A downhole flow device has a sliding and ported sleeves. A seal has a first component on the sliding sleeve and a second component on the ported sleeve. These components engage one another to seal flow through the ports in the ported sleeve. The components move apart to allow fluid flow through the ports. The components are protected from abrasion and flow by virtue of the seal's structure and how it is opened. The sliding sleeve moves hydraulically along an axis of the ported sleeve to reveal successive ports defined along the sleeve's axis. Operation of the device and the seal address both erosion and damage from differential pressure problems. Thus, the seal prevent damage when unloading a differential pressure across it, and abrasive flow does not have the opportunity to impinge on the sealing surfaces to cause erosion.

BACKGROUND 
       [0001]    The problem of erosive damage to seals and metal components in downhole flow devices has been a challenge in the industry for quite some time. In a wellbore, for example, sliding sleeves are used in applications where high velocity flow can create a very hostile environment. The high velocity flow, especially when it contains solids, can induce flow erosion even in the hardest materials available. Additionally, when a pressure differential is unloaded across a conventional seal, severe damage can occur that renders the seal inoperable. 
         [0002]    In the prior art, techniques that address unloading of a pressure differential across seals have used thin equalizing slots and diffuser type seals. The arrangement is intended to prevent damage to two sets of seals, or packing units, that create a barrier between the annulus and tubing pressure. Examples of this prior art technique are disclosed in U.S. Pat. Nos. 5,316,084 and 5,156,220. Prior designs such as these may not prevent damage to seals caused by abrasive flow because the seals may never be adequately protected from an initial surge of pressure during the opening sequence. 
         [0003]    Although prior art sealing techniques may be effective, operators are continually striving for improvements to reduce the effects of erosion or pressure differential on seals used downhole. Accordingly, the subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
       SUMMARY 
       [0004]    A downhole flow device has a sliding sleeve and a ported sleeve. The sliding sleeve moves hydraulically along an axis of the ported sleeve to reveal successive ports defined along the axis of the ported sleeve. Fluid pressure applied to an open control line enters a sealed chamber between the sliding sleeve and the housing and moves the sliding sleeve along the ported sleeve. 
         [0005]    To limit movement of the sliding sleeve, a catch has a dog that engages in a slot in the sliding sleeve. As the sliding sleeve moves, the dog moves the catch with the sliding sleeve. At a pinnacle position of the catch, the sliding sleeve can no longer be moved by the hydraulic fluid due to the catch engaging a stop. When moving the catch to its stop, the sliding sleeve reveals one of the ports in the ported sleeve, allowing flow to pass through the device. 
         [0006]    To reset the catch so the sliding sleeve can be advanced to reveal the next port, a trigger between the sliding sleeve and housing can also move by the hydraulic pressure applied. This trigger moves on the sliding sleeve until it reaches another stop that limits its movement. When hydraulic pressure is released, the trigger moves by the bias of a spring to a reset position on the sliding sleeve. As it moves, the trigger dislodges the catch's dog from the sleeve's slot. This allows a spring to move the catch to a next lower position where the dog can then engage in a next slot on the sliding sleeve. Once completed, the mechanism is reset so that reapplication of hydraulic pressure can move the sliding sleeve to its next position. Applying hydraulic pressure to another port can move the sliding sleeve all the way back to its closed condition. 
         [0007]    A seal is provided between the sliding sleeve and the ported sleeve. The seal has a first seal component disposed on the sliding sleeve and has a second seal component disposed on the ported sleeve. These seal components engage one another to seal flow, and they move apart to allow fluid flow through the ports in the ported sleeve. Operation of the device and the seal reduce both erosion and damage caused by high velocity flow, abrasive flow, and differential pressures. In other words, the device and seal prevent damage to the seal when unloading a differential pressure across it, and the seal is designed in such a way that abrasive flow does not have the opportunity to impinge on the sealing surface to cause erosion. 
         [0008]    The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  illustrates a cross-sectional view of a downhole tool according to the present disclosure. 
           [0010]      FIG. 1B  illustrates a detailed view of a portion of the downhole tool. 
           [0011]      FIG. 2  illustrates a seal of the disclosed tool in more detail. 
           [0012]      FIG. 3  illustrates a graph of flow passages for the seal of  FIG. 2 . 
           [0013]      FIGS. 4A-4B  show pressure assistance of the seal for the downhole tool when exposed to internal or external pressure differentials. 
           [0014]      FIG. 5  shows the downhole tool in a closed condition. 
           [0015]      FIG. 6  shows the downhole tool in a first condition towards opening. 
           [0016]      FIGS. 7-9  show the downhole tool in several subsequent conditions towards opening. 
           [0017]      FIGS. 10-14  show the downhole tool being hydraulically actuated in various stages of opening. 
       
    
    
     DETAILED DESCRIPTION 
     A. Downhole Flow Device 
       [0018]    In  FIGS. 1A-1B , a downhole flow device  100  has a housing  110 , a sliding sleeve  120 , a ported sleeve  170 , a landing  180 , and a seal  200 . As shown, the housing (indicated generally by  110 ) can have a number of interconnecting housing portions  110   a - f  that facilitate assembly. In the present implementation, the flow device  100  is a reservoir control tool that couples at uphole and downhole ends  102 / 104  to other tubing components (not shown), although the teachings of the present disclosure may be used on any other downhole flow device, such as a sliding sleeve, a downhole control valve, a crossover tool, etc. When used for reservoir control, the tool  100  operates as a hydraulically-actuated variable choke valve and can adjust the rate of production or injection of fluid through the tool  100 . 
         [0019]    For example, the tool  100  can be run as part of a completion tubing string in the well. Once deployed, operators can operate the tool  100  to variably choke back the production from the well's annulus into the tool  100 . This may be done to reduce the rate of water produced from the well or to balance the rate of production (and the rate of pressure drop) of one producing zone against another. In some cases, each production zone could have a corresponding tool  100  that can be varied. As opposed to production, the tool  100  may also be used for varied injection of fluids from the tubing string into the annulus of the well. 
         [0020]    The ported sleeve  170  has a plurality of ports  174   a - g  disposed on an axis of the sleeve  170 . Exposure of more or less of the ports  174   a - g  increases or decreases the flow through the tool  100 . Although shown having several separate ports  174   a - g,  the ported sleeve  170  can have one or more ports disposed along the axis of the sleeve  174  so that more or less exposure of the one or more ports can increase or decrease flow through the tool  100 . For example, the ported sleeve  170  can having one port that increases in size along the axis of the ported sleeve  170  and can have any desirable shape. 
         [0021]    To choke the flow into or out of the tool  100  completely, the sliding sleeve  120  fits all the way onto the ported sleeve  170  as shown in  FIGS. 1A-1  B so that none of the ports  174   a - g  in the ported sleeve  170  are exposed. As shown, the seal  200  on the closed sleeves  120 / 170  seals flow into (or out of) the tool  100  when the sliding sleeve  120  is in a closed position on the ported sleeve  170 . To achieve variable choking, the tool's sliding sleeve  120  can be hydraulically moved relative to the ported sleeve  170 , and the changing position of the sliding sleeve  120  controls the flow into (or out of) the sleeve's bore  172  by disengaging the seal  200  and exposing more or less ports  174  in the ported sleeve  170 . 
         [0022]    When the sliding sleeve  120  is moved, for example, the seal  200  separates, and the sliding sleeve  120  opens relative to the ports  174  to allow fluid to flow from a surrounding annulus through windows  106  in the tool's housing  110  (i.e., portion  110   e ) and into the ported sleeve's bore  172  (or vice versa). As best shown in  FIG. 1B , the ports  174   a - g  defined in the ported sleeve  170  generally increase in size (diameter) along the axis of the sleeve  170 . Therefore, the first ports  174   a  (four of which are defined around the circumference of the ported sleeve  170 ) have a first diameter, while the other ports  174   b - e  above them have a slightly greater diameter. The next highest port  174   f  has an even greater diameter, and the last port  174   g  has the largest diameter. In this way, as the sliding sleeve  120  moves along the ported sleeve  170 , the sliding sleeve  120  successively reveals more of the ports  174   a - g,  which increases the flow through the tool  100 . 
         [0023]    In the current arrangement, the tool  100  can operate at eight discrete positions to control the amount of flow area through the tool  100 . These positions are defined in percentages of the flow area of the tubing string (specifically the diameter of the ported sleeve's bore  172 ). For example, the tool's positions can be defined as follows: 0% closed, 1% open, 3% open, 5% open, 7% open, 9% open, 15% open, and 100% open. Therefore, with the tool  100  set at the 5% position, the ports  174   a - c  are exposed, and the flow area through the tool  100  is 5% of the flow area through comparably sized tubing. As will be appreciated, these values are illustrative. The actual size and number of ports  174   a - g  for an implementation depends on the overall size of the tool  100  and the desired or expected flow characteristics as well as other implementation specific details. In other examples, the tool  100  may have more or less ports, and some or all of the ports may have the same diameters. 
       B. Seal for Downhole Flow Device 
       [0024]    As best shown in  FIG. 1B , the seal  200  has first and second seal components  210 / 250  that mate with one another when the sliding sleeve  120  is closed. The first (moving) component  210  moves with the sliding sleeve  210 , while the second (stationary) component  250  remains stationary. Either one or both of these components  210 / 250  can be incorporated into its respective sleeve (as is the stationary component  250 ) or can be an independent component affixed onto its respective sleeve (as is the movable component  210 ). As discussed below, the seal components  210 / 250  are intended to reduce damage to the seal  200 , and the design of the seal  200  is such that it resists erosion and is self-protecting. 
         [0025]    Details of the seal  200  are shown in  FIG. 2 . The moving component  210  has a first inner shelf  212 , a first inner ledge  214 , a second inner shelf  216 , and a second inner ledge  218 —each of which face inward toward the ported sleeve (not shown). The stationary component  250  has a somewhat complimentary configuration, including a first outer shelf  252 , a first outer ledge  254 , a second outer shelf  256 , and a second outer ledge  258 —each of which face outward from the ported sleeve (not shown). The stationary component  250  may also define a well  255  where the second outer shelf  256  mates with the first outer ledge  254 . 
         [0026]    The shelves  212 / 252  define a first flow passage  202 , the first ledges  214 / 254  define a second flow passage  204 , and the second shelves  216 / 256  define a third flow passage  206  through which fluid can flow through the seal  200 . The flow passages  202 ,  204 , and  206  create seal points between the metal-to-metal seal produced between the components  210 / 250 . Engagement between the first ledges  214 / 254  produces the primary sealing function when the components  210 / 250  are closed against one another. 
         [0027]    With an understanding of the seal  200  and its components  210 / 250 , discussion now turns to how the seal  200  achieves pressure assisted and erosion resistant sealing on the tool  100 . 
         [0028]    1. Pressure Assisted Sealing 
         [0029]    The seal  200  is assisted closed in metal-to-metal engagement by either internal pressure acting inside the tool  100  or by external pressure acting outside the tool  100 . In  FIGS. 4A-4B , the tool  100  is shown closed, and the seal components  210 / 250  are shown mated with one another. A lower packing element or seal  178  seals between the ported sleeve  170  and the housing  110  (i.e., portion  110   f ) and isolates fluid pressure inside the tool  100  from outside the tool  100 . 
         [0030]    As noted previously, the primary sealing function of the closed seal  200  is provided by engagement of ledges  214 / 254 . As constructed, the engagement  214 / 254  are set at a circumference that matches a centerline circumference of the lower packing seal  178  on the tool  100 . As described below, the arrangement of the ledges  214 / 254 , centerline, the packing seal  178 , and other features give pressure assistance to the seal  200  regardless of whether the tool  100  is exposed to internal or external pressure differentials. 
         [0031]    In  FIG. 4A , an internal pressure differential in the bore  112  is shown acting on the tool  100 . Fluid pressure is capable of acting against the distal end of the ported sleeve  120 , which is exposed and unsealed relative to the fluid pressure in the bore  112 . As a consequence, the fluid pressure can act against the lower shoulder of the packing seal  178 . This fluid pressure creates a piston effect on the ported sleeve  170 . The resulting pressure pushes the ported sleeve  170  and its seal component  250  toward the sliding sleeve  120  and its seal component  210 , thereby assisting the sealing engagement between them. 
         [0032]    In  FIG. 4B , an external pressure differential is shown acting on the tool  100 , but the seal  200  is also pressure assisted in this circumstance. The external fluid pressure acts against the upper shoulder of the packing seal  178 . This moves the packing seal  178  away from the ported sleeve's adjacent shoulder so that the seal  178  abuts a landing  180  unconnected to the ported sleeve  170 . As a consequence, the fluid pressure can act against the ported sleeve's shoulder. Again, this tends to create a piston effect on the ported sleeve  170  that attempts to push the ported sleeve  170  and its seal component  250  toward the sliding sleeve  120  and its seal component  210 . Therefore, the seal  200  and configuration of the ledges  214 / 254  and seal  178  help pressure assist the seal produced regardless of whether exposed to an internal or external pressure differential. 
         [0033]    2. Erosion Resistant Sealing 
         [0034]    As noted previously, the tool  100  can encounter problems caused by erosive damage to seals and metal components when varying flow therethrough. The seal  200  of the present disclosure is intended to control the velocities of abrasive flow and isolates portion of the seal  200  from the flow as much as possible to mitigate erosive damage. 
         [0035]    Returning to  FIG. 2 , the first flow passage  202  from the shelves  212 / 252  creates a very small choke when the components  210 / 250  are closed or slightly open. The second shelves  216 / 256  providing the second flow passage  206  also provide a secondary choke that reduces the flow possible through the seal components  210 / 250 . 
         [0036]    At the instant the seal components  210 / 250  start to separate and break the seal between the ledges  214 / 254 , the first flow passage  202  allows fluid to flow through the seal  200 , but the small gap between the shelves  212 / 252  defines the smallest available flow area through the seal  200 . This secondary choke from the sealing ledges  214 / 254  also limits the detrimental flow when the seal components  210 / 250  are first separated. 
         [0037]    The limited flow area through the first flow passage  202  means that any sudden erosive flow from fluids flowing from the annulus into the tool (or vice versa) mainly interacts with the shelves  212 / 252 . Accordingly, the shelves  212 / 252  take the brunt of the erosive flow rather than the sealing ledges  214 / 254  themselves, which are susceptible to detrimental erosion. In this way, the seal  200  can be self-protecting by making erosion occur away from the sealing ledges  214 / 254  at initial opening of the seal  200 . 
         [0038]    As the sliding sleeve  120  is moved on the ported sleeve  170 , the area of the flow through passages  202 ,  204 ,  206  changes. Details of how the flow area changes are shown in  FIG. 3 , which graphs some calculations for a tool  100  having an internal diameter of about 5-in. As evident from  FIG. 3 , the first flow passage  202  defines a limiting flow area through the tool  100  as the seal  200  is initially opened (i.e., when the sleeve  120  has traveled from 0 to 1-in.). 
         [0039]    In one implementation, the sliding sleeve ( 120 ) travels approximately 0.5-in. open from the ported sleeve ( 170 ) to expose the first port ( 174   a ) and allow 1% of flow through the tool  100 . In this way, the shelves  212 / 252  act to choke the flow and take the brunt of any erosive flow until the valve is 1% open. Even after that point, the first inner ledge  214  is already moved clear of the first port ( 174   a ) so the ledge  214  can avoid erosive flow, as detailed below. 
         [0040]      FIGS. 5-9  show some initial conditions of the seal  200  as the tool  100  opens (or closes in the reverse). In the closed condition shown in  FIG. 5 , the flow area is zero, and the sliding sleeve  120  has not moved. Although the flow passages  202 ,  206  (shown in  FIG. 2 ) may allow for some amount of flow, the second flow passage  204  closes off the seal  200  when the ledges  214 / 254  are engaged. 
         [0041]    In a first open condition shown in  FIG. 6 , the sliding sleeve  120  is moved upward. The ported sleeve  170  also moved upward because the landing  180  moves by the bias of the spring  182  and pushes the ported sleeve  170  upward. This keeps the seal  200  closed. Eventually, the pins  176   a  in the sleeve's slots  176   b  limit the travel of the sleeve  170  and landing  180 . 
         [0042]    As the sliding sleeve  120  continues to open, it reaches a first equalizing condition shown in  FIG. 7  when the sleeve  120  travels from 0.00-in. to about 0.125-in. The ledges  214 / 254  move apart. The length and diametric gap of the ledges  214 / 254  provides for an orifice effect of any flow through the seal  200 . This helps to protect the metal seal surfaces during initial unloading of pressure and flow as described previously. The timing of this orifice effect is minimal as it is needed only during the first movement of separation of the two seal components  210 / 250 . However, the flow passage  202  (See also,  FIG. 2 ) from the shelves  212 / 252  act to choke the flow, thereby limiting the actual flow that travels through the seal  200 . 
         [0043]    The first flow passage  202  from the first shelves  212 / 252  is extended in comparison to the others so that these shelves  212 / 252  can define a sacrificial component during initial unloading of pressure. As the two sealing components  210 / 250  continue to separate, the external extension from the first flow passage  202  maintains a tight clearance and creates an orifice effect of any flow therethrough. As the sealing shelves  212 / 252  move further apart, the volume and area increases between the two seal components  210 / 250 , thus causing a low pressure area and a drop in flow to develop. 
         [0044]    The choke effect from the shelves  212 / 252  continues until the moving component  210  has moved until its distal ledge  211  reaches the end of the first outer shelf  252  as shown in  FIG. 8 . Beyond this position, the seal  200  reaches a second equalizing condition when the distal ledge  211  comes to separate from the ledge  254 . When this occurs, the first inner ledge  214  has preferably already passed free of the first ports  174   a  in the ported sleeve  170 . Therefore, erosive damage to the ledge  214  used for closed sealing can be reduced. The shelves  212 / 252  and the distal ledge  211 , although they may be subject to more of the erosive flow, are more suited places for such damage to occur. Once the two sealing shelves  212 / 252  slide far enough apart, the movable component  210  becomes disengaged, allowing full flow into the flow port  172   a.    
         [0045]    At a subsequent opened conditions after  FIG. 8 , the flow through the seal  200  increases as flow ports  174   a  are further revealed. Finally, at the opened condition shown in  FIG. 9  when the sliding sleeve  120  has traveled to about 2.00-in., the flow area through the ports  174   a  is 1% of the flow possible through the diameter of the ported sleeve  170 . 
         [0046]    With further movement of the sliding sleeve  120 , more of the ports  174  in the ported sleeve  170  can be revealed. Again, as note previously, the tool has eight discrete positions in which the sliding sleeve  120  can reveal ports  174  on the ported sleeve  170  to control flow between 0%, 1%, 3%, 5%, 7%, 9%, 15%, and 100%. Details on how the sliding sleeve  120  is moved relative to the ported sleeve  170  are discussed below. 
       C. Hydraulic Activation 
       [0047]    As noted previously, the sliding sleeve  120  is moved relative to the ported sleeve  170 . In general, the sliding sleeve  120  can be moved by any of the techniques conventionally used in the art for a flow device. For example, the sliding sleeve  120  can be moved manually using an appropriate pulling tool, hydraulically by a piston arrangement, or other suitable mechanism. In the current implementation, the disclose tool  100  uses a hydraulically actuated ratcheting motion to move the sliding sleeve  120  relative to the ported sleeve  170 . Details of how the tool  100  operates hydraulically are provided in  FIGS. 10-14 . 
         [0048]    In  FIG. 10 , portion of the tool  100  is shown in its closed condition so that the sliding sleeve  120  engages the ported sleeve (not shown) with the sealing arrangement as discussed previously. As shown in  FIG. 10 , two control lines  103   a - b  connect to hydraulic connections  130  (only one shown) on the tool  100 . Control fluid in the control lines  103   a - b  hydraulically move the sliding sleeve  120  relative to the ported sleeve ( 170 ). These control lines  103   a - b  run from surface equipment down the tubing string to the tool  100 . When operators apply pressure to an open control line  103   a,  the tool's sliding sleeve  120  moves from its current position to a next open position (in the order listed previously). When operators apply pressure to a close control line  103   a,  the tool's sliding sleeve  120  moves back completely to its closed position. 
         [0049]    In the opening procedure, for example, pressure from the open control line  130   a  enters an open port  135  in the housing  110  (i.e., portion  110   b ) and travels to an outlet at a first chamber  132  between the sliding sleeve  120  and the housing portion  110   b.  The first chamber  132  is formed by upper and lower seals  123   a - b  between the sliding sleeve  120  and housing portions  110   a - b.  Fluid pressure fills this first chamber  132  and acts against a shoulder at upper seal  123   b  to force the sliding sleeve  120  upward in the housing  110  (i.e., the sleeve  120  moves to the left in  FIG. 10 ). 
         [0050]    At the same time, fluid pressure from the open port  135  fills a second chamber  134  at another of the port's outlets. Fluid pressure fills this second chamber  134  and acts against a trigger or unlocking sleeve  140  disposed on the sliding sleeve  120 . This unlocking sleeve  140  having a shape of a sleeve seals against the housing portions  110   b - c  with upper and lower seals  143   a - b.  The fluid pressure moves the unlocking sleeve  140  upward in the housing  110  along the sliding sleeve  120  (i.e., to the left in  FIG. 10 ). When moved, the unlocking sleeve  140  acts against the bias of a spring  124 . 
         [0051]    The results of this movement are shown in  FIG. 11 . As the open control line  130   a  supplies fluid pressure to the chambers  132  and  134 , the sliding sleeve  120  moves a first extent inside the housing  110 , and the unlocking sleeve  140  also moves along with the sliding sleeve  120  against the bias of the spring  124 . 
         [0052]    A catch  150  having dogs  155  is also disposed on the sleeve  120 . This catch  150  has the shape of a sleeve and has windows for the dogs  155 . As the fluid pressure moves the sliding sleeve  120 , the catch  150  remains in position relative to the housing  110  due to the bias of another spring  126 . Eventually, the sliding sleeve  120  moves a certain distance so that the dogs  155  in the catch  150  engage a shoulder of the first slot  125   a  in the sliding sleeve  120 , as shown in  FIG. 11 . 
         [0053]    Continued pressure at the open control lines  103   a  moves the sleeve  120  further in the housing  110 . The catch  150  engaged by dogs  155  in the first groove  125   a  also moves upward as shown in  FIG. 12 . Once the catch  150  reaches its topmost stroke, it engages an internal shoulder  138  in the housing portion  110   c.  This prevents further movement upward of the sliding sleeve  120 . 
         [0054]    At this point, the sliding sleeve  120  has opened to its first position (i.e., 1% open) to expose the first ports ( 174   a ) on the ported sleeve ( 170 ) (See  FIG. 9 ). To be able to open further, the mechanism is reset. To do this, fluid pressure at the open control line  103   a  is released. The trigger  150  is now freed from upward pressure, and the spring  124  biases the trigger or unlocking sleeve  140  downward (i.e., to the right in  FIG. 12 ). The end of the unlocking sleeve  140  engages the dogs  155 , freeing them from the slot  125   a  as shown in  FIG. 13 . 
         [0055]    Although fluid pressure at the open control line  130   a  is released, the sliding sleeve  120  does not move back downward in the housing  110 . As noted previously and as shown in  FIG. 1A , a pair of C-rings  128   a - b  help to hold the sliding sleeve  120  when positioned at varying stages along the ported sleeve  170 . A larger C-ring  128   b  engages a circumferential groove in the housing portion  110   d  to hold the sliding sleeve  120  when in the closed position. The smaller C-ring  128   a  engages in a series of smaller circumferential grooves  115  in the housing portion  110   d  as the sliding sleeve  120  is moved in stages along the ported sleeve  170 . 
         [0056]    Returning to  FIG. 13 , the unlocking sleeve  140  engaging the dogs  155  and moved by the spring  124  frees the dogs  155  from the slot  125   a.  This allows the catch  150  to reset. As shown in  FIG. 14 , the spring  126  pushes the freed catch  150  downward until the dogs  155  engage in the next circumferential slot  125   b  on the sliding sleeve  120 . 
         [0057]    Further opening of the sliding sleeve  120  can then be achieved through the same process outlined above. Pressure can again be applied to the open control line  103   a,  and the sliding sleeve  120  can be ratcheted upward in the housing to the next slotted position by the repeated actions. Release of pressure at the open control line  103   a  can then reset the hydraulic components for the next movement. Operated in this manner, the tool  100  can be set to any open condition to vary and control the flow from 1% to 100% at the discrete positions in the present example. 
         [0058]    In any of the open conditions, the sliding sleeve  120  can be fully closed on the ported sleeve ( 170 ) to stop flow. As best shown in  FIG. 14 , the close control line  103   b  connects by another port  137  to a chamber. In this case, the chamber is formed by upper seal  123   a  between the sliding sleeve  120  and housing portion  110   a  and by lower seal ( 123   c;    FIGS. 1A & 9 ) between the sleeve  120  and housing portion  110   d.  When operators apply pressure to the close control line  103   b  at any time, the tool's sleeve  120  moves back to its fully closed position, which isolates the tubing from the annulus and stops flow through the tool  100 . In the catch  150 , the dogs  155  with their angled edges simply ratchet past the various slots  125  along the sleeve  120  as the sleeve  120  can return to its closed position. Likewise, the C-rings  128   a - b  shown in  FIG. 1A  also ride along the respective grooves  115  in the housing  110  until the larger C-ring  128   b  engages in the lowest groove when the sleeve  120  has fully closed. The tool  100  can then be opened by applying pressure to the open control line  103   a  according to the previous procedures. 
         [0059]    In the current implementation, applying pressure to the close line  103   b  closes the tool  100  all the way no matter what current position the sliding sleeve  120  has. In some implementations, closing at discrete positions may be desired. To do this, an entire reverse assembly of a catch, trigger, dogs, chambers, and slots can be provided on the tool  100  opposite to those already shown. When hydraulic pressure is applied to the close line  103   b,  these reverse components can operate in the same manner described above, but only in the reverse direction. In this way, the sliding sleeve  120  can ratchet closed in discrete positions. To operate, the reverse (downward) components must accommodate the upward movement of the sliding sleeve  120  from the (upward) components (i.e., catch, trigger, dogs, etc. described previously) and vice versa. 
         [0060]    The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the inventive concepts conceived of by the Applicants. In exchange for disclosing the inventive concepts contained herein, the Applicants desire all patent rights afforded by the appended claims. Therefore, it is intended that the appended claims include all modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.