Patent Publication Number: US-2015083434-A1

Title: Annular relief valve

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/880,690, filed Sep. 20, 2013, which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention generally relate to a pressure relief valve assembly for a casing. 
     2. Description of the Related Art 
     Traditional well construction, such as the drilling of an oil or gas well, includes a wellbore or borehole being drilled through a series of formations. Each formation, through which the well passes, must be sealed so as to avoid an undesirable passage of formation fluids, gases or materials out of the formation and into the borehole. Conventional well architecture includes cementing casings in the borehole to isolate or seal each formation. The casings prevent the collapse of the borehole wall and prevent the undesired inflow of fluids from the formation into the borehole. 
     In standard practice, each succeeding casing placed in the wellbore has an outside diameter significantly reduced in size when compared to the casing previously installed. The borehole is drilled in intervals whereby a casing, which is to be installed in a lower borehole interval, is lowered through a previously installed casing of an upper borehole interval and then cemented in the borehole. The purpose of the cement around the casing is to fix the casing in the well and to seal the borehole around the casing in order to prevent vertical flow of fluid alongside the casing towards other formation layers or even to the earth&#39;s surface. 
     If the cement seal is breached, due to high pressure in the formations and/or poor bonding in the cement for example, fluids (liquid or gas) may begin to migrate up the borehole. The fluids may flow into the annuli between previously installed casings and cause undesirable pressure differentials across the casings. The fluid gas may also flow into the annuli between the casings and other drilling or production tubular members that are disposed in the borehole. Some of the casings and other tubulars, such as the larger diameter casings, may not be rated to handle the unexpected pressure increases, which can result in the collapse or burst of a casing or tubular. 
     Therefore, there is a need for apparatus and methods to prevent wellbore casing or tubular failure due to unexpected downhole pressure changes. 
     SUMMARY OF THE INVENTION 
     A pressure relief valve assembly may be coupled to one or more casings and/or tubular members to control fluid communication therebetween. The valve assembly is a one-way valve assembly that relieves pressure within an annulus formed between adjacent casings and/or tubular members to prevent burst or collapse of the casings and/or tubular members. In one embodiment, the valve assembly includes a tubular body having a port for fluid communication between an exterior of the valve assembly and an interior of the valve assembly; a chamber formed in a wall of the tubular body, the chamber in fluid communication with the port; a closure member disposed in the chamber and configured to control fluid communication through the port in response to a pressure differential; and a retaining member coupled to the closure member for retaining the closure member in an open position. 
     In another embodiment, the valve assembly includes a biasing member for biasing the closure member in a closed position. The valve assembly may include a plug disposed on an end opposite the closure member. In one aspect, the activation force of the closure member is adjustable. The activation force may be adjusted by changing a location of the plug. In another embodiment, the activation force may be adjusted by changing a length of the piston. 
     In another embodiment, a method of operating a valve assembly includes coupling a valve assembly to a casing and the valve assembly having a tubular body having a port for fluid communication between an exterior of the valve assembly and an interior of the valve assembly; a chamber formed in a wall of the tubular body, the chamber in fluid communication with the port; a closure member disposed in the chamber and configured to control fluid communication through the port; and a retaining member coupled to the closure member for retaining the closure member in an open position. The method further includes opening the valve assembly in response to a predetermined pressure differential between the exterior and the interior of the valve assembly, and retaining the closure member in the open position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic view of a wellbore. 
         FIG. 2  illustrates an exemplary embodiment of a valve assembly.  FIG. 2A  is a longitudinal cross-sectional view of a tubular body containing the valve assembly. 
         FIG. 3  is an enlarged cross-sectional view of the valve assembly of  FIG. 2  in the closed position. 
         FIG. 4  is an enlarged cross-sectional view of the valve assembly of  FIG. 2  in the open position. 
         FIG. 5  is a cross-sectional view of another embodiment of a valve assembly in the closed position.  FIG. 5A  is an enlarged, partial cross-sectional view of the valve assembly of  FIG. 5 . 
         FIG. 6  is a cross-sectional view of another embodiment of a valve assembly in the open position.  FIG. 6A  is an enlarged, partial cross-sectional view of the valve assembly of  FIG. 6 . 
         FIG. 7  illustrates an exemplary embodiment of a closure member. 
         FIG. 8  illustrates another exemplary embodiment of a closure member. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, a pressure relief valve assembly may be coupled to one or more casings and/or tubular members to control fluid communication there between. The valve assembly is a one-way valve assembly that relieves pressure within an annulus formed between adjacent casings and/or tubular members to prevent burst or collapse of the casings and/or tubular members. The valve assembly may be resettable downhole. 
       FIG. 1  illustrates a wellbore  5  formed within an earthen formation  80 . The walls of the wellbore  5  are reinforced with a plurality of casings  10 ,  20 ,  30  of varying diameters that are structurally supported within the formation  80 . The casings  10 ,  20 ,  30  are fixed within the formation  80  using a sealing material  15 ,  25 ,  35 , such as cement, which prevents the migration of fluids from the formation  80  into the annuli between the casings  10 ,  20 ,  30 . One or more tubular members  40 ,  45 , such as drilling or production tubular members, may also be disposed in the wellbore  5  for conducting wellbore operations. An annulus “A” is formed between the casing  10  and the casing  20 , and an annulus “B” is formed between the casing  20  and the tubular member  40 , which may also be a casing. It is important to note that the embodiments described herein may be used with other wellbore arrangements and are not limited to use with the wellbore configuration illustrated in  FIG. 1 . 
     The wellbore  5  may intersect a high pressure zone  50  within the formation  80 . Fluids within the high pressure zone  50  are sealed from the annulus A and B by the sealing material  25  that is disposed between the casing  20  and the wellbore wall. In the event that the sealing material  25  is breached or otherwise compromised, pressurized fluids may migrate upward into the annulus A and cause an unexpected pressure increase. The pressure rise may form a pressure differential across the casings  10 ,  20  that, if unchecked, may result in leakage through or burst of casing  10 , and/or leakage through or collapse of casing  20 . One or more valve assemblies  300 ,  700  are provided to relieve the pressure in the annulus A prior to failure of one or both of the casings  10 ,  20 . 
       FIG. 2  illustrates an exemplary embodiment of a valve assembly  700  for relieving pressure in annulus A to prevent failure of the casings  10 ,  20 . The valve assembly  700  may be coupled to the casing  20  in  FIG. 1 , but each of the casings  10 ,  20 ,  30  and/or the tubular members  40 ,  45  may similarly include one or more of the valve assembly  700  as described herein. The valve assembly  700  may be coupled to the casings  10 ,  20 ,  30  and/or the tubular members  40 ,  45  using a thread connection, a welded connection, and/or other similar connection arrangements. The valve assembly  700  may also be integral with the casings. 
       FIG. 2  is a cross-sectional view of an exemplary valve assembly  700  positioned in a wall of a tubular body  705 .  FIG. 2A  is a longitudinal cross-sectional view of the tubular body  705  containing the valve assembly  700 . The tubular body  705  has an axial bore  701  formed therethrough and may include threads for connection to a tubular such as casing  20 . In another embodiment, the tubular body may be integral with the casing. In yet another embodiment, the valve assembly  700  may be disposed in an enlarged section of a tubular body. 
       FIGS. 3 and 4  are enlarged cross-sectional views of the valve assembly  700  in the closed position and the open position, respectively. The tubular body  705  has a relief port  715  formed through the wall of the body  705  for selective fluid communication between an exterior of the casing  20  and an interior of the casing  20 . In another embodiment, the body  705  may include a plurality of valve assemblies circumferentially spaced around the body  705 . Additionally, the body  705  may include multiple valve assemblies disposed at different locations along the length of the body  705 . Valve assemblies disposed at different axial locations on the body  705  may reduce the effect the valve assemblies have on the integrity, e.g., tensile strength, of the valve body  705 . In yet another embodiment, the valve assemblies may be positioned in an enlarged, concentric or eccentric section of the tubular body. Placement of the valve assembly in the enlarged cross section of the concentric or eccentric section may offset the effects on tensile strength, burst resistance, and collapse resistance on the body. 
     The tubular body  705  includes a chamber  713  for housing a closure member  720 . The closure member  720  is used to operate the relief port  715 . An exemplary closure member is a piston  720 . In one embodiment, the piston  720  includes a first portion  721  having a smaller diameter than a second portion  722 . A seal  731 ,  732  is disposed around each of the first and second portions  721 ,  722  of the piston  720  for sealing engagement with the chamber  713 . An exemplary seal is an o-ring. The piston  720  is movably disposed in the chamber  713  to operate the valve. As shown, the piston  720  is biased in the closed position using a biasing member  735 . Exemplary biasing members  735  include a coil spring or a wave spring. The biasing member  735  may be configured to retract in response to a force near or below the burst or collapse rating of the casing  20 . One or more plugs may optionally be used to enclose the chamber  713 . In the embodiment as shown, three plugs  727 ,  728  are used to close off openings in the tubular body  705  formed during manufacture of the valve assembly  700 . The plugs  727 ,  728  may optionally include a seal  726 , a retaining ring  729 , or both. 
     In one embodiment, the chamber  713  can fluidly communicate with the relief port  715  and a chamber port  719  of the body  705 . The relief port  715  allows fluid communication between the bore  701  and the portion  741  of the chamber  713  defined by the first seal  731 . The chamber port  719  allows fluid communication between the bore  701  and the portion  742  of the chamber  713  defined by the second seal  732 . An inflow port  718  and an actuation port  745  allow fluid communication between the exterior of the tubular body  705  and the portion  743  of the chamber  713  between the first seal  731  and the second seal  732 . In this respect, these ports  718 ,  745  are blocked from fluid communication with the bore by the closure member  720  when the valve assembly  700  is in the closed position. The inflow port  718  and the actuation port  745  are positioned such that in the open position, the inflow port  718  is allowed to communicate with the relief port  715 , and the actuation port  745  remains blocked from communication with the bore  701 . 
     Referring back to  FIG. 1 , the valve assembly  700  may be operable to control fluid communication between the annulus A and the annulus B. The annulus A surrounds the valve assembly  700 , and the annulus B is in fluid communication with the bore  701  of the valve assembly  700 . 
       FIG. 3  shows the valve assembly  700  in the closed position. During operation, the biasing member  735  and the pressure in annulus B are acting on the piston  720  to keep the valve assembly closed. The pressure in annulus B is acting on both sides of the piston  720  via the relief port  715  and the chamber port  719 . Because the second portion  722  of the piston  720  has a larger diameter than the first portion  721 , the pressure in annulus B has an overall effect of urging piston  720  to the closed position. The pressure in annulus A may act on the piston  720  via the actuation port  745 . The annulus A pressure acts on a tapered section of the piston  720  where the diameter changes to urge the piston  720  toward the open position. 
     When the pressure in annulus A is sufficient to overcome the biasing force and the force from the annulus B pressure, the piston  720  is retracted to open the inflow port  718  and place the inflow port  718  in fluid communication with the relief port  715 .  FIG. 4  shows the valve assembly  700  in the open position. As shown, the piston  720  has moved to a position where the first seal  731  is disposed between the actuation port  745  and the inflow port  718 . Pressurized fluid may flow from the annulus A to the annulus B through the inflow port  718 , the chamber  713 , and the relief port  715  of the valve assembly  700 . Fluid from the actuation port  745  is blocked from communication with the relief port  715  by the first seal  731 . The valve assembly  700  is thus operable to relieve and prevent any pressure differential that may cause burst or collapse of the casings  10 ,  20 . 
     When the force on piston  720  due to pressure in the annulus A decreases below the sum of the force on piston  720  due to pressure in annulus B plus the biasing force of the biasing member  735 , the biasing member  735  returns the piston  720  to the closed position, thereby closing off fluid communication through the relief port  715 . In this manner, the valve assembly  700  is operable as a one-way valve in that it will permit fluid flow into the bore  701  of the valve assembly  700  but will prevent fluid flow out of the bore  701  via the relief port  715 . The valve assembly  700  is automatically resettable downhole and may be operated multiple times in response to any pressure fluctuations within the wellbore  5 . As stated above, any of the casings  10 ,  20 ,  30  and/or the tubular members  40 ,  45  may each be provided with one or more valve assemblies  700  to allow fluid flow from a surrounding casing or tubular member to an inner casing or tubular member, while preventing fluid flow in the opposite direction. 
       FIGS. 5 and 6  are cross-sectional views of another exemplary embodiment of a valve assembly  300  positioned in a wall of a tubular body  305 .  FIG. 5  shows the valve assembly  300  in the closed position, and  FIG. 6  shows the valve assembly  300  in the open position.  FIGS. 5A and 6A  are enlarged, partial views of  FIGS. 5 and 6 , respectively. The tubular body  305  may be the tubular body  705  shown in  FIG. 2A . The tubular body  305  has an axial bore  301  formed therethrough and may include threads for connection to a tubular such as casing  20 . In another embodiment, the tubular body  305  may be integral with the casing  20 . In yet another embodiment, the valve assembly  300  may be disposed in an enlarged section of a tubular body  305 . 
     Referring to  FIGS. 5 and 5A , the tubular body  305  has a relief port  315  formed through the wall of the body  305  for selective fluid communication between an exterior of the body  305  and an interior of the body  305 . In another embodiment, the body  305  may include a plurality of valve assemblies circumferentially spaced around the body  305 . Additionally, the body  305  may include multiple valve assemblies disposed at different locations along the length of the body  305 . Valve assemblies disposed at different axial locations on the body  305  may reduce the effect the valve assemblies have on the integrity, e.g., tensile strength, of the valve body  305 . In yet another embodiment, the valve assemblies may be positioned in an enlarged, concentric or eccentric section of the tubular body. Placement of the valve assembly in the enlarged cross section of the concentric or eccentric section may offset the effects on tensile strength, burst resistance, and collapse resistance on the body. 
     The tubular body  305  includes a chamber  313  for housing a closure member  320 . The chamber  313  is in fluid communication with the bore  301  via the relief port  315  and a chamber port  319 . Also, the chamber  313  is in selective fluid communication with the exterior of the tubular body  305  via an inflow port  318 . In one embodiment, the chamber  313  may include a shoulder  344  disposed between a smaller diameter section  311  of the chamber  313  and a larger diameter section  312  of the chamber  313 . 
     The closure member  320  is used to selectively control fluid communication between the relief port  315  and the inflow port  318 . An exemplary closure member is a piston  320 . In one embodiment, as shown in  FIG. 5A , the piston  320  includes a body portion  321 , a head portion  322 , a retaining member  323 , and a base portion  324 . The body portion  321  may include a stem coupled to the head portion  322 . The head portion  322  is configured to block fluid communication through the inflow port  318 . In one embodiment, the inflow port  318  has a smaller diameter than the smaller diameter section  311  of the chamber  313 . In this embodiment, the head portion  322  may include a smaller diameter nose section configured to seal the inflow port  318 . A sealing member  332  is disposed around the nose section for sealingly engaging the inner surface of the inflow port  318 . It is contemplated that the head portion  322  may take on any suitable shape so long as the head portion  322  is adapted to block fluid communication between the inflow port  318  and the relief port  315 . The body portion  321  may be configured to be at least partially disposed in the smaller diameter section of the chamber  313 . The base portion  324  is coupled to the other end of the body portion  321  and is adapted to engage a biasing member  335 . A sealing member  331  is disposed between the body portion  321  and the base portion  324  and is configured to sealingly engage the chamber  313 . Exemplary sealing member  331 ,  332  is an o-ring. Although the piston  320  is described as having multiple portions, it is contemplated that one or more of the portions may be integrated with each other. For example, the head portion  322  and the body portion  321  may form a single body portion. The portions of the piston  320  may be connected using threads, interference fit, and other suitable connection mechanisms. The base portion  324  may optionally include a retrieval receptacle for receiving a retrieval tool to facilitate removal of the piston  320  from the chamber  313 . 
     The retaining member  323  is coupled to the head portion  322  and is configured to retain the piston  320  in the open position. In one embodiment, the retaining member is a collet  323 . The collet  323  may extend along the stem of the body portion  321  and may flex radially inwardly and outwardly. As shown in  FIG. 5A , the collet  323  is flexed inwardly due to being positioned in the smaller diameter section  311  of the chamber  313 . The collet  323  flex outwardly when it is in the larger diameter section  312  of the chamber  313 , as shown in  FIG. 6A . The collet  323  may help resist retraction of the piston  320 . 
     Referring back to  FIG. 5 , the piston  320  is movably disposed in the chamber  313  to operate the valve  300 . As shown, the piston  320  is biased in the closed position using a biasing member  335 . Exemplary biasing members  335  include a coil spring or a wave spring. The biasing member  335  may be configured to retract in response to a force near or below the collapse rating of the casing  20 . 
     A plug  328  is provided to engage the other end of the biasing member  335  and to enclose the chamber  313 . The plug  328  is disposed in an opening  375  of the tubular body  305  that leads to the chamber  313 . As shown, the opening  375  has a larger diameter than the chamber  313 , thereby forming a shoulder  376  at the interface. In another embodiment, the opening  375  may have the same or different diameter than the chamber  313 . The plug  328  may optionally include a seal  326  to prevent communication through the opening  375 . The plug  328  may include a recess for receiving the seal  326 . The plug  328  may separate into a front section and a body section at the recess to facilitate installation of the seal  326 . The two sections may be connected using threads, interference fit, and other suitable connection mechanisms. The front section may include an outer diameter of sufficient size to engage the shoulder  376 . The plug  328  may optionally include a retrieval receptacle for receiving a retrieval tool to facilitate removal of the plug  328  from the opening  375 . In another embodiment, the body section may include threads for attachment to the opening  375 . In addition to threads, it is contemplated that the plug  328  may attach to the opening  375  using an interference fit, a locking mechanism such as a pin or screw, or any suitable attachment mechanism. 
     In one embodiment, the valve assembly  300  includes an adjustable activation pressure feature. Referring again to  FIGS. 5 and 5A , the opening force may be adjusted by changing the distance between the plug  328  and the piston  320  in the closed position. The change in distance, in turn, changes the force required to compress the biasing member  335 , thereby retracting the piston  320  to the open position. In one embodiment, the plug  328  is threadedly connected to the opening  375 . The threads allow adjustment of the distance between the plug  328  and the piston  320 . In another embodiment, the distance may be changed by adjusting the length of the stem of the body portion  321 . 
     Referring to  FIG. 5 , the chamber  313  can fluidly communicate with the relief port  315  and the chamber port  319  of the tubular body  305 . The relief port  315  allows fluid communication between the bore  301  and the portion of the chamber  313  between seals  331 ,  332  of the piston  320 . The chamber port  319  allows fluid communication between the bore  301  and the portion of the chamber  313  defined by the first seal  331  and the plug  328 . The inflow port  318  allows selective fluid communication between the exterior of the tubular body  305  and the interior of the tubular body  305 . The inflow port  318  is blocked from fluid communication with the bore  301  by the closure member  320  when the valve assembly  300  is in the closed position. 
     Referring back to  FIG. 1 , the valve assembly  300  may be operable to control fluid communication between the annulus A and the annulus B. The annulus A surrounds the valve assembly  300 , and the annulus B (i.e., the interior of the tubular body  305 ) is in fluid communication with the bore  301  of the valve assembly  300 . 
       FIG. 5  shows the valve assembly  300  in the closed position. During operation, the biasing member  335  and the pressure in annulus B are acting on the piston  320  to keep the valve assembly  300  closed. The pressure in annulus B is acting on both sides of the first seal  331  of the piston  320  via the relief port  315  and the chamber port  319 . The pressure in annulus B is also acting on the interior side of the second seal  332 . The pressure in annulus A may act on the front of the piston  320  via the inflow port  318  to urge the piston  320  toward the open position. 
     When the pressure in annulus A is sufficient to overcome the biasing force of the biasing member  335  and the force from the annulus B pressure, the piston  320  is retracted to open the inflow port  318  and place the inflow port  318  in fluid communication with the relief port  315 .  FIGS. 6 and 6A  show the valve assembly  300  in the open position. In one embodiment, the activation force required to open the inflow port  318  is set below the collapse pressure of the casing  20 . As shown, the piston  320  has moved to a position where pressurized fluid is allowed to flow from annulus A to annulus B through the inflow port  318 , the chamber  313 , and the relief port  315  of the valve assembly  300 . Also, the collet  323  has moved to the larger diameter section of the chamber  313 , whereby the collet  323  is allowed to flex outward to engage the shoulder  344 . In this respect, the collet  323  helps maintain the piston  320  in the open position. The valve assembly  300  is thus operable to relieve and prevent any pressure differential that may cause collapse of the casings  10 ,  20 . 
     The relief port  315  is closed when the net force acting on the piston  320  (due to pressure differential between annulus A and annulus B and to the spring force) decreases to a threshold closing force sufficient to release the collet  323 , which in turn, returns the piston  320  to the closed position. Because the collet  323  helps to retain the piston  320  in the open position, the pressure differential between annulus A and annulus B required to close the port  315  is smaller than the pressure differential required to open the port  315 . If the pressure in annulus A decreases, the port  315  will remain open as long as the pressure differential is greater than the closing pressure differential. In this manner, the valve assembly  300  is operable as a one-way valve that permits fluid flow into the bore  301  of the valve assembly  300  but prevents fluid flow out of the bore  301  via the relief port  315 . The valve assembly  300  is automatically resettable downhole and may be operated multiple times in response to pressure fluctuations within the wellbore  5 . As stated above, any of the casings  10 ,  20 ,  30  and/or the tubular members  40 ,  45  may each be provided with one or more valve assemblies  300  to allow fluid flow from a surrounding casing or tubular member to an inner casing or tubular member, while preventing fluid flow in the opposite direction. 
       FIG. 7  illustrates another embodiment of a closure member  420 . The closure member  420  is suitable for use with the valve  300  of  FIG. 5 . In this embodiment, the closure member is a piston  420 . As shown, the piston  420  includes a head portion  422 , a body portion  421 , and a base portion  424  that are integrated as a single body  421 . In another embodiment, the portions  421 ,  422 ,  424  may be made of two or more connected portions. The piston  420  also includes a retaining member  423  disposed around the body portion  421 . The head portion  422  is configured to block fluid communication through the inflow port  318 . In this embodiment, the head portion  422  may include a smaller diameter nose section configured to seal the inflow port  318 . A sealing member  432  is disposed around the nose section for sealingly engaging the inner surface of the inflow port  318 . It is contemplated that the head portion  422  may take on any suitable shape so long as the head portion  422  is adapted to block fluid communication between the inflow port  318  and the relief port  315 . The body portion  421  may be configured to be at least partially disposed in the smaller diameter section  311  of the chamber  313 . The base portion  424  is adapted to engage a biasing member  335 . A sealing member  431  is disposed around the base portion  424  and is configured to sealingly engage the chamber  313 . Exemplary sealing member  431 ,  432  is an o-ring. The base portion  424  may optionally include a retrieval receptacle for receiving a retrieval tool to facilitate removal of the piston  420  from the chamber  313 . 
     The retaining member  423  is coupled to the body portion  421  and is configured to retain the piston  420  in the open position. In this embodiment, the retaining member is an o-ring  423  that may be disposed in a recess in the body portion  421 . The o-ring  423  is compressed when disposed in the smaller diameter section of the chamber  313 . When the piston  420  is retracted to open the inflow port  318 , the o-ring  423  is moved to the larger diameter section  312  of the chamber  313 , whereby the o-ring is allowed to expand outward to engage the shoulder  344 . In this respect, the o-ring  423  can help maintain the piston  420  in the open position. The relief port  315  is closed when the forces acting on the piston  320  due to pressure differential between annulus A and annulus B and to the spring force decreases to a threshold closing force sufficient to compress the o-ring  423  sufficiently to allow the o-ring  423  to move into the smaller diameter section of the chamber  313 . 
       FIG. 8  illustrates another embodiment of a closure member  520 . The closure member  520  is suitable for use with the valve  300  of  FIG. 5 . In this embodiment, the closure member is a piston  520 . As shown, the piston  520  includes a head portion  522 , a body portion  521 , and a base portion  524  that are integrated as a single body  521 . In another embodiment, the portions  521 ,  522 ,  524  may be made of two or more connected portions. The piston  520  also includes a retaining member  523  disposed around the body portion  521 . The head portion  522  is configured to block fluid communication through the inflow port  318 . In this embodiment, the head portion  522  may include a smaller diameter nose section configured to seal the inflow port  318 . A sealing member  532  is disposed around the nose section for sealingly engaging the inner surface of the inflow port  318 . It is contemplated that the head portion  522  may take on any suitable shape so long as the head portion  522  is adapted to block fluid communication between the inflow port  318  and the relief port  315 . The body portion  521  may be configured to be at least partially disposed in the smaller diameter section of the chamber  313 . The base portion  524  is adapted to engage a biasing member  335 . A sealing member  531  is disposed around the base portion  524  and is configured to sealingly engage the chamber  313 . Exemplary sealing member  531 ,  532  is an o-ring. The base portion  524  may optionally include a retrieval receptacle for receiving a retrieval tool to facilitate removal of the piston  520  from the chamber  313 . 
     The retaining member  523  is coupled to the body portion  521  and is configured to assist with retaining the piston  520  in the open position. In this embodiment, the retaining member is a snap ring  523  that is disposed in a recess in the body portion  521 . The snap ring  523  is compressed when disposed in the smaller diameter section  311  of the chamber  313 . When the piston  520  is retracted to open the inflow port  318 , the snap ring  523  is moved to the larger diameter section  312  of the chamber  313 , whereby the snap ring  523  is allowed to expand outward to engage the shoulder  344 . In this respect, the snap ring  523  can help maintain the piston  520  in the open position. The relief port  315  is closed when the forces acting on the piston  320  due to pressure differential between annulus A and annulus B and to the spring force decreases to a threshold closing force sufficient to compress the snap ring  523  sufficiently to allow the snap ring  523  to move into the smaller diameter section of the chamber  313 . 
     In yet another embodiment, the valve assembly  700  of  FIG. 3  may be equipped with a retaining member as described herein, including a collet, an o-ring, or a snap ring. The retaining member may be used to retain the closure member  720  in the open position. In this respect, the pressure differential needed to close the valve assembly  700  must be sufficient to release the retaining member before the closure member  720  is allowed to close. 
     In any of the embodiments described herein, any of the casings  10 ,  20 ,  30  and/or the tubular members  40 ,  45  may each be provided with one or more valve assemblies  300  and  700  to allow fluid flow from a surrounding casing or tubular member to an inner casing or tubular member, while preventing fluid flow in the opposite direction. In one embodiment, a casing or tubular member may be provided with multiple valve assemblies that are spaced apart along the length of the casing or tubular member. The valve assemblies  300  and  700  may be operable to open and/or close at different pre-determined pressure setting. 
     Embodiments of the valve assemblies  300  and  700  may be used to prevent collapse of a casing. For example, during an uncontrolled flow situation such as a catastrophic blowout, the hot hydrocarbon fluids from lower portions of the well may heat the fluid which is trapped in the annular space between an outer casing and an inner casing. The annular space may extend from top of the cement level to liner hanger. If the inner casing extends to the surface, then the annul area may extend from the top of the cement level and up to the surface. When the trapped fluid in the annular space is heated by the hot hydrocarbon fluids, the trapped fluid will expand. In some instances, this expansion can collapse the inner casing, thereby making future mitigation of the well more problematic. In this situation, presence of the valve assemblies  300  and  700  allow the inner casing to bleed the pressure caused by the heat expansion. As a result, easier methods such as a capping stack can be used to get the well under control again. 
     In one or more embodiments described herein, the valve assembly is configured to open at a predetermined pressure differential, thereby to preventing burst or collapse of the casings and/or tubular members. 
     In one embodiment, the valve assembly includes a tubular body having a port for fluid communication between an exterior of the tubular body and an interior of the tubular body; a chamber formed in a wall of the tubular body, the chamber in fluid communication with the port; a closure member disposed in the chamber and configured to control fluid communication through the port in response to a pressure differential; and a retaining member coupled to the closure member for retaining the closure member in an open position. 
     In one or more of the embodiments described herein, the valve assembly includes a biasing member for biasing the closure member in a closed position. 
     In one or more of the embodiments described herein, the valve assembly may include a plug disposed on an end opposite the closure member. 
     In one or more of the embodiments described herein, the activation force of the closure member is adjustable. In one or more of the embodiments described herein, the activation force may be adjusted by changing a location of the plug. In another embodiment, the activation force may be adjusted by changing a length of the piston. 
     In one or more of the embodiments described herein, the retaining member is configured to retain the closure member in the open position until reaching a predetermined differential pressure between the exterior and the interior of the valve assembly. 
     In one or more of the embodiments described herein, the retaining member is configured to engage a wall of the chamber to retain the closure member in the open position. 
     In one or more of the embodiments described herein, the retaining member is selected from the group consisting of a collet, an o-ring, a snap ring, and combinations thereof. 
     In another embodiment, a method of operating a valve assembly includes coupling a valve assembly to a casing and the valve assembly having a tubular body having a port for fluid communication between an exterior of the valve assembly and an interior of the valve assembly; a chamber formed in a wall of the tubular body, the chamber in fluid communication with the port; a closure member disposed in the chamber and configured to control fluid communication through the port; and a retaining member coupled to the closure member for retaining the closure member in an open position. The method further includes opening the valve assembly in response to a predetermined pressure differential between the exterior and the interior of the valve assembly, and retaining the closure member in the open position. 
     In one or more of the embodiments described herein, the method further includes closing the valve assembly in response to a second predetermined pressure differential. 
     In one or more of the embodiments described herein, the predetermined pressure differential to open the valve assembly is different from the second predetermined pressure differential to close the valve assembly. 
     In one or more of the embodiments described herein, the method further includes repeatedly opening and closing the valve assembly in response to respective predetermined pressure differentials. 
     In one or more of the embodiments described herein, a second pressure differential to close the port is smaller than the predetermined pressure differential. 
     In one or more of the embodiments described herein, a net force acting on the closure member is sufficient to release the retainer member. 
     While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.