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CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present document is based on and claims priority to U.S. Provisional Application Ser. No. 61/153,671, filed 19 Feb., 2009, the contents of which are herein incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section. 
         [0003]    Inline barrier valves are used in downhole well applications. Accidental and inadvertent closing or opening of these valves can cause catastrophic failures. For example, inline lubricator valves are used to balance pressure while running an intervention tool downhole. If a failure occurs that results in an inadvertent opening or closing of the valve, substantial risk arises with respect to damage to equipment and/or injury to personnel. 
       SUMMARY 
       [0004]    In general, embodiments of the present disclosure provide a technique for enabling failsafe control of actuators used to actuate downhole tools, such as downhole valves. According to one embodiment, a well system may comprise a tool having an adjustable member. An actuation mechanism serves as a fail-as-is mechanism and works in cooperation with the adjustable member. The actuation member is shiftable upon receiving a predetermined input; however the actuation member does not move the adjustable member upon each shift. Once the actuation member has been shifted the requisite number of times to move the adjustable member to another position, at least one subsequent shift of the actuation member is not able to cause movement of the adjustable member. This provides a fail-as-is technique for ensuring the tool, e.g. valve, is not inadvertently actuated to another operational position. 
         [0005]    Other or alternative features will become apparent from the following description, from the drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying drawings illustrate only the various implementations described herein and are not meant to limit the scope of various technologies described herein. The drawings are as follows: 
           [0007]      FIG. 1  is a schematic illustration of a well with a well system incorporating an actuation/fail-as-is mechanism, according to an embodiment of the present disclosure; 
           [0008]      FIG. 2  is a cross-sectional view of one example of a fail-as-is mechanism coupled with a well tool, according to an embodiment of the present disclosure; 
           [0009]      FIG. 3  is a front elevation view of one example of the fail-as-is mechanism illustrated in  FIG. 2 , according to an embodiment of the present disclosure; 
           [0010]      FIG. 4  is a schematic illustration of the fail-as-is mechanism and cooperating tool in an operational position, according to an embodiment of the present disclosure; 
           [0011]      FIG. 5  is a schematic illustration of the fail-as-is mechanism and cooperating tool in another operational position, according to an embodiment of the present disclosure; 
           [0012]      FIG. 6  is a schematic illustration of the fail-as-is mechanism and cooperating tool in another operational position, according to an embodiment of the present disclosure; 
           [0013]      FIG. 7  is a schematic illustration of the fail-as-is mechanism and cooperating tool in another operational position, according to an embodiment of the present disclosure; and 
           [0014]      FIG. 8  is a schematic illustration of the fail-as-is mechanism and cooperating tool in another operational position, according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it will be understood by those of ordinary skill in the art that embodiments of the present disclosure may be practiced without these details, and that numerous variations or modifications from the described embodiments may be possible. In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, “connecting”, “couple”, “coupled”, “coupled with”, and “coupling” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. 
         [0016]    Embodiments of the present disclosure generally relate to a well system and well devices employing a failsafe control. According to one embodiment, the well system comprises a well tool and an actuation mechanism which cooperates with the well tool to move or shift the well tool between operational positions. The actuation mechanism is designed and serves as a fail-as-is mechanism that reduces or eliminates the risk of inadvertent actuation of the well tool. 
         [0017]    According to one specific example, the well tool comprises a valve coupled in cooperation with the actuation mechanism. The actuation mechanism is designed as a fail-as-is mechanism that allows the valve to remain in a current position if there is a failure in a control mechanism, such as a loss of hydraulic pressure in a control line maintaining the valve in an open position. The fail-as-is mechanism also enables the tool, e.g., valve, to remain in a current position in the case of a related component failure. If the valve is in an open position when the component failure occurs, for example, the valve remains open. Similarly, if the valve is in the closed position when the failure occurs, the valve remains closed. 
         [0018]    The tool and its actuation mechanism may have a variety of forms for use with a variety of overall well systems. In one well system embodiment, the tool comprises a valve deployed in an intervention tool. The valve may comprise a lubricator valve deployed in the intervention tool to balance pressure as the intervention tool is run downhole into a wellbore. The fail-as-is mechanism prevents inadvertent shifting of the valve to another operational position even if a control line or other valve component fails during run-in of the intervention tool. 
         [0019]    Referring generally to  FIG. 1 , a well system  20  is illustrated, according to one embodiment of the present disclosure. In the example illustrated, a well  22  comprises a wellbore  24  which may be lined with a casing  26 , although in other situations the wellbore may be either an open, or partially cased wellbore. In this example, the well system  20  comprises a well string  28  having a variety of operational components  30 . The specific types of operational components  30  depend on the well operation to be performed. Well string  28  further comprises a well tool  32  that may be moved/shifted between operational positions via an actuation mechanism  34 . In this example, actuation mechanism  34  comprises a fail-as-is mechanism to help prevent inadvertent actuation of the well tool  32  to another operational position. 
         [0020]    The well string  28  may be deployed downhole by a conveyance  36  which may have a variety of forms, such as production tubing, coiled tubing, cable, or other suitable conveyances. 
         [0021]    The conveyance  36  is used to deliver well string  28  and its well tool  32  downhole to a desired location in a wellbore  24 . Generally, conveyance  34  is delivered downhole beneath surface equipment  38  positioned at a surface location  40 . By way of example, surface equipment  38  may comprise a wellhead and/or rig equipment. In one specific example, the well string  28  comprises an intervention tool system, and well tool  32  is a valve, such as a lubricator valve. It also should be noted that the illustrated wellbore  24  is a generally vertical wellbore, however the system and methodology also may be utilized in deviated, e.g. horizontal, wellbores. 
         [0022]    Referring generally to  FIG. 2 , one exemplary embodiment of well tool  32  and the cooperating actuation mechanism  34  is illustrated. In this embodiment, well tool  32  comprises a movable member  42  that may be moved between operational positions. Although well tool  32  may comprise a variety of tools, the illustrated well tool example comprises a valve, and movable member  42  comprises a valve member movable/shiftable between operational flow positions. Well tool  32  may comprise an inline barrier valve, for example, in which movable valve member  42  is movable between a closed position and an open position. The open position allows fluid flow through a primary flow passage  44  extending through well tool  32  and actuation mechanism  34 . 
         [0023]    In the embodiment illustrated in  FIG. 2 , movable member  42  is a ball valve member having an interior flow passage  46 . The ball valve member  42  is pivotably mounted in a surrounding valve housing  48  against a ball seal  50 . Ball valve member  42  is pivoted against ball seal  50  between an open position, allowing flow along flow passage  44  and interior flow passage  46 , and a closed position blocking flow along flow passage  44 . In  FIG. 2 , the movable member/ball  42  is illustrated in the open flow position. 
         [0024]    The movable member  42  is coupled into cooperation with the actuation mechanism  34 , which serves as a fail-as-is mechanism. As illustrated, actuation mechanism  34  comprises a mandrel  52  translatably mounted in a cylinder  54  defined by an actuation mechanism housing  56 . Although valve housing  48  and actuation mechanism housing  56  may be formed as separate housings, the illustrated embodiment shows the valve housing  48  and actuation mechanism housing  56  as a single integral housing. 
         [0025]    Mandrel  52  is sealed with respect to the surrounding actuation mechanism housing  56  via a plurality of seals  58 . By way of example, seals  58  may comprise circular seals mounted in corresponding grooves  60  formed circumferentially along the interior surface of actuation mechanism housing  56 . The mandrel  52  also comprises a longitudinal passage  62  through which fluid may be conducted as it flows along flow passage  44 . Mandrel  52  is coupled with movable member  42  via a suitable mandrel operator  64 . If movable member  42  comprises a ball valve, as illustrated, mandrel operator  64  comprises a linkage configured to pivot the ball valve between open and closed positions as mandrel  52  translates back and forth in a longitudinal direction along cylinder  54 . 
         [0026]    Shifting of mandrel  52  back and forth within the actuation mechanism housing  56  may be achieved via actuation of a piston  66  cooperatively coupled with mandrel  52 . Piston  66  is slidably mounted within a recessed region  68  that is recessed into an interior wall of actuation mechanism housing  56  at a location surrounding mandrel  52 . A predetermined input may be applied to piston  66  to selectively shift the piston back and forth in recessed region  68 . However, every transition of the piston  66  along recessed region  68  does not impart motion to mandrel  52 , and at least one “dummy” shifting of piston  66  is provided between each actual movement of mandrel  52 . In other words, the interaction of piston  66  and of mandrel  52  enables the actuation mechanism  34  to perform as a fail-as-is mechanism by limiting movement of mandrel  52  (and thus valve member  42 ) to specific shifts within a series of shifts. Effectively, piston  66  is decoupled from mandrel  52  in that movement of piston does not necessarily move mandrel  52 . 
         [0027]    The predetermined input applied to shift piston  66  may be in a variety of forms, such as electrical, electro-hydraulic, hydraulic, or other types of inputs. In the specific example illustrated, the input is a hydraulic input provided by one or more hydraulic lines  70 . If hydraulic inputs are used, single hydraulic lines may be used to move piston  66  against a resilient member; or two or more hydraulic lines  70  may be employed to selectively move the piston  66  back and forth along recessed region  68 . In the embodiment illustrated, for example, the predetermined hydraulic input is provided by a pair of hydraulic lines  70  with an individual hydraulic line positioned on each side of piston  66  to selectively move the piston back and forth. 
         [0028]    The hydraulic lines  70  are located to deliver hydraulic fluid into recessed region  68  on opposite sides of piston  66  via ports  72  extending through housing  56 . The piston  66  may comprise a plurality of seals  74  positioned to form a seal between piston  66  and mandrel  52  on one side of the piston; and between piston  66  and an interior surface defining recessed region  68  on a radially opposite side of the piston. Pressurized hydraulic fluid is selectively applied to each side of piston  66  to drive the piston back and forth in recessed region  68  and to ultimately shift mandrel  52 , thereby moving the movable member  42  to another operational position. 
         [0029]    For each shift of piston  66  that causes movement of mandrel  52  and movable member  42 , at least one subsequent shifting of the piston  66  is not able to cause movement of the mandrel  52 . In many applications, a plurality of subsequent shifts of the piston  66  may not move mandrel  52 . These “dummy” shifts ensure actuation mechanism  34  functions as a fail-as-is mechanism and prevents inadvertent actuation of movable member  42  to another operational position. The selective movement of mandrel  52  under the influence of piston  66  is caused by a selective engagement mechanism  76 , which enables cooperation between actuation mechanism  34  and well tool  32  without directly coupling piston  66  to mandrel  52 . 
         [0030]    According to one embodiment, selective engagement mechanism  76  is an indexer or indexing system in which piston  66  comprises a plurality of slots  78  that move in cooperation with corresponding keys  80  mounted on mandrel  52 . In  FIG. 3 , one example of an indexing system  76  is illustrated in greater detail. In this example, piston  66  comprises the plurality of slots  78  formed by a series of short slots  82  and a series of long slots  84  which are longitudinally oriented along piston  66 . By way of specific example, the indexing system may comprise a J-slot indexing system with at least one long J-slot  84  between each sequential pair of short J-slots  82  moving in a circumferential direction around piston  66 . In the specific example, a plurality of long J-slots  84 , e.g. two J-slots, is positioned between each sequential pair of short J-slots  82 . Additionally, the piston  66  may have two sets of the plurality of slots  78  in which each set of slots is positioned at an opposed longitudinal end of piston  66 . The slots  78  are oriented for engagement with corresponding sets of keys  80  mounted to mandrel  52 , on both longitudinal ends of piston  66 . 
         [0031]    When the piston  66  is shifted, sloped surfaces  86  engage corresponding keys  80  and slightly rotate the piston  66  relative to the mandrel  52  so that the keys  80  move along the corresponding slots  78 . If the keys  80  move into a short slot  82 , continued movement of piston  66  forces a corresponding movement of mandrel  52 . By having slots  78  on both longitudinal ends of piston  66 , a similar engagement occurs as the piston  66  is shifted longitudinally in each direction. The engagement of keys  80  at one longitudinal end of the piston  66  effectively rotates the piston slightly for appropriate engagement with keys  80  at an opposite longitudinal end of the piston  66  when the piston  66  is transitioned in the opposite longitudinal direction. However, between each sequential pair of short slots  82 , one or more long slots  84  prevent movement of the mandrel  52  during one or more subsequent shifts. This is accomplished by forming long slots  84  with sufficient length to prevent the “bottoming out” of keys  80  over the full longitudinal transition or stroke of piston  66 . 
         [0032]    As a result, the decoupling between piston  66  and mandrel  52  creates a fail-as-is mechanism that can be used in a variety of downhole tools. A few examples of suitable downhole tools include downhole completion tools, which may be in the form of valves, e.g. barrier valves, ball valves, safety valves, inflow control valves, as well as a variety of other tools. The unintended actuation of the downhole tool is prevented because the motion of piston  66  is decoupled from the mandrel  52  following the transition of mandrel  52 . In the embodiment illustrated, movable member  42  is a ball valve movable via appropriate activation of selective engagement mechanism  76 . The selective engagement mechanism  76  may be an index system comprising J-slots located on opposite longitudinal ends of the piston  66  such that each set of slots  78  is arranged in a pattern with short J-slots  82  separated by two long J-slots  84 , for example. 
         [0033]    In the embodiment illustrated, mandrel  52  has two sets of matching sized lugs or keys  80 . When piston  66  moves through a full stroke along recessed region  68  and the subject mandrel keys  80  move into a long slot  84 , the mandrel  52  does not move. On the other hand, if the mandrel keys  80  move into one of the short slots  82 , the mandrel  52  moves according to the corresponding movement of the piston  66  as it transitions through its piston stroke. In the illustrated example, the movement of mandrel  52  cycles the valve member  42  between open and closed positions. After intentionally actuating the movable member  42 , the subsequent, repeated cycling of piston  66  results in the next two piston strokes moving through two dummy cycles in which the mandrel keys  80  engage long slots  84 . Accordingly, in the case of a failure, e.g. a control line leak, the next two cycles or strokes of piston  66  produce two non-activating movements which fail to move mandrel  52 . This prevents inadvertent actuation of the downhole well tool  32 . 
         [0034]    In the embodiment illustrated in  FIG. 2 , the actuation mechanism  34  is a hydraulic actuation mechanism with a displacement based fail-as-is feature for selectively moving a ball type, downhole barrier valve while protecting the valve from inadvertent actuation. However, other embodiments of the fail-as-is feature may comprise other components, actuation techniques, and configurations for moving a variety of tools between operational positions while protecting the tool from inadvertent actuation. Furthermore, the series of actuations of piston  66  between each movement of movable member  42  may be selected according to the requirements of a specific application, well tool, and/or operator considerations. In the example illustrated, two long slots  84  are followed with a short slot  82 , resulting in two “dead” cycles prior to actuating the well tool  32 . The number of “dead” cycles in which the piston  66  does not actuate the mandrel  52  may be as few as one or as many as three or more depending on the specific application. In some cases, the “dead” cycles may only follow one of the operational sequences. For example, two operational cycles may occur sequentially followed by one or more “dead” cycles. 
         [0035]    Referring generally to  FIGS. 4-8 , a series of actuation cycles is provided in sequential figures to help illustrate the cooperation of actuation mechanism  34  and well tool  32 . The cooperation results in selective movement of the movable member  42 , e.g. valve member, between operational positions while protecting the well tool from inadvertent actuation. In the illustrated sequence, the piston  66  is initially in a rightmost position and the keys  80  located on the right side of piston  66  are engaged with the short slots  82 , as illustrated in  FIG. 4 . The piston  66  is illustrated as actuated through its full stroke to the right, thus transitioning mandrel  52  to the right side which, in turn, moves valve member  42  to an open position. (See  FIG. 2 ). 
         [0036]    As described above, when selective engagement mechanism  76  comprises and indexing system, piston  66  and slots  78  may be partially rotated around the mandrel  52  during each engagement to allow progression from one cycle to the next. When the piston  66  is subsequently cycled or stroked to the left, the keys  80  located on the left side of piston  66  are engaged with long slots  84 , as illustrated in  FIG. 5 . During this stroke of piston  66 , the mandrel  52  does not move. In the example illustrated, this subsequent stroke is called the “dummy up” cycle. The next sequential cycle or stroke of the piston  66  is again to the right, but this stroke results in engagement of the keys  80  located on the right side of piston  66  with long slots  84 , as illustrated in  FIG. 6 . This stroke is also a dummy stroke and may be referred to as a “dummy down” stroke, which again protects valve member  42  from inadvertent actuation to a next operational position, e.g. a closed position. 
         [0037]    During the next actuation of piston  66 , the piston is cycled or stroked to the left and the left keys  80  are engaged by short slots  82 , as illustrated in  FIG. 7 . Continued movement of piston  66  through its full stroke, along recessed region  68 , causes movement of the keys  80  and mandrel  52  toward the left, as illustrated in  FIG. 8 . This actuation of piston  66  and the resultant movement of mandrel  52  cause movement of valve member  42  to a subsequent operational position. In this particular example, the valve member  42  is transitioned from an open position to a closed position. 
         [0038]    The fail-as-is feature of the actuation mechanism  34  protects the well tool against inadvertent actuation by providing at least one dummy cycle, e.g. two dummy cycles, between actual actuation steps. For example, after the ball valve is cycled open, the piston  66  is in the initial actuation position illustrated in  FIG. 4 . If one of the control lines  70  breaks and causes a pressure imbalance across piston  66 , the piston may be actuated through the “dummy up” cycle. Because this cycle is a dummy cycle, the movable member  42 , e.g. ball valve, is not actuated and remains in its current position. This same protection against inadvertent actuation also is provided when the movable member  42  is in a different operational position, e.g. when the ball valve is in a closed position. Again, if a control line  70  or other component breaks and creates a pressure imbalance across piston  66 , the piston is simply moved through a dummy cycle and the movable member  42  remains in its current position. Accordingly, the actuation mechanism  34  serves as a fail-as-is mechanism that enables well tool actuation, while protecting the well tool from inadvertent actuation. 
         [0039]    The overall well system  20  may be designed for use in a variety of well applications and well environments. Accordingly, the number, type and configuration of components and systems within the overall system may be adjusted to accommodate different applications. For example, the well tool and actuation mechanism may be employed in an intervention tool system or in a variety of other types of well systems. The technique for shifting actuation mechanism  34  may rely on a variety of predetermined inputs, such as hydraulic inputs, electrical inputs, electro-hydraulic inputs, and other inputs suitable for imparting motion to the shiftable piston. Furthermore, the piston, mandrel, selective engagement mechanism, and other components of the actuation mechanism may be adjusted to the specifics of a given well application and well tool. Similarly, the well tool may comprise a variety of valves and other types of well tools actuated between operational positions via various linkages between the actuation mechanism and the movable element of the well tool. 
         [0040]    Elements of the embodiments have been introduced with either the articles “a” or “an.” The articles are intended to mean that there are one or more of the elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the elements listed. The term “or” when used with a list of at least two elements is intended to mean any element or combination of elements. 
         [0041]    Although only a few embodiments of the present disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.

Summary:
A technique enables failsafe control over actuators used to actuate downhole tools. The technique may utilize a well system having a tool with an adjustable member. An actuation mechanism serves as a fail-as-is mechanism and works in cooperation with the adjustable member. The actuation member is shiftable upon receiving a predetermined input; however the actuation member does not move the adjustable member upon each shift. Once the actuation member has been shifted the requisite number of times to move the adjustable member to another position, at least one subsequent shift of the actuation member is not able to cause movement of the adjustable member. The result is a fail-as-is technique for ensuring the tool is not inadvertently actuated to another operational position.