144  is a tag bar positioned across the valve bore  112  of the housing  110 . The tag bar  144  is typically inserted into the housing  110  through mounting holes  146  in the housing&#39;s wall. 
         [0052]    As shown in  FIGS. 2A and 7 , embodiments of the invention incorporate a unique sealing arrangement for sealing above and below the one or more drain ports  118  in the production position and below the one or more drain ports  118  in the drain position. The sleeve  114  has a stepped outer wall  148 , which forms a major diameter Mj at the downhole end  122  and a minor diameter Mn at the uphole end  126 . A seal  150  is housed in the major diameter Mj of the sleeve  114  to seal between the sleeve  114  and the housing  110  at a corresponding major diameter  115  in the valve bore  112 . The seal  150  remains below the one or more drain ports  118  during reciprocation of the sleeve  114  between the production position and the drain position. The housing  110  is stepped inwardly above the one or more drain ports for forming a corresponding minor or reduced diameter  152 . A seal  154  is positioned between the sleeve&#39;s minor diameter Mn and the valve bore  116 . As shown in  FIG. 2A , the seal  154  is housed in the housing&#39;s reduced diameter  152  to seal against the minor diameter Mn of the sleeve  114  when the sleeve  114  is moved uphole to the production position. Thus, sliding contact between the seals  150 , 154  and the one or more drain ports  118 , which could act to prematurely wear the seals, is avoided. 
         [0053]    As shown in  FIGS. 2A ,  2 B,  3 ,  8  and  9 , in embodiments of the invention for the purposes of manufacture, the housing  110  comprises a lower tubular housing  156  and an upper tubular housing  158 . The upper and lower housings  156 , 158  together define the valve&#39;s bore  112 , in which the sleeve  114  and check valve assembly  130  are mounted. 
         [0054]    In one embodiment best seen in  FIGS. 2A ,  3 ,  8  and  9 , the lower housing  156  comprises the one or more drain ports  118  formed adjacent an uphole end  160 , the downhole shoulder  142  and the downhole reduced diameter portion  136 . The upper housing  158  comprises the inwardly stepped, reduced diameter  152  at a downhole end  162  which houses the seal  154  which engages the sleeve&#39;s minor diameter Mn, the uphole shoulder  140  and the mounting holes  146  for the tag bar  144 , positioned thereabove. 
         [0055]      FIG. 2B  illustrates another embodiment for manufacture of the housing  120  wherein the lower housing  156  comprises the downhole reduced diameter bore portion  136  and forms the downhole shoulder  142 . The upper housing  158  comprises the one or more drain ports  118  and the uphole shoulder  140 . The seal  154  is housed about the minor diameter Mn of the sleeve  114  which seals to the housing&#39;s reduced diameter  152 , above the one or more drain ports  118 . 
       In Operation 
       [0056]    In operation, as illustrated in  FIGS. 10A to 10F , embodiments of the drain valve  100  operatively shift between a drain position ( FIG. 10B ) and a production position ( FIG. 10F ), substantially through fluid actuation. 
         [0057]    As shown in  FIG. 10A , after the pump is stopped, the second check valve  124 , is moved downhole to engage the uphole end  126  of the sleeve  114 . The second check valve  124  and the sleeve  114  form the uphole piston face UH which seals the flow passage  134  of the central bore  116  through the sleeve  114  and therefore seals the valve&#39; bore  112  therebelow. 
         [0058]    As shown in  FIG. 10B , produced fluid F in the production tubing above the uphole piston face UH acts at the uphole piston face UH to shift the sleeve  114  downhole to open the one or more drain ports  118 . The produced fluid F is drained through the one or more open drain ports  118  to the annulus thereabout. 
         [0059]    As shown in  FIG. 10C , when the pump is operating, fluid is received from the pump and the first check valve  120  is shifted uphole to engage the downhole end  122  of the sleeve  114  for forming the downhole piston face DH. In the case of a reduced diameter  136 , the fluid positively drives the first check valve  120  out of the reduced diameter  136  to engage the sleeve  114 . The downhole piston face DH seals the flow passage  134  through the sleeve  114  and the valve bore  112  thereabove. 
         [0060]    As shown in  FIG. 10D , fluid from the pump acts at the downhole piston face DH to lift the sleeve  114  uphole to block the one or more drain ports  118 . 
         [0061]    As shown in  FIG. 10E , the sleeve  114  engages the upper seal  154  to seal against the housing  110  above the one or more drain ports  118  and thereafter, uphole movement of the first check valve  120  is arrested. 
         [0062]    As shown in  FIG. 10F , thereafter the sleeve  114  is further shifted axially uphole to unseal from the first check valve  120  for opening the flow passage  134 . Fluid from the pump flows uphole through the flow passage  134  to the production tubing thereabove. 
         [0063]    The method is described herein in greater detail for an embodiment wherein the first and second check valves  120 , 124  are spaced apart by the valve stem  128 , forming the check valve assembly  130 . 
         [0064]    After the pump[is stopped ( FIG. 10A ), the check valve assembly  130 , having been restrained at the tag bar  144  during production, is caused to move downhole such as by gravity or under the influence of produced fluid F received from the production tubing S thereabove. The second check valve  124  engages (A) the sleeve&#39;s uphole end  126 , forming the uphole piston face UH. The produced fluid F in the production tubing thereabove acts at the uphole piston face UH to create a force for moving the check valve assembly  130  and sleeve  114  downhole as a unitary piston. 
         [0065]    Having reference to  FIG. 10B , the valve  100  is shown in the drain position. The sleeve  114  and check valve assembly  130  are shifted downhole until the sleeve&#39;s downhole end  122  engages the downhole shoulder  142  in the valve bore  112 . The one or more drain ports  118  are opened to permit the produced fluid F to drain from the production tubing to the annulus. The first check valve  120  seals in the downhole, reduced diameter portion  136  of the valve bore  112  forming the check valve piston  138  therein. 
         [0066]    As shown in  FIG. 10C , when the pump is started and is operating, the discharge fluid flow from the pump is received and acts at the check valve piston  138 , positioned below the sleeve  114 , to shift the check valve assembly  130  axially uphole until the first check valve  120  engages (B) the downhole end  122  of the sleeve  114  forming the downhole piston face DH. 
         [0067]    Having reference to  FIG. 10D , the discharge fluid from the pump continues to act at the check valve piston  138  to shift the sleeve  114  and the check valve assembly  130  axially uphole within the valve bore  112 . The check valve piston  138  moves uphole out of the reduced diameter portion  136  of the valve bore  112 . Thereafter, the discharge fluid acts at the downhole piston face DH created by the engagement (B) of the first check valve  120  with the downhole end  122  of the sleeve  114 . 
         [0068]    As shown in  FIG. 10E , the discharge fluid continues to act at the downhole piston face DH to shift the check valve assembly  130  and sleeve  114  uphole to block the one or more drain ports  118 . The sleeve  114  seals to the housing  110  at seal  154  thereabove. Thereafter, the second check valve  124  engages (C) the tag bar  144 , arresting further uphole movement of the check valve assembly  130 . The first check valve  120  remains engaged at the downhole end  122  of the sleeve  114 , preventing flow of discharge fluids through the sleeve&#39;s flow passage  134 . 
         [0069]    Thereafter, as shown in  FIG. 10F , the discharge from the pump acts at the major diameter Mj at the downhole end  122  of the sleeve  114  to shift the sleeve  114  axially uphole, independent of the check valve assembly  130 . The sleeve  114  is shifted uphole until the sleeve&#39;s uphole end  126  engages the uphole shoulder  140  (D) in the valve bore  112 , the sleeve  114  unsealing from the first check valve  120  for opening the flow passage  134  through the sleeve  114 . 
         [0070]    The valve stem  128  is of sufficient length such that when the second check valve  124  has engaged the tag bar  144  and the sleeve  114  has engaged the uphole shoulder  140 , both the first and second check valves  120 , 124  are spaced from the downhole and uphole ends  122 , 126  of the sleeve  114 , opening the flow passage  134  therethrough. Thus, discharge flow from the pump is permitted to flow past the first check valve  120  into the fluid ports  134  in the sleeve  114  and from the fluid ports  134  in the sleeve  114  past the second check valve  124  to the production tubing S thereabove. 
         [0071]    In an embodiment of the invention, as the sleeve  114  is moved axially uphole to close the one or more drain ports  118 , the minor diameter Mn of the sleeve  114  passes the one or more drain ports  118  without contact. The sleeve  114  remains sealed to the housing  110  at the major diameter Mj, below the one or more drain ports  118  throughout the uphole movement of the sleeve  114 . Thus, the life of the seals  150 , 154  is extended as damage due to engagement of the seals  150 , 154  with the one or more drain ports  118  is avoided. 
       Example 
       [0072]    A tubing drain valve according to an embodiment of the invention is designed for use with 2⅞ inch external upset end (EUE) tubing. The valve is designed to operate at a pressure of 5,000 psi and at a design temperature of 150° F. The design flow rate is 50-1000 bbl/day. The valve is pressure-actuated as discussed herein and the materials for manufacture of the drain valve are selected to be compatible with produced fluids containing at least oil, water, solids, associated gas and CO 2 .