Abstract:
Systems and methods for downhole completions. A downhole running tool can have a body having a bore formed therethrough. A latch member can be disposed on a first portion of the body. A reset member can be disposed on a second portion of the body. A conduit can be formed within a sidewall of the body. The conduit can be located between the first and second portions of the body. A pressure relief port can be disposed at a first end of the conduit; and a first flow port can be disposed at a second end of the conduit. The pressure relief port and first flow port can be in communication with an outer diameter of the body.

Description:
BACKGROUND 
     In many subterranean environments, such as wellbore environments, downhole tools are used to carry out a variety of procedures. For example, downhole tools may comprise a variety of flow control valves, safety valves, flow controllers, packers, gas lift valves, sliding sleeves, and other well tools. Many of these well tools can be hydraulically controlled via input from hydraulic control lines that are run downhole. Conventional well tools often rely on a dedicated hydraulic control line or lines routed to a specific tool positioned in a wellbore. The number of well tools placed downhole can be limited by the number of control lines available in a given wellbore. The wellbore and/or wellbore equipment, e.g. packers, used in a given application also can provide space constraints or routing constraints which limit the number of control lines. Furthermore, even in applications that would allow the addition of control lines, the additional lines tend to slow installation and increase the cost of installing equipment downhole. 
     Attempts have been made to reduce the number of hydraulic control lines necessary to carry out given well related procedures. For example, multiplexers have been used to limit the number of hydraulic control lines. However, multiplexing systems often rely on an ability to generate multiple levels of pressure that are interpreted downhole. In some custom designed systems, the maximum number of well tools is limited to a number equal to the number of hydraulic control lines. In other attempts, electric/solenoid controlled valves or custom hydraulic devices and tools have been designed to respond to pressure pulse sequences delivered downhole. However, many such systems have proved to be fairly costly and relatively slow to actuate. 
     SUMMARY 
     In general, the present invention provides a system and method for controlling multiple well tools. A plurality of well tools can be actuated between operational positions. The well tools are coupled to a plurality of multidrop modules with each multidrop module typically being coupled to one or two well tools. A plurality of control lines are connected to the multidrop modules, and the number of multidrop modules and attached well tools can be greater than the number of control lines. Also, each well tool can be actuated individually by providing pressure inputs through one or more of the control lines. The pressure inputs can be provided at a single pressure level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is a schematic view of a well tool actuation system having a plurality of well tools and multidrop modules deployed in a wellbore, according to an embodiment of the present invention; 
         FIG. 2  is a schematic illustration of another example of the well tool actuation system, according to an alternate embodiment of the present invention; 
         FIG. 3  is a schematic illustration of one example of a multidrop module utilized in the well tool actuation system, according to an embodiment of the present invention; 
         FIG. 4  is a view of the multidrop module illustrated in  FIG. 3  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 5  is a view of the multidrop module illustrated in  FIG. 3  but in a different state of actuation, according to another embodiment of the present invention; 
         FIG. 6  is a table illustrating one example of a multidrop module program for individually actuating specific well tools, according to an embodiment of the present invention; 
         FIG. 7  is a table illustrating another example of a multidrop module program for individually actuating specific well tools, according to an alternate embodiment of the present invention; 
         FIG. 8  is a schematic illustration of another example of the well tool actuation system, according to an alternate embodiment of the present invention; 
         FIG. 9  is a schematic illustration of another example of the well tool actuation system, according to an alternate embodiment of the present invention; 
         FIG. 10  is a schematic illustration of one example of a multidrop module utilized in the well tool actuation system illustrated in  FIGS. 8 and 9 , according to an embodiment of the present invention; 
         FIG. 11  is a view of the multidrop module illustrated in  FIG. 10  but in a different state of actuation, according to an embodiment of the present invention; 
         FIG. 12  is a view of the multidrop module illustrated in  FIG. 10  but in a different state of actuation, according to an embodiment of the present invention; 
         FIG. 13  is a table illustrating one example of a multidrop module program for individually actuating specific well tools, according to an embodiment of the present invention; 
         FIG. 14  is a table illustrating another example of a multidrop module program for individually actuating specific well tools, according to an alternate embodiment of the present invention; 
         FIG. 15  is a schematic illustration of one example of a multidrop module with a module program override mechanism, according to an embodiment of the present invention; 
         FIG. 16  is a view of the multidrop module illustrated in  FIG. 15  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 17  is a view of the multidrop module illustrated in  FIG. 15  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 18  is a view of the multidrop module illustrated in  FIG. 15  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 19  is a view of the multidrop module illustrated in  FIG. 15  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 20  is a schematic illustration of another example of a multidrop module with a module program override mechanism, according to an alternate embodiment of the present invention; 
         FIG. 21  is a view of the multidrop module illustrated in  FIG. 20  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 22  is a view of the multidrop module illustrated in  FIG. 20  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 23  is a view of the multidrop module illustrated in  FIG. 20  but with a different flow pattern, according to another embodiment of the present invention; 
         FIG. 24  is a view of the multidrop module illustrated in  FIG. 20  but with a different flow pattern, according to another embodiment of the present invention; and 
         FIG. 25  is a view of the multidrop module illustrated in  FIG. 20  but with a different flow pattern, according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention generally relates to a system and method for controlling well tools. A multidrop module is deployed between a well tool and control lines that extend to the surface. Multiple well tools and associated multidrop modules can be coupled to the control lines, and the multidrop modules require only one level of pressure for operation. Use of the multidrop modules enables selection of one or several well tools for actuation out of all of the well tools deployed. Additionally, each multidrop module is able to memorize the last selection made based on the pressure input delivered downhole via the control lines. 
     Referring generally to  FIG. 1 , one embodiment of a well tool actuation system  30  is illustrated. The actuation system  30  may be mounted along or otherwise coupled to equipment  32  used in a subterranean environment, e.g. a wellbore environment. Equipment  32  comprises, for example, a downhole completion or other equipment utilized in a wellbore  34 , such as an oil or gas related wellbore. 
     In the embodiment illustrated, well tool actuation system  30  comprises a plurality of well tools  36 . Actuation of well tools  36  is based on fluid inputs supplied along a plurality of control lines, e.g. control lines  38 ,  40  and  42  ( 1 ,  2  and  3 ). In this embodiment, three control lines are utilized, and the control lines extend upwardly to, for example, a surface location. The number of well tools  36  that can be controlled independently can be greater and even substantially greater than the number of control lines. In  FIG. 1 , the well tool illustrated in dashed lines represents one or more well tools in addition to the other illustrated well tools. 
     The well tools  36  can be actuated by fluid, such as hydraulic fluid flowing through one or more of the control lines  38 ,  40 ,  42 . Additionally, the plurality of well tools  36  may comprise a variety of well tool types and combinations of tools depending on the application. For example, the well tools  36  may comprise flow control valves, flow controllers, packers, gas lift valves, sliding sleeves, and other tools that can be actuated by a fluid, e.g. hydraulic fluid. In  FIG. 1 , the well tools  36  are illustrated as dual-line tools that are actuated via inputs from two control lines. However, the well tools  36  also may comprise single-line tools, as illustrated in  FIG. 2 . 
     As illustrated in  FIG. 1 , each dual-line well tool  36  is coupled with a multidrop module  44  that may be positioned downhole proximate the corresponding well tool  36 . In the embodiment illustrated in  FIG. 2 , a pair of single-line tools can be coupled with each multidrop module  44 . The plurality of multidrop modules  44  serves to control the flow of actuating fluid and thus the actuation of the corresponding well tools  36 . In the embodiments illustrated, each well tool can be actuated individually via single level pressure inputs provided to the multidrop modules  44  through, for example, one of the control lines. Each multidrop module  44  has a specific program, as illustrated schematically in the diagrams labeled with reference numeral  46  in  FIG. 1 . For example, each multidrop module  44  can be programmed to respond and to enable actuation of its corresponding well tool  36  upon receipt of a specific number of pressure pulses. The number of pressure pulses, e.g. single level pressure pulses, applied can be detected and tracked by indexers that are unique to specific multidrop modules  44 , as explained in greater detail below. 
     Referring generally to  FIG. 3 , one embodiment of a multidrop module  44  is illustrated. In this embodiment, each multidrop module  44  comprises a housing  48  containing a valve  50 , such as a two position valve, that may be positioned between an actuation position and a no-actuation position. By way of example, valve  50  may be mounted within housing  48  for translating/sliding motion along an interior  52  of housing  48 . Valve  50  is operatively coupled with an indexer  54  across a piston  56 . In this example, indexer  54  comprises an indexer sleeve  58  and a cooperating indexer pin  60  that may be mounted to housing  48 . The indexer  54  may be a two-position/x-increments, J-slot indexer programmed to shift the multidrop module  44  to an actuation position at a predetermined number of pressure inputs applied to the indexer  54  via control line  38 . 
     As illustrated, a seal  61  may be positioned about piston  56  to form a seal with an interior surface of housing  48 . Additionally, a return spring  62  can be positioned within housing  48  to act against valve  50  in a direction that provides a bias against the pressure applied to indexer  54  and piston  56  via control line  38 . For example, valve  50  is displaced via piston  56  when a pressure input is applied through control line  38 , and return spring  62  returns valve  50  in an opposite direction once the pressure input is reduced. 
     When pressure is applied to control line  38 , the piston  56  moves against spring  62  and compresses the spring. The stroke of piston  56  is limited by the slot profile of indexer sleeve  58  and the cooperating indexer pin  60 . When pressure is bled from control line  38 , the return spring  62  forces piston  56  in an opposite direction. Again, the slot profile of indexer sleeve  58  and cooperating indexer pin  60  limits the stroke of piston  56  and thus determines its final position. Each time pressure is applied via control line  38 , the indexer  54  is advanced to its next increment. Depending on the specific indexer program, e.g. indexer slot profile, valve  50  either remains at its current position or is shifted to its other position. For example, indexer  54  can be programmed with an appropriate slot profile so the valve  50  is in an “actuation” position at the first increment, i.e. following the first pressure input via control line  38 , and subsequently remains in the “no-actuation” position for the remaining indexer increments. If the indexer  54  has x increments, then x applications of the pressure input, e.g. a single-level pressure input, through control line  38  moves the indexer through its entire profile. 
     In  FIG. 3 , valve  50  is positioned in an actuation position that enables actuation of the corresponding well tool  36 . In this position, hydraulic power can be transmitted along control line  40 , through multidrop module  44 , and into a well tool actuation line  64  to actuate well tool  36  in a first direction. For example, if well tool  36  comprises a valve, actuation line  64  may be an “open” line that enables opening of the valve. When multidrop module  44  remains in this actuation position, hydraulic power also can be transmitted along control line  42 , through multidrop module  44 , and into a second well tool actuation line  66  to actuate well tool  36  to a different operational position, as illustrated in  FIG. 4 . If well tool  36  comprises a valve, for example, actuation line  66  may comprise a “close” line that enables closing of the valve. In some embodiments, the well tool  36  comprises a fluid volume that is returned during actuation. For example, actuation of well tool  36  via actuation line  64  causes the flow of return fluid along actuation line  66 . Similarly, actuation of well tool  36  via actuation line  66  causes the flow of return fluid along line  64 . 
     Upon application of the predetermined or programmed number of pressure inputs to multidrop module  44  via control line  38 , indexer  54  and multidrop module  44  are shifted to the no-actuation position, as illustrated in  FIG. 5 . As illustrated, indexer  54 , via piston  56 , holds valve  50  at a position that prevents actuation of well tool  36  regardless of the pressure inputs applied along control line  40  or control line  42 . The valve  50  remains in the no-actuation position until the appropriate number of pressure inputs are applied through control line  38  to cause shifting of indexer  54 , and thus valve  50 , back to the actuation position illustrated in  FIG. 3 . 
     Each indexer may be uniquely programmed, e.g. contain a unique slot profile, to correspond with the desired number of pressure inputs required to transition the multidrop module  44  from an actuation position to a no-actuation position and back again. The indexer program for each multidrop module is unique relative to the indexer program for other multidrop modules. In some embodiments, each multidrop module has its own unique program. Accordingly, every time control line  38  is pressurized with a pressure input, every multidrop module  44  transitions through an increment via its indexer  54 . However, any resulting change in position of a specific valve  50  depends on the unique program or slot profile of its indexer. The indexers  54  of the various multidrop modules  44  can be programmed to enable selection of one tool at a time or several tools at a time. The changes, of course, are predictable based on the predetermined program, e.g. slot profile, of each indexer sleeve. 
     As illustrated in  FIG. 6 , for example, a plurality of multidrop modules  44  can be uniquely programmed. In this example, a first pressure input to the multidrop modules  44  causes shifting of the first module to an actuation position, while the second and third modules remain in a no-actuation position. A second pressure input causes the second incremental movement of the indexers  54  in each multidrop module  44 , resulting in shifting of the second multidrop module to an actuation position and the first and third multidrop modules to a no-actuation position. A third pressure input applied to the multidrop modules causes the first and second modules to remain or shift to a no-actuation position, while the third multidrop module is transitioned to an actuation position. However, many different programs can be applied for shifting the multidrop modules between actuation and no actuation positions, as desired for a specific application. Additionally, multiple or all of the multidrop modules can be programmed to shift to an actuation position or a no-actuation position at the same time, as illustrated in  FIG. 7 . In this example, the first pressure input and the first incremental movement of the indexers  54  causes all of the illustrated multidrop modules to shift to an actuation position. Subsequent pressure inputs cause the multidrop modules to be individually transitioned between actuation and no-actuation positions, as illustrated. 
     Referring generally to  FIGS. 8 and 9 , another embodiment of well tool actuation system  30  as illustrated. In this embodiment, well tools  36  and multidrop modules  44  are controlled via a pair of control lines  68 ,  70 . As illustrated, each multidrop module  44  can each be used to control the actuation of, for example, a single dual-line tool, as illustrated in  FIG. 8 . Alternatively, the multidrop modules  44  can be used to control the actuation of single-line tools  36 , such as the pairs of single-line tools  36  controlled by each multidrop module  44 , as illustrated in  FIG. 9 . 
     An example of a multidrop module  44  that can be utilized in a two control line system is illustrated in  FIG. 10 . In this embodiment, each multidrop module  44  again comprises the housing  48  that contains valve  50 . However, valve  50  is a three position valve having three different operational positions comprising a first actuation position, a second actuation position, and a no-actuation position. If the well tool  36  comprises a valve or similar device, the first actuation position can be an “open tool” position and the second actuation position can be a “close tool” position. The three position valve  50  is operatively coupled with an indexer  54  across a piston  56 . In this embodiment, however, indexer  54  comprises a three position indexer, such as a three position/x increment, J-slot indexer, able to shift valve  50  between its three operational positions. 
     When pressure is applied to control line  68 , the piston  56  moves against spring  62  and compresses the spring. The stroke of piston  56  is limited by the slot profile of indexer sleeve  58  and the cooperating indexer pin  60 . When pressure is bled from control line  68 , return spring  62  forces piston  56  in an opposite direction. Again, the slot profile of indexer sleeve  58  and cooperating indexer pin  60  limits the stroke of piston  56  and thus determines its final position. Each time pressure is applied via control line  68 , the indexer  54  is advanced to its next increment. Depending on the specific indexer program, e.g. indexer slot profile, valve  50  either remains at its current position or is shifted to its next position. For example, indexer  54  can be programmed with an appropriate slot profile so the valve  50  is in a “close tool” position at the first increment, in an “open tool” position for the second increment, and in the “no-actuation” position for the remaining indexer increments of the indexer profile. If the indexer  54  has x increments, then x applications of the pressure input, e.g. a single-level pressure input, through control line  68  moves the indexer through its entire profile and back to the “close tool” position. 
     In  FIG. 10 , valve  50  is positioned in the first actuation position, e.g. an open tool position, that enables actuation of the corresponding well tool  36  in a first direction. In this position, hydraulic power can be transmitted along control line  70 , through multidrop module  44  (via, in part, a flow passage  72  through valve  50 ), and into the well tool actuation line  64  to actuate well tool  36  in a first direction, e.g. to open the well tool. Return fluid flows can be conducted through actuation line  66 , through multidrop module  44 , and into control line  68  via a secondary flow passage  74 . A check valve  76  is placed along secondary flow passage  74  to allow movement of return flow from multidrop module  44  to control line  68  while blocking the reverse flow of fluid during application of pressure inputs through control line  68 . 
     Upon application of the predetermined number of pressure inputs to multidrop module  44  via control line  68 , indexer  54  and multidrop module  44  are shifted to the no-actuation position, as illustrated in  FIG. 11 . Indexer  54  holds valve  50 , via piston  56 , at a position that prevents actuation of well tool  36  regardless of the fluid pressure applied along control line  70 . The valve  50  remains in the no-actuation position until the appropriate number of pressure inputs are applied through control line  68  to cause shifting of indexer  54 , and thus valve  50 , to the second actuation position, e.g. the close tool position, illustrated in  FIG. 12 . In this position, hydraulic power can be transmitted along control line  70 , through multidrop module  44  (via flow passage  72  through valve  50 ), and into the well tool actuation line  66  to actuate well tool  36  in a second direction, e.g. to close the well tool. Return fluid flows can be conducted through actuation line  64 , through multidrop module  44 , and into control line  68  via the secondary flow passage  74 . 
     Again, each indexer can be programmed with a unique slot profile that corresponds to the desired number of pressure inputs required to transition the multidrop module  44  between the two actuation positions and the no-actuation position. The indexer program for each multidrop module may be unique relative to the indexer program for other multidrop modules. In some embodiments, each multidrop module may have its own individual program. Accordingly, every time control line  38  is pressurized with a pressure input, every multidrop module  44  transitions through an increment via its indexer  54 . However, any resulting change in position of valve  50  depends on the unique program or slot profile of its indexer. 
     As illustrated in  FIG. 13 , for example, a plurality of multidrop modules  44  can be uniquely programmed. In this example, a first pressure input to the multidrop modules  44  causes shifting of the first module to a first actuation position, while the second and third modules remain in a no-actuation position. A second pressure input causes the second incremental movement of the indexers  54  in each multidrop module  44 , resulting in shifting of the first multidrop module to a second actuation position, while the second and third modules remain in a no-actuation position. A third pressure input applied to the multidrop modules causes the second multidrop module to shift to a first actuation position, while the first and third multidrop modules shift or remain in a no-actuation position. A fourth pressure input causes the second multidrop module to move to a second actuation position, while the first and third modules remain in a no-actuation position. A fifth pressure input causes the third multidrop module to shift to a first actuation position, while the first and second multidrop modules shift or remain in a no-actuation position. The sixth pressure input causes the third multidrop module to shift to a second actuation position, while the first and second multidrop modules remain in a no-actuation position. Here again, the pressure inputs can all be provided at the same pressure level. 
     Similar to the first illustrated embodiment, this embodiment allows the use of many different programs for shifting the multidrop modules between first actuation, second actuation, and no-actuation positions, as desired for a specific application. Additionally, multiple or all of the multidrop modules can be programmed to shift to an actuation position or a no-actuation position at the same time. As illustrated in  FIG. 14 , for example, the first pressure input and the first incremental movement of the indexers  54  causes all of the illustrated multidrop modules to shift to a first actuation position. The second pressure input through control line  68  shifts the multidrop modules to a second actuation position. Subsequent pressure inputs may cause the multidrop modules to be individually transitioned between first actuation, second actuation, and no-actuation positions, as illustrated. 
     In another embodiment, each multidrop module may comprise an override mechanism that enables selective actuation of all well tools to a default position, e.g. a closed position, at any selected time. The override mechanism may be particularly useful in well actuation systems operating dual-line well tools. 
     Referring generally to  FIG. 15 , one embodiment of a multidrop module  44  incorporating an override mechanism  78  is illustrated. In this embodiment, the multidrop module  44  comprises a two position indexer  54 , such as the indexer described with reference to  FIG. 3 , and a three position valve  50 , such as the valve described with reference to  FIG. 10 . By way of example, the indexer  54  may utilize the J-slot indexer sleeve  58  that cooperates with indexer pin  60 . However, the override mechanism  78  is able to override the J-slot indexer sleeve  58  at any time when a given sequence of pressure is applied. This allows all well tools  36  to be moved to a default position, such as a closed position, at any desired point of time. 
     Override mechanism  78  may have a variety of configurations designed to capture and hold valve  50  at a position that allows fluid flow through the multidrop module  44  to actuate well tool  36  to a desired default position. In the embodiment illustrated, however, override mechanism  78  comprises a locking mechanism  80  mounted within housing  48  and having a portion slidably received in an extended portion  82  of piston  56 . Valve  50  and extended portion  82  can be forced along locking mechanism  80  toward the close-all-tools position. Movement of extended portion  82  along locking mechanism  80  compresses an override mechanism spring  84 . 
     The multidrop module  44  illustrated in  FIG. 15  can be shifted between an actuation position, e.g. an open tool position, a no-actuation position, e.g. cannot open tool position, and a close-all-tools position. The indexer  54  is used to selectively transition valve  50  between the first two operational positions. For example, the indexer  54  can be used to transition multidrop module  44  to the actuation position, illustrated best in  FIG. 15 . In this position, fluid under pressure can be supplied through control line  40  and routed through valve  50  to actuation line  64  for actuating, e.g. opening, the well tool  36 . Application of pressure inputs through control line  38  moves indexer  54  the desired number of increments to transition valve  50  and multidrop module  44  to the no-actuation position, illustrated in  FIG. 16 . The indexer  54  is operated as described above by applying pressure inputs, e.g. single level pressure inputs, via control line  38  which shift piston  56  in one direction, while return spring  62  causes movement in the opposite direction to incrementally shift indexer  54  along its predetermined profile. In the position illustrated in  FIG. 16 , tool  36  cannot be actuated even if fluid is supplied via control line  40  and/or control line  42 . Any fluid supplied by control line  42  is blocked from moving through valve  50  by a check valve  86 . 
     However, all of the valves  50  of the plurality of multidrop modules  44  can be shifted to the close-all-tools position by application of a given pressure sequence. For example, sufficient pressure can be applied via control line  42  to act against valve  50  and to cause valve  50  to shift to the left, as illustrated in  FIG. 17  by arrow  88 . Check valve  86  prevents pressure from being transmitted to well tool  36 . The translation of valve  50  and piston  56  compresses override mechanism spring  84  until piston extension  82  slides a sufficient distance over locking mechanism  80 , as illustrated in  FIG. 18 . While spring  84  is compressed, the two position indexer  54  does not move. Furthermore, while maintaining pressure in control line  42 , pressure is applied through control line  40  to cause translation of locking mechanism  80  in a manner that holds or locks main piston  56  and valve  50  in the close-all-tools position. The piston  56  remains in this position as long as pressure is maintained in control line  40 . At this stage, pressure can be bled from control line  42  which allows the pressurized fluid in control line  40  to shift well tool  36  to a default position, e.g. a closed position, as illustrated in  FIG. 19 . The ability to shift all multidrop modules  44  to the close-all-tools position enables all of the well tools  36  to be simultaneously actuated to a desired default position. In other words, the programmed valve positions directed by indexers  54  can be overridden to force all well tools  36  to the default position. If, for example, the well tools  36  comprise downhole valves, all the valves can be forced to a closed position at any time. 
     Another embodiment of multidrop module  44  is illustrated in  FIG. 20 . In this embodiment, multidrop module  44  combines the override mechanism  78  with a three position valve  50  and a three position indexer  54 . The three position valve  50  in combination with the three position indexer  54  enables valve  50  and multidrop module  44  to have a first actuation position, e.g. open tool position, a second actuation position, e.g. a close tool position, and a no-actuation position. Additionally, the override mechanism  78  enables all of the valves  50  and all of the multidrop modules  44  in a given well tool actuation system  30  (e.g., see  FIG. 1 ) to be moved to a default position simultaneously. As described above, when a given pressure sequence is applied, the override mechanism  78  is able to override the valve positions determined by the indexers  54 . For example, all of the well tools in system  30  can be moved to a closed position simultaneously. 
     In  FIG. 20 , valve  50  and multidrop module  44  are positioned in the first actuation, e.g. open tool, position. In this position, hydraulic power can be transmitted along control line  40 , through multidrop module  44 , and into a well tool actuation line  64  to actuate well tool  36  in a first direction. For example, if well tool  36  comprises a valve, actuation line  64  may be an “open” line that enables opening of the valve. Upon input of the predetermined number of pressure inputs to move indexer  54  through a corresponding predetermined number of increments, valve  50  and multidrop module  44  may be shifted to a no-actuation position, as illustrated in  FIG. 21 . In this position, valve  50  prevents actuation of well tool  36  regardless of whether tool actuation fluid is supplied through control line  40  or control line  42 . An additional pressure input or inputs via control line  38  causes indexer  54  to shift valve  50  to the second actuation, e.g. close tool, position. In this position, pressurized fluid can again flow through control line  40 , multidrop module  44 , and actuation line  66  to actuate well tool  36 , e.g. close well tool  36 , as illustrated in  FIG. 22 . Whether well tool  36  is actuated to the first actuation position or the second actuation position, return fluids can be routed through multidrop module  44 , through check valve  86 , and into control line  42 . 
     The latter embodiment also enables simultaneous shifting of all valves  50  and all multidrop modules  44  to a default position at any selected time upon the application of a given pressure sequence. If well tool actuation system  30  (e.g., see  FIG. 1 ) comprises well tools in the form of valves, for example, all the valves can be closed simultaneously at any desired time. To override the programmed tool positions, sufficient pressure is applied via control line  42  to act against valve  50  and cause valve  50  to shift to the left, as illustrated in  FIG. 23 . Check valve  86  again prevents pressure from being transmitted to well tool  36 . While maintaining pressure in control line  42 , pressure is applied through control line  40  to cause translation of locking mechanism  80  in a manner that holds or locks main piston  56  and valve  50  in the close-all-tools position, as illustrated in  FIG. 24 . At this stage, pressure can be bled from control line  42  which allows the pressurized fluid in control line  40  to shift well tool  36  to the default position, e.g. the closed position, as illustrated in  FIG. 25 . Any return fluids can freely flow through actuation line  64 , through check valve  86 , and into control line  42 . All of the well tools  36  can be similarly and simultaneously closed or otherwise actuated to a default position. 
     Well tool actuation system  30  (e.g., see  FIGS. 1 ,  2 ,  8  and  9 ) can be designed in a variety of configurations for use in a variety of wellbores and other subterranean environments. The number of multidrop modules can be greater and even substantially greater than the number of control lines used to control the multidrop modules and their corresponding well tools. Additionally, even if the multidrop modules are greater in number than the control lines, the multidrop modules and their corresponding well tools can be controlled individually with pressure inputs directed to all of the multidrop modules at a single pressure level. Furthermore, the type and configuration of the well tools  36  and the multidrop modules  44  can differ from one application to another (e.g., see  FIGS. 3 ,  10  and  15 ). The components within the multidrop modules also can be selected according to the desired actuation for a given application or environment. For example, a variety of valve styles and indexer styles can be utilized in a given multidrop module. Additionally, the override mechanism can be constructed in different forms, and a variety of locking mechanisms can be used to hold the valves in the override position. 
     Accordingly, although only a few embodiments of the present invention 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 invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.