Patent Publication Number: US-6659186-B2

Title: Valve assembly

Description:
This application is a continuation-in-part of U.S. patent application Ser. No. 09/569,792, filed on May 12, 2000 now U.S. Pat. No. 6,352,119, and U.S. patent application Ser. No. 09/848,901, filed on May 4, 2001 now U.S. Pat. No. 6,550,541. 
    
    
     BACKGROUND 
     Reversing and circulating valves are often used in a tubular string in a subterranean well for purposes of communicating fluid between the annular region that surrounds the string and a central passageway of the string. The valves may be operated via fluid pressure that is applied to the annular region, especially for the case in which gas exists in the central passageway of the string. Some of these valves are single shot devices that are run downhole closed and then opened in a one time operation. Valves that may be repeatedly opened and closed are typically complex devices that may have reliability problems and interfere with other valves in the string. 
     Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above. 
     SUMMARY 
     In an embodiment of the invention, a technique that is usable with a subterranean well includes running a valve downhole in a first state and changing the valve to a second state in response to pressure that is applied to an annular region that surrounds the valve. The valve is changed between the first and second states by regulating a differential pressure between the annular region and an inner passageway of the valve. 
     In another embodiment of the invention, an apparatus usable in a subterranean well includes a valve, a first mechanism and a second mechanism. The valve controls communication between an annular region that surrounds the valve and an inner passageway of the valve. The first mechanism cause the valve to transition from a first state to a second state in response to pressure in the annular region. The second mechanism causes the valve to transition between the first state and the second state in response to a pressure differential between the annular region and the inner passageway. 
     Advantages and other features of the invention will become apparent from the following description, drawing and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic diagram of a completion valve assembly according to an embodiment of the invention. 
     FIGS. 2,  3 ,  4 ,  5 ,  7  and  8  are more detailed schematic diagrams of sections of the completion valve according to an embodiment of the invention. 
     FIG. 6 is a schematic diagram of a flattened portion of a mandrel of the completion valve assembly depicting a J-sot according to an embodiment of the invention. 
     FIG. 9 is a schematic diagram of a tubing fill valve according to an embodiment of the invention. 
     FIG. 10 is a schematic diagram of a ratchet mechanism of the tubing fill valve according to an embodiment of the invention. 
     FIGS. 11 and 12 are schematic diagrams of sections of a valve assembly in a closed state according to an embodiment of the invention. 
     FIGS. 13 and 14 are schematic diagrams of sections of the valve assembly in an open state according to an embodiment of the invention. 
     FIGS. 15 and 16 are schematic diagrams of sections of the valve assembly wherein locked in the closed state according to an embodiment of the invention. 
     FIG. 17 is a cross-sectional view of the valve assembly taken along line  17 — 17  of FIG.  11 . 
     FIG. 18 is a cross-sectional view of the valve assembly taken along line  18 — 18  of FIG.  12 . 
     FIG. 19 is a cross-sectional view of a valve assembly with one half showing the valve assembly in an open state and the other half showing the valve assembly in a closed state according to an embodiment of the invention. 
     FIG. 20 is a cross-sectional view of the valve assembly of FIG. 19 with one half showing the valve assembly in a closed, unlocked state, and the other half showing the valve assembly in a closed, locked state according to an embodiment of the invention. 
     FIG. 21 is a cross-sectional view of the valve assembly taken along line  21 — 21  of FIG.  20 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, an embodiment  10  of a completion valve assembly in accordance with the invention include a hydraulically set packer  14  that is constructed to be run downhole as part of a tubular string. Besides the packer  14 , the completion valve assembly  10  includes a tubing fill valve  35 , a packer isolation valve  22  and a formation isolation valve  31 . As described below, due to the construction of these tools, several downhole operations may be performed without requiring physical intervention with the completion valve assembly  10 , such as a physical intervention that includes running a wireline tool downhole to change a state of the tool. For example, in some embodiments of the invention, the following operations may be performed without requiring physical intervention with the completion valve assembly  10 : the tubing fill valve  35  may be selectively opened and closed at any depth so that pressure tests may be performed when desired; the packer  14  may be set with the tubing pressure without exceeding a final tubing pressure; the packer  14  may be isolated (via the packer isolation valve  22 ) from the internal tubing pressure while running the completion valve assembly  10  downhole or while pressure testing to avoid unintentionally setting the packer  14 ; and the formation isolation valve  31  may automatically open  31  (as described below) after the packer  14  is set. 
     More specifically, in some embodiments of the invention, the packer isolation valve  22  operates to selectively isolate a central passageway  18  (that extends along a longitudinal axis  11  of the completion valve assembly  10 ) from a control line  16  that extends to the packer  14 . In this manner, the control line  16  communicates pressure from the central passageway  18  to the packer  14  so that the packer  14  may be set when a pressure differential between the central passageway  18  and a region  9  (call the annulus) that surrounds the completion valve assembly  10  exceeds a predetermined differential pressure threshold. It may be possible in conventional tools for this predetermined differential pressure threshold to unintentionally be reached while the packer is being run downhole, thereby causing the unintentional setting of the packer. For example, pressure tests of the tubing may be performed at various depths before the setting depth is reached, and these pressure tests, in turn, may unintentionally set the packer. However, unlike the conventional arrangements, the completion valve assembly  10  includes the packer isolation valve  22  that includes a cylindrical sleeve  20  to block communication between the control line  16  and the central passageway  18  until the packer  14  is ready to be set. 
     To accomplish this, in some embodiments of the invention, the sleeve  20  is coaxial with and circumscribes the longitudinal axis  11  of the completion valve assembly  10 . The sleeve  20  is circumscribed by a housing section  15  (of the completion valve assembly  10 ) that include ports for establishing communication between the control line  16  and the central passageway  18 . Before the packer  14  is set, the sleeve  20  is held in place in a lower position by a detent ring (not shown in FIG. 1) that resides in a corresponding annular slot (not shown in FIG. 1) that is formed in the housing section  15 . In the lower position, the sleeve  20  covers the radial port to block communication between the control line  16  and the central passageway  18 . O-rings  23  that are located in corresponding annular slots of the sleeve  20  form corresponding seals between the sleeve  20  and the housing section  15 . When the packer  14  is to be set, a mandrel  24  may be operated (as described below) to dislodge the sleeve  20  and move the sleeve  20  to an upper position to open communication between the control line  16  and the central passageway  18 . The sleeve  20  is held in place in its new upper position by the detent ring that resides in another corresponding annular slot (not shown in FIG. 1) of the housing section  15 . 
     In some embodiments of the invention, the mandrel  24  moves up in response to applied tubing pressure in the central passageway  18  and moves down in response to the pressure exerted by a nitrogen gas chamber  26 . The nitrogen gas chamber  26 , in other embodiments of the invention, may be replaced by a coil spring or another type of spring, as examples. This operation of the mandrel  24  is attributable to an upper annular surface  37  (of the mandrel  24 ) that is in contact with the nitrogen gas in the nitrogen gas chamber  26  and a lower annular surface  29  of the mandrel  24  that is in contact with the fluid in the central passageway  18 . Therefore, when the fluid in the central passageway  18  exerts a force (on the lower annular surface  29 ) that is sufficient to overcome the force that the gas in the chamber  26  exerts on the upper annular surface  37 , a net upward force is established on the mandrel  24 . Otherwise, a net downward force is exerted on the mandrel  24 . As described below, the mandrel  24  moves down to force a ball valve operator mandrel  33  down to open a ball valve  31  after the packer  14  is set. However, as described below, the upward and downward travel of the mandrel  24  may be limited by an index mechanism  28  that controls when the mandrel  24  opens the packer isolation valve  22  and when the mandrel  24  opens the ball valve  31 . 
     In this manner, the completion valve assembly  10 , in some embodiments of the invention, includes an index mechanism  28  that limits the upward and downward travel of the mandrel  24 . More particularly, the index mechanism  28  confines the upper and lower travel limits of the mandrel  24  until the mandrel  24  has made a predetermined number (eight or ten, as examples) of up/down cycles. In this context, an up/down cycle is defined as the mandrel  24  moving from a limited (by the index mechanism  28 ) down position to a limited (by the index mechanism  28 ) up position and then back down to the limited down position. A particular up/down cycle may be attributable to a pressure test in which the pressure in the central passageway  18  is increased and then after testing is completed, released. 
     After the mandrel  24  transitions through the predetermined number of up/down cycles, the index mechanism  28  no longer confines the upper travel of the mandrel  24 . Therefore, when the central passageway  18  is pressurized again to overcome the predetermined threshold, the mandrel  24  moves upward beyond the travel limit that was imposed by the index mechanism  28 ; contacts the sleeve  20  of the packer isolation valve  22 ; dislodges the sleeve  20  and moves the sleeve  20  in an upward direction to open the packer isolation valve  22 . At this point, the central passageway  18  may be further pressurized to the appropriate level to set the packer  14 . After pressure is released below the predetermined pressure threshold, the mandrel  24  travels back down. However, on this down cycle, the index mechanism  28  does not set a limit on the lower travel of the mandrel  24 . Instead, the mandrel  24  travels down; contacts the ball valve operator mandrel  33 ; and moves the ball valve operator mandrel  33  down to open the ball valve  31 . Thus, after some predetermined pattern of movement of the mandrel  24 , the mandrel  24  may on its upstroke actuate one tool, such as the packer isolation valve  22 , and may on its downstroke actuate another tool, such as the ball valve  31 . Other tools, such as different types of valves (as examples), may be actuated by the mandrel  24  after a predetermined movement in a similar manner, and these other tools are also within the scope of the appended claims. 
     The tubing fill valve  35  selectively opens and closes communication between the annulus and the central passageway  18 . More particularly, the tubing fill valve  35  includes a mandrel  32  that is coaxial with and circumscribes the longitudinal axis  11  and is circumscribed by a housing section  13 . When the tubing fill valve  35  is open, radial ports  43  in the mandrel  32  align with corresponding radial ports  34  in the housing section  13 . The mandrel  32  is biased open by a compression spring  38  that resides an annular cavity that exists between the mandrel  32  and the housing section  13 . The cavity is in communication with the fluid in the annulus via radial ports  36 . The upper end of the compression spring  38  contacts an annular shoulder  41  of the housing section  13 , and the lower end of the compression spring  38  contacts an upper annular surface  47  of a piston head  49  of the mandrel  32 . A lower annular surface  45  of the piston head  49  is in contact with the fluid in the central passageway  18 . 
     Therefore, due to the above-described arrangement, the tubing fill valve  35  operates in the following manner. When a pressure differential between the fluids in the central passageway  18  and the annulus is below a predetermined differential pressure threshold, the compression spring  38  forces the mandrel  32  down to keep the tubing fill valve  35  open. To close the tubing fill valve  35  (to perform tubing pressure tests or to set the packer  14 , as examples), fluid is circulated at a certain flow rate through the radial ports  34  and  43  until the pressure differential between the fluids in the central passageway  18  and the annulus surpasses the predetermined differential pressure threshold. At this point, a net upward force is established to move the mandrel  32  upward to close off the radial ports  34  and thus, close the tubing fill valve  35 . 
     In the proceeding description, the completion valve assembly  10  is described in more detail, including discussion of the above referenced tubing fill valve  35 ; packer isolation valve  22 ; and index mechanism  28 . In this manner, sections  10 A (FIG.  2 ),  10 B (FIG.  3 ),  10 C (FIG.  4 ),  10 D (FIG.  5 ),  10 E (FIG. 7) and  10 F (FIG. 8) of the completion valve assembly  10  are described below. 
     Referring to FIG. 2, the uppermost section  10 A of the completion valve assembly  10  includes a cylindrical tubular section  12  that is circumscribed by the packer  14 . The tubular section  12  is coaxial with the longitudinal axis  11 , and the central passageway of the section  12  forms part of the central passageway  18 . The upper end of the section  12  may include a connection assembly (not shown) for connecting the completion valve assembly  10  to a tubular string. 
     The tubular section  12  is received by a bore of the tubular housing section  13  that is coaxial with the longitudinal axis  11  and also forms part of the central passageway  18 . As an example, the tubular section  12  may include a threaded section that mates with a corresponding threaded section that is formed inside the receiving bore of the housing section  13 . The end (of the tubular section  12 ) that mates with the housing section  13  rests on a protrusion  52  (of the housing section  13 ) that extends radially inward. The protrusion  52  also forms a stop to limit the upward travel of the mandrel  32  of the tubing fill valve  35 . An annular cavity  54  in the housing section  13  contains the compression springs  38 . The mandrel  32  includes annular O-ring notches above the radial ports  43 . These O-ring notches hold corresponding O-rings  50 . 
     Referring to FIG. 3, in the section  10 B of the completion valve assembly  10 , the mandrel  32  includes an exterior annular notch to hold O-rings  58  to seal off the bottom of the chamber  54 . The housing section  13  has a bore that receives a lower housing section  15  that is concentric with the longitudinal axis  11  and forms part of the central passageway  18 . The two housing sections  13  and  15  may be mated by a threaded connection, for example. Near its upper end, the housing section  15  includes an annular notch  64  on its interior surface that has a profile for purposes of mating with a detent ring  60  when the packer isolation valve  22  is open. The detent ring  60  rests in an annular notch  63  that is formed on the exterior of the sleeve  20  near the sleeve&#39;s upper end. When the packer isolation valve  22  is closed, the detent ring  60  rests in the annular notch  62  that is formed in the interior surface of the housing section  15  below the annular notch  64 . When the packer isolation valve  22  is opened and the sleeve  20  moves to its upper position, the detent ring  60  leaves the annular notch  62  and is received into the annular notch  64  to lock the sleeve  20  in the opened position. O-ring seals  70  may be located in an exterior annular notch of the housing section  15  to seal the two housing sections  13  and  15  together. O-ring seals  72  may also be located in corresponding exterior annular notches in the sleeve  20  to seal off a radial port  74  (in the housing section  15 ) that is communication with the control line  16 . 
     Referring to FIG. 4, the section  10 C of the completion valve assembly  10  includes a generally cylindrical housing section  17  that is coaxial with the longitudinal axis  11  and includes a housing bore (see also FIG. 3) for receiving an end of the housing section  15 . O-rings  82  reside in a corresponding exterior annular notch of the housing section  17  to seal the two housing sections  15  and  17  together. O-rings  84  are also located in a corresponding interior annular notch to form a seal between the housing section  15  and the mandrel  24  to seal off the nitrogen gas chamber  26 . In this manner, the nitrogen gas chamber  26  is formed below the lower end of the housing section  15  and above an annular shoulder  80  of the housing section  17 . An O-ring  86  resides in a corresponding exterior annular notch of the mandrel  24  to seal off the nitrogen gas chamber  26 . 
     Referring to FIG. 5, in the section  10 D of the completion valve assembly  10 , the lower end of the housing section  17  is received into a bore of an upper end of a housing section  19 . The housing section  19  is coaxial with and circumscribes the longitudinal axis  11 . O-rings  91  reside in a corresponding exterior annular notch of the housing section  17  to seal the housing sections  17  and  19  together. 
     The index mechanism  28  includes an index sleeve  94  that is coaxial with the longitudinal axis of the tool assembly  10 , circumscribes the mandrel  24  and is circumscribed by the housing section  19 . The index sleeve  94  includes a generally cylindrical body  97  that is coaxial with the longitudinal axis of the tool assembly  20  and is closely circumscribed by the housing section  19 . The index sleeve  94  includes upper  98  and lower  96  protruding members that radially extend from the body  97  toward the mandrel  24  to serve as stops to limit the travel of the mandrel  24  until the mandrel  24  moves through the predetermined number of up/down cycles. The upper  98  and lower  96  protruding members are spaced apart. 
     More specifically, the mandrel  24  includes protruding members  102 . Each protruding member  102  extends in a radially outward direction from the mandrel  24  and is spaced apart from its adjacent protruding member  102  so that the protruding member  102  shuttles between the upper  98  and lower  96  protruding members. Before the mandrel  24  transitions through the predetermined number of up/down cycles, each protruding member  102  is confined between one of the upper  98  and one of the lower  96  protruding members of the index sleeve  94 . In this manner, the upper protruding members  98 , when aligned or partially aligned with the protruding members  102 , prevent the mandrel  24  from traveling to its farthest up position to open the packer isolation valve  20 . The lower protruding members  96 , when aligned with the protruding members  102 , prevent the mandrel  24  from traveling to its farthest down position to open the ball valve  31 . 
     Each up/down cycle of the mandrel  24  rotates the index sleeve  94  about the longitudinal axis  11  by a predetermined angular displacement. After the predetermined number of up/down cycles, the protruding members  102  of the mandrel  24  are completely misaligned with the upper protruding members  98  of the index sleeve  94 . However, at this point, the protruding members  102  of the mandrel  24  are partially aligned with the lower protruding members  96  of the index sleeve  94  to prevent the mandrel  24  from opening the ball valve  31 . At this stage, the mandrel  24  moves up to open the packer isolation valve  22 . The upper travel limit of the mandrel  24  is established by a lower end, or shoulder  100 , of the housing section  17 . The mandrel  24  remains in this far up position until the packer  14  is set. In this manner, after the packer  14  is set, the pressure inside the central passageway  18  is released, an event that causes the mandrel  24  to travel down. However, at this point the protruding members  102  of the mandrel  24  are no longer aligned with the lower protruding members  96 , as the latest up/down cycle rotated the index sleeve  94  by another predetermined angular displacement. Therefore, the mandrel  24  is free to move down to open the ball valve  31 , and the downward travel of the mandrel  24  is limited only by an annular shoulder  103  of the housing section  19 . 
     In some embodiments of the invention, a J-slot  104  (see also FIG. 6) may be formed in the mandrel  24  to establish the indexed rotation of the index sleeve  94 . FIG. 6 depicts a flattened portion  24 A of the mandrel  24 . In this J-slot arrangement, one end of an index pin  92  (see FIG. 5) is connected to the index sleeve  94 . The index pin  92  extends in a radially inward direction from the index sleeve  94  toward the mandrel  24  so that the other end of the index pin  92  resides in the J-slot  104 . As described below, for purposes of preventing rotation of the mandrel  24 , a pin  90  radially extends from the housing section  17  into a groove (of mandrel  24 ) that confines movement of the mandrel  24  to translational movement along the longitudinal axis  11 , as described below. 
     As depicted in FIG. 6, the J-slot  104  includes upper grooves  108  (grooves  108   a ,  108   b  and  108   c , as examples) that are located above and are peripherally offset from lower grooves  106  (groove  106   a , as an example) of the J-slot  104 . All of the grooves  108  and  106  are aligned with the longitudinal axis  11 . The upper  108  and lower  106  grooves are connected by diagonal grooves  107  and  109 . Due to this arrangement, each up/down cycle of the mandrel  24  causes the index pin  92  to move from the upper end of one of the upper grooves  108 , through the corresponding diagonal groove  107 , to the lower end of one of the lower grooves  106  and then return along the corresponding diagonal groove  109  to the upper end of another one of the upper grooves  108 . The traversal of the path by the index pin  92  causes the index sleeve  94  to rotate by a predetermined angular displacement. 
     The following is an example of the interaction between the index sleeve  94  and the J-slot  104  during one up/down cycle. In this manner, before the mandrel  24  transitions through any up/down cycles, the index pin  92  resides at a point  114  that is located near the upper end of the upper groove  108   a . Subsequent pressurization of the fluid in the central passageway  18  causes the mandrel  24  to move up and causes the index sleeve  94  to rotate. More specifically, the rotation of the index sleeve  94  is attributable to the translational movement of the index pin  92  relative to the mandrel  24 , a movement that, combined with the produced rotation of the index sleeve  94 , guides the index pin  92  through the upper groove  108   a , along one of the diagonal grooves  107 , into a lower groove  106   a , and into a lower end  115  of the lower groove  106   a  when the mandrel  24  has moved to its farthest upper point of travel. The downstroke of the mandrel  24  causes further rotation of the index sleeve  94 . This rotation is attributable to the downward translational movement of the mandrel  24  and the produced rotation of the index sleeve  94  that guide the slot of the mandrel  24  relative to the index pin  92  from the lower groove  106   a , along one of the diagonal grooves  109  and into an upper end  117  of an upper groove  108   b . The rotation of the index sleeve  94  on the downstroke of the mandrel  24  completes the predefined angular displacement of the index sleeve  94  that is associated with one up/down cycle of the mandrel  24 . 
     At the end of the predetermined number of up/down cycles of the mandrel  24 , the index pin  92  rests near an upper end  119  of the upper groove  108   c . In this manner, on the next up cycle, the index pin  92  moves across one of the diagonal grooves  107  down into a lower groove  110  that is longer than the other lower grooves  106 . This movement of the index pin  92  causes the index sleeve  94  to rotate to cause the protruding members  102  of the mandrel  24  to become completely misaligned with the upper protruding members  98  of the index sleeve  94 . As a result, the index pin  92  travels down into the lower groove  110  near the lower end  116  of the lower groove  110  as the mandrel  24  travels in an upward direction to open the packer isolation valve  22 . When the mandrel  24  subsequently travels in a downward direction, the index pin  92  moves across one of the diagonal grooves  109  and into an upper groove  112  that is longer than the other upper grooves  108 . This movement of the index pin  92  causes the index sleeve  94  to rotate to cause the protruding members  102  of the mandrel  24  to become completely misaligned with the lower protruding members  96  of the index sleeve  94 . As a result, the index pin  92  travels up into the upper groove  112  as the mandrel  24  travels in a downward direction to open the formation isolation valve  31 . 
     The index pin  90  (see FIG. 5) always travels in the upper groove  112 . Because the index pin  90  is secured to the housing section  19 , this arrangement keeps the mandrel  24  from rotating during the rotation of the index sleeve  94 . 
     Referring to FIG. 7, in a section  10 E of the completion valve assembly  10 , the lower end of the housing section  19  is received by a bore of a lower housing section  21  that is coaxial with the longitudinal axis  11  and forms part of the central passageway  18 . O-rings  122  are located in an exterior annular notch of the housing section  19  to seal the two housing sections  19  and  21  together. Referring to FIG. 8, the mandrel  33  operates a ball valve element  130  that is depicted in FIG. 8 in its closed position. There are numerous designs for the ball valve  31 , as can be appreciated by those skilled in the art. 
     Other embodiments are within the scope of the following claims. For example, FIG. 9 depicts a tubing fill valve  300  that may be used in place of the tubing fill valve  35 . Unlike the tubing fill valve  35 , the tubing fill valve  300  locks itself permanently in the closed position after a predetermined number of open and close cycles. 
     More particularly, the tubing fill valve  300  includes a mandrel  321  that is coaxial with a longitudinal axis  350  of the tubing fill valve  300  and forms part of a central passageway  318  of the valve  300 . The mandrel  321  includes radial ports  342  that align with corresponding radial ports  340  of an outer tubular housing  302  when the tubing fill valve  300  is open. The mandrel  321  has a piston head  320  that has a lower annular surface  322  that is in contact with fluids inside the central passageway  318 . An upper annular surface  323  of the piston head  320  contacts a compression spring  328 . Therefore, similar to the design of the tubing fill valve  35 , when the fluid is circulated through the ports  340 , the pressure differential between the central passageway  318  and the annulus increases due to the restriction of the flow by the ports  340 . When this flow rate reaches a certain level, this pressure differential exceeds a predetermined threshold and acts against the force that is supplied by the compression spring  328  to move the mandrel  321  upwards to close communication between the annulus and the central passageway  318 . 
     Unlike the tubing fill valve  35 , the tubing fill valve  300  may only subsequently re-open a predetermined number of times due to a ratchet mechanism. More specifically, this ratchet mechanism includes ratchet keys  314 , ratchet lugs  312  and flat springs  310 . Each ratchet key  314  is located between the mandrel  321  and a housing section  306  and partially circumscribes the mandrel  321  about the longitudinal axis  350 . The ratchet key  314  has annular cavities, each of which houses one of the flat spring  310 . The flat springs  310 , in turn, maintain a force on the ratchet key  314  to push the ratchet key  314  in a radially outward direction toward the housing section  306 . 
     Each ratchet lug  312  is located between an associated ratchet key  314  and the housing section  306 . Referring also to FIG. 10 that depicts a more detailed illustration f the ratchet key  314 , lug  312  and housing section  306 , the ratchet lug  312  has interior profiled teeth  342  and exterior profiled teeth  340 . As an example, each tooth of the interior profiled teeth  342  may include a portion  343  that extends radially between the ratchet lug  312  and the ratchet key  314  and an inclined portion  345  that extends in an upward direction from the ratchet key  314  to the ratchet lug  312 . The ratchet key  314  also has profiled teeth  315  that are complementary to the teeth  342  of the ratchet lug  312 . The exterior profiled teeth  340  of the ratchet lug  312  includes a portion  360  that extends radially between the ratchet lug  312  and the housing section  306  and an inclined portion  362  that extends in an upward direction from the housing section  306  to the ratchet lug  312 . The housing  306  has profiled teeth  308  that are complementary to the teeth  340  of the ratchet lug  312 . 
     Due to this arrangement, the ratchet mechanism operates in the following manner. The tubing fill valve  300  is open when the completion valve assembly  10  is run downhole. Before the tubing fill valve  300  is closed for the first time, the ratchet lugs  312  are positioned near the bottom end of the mandrel  321  and near the bottom end of the teeth  308  of the housing section  306 . When the rate of circulation between the central passageway  318  and the annulus increases to the point that a net upward force moves the mandrel  321  in an upward direction, the ratchet lugs  312  move with the mandrel  321  with respect to the housing section  306 . In this manner, due to the flat springs  310  and the profile of the teeth, the ratchet lugs  312  slide up the housing section  306 . 
     When the tubing fill valve  300  re-opens and the mandrel  321  travels in a downward direction, the ratchet lugs  312  remain stationary with respect to the housing section  306  and slip with respect to the mandrel  321 . The next time the tubing fill valve  300  closes, the ratchet lugs  312  start from higher positions on the housing section  306  than their previous positions from the previous time. Thus the ratchet lugs  312  effectively move up the housing section  306  due to the opening and closing of the tubing fill valve  35 . 
     Eventually, the ratchet lugs  312  are high enough (such as at the position  312 ′ that is shown in FIG. 9) to serve as a stop to limit the downward travel of the mandrel  321 . In this manner, after the tubing fill valve  300  has closed a predetermined number of times, the lowered surface  322  of the piston head  320  contacts the ratchet lugs  312 . Thus, the mandrel  321  is prevented from traveling down to re-open the tubing fill valve  300 , even after the pressure in the central passageway  318  is released. 
     Among the other features of the tubing fill valve  300 , the valve  300  may be formed from a tubular housing that includes the tubular housing section  302 , a tubular housing section  304  and the tubular housing section  306 , all of which are coaxial with the longitudinal axis  350 . The housing section  304  has a housing bore at its upper end that receives the housing section  302 . The two housing sections  302  and  304  may be threadably connected together, for example. The housing section  304  may also have a housing bore at its lower end to receive the upper end of the housing section  306 . The two housing sections  304  and  306  may be threadably connected together, for example. 
     In accordance with another embodiment of the invention, FIGS. 11 (depicting an upper  401   a  section) and  12  (depicting a lower  401   b  section) depict a valve assembly  400  in a closed state, and FIGS. 13 (depicting the upper  401   a  section) and  14  (depicting the lower  401   b  section) depict the assembly  400  in an open state. In some embodiments of the invention, the valve assembly  400  may be run downhole as part of a tubular string and control communication between a inner central passageway  460  of the valve assembly  400  and an annular region  403  that surrounds the valve assembly  400 . Thus, the valve assembly  400  may serve as a circulating valve, in some embodiments of the invention. 
     The valve assembly  400  includes a housing  402  that is formed from upper  402   a , middle  402   b  and lower  402   c  sections. The upper housing section  402   a  may include a mechanism (threads  440 , for example) to couple the valve assembly  400  in line with the tubular string. The upper housing section  402   a  is coaxial with and extends into an upper end of the middle housing section  402   b . The middle housing section  402   b , in turn, receives the upper end of the lower housing  402   c , a housing section that is also coaxial with the housing sections  402   b  and  402   c.    
     For purposes of controlling communication between the annular region  403  that surrounds the valve assembly  400  and the central passageway  460 , the valve assembly  400  includes an operator mandrel  414  that is circumscribed at least in part by the upper housing section  402   a  and the middle housing section  402   b.    
     As described below, the fluid communication between the central passageway  460  and the annular region  403  is isolated (i.e., the valve assembly  400  is closed) when the mandrel  414  is in its lower position (as depicted in FIGS.  11  and  12 ), and communication is permitted (i.e., the valve assembly is open) when the mandrel  414  travels to its upper position, a position that is depicted in FIGS. 13 and 14. 
     In the mandrel&#39;s upper position, radial flow ports  420  that are formed in the middle housing section  402   b  are aligned with corresponding radial flow ports  424  of the mandrel  414 , as depicted in FIGS. 13 and 14. However, when the mandrel  414  is in its lower position (the position depicted in FIGS.  11  and  12 ), the radial ports  424  of the mandrel  414  are located below the radial ports  420  of the middle housing section  402   b , thereby blocking fluid communication between the annular region  403  and the central passageway  460  via the valve assembly  400 . In this manner, in this lower position, upper  450  and lower  452  O-rings that are located between the mandrel  414  and the middle housing section  401   b  seal off the radial ports  420  from the central passageway  460 . 
     A compression spring  426  of the valve assembly  400  is coaxial with the longitudinal axis of the valve assembly  400 , has a lower end that abuts an inwardly protruding upper shoulder  427  of the lower housing section  402   c  and has an upper end that contacts the lower end  425  of the mandrel  414 . Therefore, the compression spring  426  exerts an upward force that tends to keep the mandrel  414  in its upper position to keep the valve assembly  400  open. However, the mandrel  414  is initially confined to the lower position (or closed position) by shear pins  404 , each of which is attached to the upper housing section  402   a  and extends radially inwardly from the upper housing section  402   a . The shear pins  404  initially prevent upper movement of the mandrel  414  by extending above an upper shoulder  405  of the mandrel  414 . 
     Thus, when the valve assembly  400  is initially run downhole, the mandrel  414  is held in its lower position (thereby closing the valve  400 ) via the shear pins  404 . Once positioned downhole, the valve assembly  400  may then be opened by the application of pressure in the annular region  403 . For example, a packer may be set downhole below the valve assembly  400  to create an annulus (containing the annular region  403 ) through which pressure may be communicated through a hydrostatic column of fluid, for example. When the applied pressure exceeds a predetermined threshold, the pressure of the fluid in the annulus ruptures one or more ruptured discs (located in rupture disc assemblies  416 ), and these rupture(s) permit fluid from the annulus to flow through the middle housing section  402   b  into grooves, or cavities  432  that exist between a shoulder of the middle housing section  402   b  and a lower surface  434  of a shoulder of the mandrel  414 . The cavities  423  are located below an O-ring  444  that is located between the exterior surface of the mandrel  414  and the interior surface of the middle housing section  402   b  and above an O-ring  450  that also extends between the outer surface of the mandrel  414  and the inner surface of the middle housing section  402   b . Thus, the cavities  432  are located within a sealed region. Therefore, when the pressure in the annulus exceeds a predetermined threshold, the rupture discs rupture to cause fluid from the annulus flows into the cavities  432  to exert an upward force on the lower surface  434  to tend to force the mandrel  414  in an upward direction. 
     Subsequently, when the pressure in the annulus reaches a sufficient level, the shear pins  404  shear under the shear forces presented by the surface  405  contacting the shear pins  404 , thereby no longer confining upward travel of the mandrel  414 . Therefore, when the shear pins  404  shear, the mandrel  414  is permitted to travel in an upward direction until the upper surface  405  of the mandrel  414  rests against a shoulder  407  that is established by the upper housing section  402   a  and serves as a stop. In this upward position, the radial flow ports  420  of the middle housing section  402   b  are aligned with the radial flow ports  424  of the mandrel  414 , thereby permitting fluid communication between the annulus and the central passageway  460  to place the valve in an open state, the state depicted in FIGS. 13 and 14. 
     Thus, initially, the valve assembly  400  is closed when the assembly  400  is being run downhole. Thereafter, in a one-shot operation, the pressure in the annulus of the well may be increased to cause the valve assembly  400  to open fluid communication between the annulus and the central passageway  460 . As described below, the valve assembly  400  may be subsequently closed and opened in response to a pressure differential that is established between the annulus and the central passageway  460 . After a predetermined number of these open and close cycles, the valve assembly  400 , in some embodiments of the invention, locks itself in the closed position (in which the mandrel  414  is in its down position) to, as its name implies, permanently close the valve assembly  400 . This state of the valve assembly  400  is depicted in FIGS. 15 and 16. 
     For purposes of making the mandrel  414  responsive to the differential pressure between the annulus and the central passageway  460 , in some embodiments of the invention, the flow ports  420  are sized such that a certain pressure drop is created across the flow ports  420  when the rate of fluid flowing from the central passageway  460  to the annulus exceeds a predetermined rate. In this manner, when the flow exceeds a predetermined rate, the differential pressure between the central passageway  460  and the annulus creates a differential pressure that acts on an upper shoulder  430  of the mandrel  414 , pushing the mandrel  414  in a downward direction to close off the flow ports  420 . A sufficient flow causes the downward force created by this differential pressure to overcome the upward force that is exerted by the compression spring  426  on the mandrel  414 . 
     Thus, in summary, the flow rate between the central passageway  460  and the annulus may be set to the appropriate rate to increase the pressure differential between the central passageway  460  and the annulus to force the mandrel  414  down to close the valve assembly  400 . Therefore, by reducing this flow rate, the downward force on the mandrel  414  may be relieved to the extent that the mandrel  414  (due to the force generated by the compression spring  426 ) is forced in an upward direction to once again open the valve assembly  400 . The above-described open and close cycle may be repeated, with the number of open and close cycles being limited by a ratchet mechanism, as described below. 
     The ratchet mechanism of the valve assembly  400  is similar in design to the ratchet mechanism of the tubing fill valve  300 . More specifically, the ratchet mechanism of the valve  400  includes ratchet keys  412 , ratchet lugs  406  and flat springs  410 . The ratchet keys  412  are regularly spaced about the longitudinal axis of the valve assembly  400 . Likewise, each lug  406  is associated with one of the ratchet keys  412 , and the lugs  406  are also regularly spaced around the longitudinal axis of the valve assembly  400 , as described below. Each ratchet key  412  is located between the mandrel  414  and the middle housing section  402   b  and partially circumscribes the mandrel  414  about the longitudinal axis of the valve assembly  400 . Each ratchet key  404  establishes an annular groove or cavity, each of which houses one of the flat spring  410 . Each flat spring  410 , in turn, maintains an outward radial force on the associated ratchet key  412  to push the ratchet key  412  in a radially outward direction toward the middle housing section  402   b.    
     Each ratchet lug  406  is located between an associated ratchet key  412  and the middle housing section  402   b . When the valve assembly  400  is run downhole, the ratchet lugs  406  are located near a lower surface  417  of the upper housing section  402   a , as depicted in FIGS. 11 and 12. 
     The ratchet lug  406  has interior profiled teeth that engage corresponding exterior profiled teeth  413  of the associated ratchet key  412 . Likewise, the ratchet lug  406  includes exterior profile teeth that engage corresponding interior profiled teeth  408  located on the inner surface of the middle housing section  402   b . The shape of the teeth of the lug  406  and the outer and interior surfaces of the ratchet key  412  and middle housing section  402   b  are similar in design to the ratchet mechanism of the valve assembly  300  except that these teeth and surfaces are rotated by 180° (i.e., FIG. 10 is rotated by 180°) to permit the ratchet lugs  406  to move in a downward motion in response to movement of the mandrel  414 , as described below. 
     Due to this configuration, the ratchet lugs  406  move down with the mandrel  414  and are prevented from moving in an upward direction when the mandrel  414  moves in an upward direction. Thus, the ratchet lugs  406  move down with the mandrel  404  every time the mandrel  414  moves down, and when the mandrel  414  subsequently moves in an upward direction, the ratchet lugs  406  stay in place relative to the middle housing section  402   b . Therefore, a gap that exists between an upward facing surface  430  of the mandrel  404  and the lower surfaces of the ratchet lugs  406  becomes progressively smaller on every open and close cycle of the mandrel  414 . On the last open and close cycle, the mandrel  414  moves down but is prevented from moving subsequently in an upward direction because the ratchet lugs  406  abut the surface  430 , as depicted in FIG.  15 . For this case, as shown in FIG. 16, the radial flow ports  420  are misaligned with the radial flow ports  424  of the mandrel  414  to lock the valve assembly  400  in the closed position. 
     Thus, to summarize, the valve assembly  400  may be run downhole on a tubular string in its closed state. After the valve assembly  400  is in position, the pressure in the annulus of the well may be increased until the rupture disc in the rupture disc assembly  416  (or multiple disc assemblies) ruptures and permits fluid communication between the annulus and the mandrel  414 . When this pressure reaches a sufficient level, the shear pins  404  of the valve assembly  400  shear, thereby allowing the mandrel  414  to move in an upward direction and open the valve assembly  400  to permit fluid communication between the central passageway  460  of the valve assembly  400  and the annulus. By controlling the flow rate between the central passageway  460  and annulus, the valve assembly  400  may be opened and closed for a predetermined number of open and close cycles. After the number of predetermined open and close cycles have occurred, the valve assembly  400  then locks itself in the closed position. 
     Referring to FIG. 17, in some embodiments of the invention, the rupture disc assembly  416  is tangentially situated with respect to the longitudinal axis of the valve assembly  400  and resides in the middle housing section  402   b . Although one rupture disc assembly  416  is depicted in FIG. 17, the valve assembly  400  may include multiple rupture disc assemblies  416  in other embodiments of the invention, as depicted in the other figures. As shown in FIG. 17, the rupture disc assembly  416  includes a tangential port  460  for receiving fluid from the annulus of the well and a radial port  464  for communicating with the central passageway  460  of the valve assembly  400 . A rupture disc  461  is located inside the rupture disc assembly  416  between the tangential port  460  and the radial port  464 . Therefore, when the pressure in the annulus exceeds a predetermined threshold, the rupture disc  461  ruptures, to permit fluid communication between the annulus and the central passageway  460 . 
     Referring to FIG. 18, in some embodiments of the invention, the middle housing section  402  includes the radial flow ports  420 , that, as shown, may be regularly spaced around the longitudinal axis of the valve assembly  400 . As depicted in FIG. 18, in some embodiments of the invention, the valve assembly  400  may include eight such flow ports  420 , although the valve assembly  400  may include fewer or more radial flow ports  420  in other embodiments of the invention. The cross-section of each radial flow port  420  is sized to create the predetermined differential pressure between the annulus and the central passageway  460  when the flow exceeds a certain rate to cause the mandrel  414  to move to close the valve assembly  414 . 
     In the embodiment shown in FIG. 19, valve  500  comprises a tube  502  having a port  504  that allows fluid communication between an interior region  506  of tube  502  and an exterior region  508 . Interior region  506  is generally a longitudinal passageway in tube  502  and exterior region  508  is typically an annular region between tube  502  and the well casing or open wellbore (not shown). Valve  500  further comprises a sleeve  510  slidingly mounted to tube  502 . Sleeve  510  has a sealing surface  512  adjacent to tube  502 . Sealing surface  512 , in conjunction with seal rings  514  disposed within retainer grooves  516  in tube  502 , forms a seal to prevent fluid passage along sealing surface  512  past seal rings  514 . Thus, sleeve  510  can block the fluid communication through port  504 . Sleeve  510  has an upper end  517 . 
     Sleeve  510  has a port  518  complementary to port  504 . When port  518  aligns with port  504 , fluid can communicate between interior region  506  and exterior region  508 . The left half of FIG. 19 shows valve  500  in the open position; that is, with ports  504  and  518  aligned. The right half of FIG. 19 shows valve  500  in the closed position; that is, with ports  504  and  518  misaligned. Spring  520 , mounted concentrically with the longitudinal axis of tube  502  within a recess  522  in tube  502 , has an upper end that bears on tube shoulder  524 . Spring  520  has a lower end that bears on sleeve shoulder  526  to bias valve  500  to the open position. Spring port  521  permits fluid communication between exterior region  508  and recess  522 , but not with interior region  506 . 
     Sleeve shoulder  526  is the uppermost portion of piston  528 . Piston  528  is an integral part of sleeve  510 . A sidewall  530  extends downward from sleeve shoulder  526 , adjacent tube  502 , defining the radially outermost portion of piston  528 . A seal ring  532 , disposed in a retainer groove  534  in sidewall  530 , prevents fluid in interior region  506  from entering recess  522  from below. 
     Piston  528  has a first lower shoulder  536  and a second lower shoulder  538 , with an intermediate sidewall  540  extending downward therebetween. First lower shoulder  536  marks the transition from sidewall  530  to intermediate sidewall  540 . Intermediate sidewall  540  is radially inward from sidewall  530 . Similarly, second lower shoulder  538  marks the transition from intermediate sidewall  540  to a locking sidewall  542 . Locking sidewall  542  is radially inward from intermediate sidewall  540 . On its lowermost end  543 , piston  528  has a collet  544  attached thereto. 
     Sleeve  510  has a profile  545  on its radially innermost surface. Profile  545  allows for manual actuation and locking of sleeve  510  using a shifting tool (not shown). 
     Valve  500  further comprises one or more lock segments  546  that are disposed in a notch  548  in tube  502 , as shown in FIGS. 19,  20 , and  21 . Lock segments  546  are biased radially inwardly by garter spring  550 , but are normally constrained from moving radially inward by intermediate sidewall  540 . Notch  548  prevents lock segments  542  from moving up and down relative to tube  502 . Lock segments  546  and intermediate sidewall  540  can, however, slide freely against each other. 
     FIGS. 19 and 20 further show a lower housing  552  attached to tube  502 . A seal ring  554  disposed between tube  502  and housing  552  prevents fluid flow through their union. Further, housing  552  has a detent  556  protruding radially inward into interior region  506 . 
     During normal operations, valve  500  is lowered, in its open state (FIG. 19, left half), into the wellbore. Ports  504 ,  518  are aligned to allow fluid communication between interior and exterior regions  506 ,  508 . At some point, however, an operator may wish to perform testing on the tubing assembly. For example, the operator may wish to test for leaks. If so, fluid is injected, under pressure, into interior region  506 . Because flow between interior and exterior regions  506 ,  508  is restricted by the size of ports  504 ,  518 , the pressure in interior region  506  tends to increase. Those surfaces in fluid communication with the injected fluid thus experience an applied force. 
     In particular, sliding sleeve  510  experiences a net upward force because the combined area of the first and second lower shoulders  536 ,  538 , along with the effective area of collet  544 , exceeds the area of upper end  517  and sleeve shoulder  526 . Sleeve shoulder  526  is subject to the pressure of exterior region  508 , whereas the other surfaces are subjected to the pressure within interior region  506 . If sufficient pressure is applied, the net upward force on sleeve  510  compresses spring  520  so that ports  504 ,  518  misalign and seal rings  514  block fluid flow into or from exterior region  508  altogether. Thus, the state of valve  500  is changed from its open state to its closed state (FIG. 19, right half and FIG. 20, left half). 
     Once testing is completed on that particular portion of tubing assembly, the operator can relieve the pressure in interior region  506  and continue adding new sections of tubing to the tubing assembly. Pressure testing of the added assembly can be performed when the operator so desires in the same manner just described. This assembly and testing procedure can be repeated as many times as necessary for the operator to assemble a tubing assembly of desired length having pressure integrity. 
     At some point in operations, usually after assembly and testing are completed, the operator may wish to place valve  500  in its closed state and lock it there permanently. That is accomplished by increasing the pressure within interior region  506  above a threshold. While a certain amount of pressure is sufficient to drive sleeve  510  upward to close valve  500 , a further increase in pressure will drive sleeve  510  even farther upward. Collet  544  and detent  556  serve to prevent an inadvertent locking should the applied pressure slightly exceed the operating norm. The resistance offered when collet  544  rides onto detent  556  provides a margin of safety between normal operating pressures sufficient to compress spring  520  and close valve  500 , and the pressure required to lock sleeve  510  in place. Alternatively, collet  544  and detent  556  can be designed to permit collet  544  to pass detent  556  regardless of the direction of traverse. In that case, with sufficient spring force or sufficient pressure in exterior region  508 , if collet  544  has been driven upward past detent  556 , collet  544  can be driven downward past detent  556  to allow valve  500  to re-open. 
     Collet  544  and detent  556  can also form a locking mechanism. As sleeve  510  is driven upwards, collet  544  rides up and over detent  556 . If pressure is then reduced, sleeve  510  is prevented from moving downward since collet  544  is designed to traverse detent  556  when moving upward, but not when moving downward. Thus, valve  500  is permanently locked in its closed state. Collet  544  and detent  556  can be arranged to lock prior to or simultaneously with the locking of lock segments  546 . 
     Alternatively, or in conjunction with collet  544  and detent  556 , as pressure is applied, intermediate sidewall  540  slides past lock segments  546  until second lower shoulder  538  slides past the upper end of notch  548 . When that occurs, garter spring  550  forces lock segments  546  radially inward to bear on locking sidewall  542 . If pressure is then reduced, sleeve  510  can move downward only until second lower shoulder  538  engages lock segments  546 , which are still constrained from moving upward or downward by notch  548 . Thus, valve  500  is permanently locked in its closed state (FIG. 20, right half). 
     In the preceding description, directional terms, such as “upper,” “lower,” “vertical,” “horizontal,” etc., may have been used for reasons of convenience to describe the completion valve assembly and its associated components. However, such orientations are not needed to practice the invention, and thus, other orientations are possible in other embodiments of the invention. 
     While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of the invention.