Patent Publication Number: US-10323482-B2

Title: Flow-actuated pressure equalization valve and method of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a National Phase entry of, and claims priority to, PCT Application No. PCT/CA2015/050259, filed Mar. 31, 2015, which is incorporated by reference herein in its entirety for all purposes. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD 
     The subject matter disclosed herein relates to an equalization valve for use in a downhole tool assembly, the valve being useful for the equalization of fluid pressures about the valve. 
     BACKGROUND 
     At various stages during the lifetime of a well, the wellbore will require that a particular operation requiring treatment by fluids, such as for example fracturing, cleaning or stimulation be performed. In performing a wellbore treatment or operation it is often desirable to deliver a fluid treatment to a particular wellbore region rather than to the entire wellbore. To this end, it is well known to use a downhole tool fit with one or more packers to selectively and sealingly engage a wellbore or a casing and isolate the region of the wellbore that is to be treated. The downhole tool is conveyed into and out of the well on a work string, such as coiled tubing. 
     A number of different types of packers are known (bridge plugs, friction cups, inflatable packers, and straddle packers) and they can be used to isolate a section of the wellbore below the packer or between a pair of packers, depending on the treatment operation to be performed. 
     Packers, by design, are a barrier to fluid movement, and yet the downhole tools bearing packers are intended to be moved up and down along the wellbore during run-in and when being pulled out of hole (POOH), and are alternately set and released, all of which occurs in a fluid environment. Thus, without fluid management about the packers or through the downhole tool, the operator can end up swabbing the well with possible detrimental effect to the wellbore or the downhole tool. 
     The downhole tools bearing packers are exposed to varying conditions during use, and debris accumulation around the tool assembly is also concern. Fluid flow during operations or movement can carry significant amounts of debris that settles over and about the sealing device, or within other portions of the tool assembly. This may result in tool damage, or in the tool assembly becoming lodged within the wellbore. 
     Further, once a particular treatment operation has been performed, it may be desirable to release the downhole tool and associated packers and move it to another location in the wellbore and set the tool again, or to remove it entirely from the wellbore. Generally, a pressure differential across the packer element will exist after an operation in the wellbore is performed, for example a fracturing operation. Unless dissipated or otherwise released, a fluid head uphole of the downhole tool imposes significant fluid forces on the tool and can maintain the packer in an energized state or hold other aspects of the downhole tool in a set condition, risking damage to the tool, the packers or the wellbore if forcibly moved, or preventing any movement at all. 
     In order to release the tool, the pressure above and below the packer should be equalized. Once the pressure is equalized, the work string can then be manipulated to unset the packer. Accordingly, equalization across a packer after a treatment or other operation has been performed is desirable to avoid debris-related tool malfunction, jamming or immobility of the tool assembly, and potential loss of the well if the tool assembly cannot be retrieved. 
     US 2011/0198082 teaches a tool assembly including a multi-function valve deployed on work string. Forward and reverse circulation pathways to an isolated interval of a wellbore allow clearing of debris from the wellbore annulus while the sealing device remains set against the well bore. The valve plug is actuable upon application of force to the work string. 
     US 2012/0055671 teaches a tool assembly deployed on work string. The tool assembly includes an equalization valve that can be opened or closed to control fluid passage between the coiled tubing and treatment zone to the wellbore below. The valve plug may be actuated from surface by pulling or pushing on the tubing to open or to seal the passageway upon application of mechanical pressure to the work string. 
     US2013/0133891 teaches an equalization valve having a valve plug movable from an open position to a seated position. The valve has a primary fluid passageway and the valve plug defines a conduit that provides for a minimal fluid flow across a sealing element, when the valve plug is at the seated position. The movement of the valve plug between the open position and the seated position is mediated by application of mechanical force applied to the work string. 
     U.S. Pat. No. 6,474,419 teaches a packer with an equalizing valve for automatically equalizing the pressure above and below the packer element. The packer comprises an equalization valve that has an open position and a closed position. The equalization valve seals to a closed position to prevent flow through the valve when the packer element is actuated to engage the wellbore. Communication above and below the packer is equalized by setting the valve to an open position, after which the packer can be unset and retrieved from the wellbore. 
     CA 2,683,432 teaches a pressure equalization valve for a work string comprising an equalization valve that closes when a fluid flow having a rate greater than a threshold actuates a shuttle to close the valve. A fluid flow rate less than the threshold maintains the shuttle biased in the open position to open the valve. 
     U.S. Pat. No. 6,666,273 teaches a plunger-type valve for use in a wellbore. The valve is arranged to be actuated by the differential pressure to selectively allow fluid flow to enter and exit the valve in both directions. The valve seat is biased for controlled flow in one direction and the plunger 704 is biased to enable controlled flow in a second direction. Subsequently, the plunger-type valve can be deactivated to selectively allow fluid flow in only one direction. 
     U.S. Pat. No. 8,141,642 teaches a valve assembly that is configured to selectively control fluid flow into a fill-up and circulation tool and out of the tool. The valve assembly comprises a movable valve head and a movable valve seat. The valve seat is biased for controlled flow in one direction and the valve stem or head is biased to enable controlled flow in a second direction. 
     What is needed in the art is an equalization valve that can be moved up and down the wellbore and used in varying positions along the wellbore, without having to pull the valve up to the surface to reset it. 
     In equalization valves that are opened by bleeding pressure off the valve to equalize pressure above and below the valve, it can be difficult to ascertain from the surface whether the valve is in fact open and able to be moved without damaging the packers. Bleeding off is a particular problem in low pressure wells. In some cases the pressure reduction can allow fluid to flow back into the well, which can carry debris that damages the packers when they are moved. Thus, it would be beneficial to avoid using bleeding off as the primary means by which the valve is opened. 
     It may at times be necessary to flow fluid through the equalization valve in order to clean components of the work string that lie below the valve. Accordingly, valves actuated by fluid flow are at risk of premature actuation. Similarly, flow-induced closure of a valve can also arise when there is a relative movement of fluid through the valve while moving the tool along a fluid-filled wellbore, thus limiting tripping rates between zones. 
     SUMMARY OF DISCLOSURE 
     Described herein is a pressure equalization valve that is used to equalize pressure across a downhole tool. The valve requires actuation by two different mechanisms, and thus provides an added degree of control when the valve is moved within the wellbore and/or used in a treatment or stimulation. The valve has a fluid flow actuation aspect that can be enabled and disabled using manipulation of the relative axial positions of an uphole and a downhole portion of the downhole tool. 
     In one aspect, described herein is a pressure equalization valve comprising:
     a downhole tubular telescopically coupled for axial movement relative to an uphole tubular and forming a contiguous axial bore therethrough, the downhole tubular delimited for axial movement towards the uphole tubular at an uphole-delimited position and away from the uphole tubular at a downhole-delimited position,   a valve seat fit within the axial bore of the downhole tubular for defining an uphole valve bore and a downhole valve bore in fluid communication therethrough;   a valve shuttle disposed in the bore of the uphole tubular and axially movable therein, the shuttle biased uphole to an uphole-biased position, and being actuable towards a downhole-delimited position by fluid flow through the uphole valve bore; and   the downhole tubular being actuable from the downhole-delimited position to a valve-enabled position, at which a valve ball on the shuttle engages the valve seat when fluid flow through the uphole valve bore is greater than a threshold flow rate; and wherein   when the downhole tubular is in the valve-enabled position,
       fluid flow greater than the threshold flow rate overcomes the biasing to move the shuttle from the uphole-biased position to a flow-extended position at which the valve ball engages the valve seat to isolate the uphole valve bore from the downhole valve bore, and fluid flow less than the threshold flow rate maintains the shuttle biased in the uphole-biased position for continued fluid communication between the uphole valve bore and the downhole valve bore; and   
       when the downhole tubular is not in the valve-enabled position, the valve ball is spaced from the valve seat so that when the shuttle is in the flow-actuated position the valve ball remains spaced from the valve seat for continued fluid communication between the uphole valve bore and the downhole valve bore.   

     In one embodiment the valve shuttle has a fluid inlet in fluid communication with the uphole valve bore, and a flow-diverting fluid outlet in fluid communication with the uphole valve bore, and fluid flow through the shuttle&#39;s fluid inlet and fluid outlet urges the shuttle downhole against resistance of the biasing. 
     In one embodiment the downhole tubular further comprises a means of immobilizing the downhole tubular in a wellbore. 
     In one embodiment the valve seat is fit at an end of the bore of the downhole tubular. 
     In one embodiment the downhole tubular moves axially within the bore of the uphole tubular. 
     In one embodiment the valve-enabled position of the downhole tubular is the uphole-delimited position of the downhole tubular. 
     In one embodiment the uphole biased position of the shuttle is an uphole-delimited position of the shuttle. 
     In another aspect described is a pressure equalization valve for a downhole tool, the valve comprising:
     an uphole tubular and a downhole tubular telescopically coupled and forming a contiguous axial bore therethrough; the downhole tubular being actuable for axial movement towards the uphole tubular to a valve-enabled position and away from the uphole tubular to a valve-disabled position;   a valve seat fit within the axial bore of the downhole tubular for defining an uphole valve bore and a downhole valve bore in fluid communication therethrough; and   a valve shuttle disposed in the bore of the uphole tubular and axially movable therein, the shuttle biased uphole to an uphole-biased position, and being actuable towards a flow-activated position by fluid flow that is greater than a threshold flow rate; and wherein,
       when the downhole tubular is in the valve-disabled position and the shuttle is in the flow-actuated position, the valve is open, for continued fluid communication between the uphole valve bore and the downhole valve bore;   when the downhole tubular is in the valve-enabled position and the shuttle is in the uphole-biased position, the valve is open, for continued fluid communication between the uphole valve bore and the downhole valve bore; and   when the downhole tubular is in the valve-enabled position, and the shuttle is in the flow-actuated position, a valve ball on the shuttle engages the valve seat and the valve is closed to fluid communication between the uphole valve bore and the downhole valve bore.   
       

     In one embodiment fluid flow through the uphole valve bore and into the downhole valve bore urges the shuttle downhole against resistance of the biasing. 
     In one embodiment the fluid flow through the uphole valve bore comprises the flow of fluid into a fluid inlet of the valve shuttle that is in fluid communication with the uphole valve bore, and out of a fluid outlet that is in fluid communication with the uphole valve bore. 
     In one embodiment the downhole tubular further comprises a means of immobilizing  5  the downhole tubular in a wellbore. 
     In one embodiment the valve seat is fit at an end of the bore of the downhole tubular. 
     In one embodiment the downhole tubular moves axially within the bore of the uphole tubular. 
     In one embodiment the valve-enabled position of the downhole tubular is an uphole-delimited position of the downhole tubular. 
     In one embodiment the valve-disabled position of the downhole tubular is a downhole-delimited position of the downhole tubular. 
     In one embodiment the uphole biased position of the shuttle is an uphole-delimited position of the shuttle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side partial sectional view of a work string with an equalization valve according to one embodiment. 
         FIG. 1B  is an enlarged side partial sectional view of the equalization valve shown in  FIG. 1A . 
         FIGS. 2A to 2C  are enlarged partial sectional views that compare three positions of the components of the equalization valve, more particularly: 
         FIG. 2A  is a view with the downhole tubular at a valve-disabled position and the valve shuttle at an uphole-biased position, and the valve is in an open configuration; 
         FIG. 2B  is a view with the downhole tubular in a valve-enabled position and the valve shuttle at an uphole-biased position, and the valve is in an open configuration; and 
         FIG. 2C  is a view with the downhole tubular in a valve-enabled position and the shuttle at a flow-extended position, and the valve is in a closed configuration. 
         FIGS. 3A to 3D  illustrate an enlarged portion of the equalization valve of  FIG. 1B  showing the detail at the valve shuttle and the valve seat, each figure demonstrating various relative positions of the valve shuttle and valve seat, namely: 
         FIG. 3A  illustrating an instance when the valve is in an open configuration, with the downhole tubular in a valve-disabled position and the valve shuttle in an uphole-biased position; 
         FIG. 3B  illustrating an instance when the valve is in an open configuration, with the downhole tubular in a valve-disabled position and the valve shuttle in a flow-extended position; 
         FIG. 3C  illustrating an instance when the valve is an open configuration, with the downhole tubular in a valve-enabled position and the valve shuttle in an uphole-biased position; and 
         FIG. 3D  illustrating an instance when the valve is a closed configuration, with the downhole tubular in a valve-enabled position and the valve shuttle in a flow-extended position, to seat and close the valve. 
         FIGS. 4A to 4D  are schematics showing the various limits on movement of the valve ball and valve seat, namely; 
         FIGS. 4A and 4B  show the valve seat of the downhole tubular at the downhole-delimited position, with the valve shuttle at its uphole- and downhole-delimited positions (A and B, respectively), in both cases the valve remaining open for equalization; and 
         FIG. 4C  shows the valve seat of the downhole tubular at its uphole-delimited position, with the valve shuttle at its uphole-delimited position, the valve remaining open for equalization; and 
         FIG. 4D  shows the downhole tubular at a valve-enabled position, with the valve shuttle at a flow-extended position, the valve being closed for treatment operations. 
         FIGS. 5A through 5F  illustrate various stages of operation of the equalization valve, and more particularly of the process of opening the valve after it has been closed: 
         FIG. 5A  illustrates the valve in an open configuration with the downhole tubular in a valve-enabled position; 
         FIG. 5B  illustrates the valve in a closed configuration, as the valve shuttle is fluid-forced to a flow-extended position such that the valve ball engages the valve seat; 
         FIG. 5C  illustrates the valve in a closed configuration, with the upper tubular pulled up an increment A while the valve shuttle remains fluid-forced closed, the valve shuttle shifting against the biasing; 
         FIG. 5D  illustrates the valve in a closed configuration, with the upper tubular pulled up a further increment B while the valve shuttle remains fluid-forced closed, the valve shuttle shifting further against the biasing; 
         FIG. 5E  illustrates the valve in an open configuration, with the upper tubular pulled up a further increment C, the valve shuttle bottoming out against the biasing, and lifting the ball from the valve seat to open and equalize across the valve; and 
         FIG. 5F  illustrates the valve in an open configuration, with maximum fluid flow downhole therethrough. 
         FIGS. 6A to 6C  illustrate the steps of operation of the equalization valve, during run into hole, treatment and pulling out of hole, more particularly: 
         FIG. 6A  is a flow chart illustrating the steps of operation that remain possible during run in when the valve is in a disabled and open configuration; 
         FIG. 6B  is a flow chart illustrating the steps of operation for fluid treatment and tool release for repositioning, the valve being in an enabled configuration and closed for well treatment, and then subsequently disabled; and 
         FIG. 6C  is a flow chart illustrating the steps of operation that remain possible during pull out, while the valve is in a disabled and open configuration. 
     
    
    
     DETAILED DESCRIPTION OF DISCLOSED EXEMPLARY EMBODIMENTS 
     The downhole tool comprises an uphole tubular portion connected to the work string manipulated from surface and a downhole tubular portion releasably anchorable in the wellbore. The valve spans the uphole and downhole tubulars and telescopic manipulation therebetween either enables or disables the valve. A valve shuttle and ball are supported in the uphole tubular and a valve seat is supported in the downhole tubular. When in an “enabled configuration”, the shuttle is actuable at a threshold fluid flow rate against biasing to close the valve. When in a “disabled configuration”, the valve remains open regardless of fluid flow rate. 
     In order to close the valve two different events occur: (a) the downhole tubular is anchored in the wellbore and sets the position of the valve&#39;s valve seat, the uphole tubular being manipulated to place the valve shuttle&#39;s ball within the operable travel range of the valve seat, the valve being in an enabled configuration, and (b) the rate of fluid flow through the valve is manipulated to be greater than a threshold rate, to overcome the biasing and actuate the valve ball towards the valve seat. When the downhole tubular is not immobilized through anchoring in the well bore, the valve cannot be closed even if the rate of fluid flow through the valve exceeds the threshold rate, as the pressure from fluid flow through the valve will force the seat away from the range of travel of the valve shuttle and ball. Therefore, even if the rate of fluid flow through the valve exceeds the threshold rate, the valve will not close. This scenario is applied, for example, if it is desired to direct fluid downhole of the valve such as to wash therebelow or to clean up any internal components of the downhole tool. Further, the tool can be pulled out of hole at high tripping rates, resulting in high displaced fluid downhole therethrough, because there is no concern that the rate of fluid flow will close the valve. 
     After closing the valve, and performing a wellbore operation such as a fracing operation, the equalization valve can be opened such as, in one embodiment, by bleeding down pressure from above the valve to release hydro-static pressure that otherwise holds the valve closed. Optionally, the equalization valve can be opened by mechanical force, that is, by pulling up on the work string and uphole tubular for disabling the valve (see  FIG. 5 ). Thus, the operator can be assured, from surface, that the valve has actually been opened. Once the pressure is equalized, the tool can be moved and damage to the tool or packer is minimized or avoided. 
       FIG. 1  shows the pressure equalization valve  10  as a component of a work string  100 , such as that formed of coiled tubing. The work string comprises slotted treatment sub  102 , a diverter nose memory gauge carrier  104 , the pair of bottom cups  106  (a straddling and upper pair of opposing cups not shown), a set down J-slot slip and drag block assembly  108 , a cone  110  and slips  112 , a casing collar locator  114  and a magnetic bar memory gauge carrier  116 . 
     The bore of pressure equalization valve  10  is in fluid communication with the bore running through the work string  100 . When the equalization valve is in an “open (or equalization) configuration” fluid can flow through the valve, thus pressure above and below the bottom cups  106  is equal. When the valve is in a “closed (or treatment) configuration” fluid cannot pass through the valve and any injected fluid exits the work string above the equalization valve, for example via ports  118  above the bottom cups  106 . An open configuration is used, for example, when running in or pulling out of hole and a closed configuration is used, for example, when performing fluid treatment such as hydraulic fracturing. Herein, the fluid treatment is described in terms of hydraulic fracturing, in which fluid at high pressure is discharged through the slotted treatment sub  102 . Other treatments as introduced above are equally applicable. 
     The pressure equalization valve  10  is shown on work string  100  in  FIG. 1A , and in more detail in  FIG. 1B . It comprises an uphole tubular  12  and a downhole tubular  14 , which are telescopically or axially movable relative to each other. In this embodiment, a portion of the downhole tubular  14  extends uphole into the bore of the uphole tubular  12  and is telescopically movable therealong. The downhole tubular  14  can move relative to the uphole tubular  12  and, conversely, the uphole tubular  12  can move relative to the downhole tubular  14 . The uphole and downhole tubulars  12 ,  14  are movable between two delimited configurations. 
     A first configuration is achieved when the downhole tubular is maximally spaced from the uphole tubular a distance  60 , between shoulder/stop  15  of the downhole tubular and shoulder/stop  13  of the uphole tubular  12 . In this first configuration the downhole tubular is at its downhole-delimited position. Contact between an internal stop  54  and shoulder  56  between the uphole and downhole tubulars respectively (see  FIG. 3A ) sets the “downhole-delimited” position of the downhole tubular (shown also for e.g., in  FIG. 2A, 3A, 3B, 5F ). 
     A second configuration is achieved when the downhole tubular is minimally spaced from the uphole tubular, such that shoulder  15  of the downhole tubular  14  contacts shoulder  13  of the uphole tubular  12 . In this second configuration the downhole tubular is at its uphole-delimited position. Contact of shoulders  15  and  13  sets the “uphole-delimited” position of the downhole tubular (shown also in  FIGS. 2B, 2C, 3C, 5A, 5B ). Thus, the downhole tubular can move between the uphole- and the downhole-delimited position. 
     The tubulars  12 ,  14  are actuated to move axially toward or away from one another by mechanical force. More particularly, when running in hole, friction and drag on the downhole tubular move it axially towards the uphole tubular, towards its uphole-delimited position. When pulling out of hole, friction and drag on the downhole tubular move it away from the uphole tubular, increasing the distance therebetween to maximum distance  60 . 
     When the downhole tool is located and a fluid treatment operation is to be performed, the downhole tubular may be anchored within the wellbore using the set down J-slot slip and drag block assembly  108 , which causes the slips  112  to engage the cone  110  and therefore to be disposed radially outwards to contact the casing. Once anchored, the downhole tubular does not move axially along the well bore. 
     The valve comprises a valve shuttle  18  fit with valve ball  20 , and a valve seat  22 . The valve shuttle  18  is disposed within the bore of the uphole tubular  12 , and is axially movable therealong between two positions: (a) a position in which the valve shuttle is maximally biased uphole, referred to herein as the “uphole-delimited” position of the shuttle (see  FIG. 2A, 2B, 3A, 3C, 5A ) and (b) a position in which the valve shuttle is moved maximally downhole, referred to herein as the “downhole-delimited” position of the shuttle (see  FIG. 3B, 5E ). Thus, the shuttle can move, within the uphole tubular, between an uphole- and a downhole-delimited position. In the embodiments shown, cooperation between a shuttle housing in the uphole tubular  12  and the shuttle  18  limits the axial range of movement of the valve shuttle  18 . 
     The valve shuttle  18  is actuable by fluid flow therethrough for axial downhole movement. The rate of fluid flow through the shuttle determines whether the valve shuttle is near or at its uphole- or downhole-delimited position. More particularly, a downhole rate of fluid flow that is below a threshold value, including no flow or uphole flow, is insufficient to overcome the biasing of the valve shuttle, and the valve shuttle will be at its uphole-delimited position. A rate of fluid flow that is greater than a threshold value will overcome the biasing and the valve shuttle will move to or towards its downhole-delimited position. 
     At a distal (downhole) end of the valve shuttle  18  is a valve ball  20  which can sealably interact with valve seat  22  at the proximal (uphole) end of the downhole tubular  14 . When the ball  20  is not seated in the seat  22 , a contiguous axial bore is formed between the uphole and downhole tubulars  12  and  14 , and a fluid can flow between the bore of the uphole tubular and the bore of the downhole tubular (referred to herein as the open, or equalization, configuration of the valve). When the ball  20  is seated in the seat  22 , the fluid can no longer flow between the bore of the uphole tubular and the bore of the downhole tubular (referred to herein as the closed, or treatment, configuration of the valve). 
     In the equalization valve described herein, when the downhole tubular is at its downhole delimited position a sealing interaction between the ball  20  and seat  22  cannot be achieved, regardless of the position of the valve shuttle (which positions the valve ball). Likewise, when the valve shuttle is at its uphole-delimited position a sealing interaction between the ball  20  and seat  22  cannot be achieved, regardless of the position of the downhole tubular (which positions the valve seat). Thus, in both scenarios, fluid can flow between the bore of the uphole tubular and the bore of the downhole tubular, that is, the valve is in an open configuration. It is only when the downhole tubular and the valve shuttle move away from their respective downhole- and uphole-delimited positions that a sealing interaction may be achieved, as described more fully below. If a sealing interaction occurs, a fluid will not be able to flow from the bore of the uphole tubular into the bore of the downhole tubular, that is, the valve will be in a closed configuration. 
     As described more fully below, the present equalization valve includes:
         a) a flow rate-independent open or equalization configuration: fluid can flow through the valve, regardless of whether the rate of fluid flow is above or below a threshold value;   b) a flow rate-dependent open or equalization configuration: fluid can flow through the valve if the rate of fluid flow is below a threshold value; and   c) a flow rate-dependent closed configuration: fluid cannot flow through the valve if the rate of fluid flow is above a threshold value.       

     When the work string is being pulled out of hole, the downhole tubular is near or at its downhole-delimited position. The valve shuttle is at its uphole-delimited position if the rate of fluid flow is below a threshold, or it is moved to or towards its downhole-delimited position if the rate of fluid flow is above a threshold. But, because the downhole tubular is near or at its downhole-delimited position, the equalization valve cannot be closed when being pulled out of hole, regardless of the rate of fluid flow. 
     When being run in hole the downhole tubular is near or at its uphole-delimited position. But, fluid flow through the valve maintains the valve shuttle at its uphole-delimited position and therefore the equalization valve cannot be closed when being run in hole. If fluid is added while running in hole, a rate of fluid flow that overcomes the biasing of the valve shuttle will also move the downhole tubular away from the uphole tubular, therefore the valve cannot be closed. 
     It is to be noted that once the equalization valve has been closed, a reduction in the rate of fluid flow will not result in movement of the valve ball  20  away from valve seat  22  and a subsequent opening of the equalization valve. A hydraulic head of fluid trapped above the valve places a large closing force on the ball against the seat, maintaining the ball in a closed position. Opening of the valve may be achieved either by pulling up on the valve shuttle, which forces the ball  20  off the seat  22 , or by bleeding off the pressure above the valve to enable the ball to bias uphole off of the seat. 
       FIGS. 2A to 2C  show the equalization valve with the valve shuttle and downhole tubular in three configurations, and the flow of fluid therethrough.  FIG. 2A  shows the downhole tubular at its downhole-delimited (pulling out of hole) position, that is, the downhole tubular is separated from the uphole tubular by a maximum distance  60 . Valve shuttle  18  is at its uphole-delimited position in  FIG. 2A , and valve ball  20  and valve seat  22  are therefore separated from one another by a maximum distance  24 . Even if valve shuttle  18  is moved to its downhole-delimited position by fluid flow, the ball and seat will still be separated from one another, although it will be by a distance that is smaller than maximum distance  24 . Thus, if the downhole tubular is in its downhole-delimited position, it is not possible to seat valve ball  20  in valve seat  22  regardless of whether valve shuttle  18  is in its uphole- or downhole-delimited position (i.e., regardless of the rate of fluid flow). 
     When pulling out of hole therefore, fluid (shown by arrows) flows down bore  26  of the uphole tubular  12 , into the uphole shuttle bore  27  of the valve shuttle  18 , through ports  28  in the valve shuttle  18 , and into the downhole valve bore  30  of downhole tubular  14 . 
       FIG. 2B  shows the downhole tubular at its uphole-delimited (run in hole) position, that is, there is no space between the ends of the uphole and downhole tubulars. Valve shuttle  18  is at its uphole-delimited position (as also shown in  FIG. 2A ), and therefore valve ball  20  and valve seat  22  remain separated, that is, they are not sealingly engaged. Thus, even when downhole tubular  14  is at its uphole-delimited position, valve ball  20  and valve seat  22  will still be separated if valve shuttle  18  is at its uphole-delimited position. In this configuration therefore, it is not possible to seat valve ball  20  in valve seat  22 . 
     When running in hole therefore, fluid (shown by arrows) flows up bore  30  of the downhole tubular  14 , through ports  28  into uphole shuttle bore  27 , and then into bore  26  of the uphole tubular  12 . 
     If for some reason the rate of fluid flow were to exceed threshold while running in hole, or before the slips  112  were set, the valve could not be closed. The pressure from a rate of fluid flow that is sufficient to cause the valve shuttle to move to or towards its downhole-delimited position will cause the downhole tubular to move away from the uphole tubular. 
       FIG. 2C  shows the downhole tubular at its uphole-delimited position (with the slips set) and valve shuttle  18  moved to or towards its downhole-delimited position, because the rate of fluid flow has exceeded a threshold. In this configuration, there is no separation between valve ball  20  and valve seat  22 , that is, the valve ball is seated in the valve seat. 
     Injected fluid therefore (shown by arrows) flows down bore  26  of the uphole tubular, into uphole shuttle bore  27 , and through ports  28 . However, the flow of injected fluid into downhole valve bore  30  is prevented by the seating of valve ball  20  in valve seat  22 . Since the fluid flow into the downhole valve bore  30  is blocked, the fluid exits the work string  100  uphole of the equalization valve, for example at ports  118 . 
       FIGS. 3A  to D show detailed cross sections of an embodiment of the valve shuttle and valve seat. Four configurations of the valve shuttle and seat are shown:
         a) the downhole tubular is at its downhole-delimited position and the valve shuttle is at its uphole-delimited position ( FIG. 3A );   b) the downhole tubular is at its downhole-delimited position and the valve shuttle is at its downhole-delimited position ( FIG. 3B );   c) the downhole tubular is at its uphole-delimited position and the valve shuttle is at its uphole-delimited position ( FIG. 3C ); and   d) the downhole tubular is at its uphole delimited position and the valve shuttle has moved towards its downhole-delimited position such that the valve ball engages the valve seat ( FIG. 3D ).       

     In this embodiment, uphole tubular  12  comprises a shuttle housing  32 , which includes an axial bore within which is disposed valve shuttle  18 , which is axially moveable therein. As shown in  FIG. 3 , the axial bore  34  of the shuttle housing  32  is contiguous with the bore  26  of the treatment tubing. The valve shuttle  18  includes a bore  27  which includes an inlet  29  in fluid communication with the bore  26  of the treatment tubing and, at its downhole (distal) end, at least one fluid outlet or port  28  that is in fluid communication with the bore  34  of the shuttle housing  32 . Valve shuttle  18  comprises at its downhole (distal) end valve ball  20 , which can sealingly engage valve seat  22 . 
     In this embodiment, shuttle housing  32  further defines a lower shoulder  36  extending radially inward that defines a stop position for valve shuttle  18  when the shoulder is engaged by stop  38  which extends radially outward from the valve shuttle. Housing  32  further accommodates an adapter  40  that extends radially outward to form an upper shoulder  42  that defines an uphole and stop position for valve shuttle  18 , when the shoulder is engaged by stop  38  on the valve shuttle. Thus in this embodiment valve shuttle  18  can move between the lower surface of stop  38  and the upper surface of shoulder  36 , and thus the maximum distance that valve ball  20  can move, within the shuttle housing, is distance  44 . 
     In this embodiment valve shuttle  18  further comprises a shoulder  46  that extends radially outward and that together with the upper surface of adapter  40  defines a space  48  within which is disposed a biasing member  50 , such as a spring. The spring may be of any spring constant desired, and preloaded to provide a range of thresholds at which the valve shuttle will begin its movement when flow rate is applied. Biasing member  50  biases shuttle  18  uphole until stop  38  engages upper shoulder  42  (see  FIGS. 3A and 3C ). If the rate of fluid flow into valve shuttle  18  exceeds a threshold rate, then the biasing is overcome and shuttle  18  can move axially downhole, until the ball  20  engages seat  22  or the stop  38  engages lower shoulder  36 . 
     In this embodiment valve shuttle  18  further comprises nozzle  52  at its uphole (proximal) end, the purpose of which is to provide a flow restriction. As fluid passes through nozzle  52 , the fluid friction imparts a force on the valve shuttle. In one embodiment, the nozzle  52  is made of a hard (ceramic) material to resist abrasion (which would change the ID of the nozzle) and maintain a consistent threshold flow rate. 
     In this embodiment, downhole tubular  14  comprises valve seat  22  fit within an axial bore  30  of the downhole tubular at the proximal (uphole) end of the bore. The valve seat delineates an uphole valve bore including housing bore  34  and shuttle bore  27 , from downhole valve bore  30 . In this embodiment the downhole tubular  14  further comprises a stop  54  which extends radially outward and which engages a shoulder  56  at the end of an adapter  58  disposed at the distal (downhole) end of upper tubular  12 . Engagement of stop  54  and shoulder  56  prevents downhole tubular  14  from being pulled out of the bore of the shuttle housing (the downhole-delimited position of the downhole tubular). 
     In this embodiment, when stop  54  and shoulder  56  are engaged, the uphole and downhole tubulars are spaced maximally apart. Movement of the downhole tubular  14  towards the uphole tubular  12  stops when its proximal shoulder  15  contacts the distal shoulder  13  of the uphole tubular (the uphole-delimited position of the downhole tubular). Thus, the positions of shoulder  56  and shoulder  13  define the maximum distance  60  that valve seat  22  can move. 
     The downhole tubular further comprises a means for immobilizing the downhole tubular in the wellbore. In the embodiments described herein the means comprises a cone  110  disposed about the periphery of the downhole tubular that engages one or more slips  112  that in turn engage the casing of the wellbore and immobilize the downhole tubular. The slips are actuated by the set down J-slot slip and drag assembly. 
       FIG. 3A  shows the valve shuttle  18  at its uphole-delimited position and the downhole tubular  14  at its downhole-delimited position, defining a maximum distance  24  between valve ball  20  and valve seat  22 . If the valve ball moves downwards in the shuttle housing by distance  44 , or if the valve seat moves upwards by distance  60 , the valve cannot close. It follows, therefore, that distance  24  is greater than either of distance  44  or distance  60 . 
     This is further shown in  FIGS. 3B and 3C .  FIG. 3B  shows the downhole tubular at its downhole-delimited position and the valve shuttle at its downhole-delimited position. Since distance  44  is less than distance  24 , the movement of the valve shuttle to its downhole-delimited position is insufficient to close the gap between valve ball  20  and valve seat  22 .  FIG. 3C  shows the downhole tubular in its uphole-delimited position and the valve shuttle in its uphole-delimited position. Since distance  60  is less than distance  24 , the movement of the downhole tubular to its uphole-delimited position is insufficient to close the gap between valve ball  20  and valve seal  22 . 
       FIG. 3D  shows the downhole tubular  14  at its uphole-delimited position, and the valve shuttle has moved towards the downhole tubular  14  until the valve ball  20  sealingly engages valve seat  22 . It follows, therefore, that in order to seat the valve ball in the valve seat, distance  24  must be less than the sum of distance  44  and distance  60 . In one embodiment distance  60  is about 1.5 inches, distance  44  is greater than about 0.25 inches and distance  24  is about 1.75 inches. 
       FIGS. 4A to 4D  demonstrate schematically how maximum distances  44  and  60  may be determined. In the embodiments shown herein, when the downhole tubular  14  is at its downhole-delimited position (as shown in  FIG. 4A, 4B ), and the shuttle valve is at its uphole-delimited position ( FIG. 4A ), a maximum distance  24  is defined between valve ball  20  and valve seat  22 . To avoid closure of the valve at a flow rate that is greater than the threshold rate, the distance  44  that the shuttle valve/valve ball can travel within the shuttle housing cannot be more than a distance that will maintain a gap  64  that ensures that there is always flow through the valve ( FIG. 4B ). 
     Likewise, to avoid closure of the valve when the flow rate is not greater than the threshold rate, the distance  60  that the downhole tubular/valve seat can travel cannot be more than a distance that will maintain a gap  66  that ensures that there is always flow through the valve ( FIG. 4C ). 
     The maximum axial distance that valve ball  20  can be moved, distance  44 , may therefore be determined by the minimum distance  64  between valve ball  20  and valve seat  22  that will provide a flow passage that is large enough to support the required fluid flow through the equalization valve when it is being pulled out of hole. Likewise, the maximum axial distance that the valve seat can be moved, distance  60 , may be determined by the minimum distance  66  between valve ball  20  and valve seat  22  that will provide a flow passage that is large enough to support the required fluid flow through the equalization valve when it is being run in hole. These distances need not be the same. 
     It is to be further noted, having reference to  FIGS. 4A-D , that if the valve seat is moved to any position within the gap distance  64 , that is, if the valve seat is moved to a position that is outside of the travel distance  44  of the shuttle valve, the equalization valve will not be able to close, regardless of the fluid flow rate. Therefore, a “valve-disabled” position of the downhole tubular may be defined as a position wherein the downhole tubular is at its downhole-delimited position, or at any position that is outside of the travel distance  44  of the shuttle valve. 
     Likewise, if the valve ball is moved to any position within the gap distance  66 , that is, if the valve ball is moved to a position that is outside of the travel distance  60  of the valve seat, the equalization valve will not be able to close. Therefore, an “uphole-biased” position of valve shuttle may be defined as a position wherein the valve shuttle is at its uphole-delimited position, or at any position that is outside of the travel distance  60  of the downhole tubular. 
       FIGS. 4A-D  (and also  5  A-F) demonstrate further aspects of the valve described herein. In preferred embodiments there is a region of overlap, shown at arrow  68 , between the travel distance  44  of the valve ball and the travel distance  60  of the valve seat. Anywhere in this region, it is possible for the valve ball and seat to engage and close the equalization valve. Therefore, a “valve-enabled” position of the downhole tubular may be defined as a position wherein the downhole tubular is at its uphole-delimited position, or at any position in the travel distance  60  of the downhole tubular that overlaps with the travel distance  44  of the shuttle valve. Likewise, a “flow-extended” position of the valve shuttle may be defined as a position wherein the valve shuttle is at its downhole-delimited position, or at any position in the travel distance  44  of the shuttle that overlaps with the travel distance  60  of the downhole tubular. As shown in  FIG. 4D , valve can close when the downhole tubular is not at its uphole delimited position, and when the shuttle is not at its downhole delimited position, provided that the seat and ball meet in the region of overlap  68 . 
     Thus, when the downhole tubular in a valve-enabled position, and
         a) the fluid flow rate is less than a threshold rate, valve shuttle  18  is biased in an uphole-biased position, and fluid can flow between the uphole valve bore and the downhole valve bore (see  FIG. 2B, 3C, 5A, 5E, 5F ), or   b) the fluid flow rate is greater than a threshold rate, valve shuttle  18  is actuated to the flow-extended position to engage seat  22  and close the valve (see  FIG. 2C, 3D, 5B -D), preventing the flow of fluid between the uphole valve bore and the downhole valve bore.       

     When the downhole tubular is at its valve-disabled position, the valve ball  20  cannot sealingly engage valve seat  22  regardless of whether the fluid flow rate is greater than or less than a threshold rate, and thus fluid can flow between the uphole valve bore and the downhole valve bore ( FIG. 2A, 3A, 3B ). 
     When the rate of fluid flow is sufficient to cause a sealing engagement between the valve ball  20  and seat  22 , a reduction in the rate of fluid flow will not result in movement of the valve ball  20  away from valve seat  22  and a subsequent opening of the equalization valve. Thus, once it is in a closed configuration, the valve will not return to an open configuration simply because the flow rate has been decreased to below the threshold. Breaking the seal can be achieved by either:
         (a) pulling up on the equalization valve which will force the seat away from the ball, or   (b) stopping the flow of fluid into the equalization valve and bleeding off the pressure at the surface by bleeding off the coiled tubing, or in some cases the casing, to move the ball from the seat.       

       FIGS. 5A through 5F  illustrate the process of opening an embodiment of the equalization valve after it has been closed, by pulling up on the equalization valve.  FIG. 5A  illustrates the valve in an open configuration. The valve is enabled, with the downhole tubular at a valve-enabled position, that is, shoulder  13  of up hole tubular  12  has engaged the shoulder  15  of downhole tubular  14 . Valve shuttle  18  is at an uphole-biased position, that is stop  38  of the shuttle has engaged shoulder  42  of the housing. Fluid flow through the valve is indicated by arrows. 
       FIG. 5B  illustrates the valve in a closed configuration because the valve shuttle has been fluid-forced to a flow-extended position, wherein the valve ball on the shuttle engages the valve seat. In this embodiment, the valve shuttle does not engage the shoulder  36  of the shuttle housing  32 ; movement of the valve shuttle  18  towards its downhole-delimited position is stopped by engagement of the valve ball  20  with the valve seat  22 . 
       FIGS. 5C to 5E  show the steps for opening the valve after the wellbore treatment is completed. The rate of fluid flow into the valve is reduced to below a threshold value, however as noted above the valve shuttle will remain biased downhole. In  FIG. 5C , as compared to  FIG. 5B , an operator at surface has pulled up on the upper tubular by increment A. The valve ball  20  remains sealingly engaged in the valve seat  22 , and the shuttle housing  32  shifts against the biasing. 
       FIG. 5D  as compared to  FIG. 5C , an operator at surface has pulled up on the upper tubular by further increment B. Again, the valve ball  20  remains sealingly engaged in the valve seat  22 , and the shuttle housing  32  shifts against the biasing. 
       FIG. 5E  as compared to  FIG. 5D , an operator at surface has pulled up on the upper tubular by further increment C. Again, the shuttle housing  32  shifts against the biasing, but this time stop  38  on shuttle  18  engages shoulder  36  of shuttle housing lifting the valve ball from the valve seat to open and equalize across the valve. 
     Because fluid flow is below threshold, biasing returns valve shuttle  18  to an uphole-biased position until stop  38  engages shoulder  42 . At the same time, or subsequently, stop  54  of downhole tubular engages shoulder  56  on the uphole tubular, to limit the uphole movement of the valve housing.  FIG. 5F  illustrates the valve in an open configuration with maximum fluid flow downhole therethrough. 
     In one embodiment, a flow rate of more than 200 L/min is the threshold flow rate that will overcome the biasing of the valve shuttle  18 . If the downhole tubular is also in its valve-enabled position and immobilized in the wellbore (e.g., by setting the slips), the equalization valve will close. Reducing the flow rate to less than 200 L/min does not open the valve. 
     If the downhole tubular is not immobilized in the wellbore, the equalization valve will not be able to close even if the flow rate is greater than the threshold rate, which in one embodiment is 200 L/min. 
     The uphole tubular  12  may be sealably connected to the downhole tubular  14 .  FIG. 3A  shows seals  62  in corresponding grooves at the distal end of adapter  58 . When the equalization valve is used downhole of the packer or other sealing element, the uphole tubular  12  and downhole tubular  14  are preferably sealably connected. However, when the equalization valve is used uphole of the packer or other sealing element, the uphole tubular  12  and downhole tubular  14  may not be sealably connected. In one embodiment the seals are made of an elastomeric material. However the seals may be made from any material suitable for the sealing of pressure. 
     The insertion and removal of the valve and work string into a wellbore will now be described in further detail.  FIGS. 6A-C  show flow charts illustrating the steps of operation that remain possible during run in, pulling out of hole, and treatment. 
     When the work string  100  is run in hole ( FIG. 6A ), downhole tubular is freely movable axially within upper tubular. Friction and drag will cause the downhole tubular to move towards the uphole tubular to its valve-enabled position, however because the downhole tubular is not set in the wellbore, the valve cannot be closed. Because wellbore fluid is flowing upwards during run in, the valve shuttle is biased upwards and therefore valve ball and valve seat cannot sealingly engage. Thus, while running in hole, without any added injection fluid (left-side path of  FIG. 6A ), the equalization valve remains in an open configuration because fluid flow biases the valve shuttle uphole. If there is an injection of fluid at a rate that is insufficient to bias valve shuttle to it a flow-extended position (middle path of  FIG. 6A ), the equalization valve remains open. 
     If there is fluid injection at a rate sufficient to bias valve shuttle to a flow-extended position, the equalization valve will not close because slips  112  have not fully engaged cone  110  and therefore the wellbore casing. The pressure from the flow of fluid that is needed to overcome the biasing of valve shuttle will force the downhole tubular away from the uphole tubular. Thus, the equalization valve remains in an open configuration because even though there is sufficient fluid flow to bias the valve shuttle towards valve seat, the downhole tubular does not remain in its valve-enabled position. 
     When desired to perform a treatment operation that requires the valve to be in a closed configuration ( FIG. 6B ), the J-slot slip and drag assembly is actuated to cause the slips to engage the cone and the wellbore casing. The downhole tubular, and hence valve seat, are now immobilized in the bore of the wellbore. The uphole tubular may then be pushed down to ensure that the space between the tubulars is closed or nearly closed (i.e., the downhole tubular is in a valve-enabled position). If fluid flow into the work string is started, and it is below the threshold, the valve shuttle will remain biased uphole and the equalization valve will be in an open configuration allowing the fluid to flow through it. If the flow of fluid is above the threshold, the valve shuttle will be biased towards its downhole-delimited position until the valve ball engages the valve seat, at which time the valve is closed and treatment, for example fracking, can begin. Thus, when the tool string is set down, the attainment of a closed configuration of the equalization valve is flow-rate dependent. 
     Before work string  100  is pulled out of hole, it is preferable to equalize pressure above and below the valve. This may be accomplished in one of two ways. The operator can pull up on the work string, which will force the valve ball away from valve seat, thus opening the equalization valve. Or, the pressure above the valve may be bled off and biasing will then cause valve shuttle to move uphole, which will unseat valve ball. 
     When the work string is being pulled out of hole ( FIG. 6C ), lower tubular is again freely movable axially along upper tubular. Friction and drag will cause the downhole tubular to move away from the uphole tubular, thus increasing the distance between the ends of these tubulars—the downhole tubular will move to a valve-disabled position. When pulling out of hole, fluid flow through the valve is oriented downhole. However, regardless of whether this fluid flow overcomes the uphole biasing of the valve shuttle, the downhole tubular is in a valve-disabled position. Thus, while pulling out of hole it is not possible to close the equalization valve. 
     While the equalization valve has been described in conjunction with the disclosed embodiments and examples which are set forth in detail, it should be understood that this is by illustration only and the equalization valve is not intended to be limited to these embodiments and examples. On the contrary, this disclosure is intended to cover alternatives, modifications, and equivalents which will become apparent to those skilled in the art in view of this disclosure.