Valves comprise a chamber having a piston disposed therein. One side of the piston defines a hydrostatic chamber in fluid communication with an outside environment, such as wellbore annulus, through a port. Operatively associated with the piston on the other side is a sleeve in sliding engagement with an inner mandrel. The inner mandrel comprises a port that is initially blocked by the sleeve. Upon an increase in pressure within the annulus, the piston is moved causing the port in the sleeve to align with the port in the inner mandrel thereby allowing fluid to flow from the annulus into the bore of the inner mandrel. As a result, fluid can be circulated through the valve, or pressure within the annulus can be reduced. A return member is operatively associated with the piston to urge the piston toward the closed position after pressure within the wellbore annulus is reduced.

BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The invention is directed to valves for compensating for pressure changes within an annulus of an oil or gas wellbore. 
         [0003]    2. Description of Art 
         [0004]    Valves can be used in oil and gas well completions to facilitate displacement of drilling fluids, such as drilling mud, out of the well by pumping completion fluids down the wellbore. In general, these valves allow the completion fluid to be pumped down the wellbore causing the drilling fluid within the wellbore annulus to flow into the valve and, thus, a tubular string containing the valve, and then upward within the tubular string to the surface of the well. 
         [0005]    Wellbore barriers such as packers, bridge plugs and the like are used to seal or isolate zones or areas of an annulus of wellbores. In general, the wellbore barriers are disposed within a wellbore above and below a “zone” or area of the wellbore in which production, or other wellbore intervention operations are performed. In some instances, the isolated zone is not being produced or intervention operations are not being performed, however, tubing, e.g., an inner casing, is disposed through this zone so that oil or gas production or other downhole operations can be performed below the isolated zone. In these instances, the fluid trapped or sealed in this isolated zone can expand do to increases in the temperature of the fluid trapped in the isolated zone. When the temperature increases, such as during production from other zones within in the wellbore, the fluid expands and can cause damage to the inner casing of the wellbore, the outer casing of the wellbore, other components within the wellbore, or the formation itself. To reduce the likelihood of such damage, devices to relieve the pressure in the isolated zone are employed. 
       SUMMARY OF INVENTION 
       [0006]    The valves disclosed herein facilitate one or both of circulation of drilling and completion fluids within an annulus of a wellbore and relief of the increased pressure within an isolated wellbore annulus. Broadly, the valves disclosed herein comprise an outer mandrel comprising an inner wall surface defining an outer mandrel bore, an outer wall surface, and an outer mandrel port disposed in the outer wall surface of the outer mandrel and in fluid communication with the outer mandrel bore. An inner mandrel disposed is within the outer mandrel bore. The inner mandrel comprises an inner wall surface defining an inner mandrel bore, an outer wall surface, and an inner mandrel port disposed in the outer wall surface of the inner mandrel and in fluid communication with the inner mandrel bore. The outer mandrel is fixed to the inner mandrel at a first end thereby providing an annulus between the outer wall surface of the inner mandrel and the inner wall surface of the outer mandrel. A sleeve, which comprises a sleeve port, is disposed within the annulus and in sliding engagement with the inner wall surface of the outer mandrel and the outer wall surface of the inner mandrel. The sleeve moves within the annulus due to an increase in pressure within an isolated outside environment until the sleeve port is at least partially aligned with the port of the inner mandrel. Fluid such as drilling and completion fluids can be circulated between the wellbore annulus and the inner mandrel bore during completion operations. Moreover, after one or more barriers, such as packers, are set to provide an isolated wellbore annulus, fluid can be transferred between the isolated wellbore annulus and the inner mandrel bore so that the valve functions as a pressure relief device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIGS. 1A and 1B  comprise a cross-sectional view of one specific embodiment of a valve disclosed herein shown in the closed position. 
           [0008]      FIGS. 2A and 2B  comprise a cross-sectional view of the valve of  FIG. 1  shown in the opened position. 
           [0009]      FIG. 3  is a cross-sectional view of the valve of  FIGS. 1A and 1B  taken along line  3 - 3  (shown in  FIG. 1B ). 
       
    
    
       [0010]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0011]    Referring now to  FIGS. 1-3 , in one specific embodiment, valve  10  is shown. Broadly, this embodiment of valve  10  comprises top sub  12  connected to piston housing  20  which is connected to inner mandrel  30  and outer mandrel  40 . Top sub  12  is connected to piston housing  20 , and piston housing  20  is connected to inner mandrel  30  and outer mandrel  40 , through any method or device known in the art such as through threads (not shown). Gage ring  50  provides port  52  in fluid communication with piston chamber  54  so that fluid flowing from outside valve  10  through port  52  and into piston chamber  54  causes piston  56  to move downward (i.e., toward the right in the Figures). Screen  53  is disposed over port  52  to restrict debris from entering port  52  and causing interference with the movement of piston  56 . 
         [0012]    Piston  56  comprises upper end  57 , lower end  58 , and piston seals  59 . Although piston  56  may comprise a circular, concentrically-disposed, sleeve-type piston, in the embodiment shown in the Figures, piston  56  comprises a partial sleeve. Downward movement, i.e., to the right in the Figures, of piston  56  is restricted by piston stop  60  shown as a restriction of the inner diameter of piston chamber  54 . Similarly, upward movement, i.e., to the left in the Figures, of piston  56  is restricted by piston stop  61  shown as a separate component disposed on the wall of piston chamber  54 . 
         [0013]    Piston mandrel  64  facilitates connection between piston  56  and upper coupling  66 . 
         [0014]    Disposed between outer wall surface  32  of inner mandrel  30  and inner wall surface  42  of outer mandrel  40  is annulus  68 . Disposed in annulus  68  is piston mandrel  64  secured to upper coupling  66 , which is operatively associated with a return member, shown in the embodiments of the Figures as including spring  70 . Spring  70  is disposed within sleeve  72 . Spring stop or detent  74  provides a surface for compression of spring  70 . Detent  74  is maintained against outer wall surface  32  of inner mandrel  30 , but is not secured to sleeve  72  or outer mandrel  40 . In one embodiment, detent  74  is maintained against outer wall surface  32  by the force generated by spring  70  pushing detent  74  into shoulder  75 . Attachment member  67 , shown as a c-ring, is also operatively associated with upper coupling  66  to secure upper coupling  66  to sleeve  72 . 
         [0015]    In addition to spring  70 , return member can also comprise atmospheric chamber  73 . As a result, as upper coupling  66  moves downward, pressure within atmospheric chamber  73  becomes compressed or energized ( FIG. 2 ) such that as the pressure below piston dissipates, the energized atmospheric chamber  73  urges piston  56  upward toward port  52 , i.e., toward the “run-in” position or closed position ( FIG. 1 ). 
         [0016]    In addition to being connected to upper coupling  66  at an upper end by attachment member  67 , sleeve  72  is connected at a lower end to lower coupling  76 . As shown in the specific embodiment of  FIGS. 1-3 , upper coupling  66  is in a sliding engagement with outer wall surface  32  of inner mandrel  30 ; however, upper coupling  66  is not required to be in contact with outer wall surface  32 . Similarly, in the specific embodiment of  FIGS. 1-3 , lower coupling  76  is shown as not being in sliding engagement with outer wall surface  32  of inner mandrel; however, lower coupling  76  can be placed in sliding engagement with outer wall surface  32 . The connection of sleeve  72  to both upper and lower couplings  66 ,  76  causes movement of lower coupling  76  when piston  56  moves downward (i.e., to the right in the Figures). 
         [0017]    Ported housing  80  is connected to lower coupling  76 . Ported housing  80  includes port  82  and is maintained within annulus  68  by a threaded connection to lower coupling  76 . The force of return member, i.e., spring  70  in the embodiment shown in the Figures, acting against detent  74  and upper coupling  66  maintains ported housing  80  in the closed position ( FIGS. 1A-1B ). 
         [0018]    Ported housing  80  can be a separate component as shown in the Figures or can be a continuation of sleeve  72 , i.e., formed as an integral component combining sleeve  72  and ported housing  80 . In addition, as shown in the embodiment of the Figures, retainer  83  can be disposed at a lower end of ported housing  80  to facilitate sealing engagement of ported housing  80  with outer wall surface  32  of inner mandrel  30 . 
         [0019]    Retainer member  84 , shown as a c-ring, is in sliding engagement with outer wall surface  32  of inner mandrel  30 . Retainer member  84  facilitates maintaining seals  88 ,  89  in place. Seals  88 ,  89  reduce fluid leakage between ported housing  80  and inner mandrel  30 . 
         [0020]    Lower guide  86  is secured to outer wall surface  32  of inner mandrel  30 . As shown in  FIG. 3 , lower guide  86  has three grooves or slots  92  milled along outer wall surface  94  of lower guide  86 . Slots  92  reduce the likelihood that sediment or other debris will collect in the void below ported housing  80  hindering the operation valve  10 . As shown in  FIG. 3 , slots  92  are milled longitudinally, however, slots  92  can be milled in any arrangement that permits fluid and debris to flow past lower guide  86 . For example, slots  92  can comprise one or more spiral-shaped slots. 
         [0021]    Screen  90  is secured to lower guide  86  and outer mandrel  40  to restrict debris from entering ports  82  and  34  when valve  10  is in the opened position ( FIG. 2 ) which could cause restriction of fluid flow from outside of valve  10  into bore  36  of inner mandrel  30 . 
         [0022]    Snap ring  38  secured to outer wall surface  32  of inner mandrel  30  acts as a detent or stop to prevent lower coupling  76  and, thus, ported housing  80  from traveling along outer wall surface  32  of inner mandrel  30  past a certain point. The point at which lower coupling  76  is stopped by snap ring  38  is the point at which port  82  is aligned with port  34 , i.e., when valve  10  is in its opened position ( FIG. 2 ). 
         [0023]    In one specific operation of valve  10 , valve  10  is placed in a work string such as production string or other string of tubing (not shown in  FIG. 1 ) and run-into a cased wellbore (not shown in  FIG. 1 ). A lower packer or other wellbore barrier is set below valve  10 . Completion fluid is then pumped down the wellbore annulus. As the pressure in the wellbore annulus increases due to the completion fluid being pumped into the wellbore annulus, the increased pressure enters piston chamber  54  and exerts a force on piston  56 . Piston  56  is then moved away from port  52  causing the upper coupling  66  to move downward which, in turn, causes sleeve  72  and ported housing  80  to also move downward until port  82  is at least partially aligned with port  34 . Upon partial alignment of port  82  with port  34 , the fluid pressure within the wellbore annulus is allowed to flow into bore  36 , thereby permitting drilling fluid that was previously disposed within the wellbore annulus to flow into the tubular string to be carried to the surface of the wellbore. As a result, the drilling fluid previously disposed in the wellbore is replaced with completion fluid. 
         [0024]    During movement of piston  56 , the return member, e.g., spring  70  and/or atmospheric chamber  73 , become compressed or energized.” Therefore, if the pressure within the wellbore annulus decreases, such as due to completion fluid no longer being pumped down the wellbore annulus, the compressed spring  70  and/or atmospheric pressure within atmospheric chamber  73  exerts a force against piston  56  that is greater than the hydrostatic pressure within piston chamber  54 . Accordingly, the return member forces piston  56  to move toward port  52  to return it to its “run-in” position causing valve  10  to return to its closed position. Thereafter, piston  56  is in position such that it can again move away from port  52  in response to a pressure increase within the wellbore annulus. 
         [0025]    Thereafter, a barrier such as a packer, can be set above valve  10  to provide an isolated wellbore annulus. The isolation of the wellbore annulus also can be established by any other method or device known in the art such as by use of one or more wellbore barriers such as bridge plugs, valves, wellheads, the bottom of the wellbore, and the like. Thereafter, in the event that the fluid contained within the isolated wellbore annulus expands, or the pressure within the isolated wellbore annulus increases, such as due to production operations being performed through the work string, the increased pressure enters piston chamber  54  and exerts a force on piston  56 . Piston  56  is then moved away from port  52  causing the upper coupling  66  to move downward which, in turn, causes sleeve  72  and ported housing  80  to also move downward until port  82  is at least partially aligned with port  34 . Upon partial alignment of port  82  with port  34 , the fluid pressure within the wellbore annulus is allowed to flow into bore  36 , thereby relieving pressure within the wellbore annulus. As a result, the pressure being exerted on the inner wall of the casing, or the inner wall of the formation, or the outer wall surface of the work string, is spread out and lessened, which decreases the likelihood of failure of any of the casing, the formation, or the work string, or any other wellbore component disposed in the isolated wellbore annulus. 
         [0026]    During movement of piston  56 , the return member, e.g., spring  70  and/or atmospheric chamber  73 , become compressed or “energized.” Therefore, if the pressure within the isolated wellbore annulus decreases, such as due to a temperature decrease due to cessation of production operations through the work string or due to sufficient pressure being relieved from the wellbore annulus through port  82  and port  34 , the compressed spring  70  and/or atmospheric pressure within atmospheric chamber  73  exerts a force against piston  56  that is greater than the hydrostatic pressure within piston chamber  54 . Accordingly, the return member forces piston  56  to move toward port  52  to return it to its “run-in” position causing valve  10  to return to its closed position. Thereafter, piston  56  is in position such that it can again move away from port  52  in response to a pressure increase within the isolated wellbore annulus. 
         [0027]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, the piston may comprise a full sleeve instead of the partial sleeve shown in the Figures. Moreover, the return member may comprise belleville springs or any other type of return member. Further, although one piston is shown in the embodiment of the Figures, two or more pistons may be used. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.