Downhole apparatus and method

Abstract

A downhole actuator (30) comprises a tubular housing (34) which includes an indexing profile (42) on an inner surface thereof, and an indexing sleeve (46) mounted within the housing (34). The indexing sleeve (46) comprises an engaging arrangement including first and second axially spaced engagement members (52, 54) which cooperate with the indexing profile (42) of the housing (34) to be sequentially engaged by an actuation object (48) passing through a central bore (50) of the indexing sleeve (46) to drive the indexing sleeve (46) one discrete step of movement through the housing (34) towards an actuation site.

Claims

1. A downhole actuator, comprising: a tubular housing which includes an indexing profile on an inner surface thereof, the housing comprising at least two housing modules connected together, wherein the at least two housing modules each comprise multiple indexing profile features arranged along an inner surface thereof such that when the at least two housing modules are connected together the complete indexing profile is formed, wherein each of the at least two housing modules comprises a first connector at a first axial end thereof and a second connector at a second axial end thereof, each of the first connectors being connectable to each of the second connectors to permit connection between one of the at least two housing modules and each other of the at least two housing modules, wherein selection of a configurable number of the at least two housing modules to be connected together permits variability in the complete indexing profile to be achieved; and an indexing sleeve mounted within the housing and comprising an engaging arrangement including first and second axially spaced engagement members which cooperate with the indexing profile of the housing to be sequentially engaged by an actuation object passing through a central bore of the indexing sleeve to drive the indexing sleeve one discrete step of movement through the housing towards an actuation site.

2. The downhole actuator according to claim 1, wherein adjacent housing modules are secured together such that one of the plurality of indexing profile features is defined at an interface therebetween.

3. The downhole actuator according to claim 1, wherein adjacent housing modules each define a portion of one of the plurality of indexing profile features such that when the adjacent housing modules are connected the complete profile feature is formed.

4. The downhole actuator according to claim 1, wherein adjacent housing modules define a portion of an annular recess, such that when connected a complete annular recess is defined, said complete annular recess defining one of the plurality of indexing profile features of the indexing profile of the housing.

5. The downhole actuator according to claim 1, wherein the plurality of indexing profile features comprise a plurality of annular recesses arranged longitudinally along the housing, wherein the annular recesses provide a variation of the inner diameter along the length of the housing, such that movement of the indexing sleeve through the housing permits the radial position of first and second engagement members to be varied.

6. The downhole actuator according to claim 1, wherein the indexing sleeve is arranged to progress within the housing towards the actuation site in a predetermined number of discrete steps of movement by passage of a corresponding number of actuation objects through the central bore of the indexing sleeve.

7. The downhole actuator according to claim 1, wherein the indexing sleeve is configured to be initially positioned at any desired location along the indexing profile to determine a required number of actuation objects, and thus required discrete steps of movement, to drive the indexing sleeve to the actuation site.

8. The downhole actuator according to claim 1, configured to permit the indexing sleeve to be disabled, such that the indexing sleeve, when disabled, is not moved upon passage of an actuation object.

9. The downhole actuator according to claim 1, wherein the first and second engagement members are arranged relative to each other to permit only a single actuation object to be positioned therebetween at one time.

10. The downhole actuator according to claim 1, wherein the first and second engagement members define a confinement region therebetween, for temporarily accommodating an actuation object during passage of said object through the indexing sleeve, wherein the confinement region is configured to permit only a single actuation object to be accommodated therein at any time.

11. The downhole actuator according to claim 1, comprising a stand-off arrangement radially positioned between the housing and the indexing sleeve to define a radial separation gap between the housing and the indexing sleeve.

12. The downhole actuator according to claim 1, wherein the indexing sleeve cooperates with the indexing profile of the housing to be moved in a discrete step in any direction of travel of a passing actuation object.

13. The downhole actuator according to claim 1, comprising first and second fingers which support a respective one of the first and second engagement members on distal ends of said fingers, wherein the fingers are deformable to permit the engagement members to move radially upon cooperation with the indexing profile.

14. The downhole actuator according to claim 13, wherein the first and second fingers extend in opposing directions.

15. The downhole actuator according to claim 1, wherein the engaging arrangement comprises: an array of first engagement members arranged circumferentially around the indexing sleeve, wherein each first engagement member is mounted on a respective first finger; and an array of second engagement members arranged circumferentially around the indexing sleeve, wherein each second engagement member is mounted on a respective second finger.

16. The downhole actuator according to claim 1, comprising a monitoring arrangement for monitoring the passage of an actuation object through the indexing sleeve.

17. The downhole actuator according to claim 16, wherein the monitoring arrangement comprises at least one of: an acoustic monitoring arrangement configured to identify an acoustic signal generated by impact of an actuation object against the first and second engagement members; and a pressure monitoring system configured to identify a pressure variation generated during engagement of an actuation object with the first and second engagement members.

18. A method for downhole actuation, comprising: arranging a downhole actuator according to claim 1 relative to a downhole tool; and passing a predetermined number of actuation objects through the downhole actuator to cause the indexing sleeve to move in a corresponding number of discrete steps of movement through the housing towards an actuation site to actuate the downhole tool.

19. The downhole actuator according to claim 1, wherein the at least two housing modules are selected from a plurality of housing modules such that the indexing profile of the housing is variable in accordance with a user selection of the at least two housing modules.

20. The downhole actuator according to claim 1, wherein the first connector at the first axial end of a first of the at least two housing modules defines a first of first and second portions of one of the multiple indexing profile features; and wherein the second connector at the second axial end of a second of the at least two housing modules connected to the first connector of the first of the at least two housing modules defines the second portion of the same one of the multiple indexing profile features.

21. A kit of parts for use in forming a downhole actuator, said kit of parts comprising a plurality of housing modules which each comprise multiple indexing profile features arranged along an inner surface thereof, wherein at least two of the housing modules are selectable from the plurality of housing modules to be connected together to define a housing with a complete indexing profile an on inner surface thereof for cooperation with an indexing sleeve mounted within the housing, wherein each of the at least two housing modules comprises a first connector at a first axial end thereof and a second connector at a second axial end thereof, each of the first connectors being connectable to each of the second connectors to permit connection between one of the at least two housing modules and each other of the at least two housing modules, wherein section of a configurable the number of the at least two housing modules permits variability in the complete indexing profile to be achieved.

22. The kit of parts according to claim 21, further comprising the indexing sleeve.

23. A method for providing a downhole actuator, comprising: selecting at least two housing modules from a plurality of housing modules which each comprise multiple indexing profile features arranged along an inner surface thereof, and which each comprise a first connector at a first axial end thereof and a second connector at a second axial end thereof, each of the first connectors being connectable to each of the second connectors to permit connection between one of the at least two housing modules and each other of the at least two housing modules; connecting together the at least two selected housing modules to collectively define a housing with a complete indexing profile on an inner surface thereof, wherein the complete indexing profile is provided by a configurable number of that at least two housing modules; and mounting an indexing sleeve within the housing, wherein the indexing sleeve comprises an engaging arrangement including first and second axially spaced engagement members which cooperate with the indexing profile of the housing to be sequentially engaged by an actuation object passing through a central bore of the indexing sleeve to drive the indexing sleeve one discrete step of movement through the housing towards an actuation site.

24. A downhole completion comprising first and second downhole actuators arranged axially along the completion, wherein the first and second actuators each comprise: a tubular housing which includes an indexing profile on an inner surface thereof, the housing comprising a plurality of housing modules connected together, wherein the housing modules each comprise multiple indexing profile features arranged along an inner surface thereof such that when the individual modules are connected together the complete indexing profile is formed, wherein each of the plurality of housing modules comprises a first connector at a first axial end thereof and a second connector at a second axial end thereof, each of the first connectors being connectable to each of the second connectors to permit connection between one of the plurality of housing modules and each other of the plurality of housing modules; and an indexing sleeve mounted within the housing and comprising an engaging arrangement including first and second axially spaced engagement members which cooperate with the indexing profile of the housing to be sequentially engaged by an actuation object passing through a central bore of the indexing sleeve to drive the indexing sleeve one discrete step of movement through the housing towards an actuation site, wherein the first and second actuators comprise a different plurality of housing modules such that the tubular housing of the first and second actuators comprise different indexing profiles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic view of a wellbore system which includes a completion/fracturing string including a number of fracturing tools according to an embodiment of the present invention;

(3) FIG. 2 is a longitudinal cross-sectional view of a downhole tool, specifically a downhole fracturing tool, according to an embodiment of the present invention;

(4) FIG. 3 is a perspective view of an indexing sleeve of the tool of FIG. 2;

(5) FIGS. 4A to 4E illustrate a sequence of operation of the indexing sleeve of the tool in FIG. 2 over one discrete linear movement step by passage of a single actuation object;

(6) FIG. 5 is an enlarged view of the tool of FIG. 2 in the region of a valve and ball catching arrangement;

(7) FIGS. 6A to 6D are perspective views of a catching sleeve component of the tool of FIG. 2, shown in different stages of manufacture;

(8) FIGS. 7A to 7E illustrate a sequence of operation by an actuation object to reconfigure the tool into an operational state;

(9) FIG. 7F provides an enlarged view of region F in FIG. 7E:

(10) FIG. 7G provides an enlarged view of region G in FIG. 7E;

(11) FIGS. 7H and 7I illustrate a subsequent sequence of operation to permit an actuation object to be released from the tool;

(12) FIGS. 8A, 8B and 8C illustrate individual fracturing tools to be arranged within a completion/fracturing string, such as shown in FIG. 1, wherein each tool is provided with the respective indexing sleeves in a different commission position;

(13) FIG. 9 illustrates the tool of FIG. 2 in combination with an inspection apparatus for use in determining the position of an indexing sleeve

(14) FIG. 10 is a cross-sectional view of a downhole tool in accordance with an embodiment of the present invention;

(15) FIG. 11 is a cross-sectional view in the region of an indexing sleeve of a downhole tool in accordance with an embodiment of the present invention, and also provides a diagrammatic representation of a shifting tool for shifting the indexing sleeve;

(16) FIG. 12 is a cross-sectional view of a downhole tool in accordance with an embodiment of the present invention, wherein the tool includes associated sealing arrangements;

(17) FIG. 13 is an enlarged view of a sealing arrangement of FIG. 12;

(18) FIGS. 14A and 14B show a seal arrangement of FIG. 12 in a run-in and set configuration, respectively;

(19) FIGS. 15A to 15D are cross-sectional views of a portion of a downhole tool in accordance with a further embodiment of the present invention, shown in different stages of operation;

(20) FIGS. 16A to 16E are cross-sectional views of a portion of a downhole tool in accordance with a further embodiment of the present invention, shown in different stages of operation;

(21) FIGS. 17A and 17B are schematic illustrations of a downhole system in accordance with an embodiment of the present invention, shown in different stages of operation;

(22) FIGS. 18A and 18B are schematic illustrations of a downhole system in accordance with an alternative embodiment of the present invention, shown in different stages of operation;

(23) FIGS. 19A to 19D are schematic illustrations of a downhole system in accordance with a further embodiment of the present invention, shown in different stages of operation;

(24) FIG. 20A is a schematic illustration of a downhole system in accordance with an further alternative embodiment of the present invention; and

(25) FIG. 20B is a lateral cross-sectional view of the system of FIG. 20A, taken through line B-B.

DETAILED DESCRIPTION OF THE DRAWINGS

(26) FIG. 1 provides a diagrammatic illustration of a well bore system 10 including a drilled borehole 12 which intercepts a subterranean reservoir or formation 14. The formation 14 may contain hydrocarbons to be produced to surface via the well system 10. Alternatively, or additionally, the subterranean formation 14 may define a target for receiving a fluid injected from surface via the wellbore system 10, for example for increasing formation pressure to improve production of hydrocarbons from the formation 14 or a neighbouring formation, for sequestration purposes, or the like.

(27) Following drilling of the borehole 12, or following a period of production/injection, the formation 14 may require to be stimulated or treated to permit improved production or injection rates to be achieved or restored. Known stimulation techniques include hydraulic fracturing which involves injecting a fracturing fluid into the formation at high pressure and/or flow rates to create mechanical fractures within the geology. These fractures may increase the effective near-wellbore permeability and fluid connectivity between the formation and wellbore. The fracturing fluid may carry proppant material, which functions to prop open the fractures when the hydraulic fracturing pressure has been removed. Matrix stimulation provides a similar effect as hydraulic fracturing. This typically involves injecting a chemical such as an acid, for example hydrochloric acid, into the formation 14 to chemically create fractures or wormholes in the geology. Such matrix stimulation may have application in particular geology types, such as in carbonate reservoirs.

(28) In most stimulation or treatment regimes it is necessary to provide the ability to inject a treatment fluid into the formation via wellbore tools and infrastructure. Embodiments of the present invention permit such injection to be achieved. In this respect, a tubular string 16 extends through the borehole 12 of FIG. 1, wherein the string 16 comprises a plurality of fracturing tools 18 according to the present invention distributed along its length at a desired interval spacing. Each tool 18 includes a plurality of circumferentially arranged ports 20, which are initially closed. Further, each tool 18 includes or is associated with a downhole actuator (not shown in FIG. 1) which is operable to actuate the tool 18 to open the associated ports 20 to allow injection of a treating fluid, such as a fracturing fluid or acid, from the string 16 into the surrounding formation 14 to create fractures 22. As will be described in more detail below, each tool 18 is operated by actuation objects, such as balls, which are delivered through the string 16 from surface.

(29) The tools 18 are capable of being actuated in a desired sequence, thus allowing the formation 14 to be treated along the length of the wellbore 12 in stages. Such ability to actuate the tools 18 sequentially may be achieved via the associated downhole actuator, as will be described in further detail below. In the particular embodiment shown in FIG. 1 the tools 18 are arranged to be actuated in an uphole sequence or direction. This is shown in FIG. 1 in which the lowermost illustrated tool 18a has previously been actuated, with an adjacent tool 18b on the uphole side shown in an actuated state with fracturing fluid from the opened ports 20b being directed into the formation 14 in the direction of arrows 24. Once appropriate fracturing has been achieved via tool 18b, the next uphole tool 18c may then be actuated. However, in other embodiments any sequence of operation of the tools may be achieved.

(30) In the exemplary embodiment shown the tools 18 include optional annular seals 26a, 26b (shown energised on actuated tool 18b) on opposing axial sides of the ports 20b. When the seals 26a, 26b are energised they provide isolation of an annular region 28 around the tools 18, thus focussing the fracturing fluid into the formation 14, which may assist with improving geological penetration. The seals 26a, 26b may be actuated or energised by the action of the fracturing fluid being injected from the tool ports 20. In some embodiments the seals 26a, 26b may comprise cup seals.

(31) A cross sectional view of a downhole tool 18, according to an exemplary embodiment of one or more aspects of the present invention is shown in FIG. 2. The tool 18 includes an actuator portion 30, provided according to an embodiment of an aspect of the present invention. The tool 18 also includes a tool portion 32 located on the downhole side of the actuator portion 30, wherein the tool portion 32 is provided according to an embodiment of an aspect of the present invention. In the embodiment shown, the actuator portion 30 and tool portion 32 and provided together to define a complete downhole tool 18. However, it should be recognised that the actuator and tool portions 30, 32 may be provided independently of each other. For example, the actuator portion 30 may be used to actuate any other downhole tool, such as a packer, ICD or the like. Further, the tool portion 32 may be actuated by any other suitable actuator arrangement.

(32) The downhole tool 18 comprises a housing 34 which defines a central bore 35 and extends between an uphole connector 36 and a downhole connector 38. The connectors 36, 38 facilitate connection of the tool 18 within the tubular string 16 (FIG. 1).

(33) Fluid ports 20 are provided radially through a wall of the housing 34 in the region of the tool portion 32, wherein the ports 20, when opened, facilitate outflow of a fluid from the central bore 35 of the housing 34. The tool portion 32 includes a valve member in the form of a sleeve 40 which is moveable axially along the housing 34 from a closed position in which the sleeve 40 blocks or closes the ports 20, as shown in FIG. 2, to an open position. Movement of the sleeve 40 towards its open position is achieved by the associated actuator portion 30, as described below.

(34) The tool portion 32 further includes a catching sleeve 41 located downhole of the valve sleeve 40. The catching sleeve 41 illustrated is an embodiment of an aspect of the present invention. Although the catching sleeve 41 is illustrated as part of the present downhole tool, it should be understood that the catching sleeve 41 may be used in any other downhole tool.

(35) The catching sleeve 41 is moveable from a free configuration, as shown in FIG. 2, in which a ball 48 may freely pass, to a catching configuration in which a ball 48 may be caught. In the present embodiment, the catching sleeve may function to catch a ball and establish diversion of any fluid from the central bore 35 outwardly through the fluid ports 20 when open. Further, in the present embodiment the catching sleeve 41 is operated to move to its catching configuration by movement of the valve sleeve 40 towards its open configuration. The form and operation of the valve sleeve 40 and catching sleeve 41 will be described in further detail below.

(36) The actuator portion 30 defines an indexing profile 42 provided on the inner surface of the housing 34. The indexing profile 42 includes a plurality of axially spaced annular recesses 44 formed in the inner surface of the housing 34. An indexing sleeve 46 is mounted within the housing 34 and is configured to cooperate with the indexing profile 42 to be driven in a number of discrete linear movement steps through the housing 34 by passage of a corresponding number of actuation objects, specifically balls 48 in the present embodiment. The indexing sleeve 46 illustrated is an embodiment of an aspect of the present invention. The indexing sleeve 46 is driven in discrete movement steps until reaching an actuation site within the tool 18, where the indexing sleeve 46 engages and moves the valve sleeve 40 in a downhole direction to open the ports 20.

(37) A perspective view of the indexing sleeve 46 removed from the housing 34 is shown in FIG. 3, reference to which is additionally made.

(38) The indexing sleeve 46 includes a tubular wall structure 49 which defines a central bore 50 corresponding with the central bore 35 of the housing 34. The central bore 50 is sized to permit an actuation object, specifically balls 48 to pass therethrough.

(39) The indexing sleeve 46 also includes first and second circumferential arrays of engagement members 52, 54 which are arranged such that the array of first engagement members 52 are axially spaced apart from the array of second engagement members 54. The engagement members are arranged within slots 56, 58 formed through the wall structure 49. As will be described in more detail below, the arrays of engagement members 52, 54 cooperate with the indexing profile 42 of the housing 34 to be sequentially engaged by a passing ball 48 to drive the indexing sleeve 46 one discrete linear movement step. More specifically, the first and second arrays of engagement members 52, 54 are arranged to be moved radially within their associated slots 56, 58 such that each array of engagement members 52, 54 is moved in an alternating or out of phase manner relative to the other array of engagement members 52, 54 by cooperation with the indexing profile 42 during movement of the indexing sleeve 46 through the housing 34. Such alternating radial movement alternately moves the first and second arrays of engagement members 52, 54 radially inwardly and into the central bore 50 of the indexing sleeve 46, to thus be sequentially engaged by a passing ball 48. In this way, a passing ball 48 may engage the engagement members 52, 54 of one of the first and second arrays to move the indexing sleeve 46 a portion of a discrete movement step, and then subsequently engage the engagement members 52, 54 of the other one of the first and second arrays to complete the discrete movement step of the indexing sleeve 46.

(40) The engagement members 52, 54 are mounted on the distal end of respective collet fingers 60 which are secured at their proximal ends to the tubular wall structure 49. The collet fingers 60 are resiliently deformable to facilitate radial movement of the engagement members 52, 54 by cooperation with the indexing profile 42. In the present embodiment the collet fingers 60 are unstressed when the engagement members 52, 54 are positioned radially outwardly and thus removed from the central bore 50. As such, the collet fingers 60 must be positively deformed by appropriate cooperation between the engagement members 52, 54 and the indexing profile 42 to move the engagement members 52, 54 radially inwardly into the central bore 50 to permit engagement by a ball 48. In such an arrangement, the collet fingers 60 may function to bias the engagement members 52, 54 in a direction to move radially outwardly from the central bore 50.

(41) In the embodiment shown each slot 56, 58 of the indexing sleeve 46 accommodates two respective engagement members 52, 54. Further, the slots 56, 58 are defined between respective elongate ribs 62, 64. Each rib 62, 64 includes a spline feature or key 66 which are received in corresponding longitudinally extending slots or key-ways (not shown in the drawings) formed in the housing 34. Engagement between the keys 66 and the longitudinal slots or key-ways may function to rotationally lock the indexing sleeve 46 relative to the housing 34, while still permitting movement of the indexing sleeve 46 linearly through the housing 34. Such an arrangement may facilitate milling of the indexing sleeve 46, if ever required.

(42) In some embodiments the indexing sleeve 46 may include a stand-off arrangement, permitting the indexing sleeve 46 to be mounted within the housing 34 with a desired clearance gap therebetween. For example, in some cases the keys 66 shown in FIG. 3 may in fact function to directly engage the inner surface of the housing 34, thus providing a stand-off clearance at least as large as the thickness of the keys 66. Providing such a stand-off with a clearance gap between the housing 34 and the indexing sleeve 46 may assist to minimise binding of the indexing sleeve 46 within the housing 34, for example by the accumulation of debris, such as proppant material.

(43) A sequential operation of the indexing sleeve 46 to move one discrete step by passage of a ball 48 will now be described in detail with reference to FIGS. 4A to 4E, which each illustrate a portion of the tool 18 in the region of the actuator portion 30.

(44) In the illustrated sequence the ball 48 travels in the direction of arrow 70, and thus functions to move the indexing sleeve 46 in the same direction. The direction of travel of the ball 48 in the present example is in the downhole direction. However, as will be described in more detail below, the indexing sleeve 46 may also be moved by passage of a ball in an opposite, uphole direction. As such, generally, the direction of travel of the ball 48 may be considered as in a downstream direction.

(45) Prior to initiation of a discrete movement step, as shown in FIG. 4A, the indexing sleeve 46 is positioned within the housing 34 such that the engagement members 52 of the first array, which may be considered an upstream array, are positioned radially inwardly and thus presented into the central bore 50, whereas the engagement members 54 of the second array, which may be considered a downstream array, are positioned radially outwardly, and in fact received within an annular recess 44a. Such positioning of the engagement members 52, 54 is achieved by the relative axial spacing of the engagement members 52, 54 and the axial spacing, or pitch, of the annular recesses 44. That is, the axial spacing between the engagement members 52, 54 differs from, and specifically is larger than that of adjacent annular recesses 44. As such, when the engagement members 52, 54 of one of the first and second arrays are received within an annular recess 44 and outwardly positioned relative to the central bore 50, the engagement members 52, 54 of the other one of the first and second arrays will be positioned intermediate adjacent recesses 44 and thus positioned inwardly relative to the bore 50. Movement of the indexing sleeve 46 through the housing therefore permits the radial position of the engagement members 52, 54 to be cyclically varied, permitting sequential engagement by a ball.

(46) When the ball 48 reaches the indexing sleeve 46 the ball 48 will seat against the first or upstream array of engagement members 52, as shown in FIG. 4A, causing the indexing sleeve 46 to begin to move, as shown in FIG. 4B. Such movement will cause the first array of engagement members 52 to eventually become aligned with a recess 44b, and thus moved radially outwardly from the central bore 50, allowing the ball 48 to pass, as shown in FIG. 4C. However, at the same time the engagement members 54 of the second array will be deflected radially inwardly, to be positioned within the central bore 50, by misalignment with an annular recess 44. In this respect, in the embodiment shown the recesses 44 and the engagement members 52, 54 define corresponding ramped or tapered sides, for example of around 45 degrees, to facilitate or assist interaction during relative axial movement of the indexing sleeve 46 through the housing 34. As the engagement members 54 of the second array are now positioned radially inwardly the ball 48 will become seated against these engagement members 54, thus continuing to drive the indexing sleeve 48, as shown in FIG. 4D.

(47) Eventually, the engagement members 54 of the second array will again become aligned with an annular recess 44c, thus permitting the ball 48 to be released and continue in the downstream direction, as shown in FIG. 4E. At the same time, the engagement members 52 of the first array will be positioned intermediate adjacent annular recesses 44a, 44b, becoming radially inwardly deflected, and positioned to be engaged by a subsequent ball.

(48) The ball 48 may drive the indexing sleeve 46 primarily by impact against the engagement members 52, 54 when positioned within the bore 50. That is, the momentum of the ball 48 passing through the indexing sleeve 46 may drive said sleeve 46.

(49) Alternatively, or additionally, the ball 48 may permit the indexing sleeve 46 to be driven by a pressure differential between upstream and downstream sides of the indexing sleeve 46. For example, the ball 48 may de driven by a fluid flow, and when the ball 48 seats against the engagement members a flow restriction may be created, which may permit a back pressure to be established, thus providing a desired pressure differential between upstream and downstream sides of the indexing sleeve 46. The flow restriction may be provided between the points of engagement of the ball 48 with individual engagement members 52, 54. Alternatively, or additionally, the flow restriction may be achieved by diversion of flow between the indexing sleeve and the housing 34 when the ball is seated against the engagement members 52, 54.

(50) The use of a pressure differential to drive the indexing sleeve 46 may permit monitoring of the progress of the ball 48 to be achieved. For example, a monitoring system 72 may be provided which monitors the variation in pressure as the ball 48 progresses through the indexing sleeve. Such pressure variations may be associated with the particular positioning of the ball 48, which may provide useful information to an operator. Such an arrangement may be advantageous in cases where multiple actuators are provided in series within a tubular string, as illustrated in FIG. 1. In an alternative embodiment, an acoustic monitoring system may be used, which monitors acoustic signals generated during interaction between the ball 48 and the indexing sleeve 46.

(51) As noted above, the indexing sleeve is operable to be driven by a ball in opposing directions. Such an arrangement will now be exemplified with reference to FIG. 4E. In FIG. 4E the indexing sleeve 46 is positioned such that the first and second arrays of engagement members 52, 54 will be sequentially engaged by a ball passing in a downhole direction. That is, the first array of engagement members 52 are positioned radially inwardly to be first engaged by a passing ball 48, while the second array of engagement members 54 are positioned radially outwardly. When in such a configuration, in the event of the ball 48 now travelling in an opposite, uphole direction, the ball 48 will pass the second array of engagement members 54 (which will now become the upstream engagement members), and will engage the first array of engagement members 52 (which will now become the downstream engagement members). Upon engagement with the first array of members 52 the indexing sleeve 46 will be driven in an uphole direction until the first array of members 52 become aligned with and received into the annular recess 44b, permitting the ball 48 to be released and continue to travel in the uphole direction. At the same time, the second array of engagement members 54 will become misaligned with a recess 44 and thus moved radially inwardly. Thus, when in this reconfigured position the first and second arrays of engagement members 52, 54 may now be sequentially engaged with a further ball passing in the uphole direction. As such, a first ball passing in the uphole direction may reconfigure the indexing sleeve 46 to permit sequential engagement of the members 52, 54 by a subsequent passing ball.

(52) In the exemplary wellbore system of FIG. 1 a number of tools 18 are arranged in series and configured to be actuated in a desired sequence. Such a desired sequence may be achieved by appropriate initial positioning of the indexing sleeve 46 in each tool 18, such that the tools 18 are operated in response to the passage of a different number of balls. Such ability to create a system which allows a desired actuation sequence to be achieved based on the initial positioning of respective indexing sleeves will be described in further detail below. However, as the sequential operation of individual tools 18 may be reliant on passage of individual balls, it is important that each ball is registered upon passing through an indexing sleeve and reliably moves the indexing sleeve a required discrete step. If a ball were to pass without driving an indexing sleeve a corresponding discrete step then this may upset a desired actuation sequence. The present inventors have identified a potential for such ball passage without registering a count if two balls were ever to pass through an indexing sleeve in quick succession. If such an occasion were not addressed a trailing ball could potentially pass behind a leading ball without registering corresponding separate discrete movement steps.

(53) In the present embodiment the first and second arrays of engagement members 52, 54 are arranged relative to each other (specifically the axial spacing of the members 52, 54) to permit only a single ball 48 to be positioned therebetween at any time. As such, the axial region between the first and second arrays of engagement members 52, 54 may define a ball trap. As shown in FIG. 4C, when the ball 48 initially enters this ball trap region between the first and second arrays of engagement members 52, 54, the ball 48 will engage the members 54 of the second array. While in this position the members 52 of the first array are positioned radially outwardly. However, any subsequent or trailing ball arriving at the indexing sleeve 46 at this time will not be permitted to progress due to engagement with the ball 48 which is positioned within the ball trap. As the indexing sleeve 46 progresses the members 54 of the second array will eventually move radially outwardly and thus permit the ball to be released, as shown in FIG. 4E. However, at the same time the members 52 of the first array will be moved radially inwardly and thus will prevent progression of any trailing ball, at least without the trailing ball now acting to drive the indexing sleeve 46 a corresponding discrete movement step.

(54) The tool portion 32 of the downhole tool 18 will now be described in further detail with reference to FIG. 5, which is an enlarged view of the tool 18 of FIG. 2 in the region of tool portion 32. The tool portion 32 is illustrated in an initial configuration, with the valve sleeve 40 in a closed position and the catching sleeve 41 in a free configuration. The following description will describe the various features of the tool portion 32 when in this initial configuration. A sequential operation to permit the tool portion 32 to be reconfigured from this initial configuration will then be provided.

(55) The valve sleeve 40 defines a central bore 45, and the catching sleeve 41 also defines a central bore 47, wherein the bores 45, 47 correspond to each other and with a central bore 35 of the housing 34.

(56) When in its closed position the valve sleeve 40 blocks the fluid ports 20, with o-ring seals 80 positioned on opposing axial sides of the fluid ports 20 to facilitate sealing. The valve sleeve 40 is axially secured relative to the housing 34 via a number of shear screws 82 (only one shown in the particular cross-section of FIG. 5). The valve sleeve 40 includes a plurality of ports 84. As will be described in more detail below, to move the valve sleeve 40 towards its open position an axial actuation force is applied by the indexing sleeve 46 (not shown in FIG. 5) to initially shear the screws 82 and aligned the sleeve ports 84 with the ports 20 in the housing 34. The valve sleeve 40 includes a key member 86 in an outer surface thereof which is received within a longitudinal key slot 88 provided in the inner surface of the housing 34. Interaction between the key 86 and slot 88 prevents relative rotation between the valve sleeve 40 and the housing 34, thus maintaining the sleeve ports 84 in the correct circumferential alignment relative to the ports 20 in the housing 34.

(57) The valve sleeve 40 includes an annular recess 90 in an outer surface thereof, extending upwardly from a downhole axial end 92 and terminating at an annular load shoulder 93. Such a recess 90 defines an annular shroud 94 which in the illustrated configuration extends into the central bore 47 of the catching sleeve 41, and specifically is positioned inside an uphole axial end 96 of the catching sleeve 41, such that the uphole end 96 of the catching sleeve 41 is positioned within the annular recess 90 of the valve sleeve 40. In this arrangement the shroud 94 physically isolates an uphole end face 98 of the catching sleeve 41, and thus functions to prevent a passing ball, or other object, from engaging the uphole end face 98 which may otherwise damage the catching sleeve 41, accidentally or prematurely cause actuation of the catching sleeve 41, or the like. That is, it has been recognised by the present inventors that a passing ball may not follow a perfect linear path through the tool 18, and in fact may continuously impact or ricochet off the inner surfaces of the tool 18. If such an impact were to occur against the end face 98 of the catching sleeve 41 then the impact force may be sufficient to cause actuation of the catching sleeve 41, and/or may cause damage to the catching sleeve 41.

(58) The catching sleeve 41 is initially secured relative to the housing 34 via a number of shear screws 100 (only one shown in FIG. 5). When in this initial configuration the catching sleeve 41 is positioned relative to the valve sleeve 40 such that an axial spacing or separation gap is defined between the load shoulder 93 of the valve sleeve 40 and the uphole end face 98 of the catching sleeve 41. Such initial separation may define a lost motion arrangement within the tool portion 32. That is, when axial movement of the valve sleeve 40 is initiated the separation gap will be closed before eventual engagement between the load shoulder 93 of the valve sleeve 40 and the end face 98 of the catching sleeve 41, wherein subsequent axial load applied by the valve sleeve 40 may shear the screws 100, and then cause axial movement of the catching sleeve 41 towards its catching configuration, as will be described in further detail below.

(59) The uphole end 96 of the catching sleeve 41 defines an uphole tubular portion which includes a number of ports 102. These ports 102 may function to permit circulation of fluid behind the catching sleeve 41, for example to facilitate circulation or removal of debris. These ports 102 may also function to prevent hydraulic lock by avoiding a pressure differential between the interior and exterior of the valve sleeve 40.

(60) The catching sleeve 41 includes a plurality of collet fingers 104 extending longitudinally from the uphole tubular portion 96, wherein each collet finger 104 supports a seat member 106 on a distal end thereof. The collet fingers 104 are resiliently deformable, by longitudinal bending, to permit the seat members 106 to be selectively radially moveable relative to the central bore 47 of the catching sleeve 41. Further, the collet fingers 104 define a tapering thickness along their length, which functions to provide more uniform bending therealong, with an associated uniform stress distribution being achieved. In the embodiment shown the fingers 104 reduce in thickness from the uphole tubular portion 96 towards the seat member 106.

(61) When the seat members 106 are positioned radially outwardly, as shown in FIG. 5, a ball may pass with minimal engagement with the seat members 106. However, when the seat members 106 are positioned radially inwardly, as will be described in more detail below, the seat members 106 collectively define a restriction within the central bore 47, and thus may be engaged by a passing ball. When the seat members 106 are positioned radially inwardly with the catching sleeve 41 configured in its catching configuration, a ball may engage and seat against the seat members 106 and thus be caught within the catching sleeve 41.

(62) The tool portion 32 further comprises an annular recess 108 which is profiled to receive the seat members 106 when said seat members 106 are positioned radially outwardly. In the present embodiment, the collet fingers 104 provide a bias force such that the seat members 106 are biased radially outwardly and received within the annular recess 108, and thus positioned to permit passage of a ball. When the seat members 106 are positioned radially outwardly and located within the recess 108, a circumferential gap 110 is provided between adjacent seat members 106. When the seat members 106 are moved radially inwardly, these circumferential gaps 110 are closed, and in some embodiments adjacent seat members 106 are engaged or are positioned in very close proximity relative to each other, defining a substantially continuous annular structure.

(63) Each seat member 106 includes an uphole seat surface 112 configured to be engaged by a ball when travelling in a downhole direction. The uphole seat surfaces 112 may be configured to provide a substantially complete or continuous engagement with a ball. Such an arrangement may facilitate sealing between a ball and the seat members 106. Such sealing may permit a ball to be sealingly engaged within the catching member 41 and thus substantially seal the central bore 47. This may allow appropriate fluid diversion from the central bore through the fluid ports 20. Also, in some embodiments such sealing against the seat members 106 may permit control of pressure uphole of the catching sleeve 41. Further, such sealing of a ball within the catching sleeve 41 may permit the catching sleeve 41 to be actuated, for example by a pressure differential established between uphole and downhole sides of the catching sleeve 41.

(64) In the present embodiment the uphole seat surfaces 112 are generally convex in shape, which provides significant advantages when engaging a ball which also has a convex surface, as will be described in more detail below.

(65) Each seat member 106 includes a downhole seat surface 114 configured to be engaged by a ball when travelling in an uphole direction. Such an arrangement may permit one or more balls to be engaged with the seat members 106 when reverse flowed through the tool, for example to permit return of the balls to surface, to permit reverse actuation of the tool, for example to close the valve sleeve 40. Further, such reverse flow may be permitted or initiated to assist in clearing a blockage within the tool or associated string.

(66) The downhole seat surfaces 114 in the embodiment shown include respective slots 116 which permit fluid to bypass a ball when engaged against the downhole seat surfaces 116. Such fluid bypass may be advantageous in an event that a ball may become trapped against the downhole seat surfaces 114. This may be particularly advantageous in production wells, as production may still be achieved even in the event of a ball becoming stuck. The slots 116 define discontinuities within the seat surfaces 114, such that when a ball is engaged therewith the discontinuities may permit a degree of fluid by-pass.

(67) The catching sleeve 41 is biased to move in an uphole direction by a coil spring 118 which acts between an annular lip 120 formed on an outer surface of the uphole tubular portion 96 of the catching sleeve 41, and an annular region 122. The coil spring 118 also functions to rotationally lock the catching sleeve 41 relative to the housing 34. That is, a downhole end of the spring 118 may be rotationally secured relative to the housing 34, and an uphole end of the spring 118 may be rotationally secured relative to the catching sleeve 41. Rotationally securing the catching sleeve 41 relative to the housing 34 may permit the catching sleeve 41 to be machined, for example milled, which may be required as part of a remedial operation, for example in the event of the catching sleeve 41 failing to release a ball.

(68) The tool portion 32 further comprises a release sleeve 124 which is initially secured in the position shown in FIG. 5 via a plurality of shear screws 126. The release sleeve 124 includes a cylindrical inner support surface 128 which defines a region of reduced inner diameter relative to the annular recess 108.

(69) When the catching sleeve 41 is moved axially in a downhole direction, which will be caused by axial movement of the valve sleeve 40 towards its open position, the seat members 106 will be displaced from the annular recess 108 and engaged with the inner support surface 128 of the release sleeve 124, and thus deflected radially inwardly, into the central bore 47 and presented in a position to be engaged by a ball. As the seat members 106 in this position are radially supported by the release sleeve 124, the engaged ball will become caught in the catching sleeve 41.

(70) The release sleeve 124 includes an annular shoulder 130 which, as will be described in further detail below, is engaged by the seat members 106 such that the catching sleeve 41 may apply an axial load in a downhole direction on the release sleeve 124.

(71) The housing 34 defines or includes a release recess 132 which is initially covered by the release sleeve 124. When a suitable axial load is applied on the release sleeve 124 by the catching sleeve 41 to shear the screws 126, the release sleeve 124 may be moved axially to uncover the release recess 132. When uncovered, the release recess 132 may receive the seat members 106, thus allowing the catching sleeve 41 to be configured in a release configuration.

(72) Reference is now made to FIGS. 6A to 6D which provide perspective views of the catching sleeve 41 in sequential stages of manufacture. A cylindrical component 41a, such as a metal component, is provided as in FIG. 6A, and the catching sleeve 41 is initially machined as a complete component to the form illustrated in FIG. 6B. As such, the catching sleeve 41 includes the uphole tubular portion 96 with ports 102, with the annular lip 120 for engaging the coil spring 118 (FIG. 5). In this respect the annular lip 120 includes circumferential gaps 140. In use at least one gap 140 receives an axial portion of the coil spring 118 to rotationally secure the catching sleeve and coil spring 118 together.

(73) The seat members 106 are initially formed as a complete annular structure 142, in the form that the seat members 106 adopt when positioned radially inwardly to catch a ball. The collet fingers 104 are provided as longitudinal ribs which extend, at a slight inward taper, from the uphole tubular portion 96 to the complete annular structure 142. The ribs define slots 105 therebetween. Once formed in this way the annular structure 142 is divided by wire cutting to form the individual seat members 106, as illustrated in FIG. 6C. Following this division, collet fingers 104 are plastically deformed radially outwardly, to the form shown in FIG. 6D, by pressing over a mandrel, for example.

(74) However, in an alternative embodiment the catching sleeve 41 may be installed within the tool in the form of FIG. 6C. As such, passage of a ball may cause the seat members 106 to be deflected radially outwardly, until the seat members 106 become radially supported by the release sleeve 124, such that a ball will no longer be able to deflect the seat members 106 and thus will become caught in the catching sleeve 41.

(75) Reference is now made to FIGS. 7A to 7I in which a complete operation cycle of the tool 18 of FIG. 2 will be described. In this respect, FIGS. 7A to 7I provide a sequential illustration of a ball 48 driving the indexing sleeve 46 over its final discrete linear movement step to actuate the valve sleeve 40 and catching sleeve 41 to perform a fracturing operation, and then subsequently permit the ball 48 to be released.

(76) Referring initially to FIG. 7A the indexing sleeve 46 is positioned in non-contact relationship with the valve sleeve 40, wherein the first array of engagement members 52 are positioned radially inwardly in preparation to be engaged by an approaching ball 48. Further, the valve sleeve 40 is located in its closed position to close the ports 20, and the catching sleeve 41 is located in its free configuration such that the seat members 106 are positioned radially outwardly.

(77) In FIG. 7B the ball 48 engages the first array of engagement members 52 to drive the indexing sleeve 46 into engagement with the valve sleeve 40, thus applying an axial load on the valve sleeve 40 and shearing the screws 82 which initially hold the valve sleeve 40 in its closed position. The ball 48 will continue to drive the indexing sleeve 46 and the valve sleeve 40 until the first array of engagement members 52 become aligned with a recess 40, permitting the ball 48 to progress and engage the second array of engagement members 54, which have become deflected radially inwardly, as illustrated in FIG. 7C. As such, the indexing sleeve 46 and valve sleeve 40 may continue to be driven through the housing 34 by the ball 48 until the load shoulder 93 of the valve sleeve 40 comes into engagement with the uphole axial end face 98 of the catching sleeve 41, permitting an axial load to be applied on the catching sleeve 41 to shear the screws 100 initially holding the catching sleeve 41 in its free configuration.

(78) The ball 48 may continue to drive the indexing sleeve 46 by engagement with the second array of engagement members 54, and thus also drive the valve sleeve 40 and the catching sleeve 41. As illustrated in FIG. 7D the valve sleeve 40 will eventually reach its fully open position in which the sleeve ports 84 become aligned with the fluid ports 20. Further, the catching sleeve 41 will eventually be configured in its catching configuration, also shown in FIG. 7D, in that the seat members 106 of the catching sleeve 41 are displaced from the corresponding recess 108 and onto the support surface 128 of the release sleeve 124, thus deflecting the seat members 106 radially inwardly as shown in FIG. 7D.

(79) As shown in FIG. 7D, eventually the second array of engagement members 54 will become aligned with an annular recess 44 within the housing 34, specifically lowermost annular recess 44d, allowing the ball 48 to be released from the indexing sleeve 46 and continue in the downhole direction. In this respect it should be noted that the two lowermost annular recesses, 44d, 44e are provided at an axial spacing which matches the axial separation of the first and second arrays of engagement members 52, 54. This permits all the engagement members 52, 54 to become positioned within a recess 44d, 44e following the final discrete linear movement step of the indexing sleeve 46, thus effectively disabling the indexing sleeve 46. Further, when in this position the indexing sleeve 46 functions to lock the valve sleeve 40 in its open position.

(80) As shown in FIG. 7E, the released ball 48 will eventually be caught by the reconfigured seat members 106 of the catching sleeve 41, thus establishing a blockage below the opened ports 20, functioning as a diverter to cause substantially all fluid flowing through the central bore 35 of the tool 18 to flow radially outwardly from the ports 20 to fracture a surrounding formation, as illustrated in FIG. 1. Further, the blockage achieved by the ball 48 may permit an appropriate fluid pressure above the ball 48 to be achieved, which may be necessary to achieve appropriate fracturing of the surrounding formation.

(81) In the specific embodiment disclosed the ports 20 become opened before the ball 48 lands in the catching sleeve 41, as illustrated in FIG. 7D. In such an arrangement the ball 48 will suddenly arrest or substantially arrest a column of fluid positioned above the ball 48 when the ball 48 lands against the seat members 106 of the catching sleeve 41, as in FIG. 7E. If the ports 20 are arranged to immediately provide full flow such fast arrest of the fluid column above the ball 48 may result in initial rapid ejection of fluid through the ports 20. This may provide an initial fluid hammer effect which could be advantageous in improving initial geological penetration of the ejected fluid.

(82) However, in some situations this initial arrest of a fluid column may provide a significant impulse load on the catching sleeve 41 and thus on the release sleeve 124. This initial impulse force may be of sufficient magnitude to actuate the release sleeve 124, perhaps causing premature release of the ball 48, before sufficient fracturing within the surrounding formation has been achieved. To address this situation the present invention may employ a choking arrangement which functions to initially choke the outflow of fluid through the ports 20 when initially opened.

(83) In the present exemplary embodiment such a choking arrangement comprises an erodible sleeve 150, illustrated most clearly in the enlarged view of FIG. 7F, which is mounted on the outer surface of the housing 34 at the location of the ports 20. The sleeve 150, which may be formed from aluminium, includes a plurality of orifices 152 which are aligned with a respective port 20. When flow through the ports 20 is initiated the orifices 152 function to choke the flow. However, over time the orifices 152 become enlarged by erosion, which may be significant in embodiments where the fluid comprises a proppant material, such that the choking effect will decrease, until a full flow condition is established.

(84) An enlarged view of the tool 18 in FIG. 7E in the region of the ball 48 and seat members 106 of the catching sleeve 41 is provided in FIG. 7G. In the illustrated configuration the seat members 106 are engaged with the load shoulder 130 of the release sleeve 124. Each seat member 106 includes a notch 160 formed in a radially outer surface which is configured to permit engagement with the load profile 130 of the release sleeve 124.

(85) As noted above, the uphole seat surfaces 112 of the seat members 106 define a convex profile. Such a convex profile permits a small region of contact to be achieved with the ball 48, and specifically a small circumferential contact region to be established. This small contact region may permit improved control over the load path from the ball 48 through the seat members 106 to be achieved. In particular, a load vector 162 established by the engaged ball 48 may be controlled to be aligned with the notches 160 formed in the seat members 106, such that the load from the ball 48 may be directly transferred to the release sleeve 124 via the load shoulder 130 of the release sleeve 124. Such an arrangement may minimise the creation of bending moments on the associated collet fingers 104.

(86) Furthermore, minimising the region of contact between the ball 48 and the seat members 106 may reduce the risk of the ball 48 becoming swaged or otherwise deformed into the seat members 106, which might otherwise cause the ball 48 to become stuck within the catching sleeve 41.

(87) When the catching sleeve 41 is to be reconfigured to its release configuration to permit release of a caught ball 48, it is necessary to displace the release sleeve 124 and expose the associated release recess 132. In the present embodiment this is achieved by increasing the pressure on the uphole side of the ball 48 to increase the load applied on the release sleeve 124 via the seat members 106, until the shear screws 126 holding the release sleeve 124 in place are sheared, such that the pressure uphole of the ball 46 may act to drive the catching sleeve 41 and the release sleeve 124 downwardly, as illustrated in FIG. 7H. When in this configuration the spring 118 is compressed by the catching sleeve 41, such that relieving pressure uphole of the ball 48 will cause the bias force of the spring 118 to force the catching sleeve 41 in an uphole direction until the seat members 106 become aligned with the uncovered release recess 132, as shown in FIG. 7I. When aligned as such, the collet fingers 104 will relax and thus move the seat members 106 radially outwardly to be received within the release recess 132, causing the ball 48 to be released.

(88) As described above and generally illustrated in FIG. 1, multiple tools 18 according to the invention may be provided as part of a downhole system, such as a fracturing system, wherein the tools are initially configured to be actuated upon passage of a different number of balls. The individual tools 18 may be initially configured by appropriate placement of the associated indexing sleeves 46 relative to the housing 34, and specifically relative to the indexing profile 42 of the housing 34. This is exemplified in FIGS. 8A, 8B and 8C. FIG. 8A provides a cross-section view of the tool 18a of FIG. 1, FIG. 8B provides a cross-sectional view of the immediate uphole tool 18b of FIG. 1, and FIG. 8C provides a cross-sectional view of tool 18c of FIG. 1.

(89) The indexing sleeve 46a of tool 18a is positioned within housing 34a such that the indexing sleeve 46a must be driven by one discrete movement step by passage of a single ball to actuate the associated valve sleeve 40a and catching sleeve 41a.

(90) The indexing sleeve 46b of tool 18b is positioned within housing 34b such that the indexing sleeve 46b must be driven by two discrete movement steps by passage of two balls to actuate the associated valve sleeve 40b and catching sleeve 41b.

(91) The indexing sleeve 46c of tool 18c is positioned within housing 34c such that the indexing sleeve 46c must be driven by three discrete movement steps by passage of three balls to actuate the associated valve sleeve 40c and catching sleeve 41c.

(92) Accordingly, an initial ball dropped through the complete system will sequentially engage the indexing sleeves 46c, 46b, 46a of each tool 18c, 18b, 18a to move a discrete movement step, with only the valve sleeve 40a and catching sleeve 41a of the lowermost tool 18a being actuated. A second ball will move each indexing sleeve 46c, 46b a single discrete movement step, with only the valve sleeve 40b and catching sleeve 41b of tool 18b being actuated. A third ball may then actuate tool 18c. This arrangement may be used to accommodate a significant number of individual tools within a common system, for example between two and fifty, and even more if necessary.

(93) In embodiments where multiple tools 18 are used in series within a common system it is important to ensure that the associated indexing sleeves 46 are positioned at the correct initial locations within the housing 34. Aspects of the present invention may permit inspection of the location of the indexing sleeves 46 prior to deploying the associated tools 18 into a wellbore. In this respect, an inspection apparatus 200 in accordance with an embodiment of aspects of the present invention is illustrated in FIG. 9, in use with a tool 18 first shown in FIG. 2.

(94) The inspection apparatus 200 comprises an inspection object 202 provided in the form of a ball, which is similar to a ball used to drive the indexing sleeve 46. The inspection apparatus further comprises an elongate member 204, wherein the inspection object is mounted on one end of the elongate member 204. The elongate member may be provided in sections coupled together via a connector 205. The elongate member 204 includes one or more markings 206. In use, the inspection object 202 is inserted into the downhole end of the tool 18 until it contacts the first array of engagement members 52 of the indexing sleeve 46, with the elongate member 204 extending from the tool 18. In such an arrangement the markings 206 may provide a visible reference which permits a user to identify or determine the position of the indexing sleeve 46.

(95) Reference is now made to FIG. 10 in which there is shown a modified embodiment of the downhole tool 18 first shown in FIG. 2. In particular, FIG. 10 provides a cross-sectional view of the modified tool 18 in the region of the actuator portion 30. In this modification the housing 34 includes a plurality of housing modules 234a, 234b, 234c, 234d which are secured together in end-to-end relation via conventional threaded connectors to define the complete housing 34. Each housing module 234a, 234b, 234c, 234d comprises a number of annular recesses 44 which collectively define the complete indexing profile of the tool 18. Such a modular arrangement of the tool 18 may minimise the requirement for bespoke systems, and may allow multiple specific situations to be accommodated with a basic inventory of individual modules 234a, 234b, 234c, 234d, for example containing five or ten recesses 44 each.

(96) In the modified embodiment of FIG. 10 the two uppermost annular recesses 44f, 44g are provided at an axial spacing which matches the axial spacing of the first and second arrays of engagement members 52, 54 provided on the indexing sleeve 46. Such an arrangement may permit the indexing sleeve to become disabled prior to actuation of the tool. For example, as illustrated in FIG. 11, a shifting tool 240 may be deployed into the tool to engage a shifting profile 242 on the indexing sleeve 46 to pull the indexing profile in an uphole direction until the engagement members 52, 54 are located within a corresponding recess 44f, 44g.

(97) As described above in relation to FIG. 1, individual tools 18 may optionally include seals 26a, 26b to assist to focus fracturing fluid into the surrounding formation 14. Such seals may be provided in accordance with flow restrictors or packers as disclosed in UK patent application GB1112744.6 and/or PCT application no. PCT/GB2012/051788.

(98) An exemplary embodiment of such seal members 26a, 26b is illustrated in FIG. 12, in which the seal members 26a, 26b are mounted, for example by slipping onto, the tool 18.

(99) FIG. 13 shows seal 26b in a run-in configuration (it should be noted that seal 26a corresponds). The seal 26b is generally cylindrical, defining a central axis 370 and having a throughbore 380. The seal 26b is made up from several components: a mandrel 310; a restrictor assembly in the form of a swabbing assembly 360; and a seal backup 350, each of these components being arranged coaxially around the central axis 370.

(100) The mandrel 310 is provided as a body or shaft for the seal 26b and is tapered towards one end 310t. At an opposing end, the mandrel 310 has an end face 310e perpendicular to the central axis 370. A cylindrical inner surface 312 of the mandrel 10 surrounds the throughbore 80 and enables the mandrel 310 to be slotted onto another tubular (not shown) as part of a tubing string. However, in some embodiments the mandrel 310 may form part of the housing 34 of the tool 18.

(101) Towards the tapered end 310t, an outer surface of the mandrel 310 has a cylindrical annular groove 311 formed therein, for receiving an end of a set screw 313 that secures the swabbing assembly 360 to the mandrel 310.

(102) Once the seal 26b has been correctly assembled, it occupies the relatively compact run-in configuration shown in FIGS. 12 and 13 (or schematically in FIG. 14A).

(103) When flow is initiated through ports 20 of the tool 18, the seal 26b (and also 26a) will be actuated. Initially fluid flow over the seal 26b causes a frictional drag over the swabbing assembly 360. The frictional effect of a sufficiently high rate of fluid flow above a threshold drags the swabbing assembly 360 outwardly in the direction of flow. Flow may then act on the underside of the swabbing assembly 360 and further urge this radially outwardly until engagement with the wall of the borehole 12, as shown in FIG. 14B. By arranging the seals 26a, 26b facing each other, the flow from the ports 20 of the tool 18 may act to actuate both seals 26a, 26b.

(104) Reference is now made to FIGS. 15A to 15D in which there is shown a tool portion 432 of a downhole tool 418 having a coupling arrangement according to an embodiment of the present invention.

(105) The downhole tool 418 and tool portion 432 are similar to the downhole tool 18 and tool portion 32 described above and like features of the downhole tool 418 and tool portion 432 are represented by like numerals incremented by 400.

(106) The downhole tool portion 432 comprises a housing 434 having a number of lateral fluid ports 420 (two lateral fluid ports 420 are shown), a valve sleeve 440 slidably disposed within the housing 434 and also having a number of lateral fluid ports 484 (two lateral fluid ports 484 are shown), a catching sleeve 441 slidably disposed within the housing 434 and a coupling arrangement C.

(107) In use, the valve sleeve 440 is actuatable between a closed configuration in which fluid flow through the ports 420, 484 is prevented and an open configuration in which fluid flow is permitted while the catching sleeve 441 is actuatable by the valve sleeve 440 between a free configuration (as shown in FIG. 15A) and a catching configuration (as shown in FIG. 15B) suitable for catching an object such as a ball. Rotational movement of the valve sleeve 440 is transmitted to the catching sleeve 441 and the housing 434 via the coupling arrangement C and provides a rotational lock and/or ensures rotational alignment of the valve sleeve 440, catching sleeve 441 and housing 434 while also permitting relative axial movement between the valve sleeve 440, the catching sleeve 441 and the housing 434.

(108) The coupling arrangement C in the illustrated embodiment comprises radially extending keys 486 disposed in recesses 485 provided in a stepped outer surface portion 489 of the valve sleeve 441, the keys 486 extending radially from the valve sleeve 441 and through corresponding slots 487 in the catching sleeve 441 and into a plurality of recesses 488 provided in an inner wall surface of the housing 434.

(109) In use, the coupling arrangement C provides a rotary coupling between the valve sleeve 440, the catching sleeve 441 and the housing 434 since the interaction between the keys 486, slots 487 and recesses 488 prevents relative rotation between the valve sleeve 440, the catching sleeve 441 and the housing 434, maintaining the sleeve ports 484 in the correct circumferential alignment relative to the ports 420 in the housing 434. Since the keys 486 can translate axially in the slots 487 of the catching sleeve 441 and the recesses 488 of the housing 434, relative axial movement of the valve sleeve 440 and the catching sleeve 441 relative to the housing 434 is permitted, the maximum stroke or length of axial travel permitted substantially defined by the length of the housing recesses 488.

(110) The tool portion 432 is illustrated in an initial configuration in FIG. 15A, with the valve sleeve 440 in a closed position and the catching sleeve 441 in a free configuration. In this position, the valve sleeve 440 is initially axially secured relative to the housing 434 via a number of shear screws 482 (one screw 482 is shown). The keys 486 are disposed at the upper end of the housing recesses 488 and at a position intermediate the ends of the slots 487 of the catching sleeve 441.

(111) In order to move the valve sleeve 440 towards its open position, that is from the position shown in FIG. 15A to the position shown in FIG. 15B, an axial actuation force is applied to the valve sleeve 440 by an indexing sleeve 446 to shear the screws 482 and substantially align the sleeve ports 484 with the ports 420 in the housing 434 in a similar manner to that described above.

(112) As can be seen from FIGS. 15A to 15D, the slots 487 of the catching sleeve 441 and the recesses 488 of the housing 434 partially axially overlap, such that axial movement of the valve sleeve 441 does not immediately result in axial movement of the catching sleeve 441 from the free configuration shown in FIG. 15A to the catching configuration shown in FIG. 15B; axial movement of the valve sleeve 440 and catching sleeve 441 occurring when the keys 486 impinge on the lower end of the slots 487 of the catching sleeve 441.

(113) It is noted that in the position shown in FIG. 15B, the catching sleeve 441 has been moved to its catching configuration but the ports 420, 484 are not fully aligned and the keys 486 are not yet in abutment with the lower end of the housing recesses 488.

(114) As with the catching sleeve 41 described above, the catching sleeve 441 includes a plurality of longitudinally extending collet fingers 404, wherein each collet finger 404 supports a seat member 406 on a distal end thereof. When the seat members 406 are positioned radially outwardly, as shown in FIG. 15A, an object such as a ball may pass without any contact or with minimal engagement with the seat members 406. However, when the catching sleeve 441 is moved axially in a downhole direction, which will be caused by axial movement of the valve sleeve 440 towards its open position (to the right as shown in the figures), the seat members 406 will be displaced from an annular recess 408 in the housing 434 and engaged with a release sleeve 424, and thus deflected radially inwardly, and presented in a position to be engaged by a ball. Thus, when the seat members 406 are positioned radially inwardly with the catching sleeve 441 configured in its catching configuration as shown in FIG. 15B, a ball may engage and seat against the seat members 406 and thus be caught within the catching sleeve 441.

(115) Each seat member 406 includes an uphole seat surface 412 configured to be engaged by a ball when travelling in a downhole direction. The uphole seat surfaces 412 may be configured to provide a substantially complete or continuous engagement with a ball, permitting a ball to be sealingly engaged within the catching member 441. Such sealing of a ball within the catching sleeve 441 permits the catching sleeve 441 to be actuated, for example by a pressure differential established between uphole and downhole sides of the catching sleeve 441, to move the tool 418 from the position shown in FIG. 15B to the position shown in FIG. 15C.

(116) In the position shown in FIG. 15C, the keys 486 abut the lower end of the housing recesses 488 and the ports 420 are now fully open. By virtue of the coupling arrangement C, the catching sleeve 441 is free to move axially relative to the valve sleeve 440 under the influence of the pressure differential created across the ball to actuate the release sleeve 424 of the downhole tool 418 without disturbing the condition of the ports 420.

(117) The housing 434 defines or includes a release recess 432 which is initially covered by the release sleeve 424. However, when a suitable axial load is applied on the release sleeve 424 by the catching sleeve 441, the release sleeve 424 is moved axially to uncover the release recess 432, as shown in FIG. 15C. In the position shown in FIG. 15C, the keys 486 abut the lower end of the slots 487 and the housing recesses 488.

(118) With reference in particular to FIGS. 15B and 15C, it can be seen that movement of the tool 418 from the position shown in FIG. 15B to the position shown in FIG. 15C compresses a coil spring 418 interposed between the catching sleeve 441 and the housing 434. The coil spring 418 is biased to move the catching sleeve 441 in an uphole direction (to the left as shown in the figures) and under the influence of the coil spring 418 the catching sleeve 441 moves from the position shown in FIG. 15C to the position shown in FIG. 15D, such that the seat members 408 are received in the uncovered release recess 432. In this position, the catching sleeve 441 is configured in a release configuration which permits the ball to be released.

(119) Reference is now made to FIGS. 16A to 16E in which there is shown a tool portion 532 of a downhole tool 518 having a coupling arrangement C according to another embodiment of the present invention. In this embodiment, the tool 518 provides a positive indication at surface that an activation event, for example opening of ports 520, has occurred.

(120) The downhole tool 518 and tool portion 532 are similar to the downhole tools 18, 418 and tool portions 32, 432 described above and like features of the downhole tool 518 and tool portion 532 are represented by like numerals incremented by 500.

(121) As shown in FIG. 16A, the downhole tool portion 532 comprises a housing 534 having a number of lateral fluid ports 520 (two lateral fluid ports 520 are shown), a valve sleeve 540 slidably disposed within the housing 534 and also having a number of lateral fluid ports 584 (two lateral fluid ports 584 are shown), a catching sleeve 541 slidably disposed within the housing 534 and a coupling arrangement C.

(122) As in the coupling arrangement C, the coupling arrangement C provides a rotary coupling between the valve sleeve 540, the catching sleeve 541 and the housing 534 by virtue of the interaction between keys 586, slots 587 and recesses 588 while permitting relative axial movement of the valve sleeve 540 and the catching sleeve 541 relative to the housing 534.

(123) The tool portion 532 is illustrated in an initial configuration in FIG. 16A, with valve sleeve 540 in a closed position and catching sleeve 541 in a free configuration.

(124) In this position, the valve sleeve 540 is initially axially secured relative to housing 534 via a number of shear screws 582 (one screw 582 is shown) and the keys 586 are disposed adjacent an upper end of the housing recesses 588 and at a position adjacent to the lower end of the slots 587 of the catching sleeve 541.

(125) In order to move the catching sleeve 541 from its free configuration shown in FIG. 16A to its catching configuration shown in FIG. 16B, an axial actuation force is applied to the valve sleeve 540 by an indexing sleeve 546 to shear the screws 582, permitting the valve sleeve 540 to move in a downhole direction (to the right as shown in the figures). In this embodiment, when the catching sleeve 541 is moved by the valve sleeve 540 from the position shown in FIG. 16A to the position shown in FIG. 16B, the valve sleeve 540 is not moved to a fully open configuration but to an intermediate position in which the ports 520 are still closed (ports 584 and 520 are not aligned).

(126) As with the catching sleeve 441 described above, the catching sleeve 541 includes a plurality of longitudinally extending collet fingers 504, wherein each collet finger 504 supports a seat member 506 on a distal end thereof. When the seat members 506 are positioned radially outwardly, as shown in FIG. 16A, an object such as a ball may pass without any contact or with minimal engagement with the seat members 506. However, when the catching sleeve 541 is moved axially in a downhole direction, which will be caused by axial movement of the valve sleeve 540 (to the right as shown in the figures), the seat members 506 will be displaced from an annular recess 508 in the housing 534 and engaged with a release sleeve 524, and thus deflected radially inwardly, and presented in a position to be engaged by a ball. Thus, when the seat members 506 are positioned radially inwardly with the catching sleeve 541 configured in its catching configuration as shown in FIG. 16B, a ball may engage and seat against the seat members 506 and thus be caught within the catching sleeve 541.

(127) Each seat member 506 includes an uphole seat surface 512 configured to be engaged by a ball when travelling in a downhole direction. The uphole seat surfaces 512 may be configured to provide a substantially complete or continuous engagement with a ball, permitting a ball to be sealingly engaged within the catching member 541. Such sealing of a ball within the catching sleeve 541 permits the catching sleeve 541 to be actuated, for example by a pressure differential established between uphole and downhole sides of the catching sleeve 541, to move the tool 518 from the position shown in FIG. 16B to the position shown in FIG. 16C.

(128) In the position shown in FIG. 16C, the keys 586 are at an intermediate position in the housing recesses 588 and the ports 520 remain closed. By virtue of the coupling arrangement C, the catching sleeve 541 is free to move axially relative to the valve sleeve 540 under the influence of the pressure differential created across the ball to actuate the release sleeve 524 of the downhole tool 518 without disturbing the condition of the ports 520.

(129) The housing 534 defines or includes a release recess 532 which is initially covered by the release sleeve 524. However, when a suitable axial load is applied on the release sleeve 524 by the catching sleeve 541, the release sleeve 524 is moved axially to uncover the release recess 532, from the position shown in FIG. 16C to the position shown in FIG. 16D. In this position, the keys 586 abut the upper end of the slots 587 and are disposed adjacent the lower end of the recesses 588.

(130) As in previous embodiments, movement of the tool 518 from the position shown in FIG. 16C to the position shown in FIG. 16D compresses a coil spring 518 interposed between the catching sleeve 441 and the housing 434. The coil spring 518 is biased to move the catching sleeve 541 in an uphole direction (to the left as shown in the figures) and under the influence of the coil spring 518 the catching sleeve 541 moves from the position shown in FIG. 16D to the position shown in FIG. 15E, such that the seat members 508 of the catching sleeve 541 are received in the uncovered release recess 532. In this position, the catching sleeve 541 is configured in a release configuration which permits the ball to be released and the valve sleeve 541 has been moved to the open configuration (ports 520 and 584 are fully aligned). With the ports 520 open, a pressure drop detectable at surface provides a positive indication that the ports 520 have been opened correctly. In this position, the keys 586 are disposed adjacent the bottom of the recesses 588 and the slots 587.

(131) As in other embodiments, the tools 418, 518 may further include an optional choke 450, 550, the choke 450, 550 associated with the fluid port 420, 520 to choke flow through the fluid port 420, 520 once opened as described above.

(132) In the various embodiments described above, downhole tools are provided with a catching arrangement which is operated to move between free and catching configurations by an associated valve member. However, in other embodiments such a catching arrangement may be operated independently of a valve member. Such an arrangement is illustrated in FIG. 17A, reference to which is now made. The embodiment shown in FIG. 17A is similar in many respects to the embodiment first shown in FIG. 2, and as such like features share like reference numerals, incremented by 700.

(133) The downhole tool, generally identified by reference numeral 718, includes a tool housing 734 which includes a plurality of ports 720 through a wall thereof. The tool 718 includes a valve sleeve 740 which includes a plurality of ports 784, wherein the sleeve 740 is illustrated in FIG. 17A in a closed position, such that the ports 720 in the housing 734 are initially closed.

(134) The housing 734 defines first and second indexing profiles 742a, 742b, which each include a plurality of annular recesses 744. A first indexing sleeve 746a is arranged within the housing 734 relative to the first indexing profile 742a and uphole of the valve sleeve 740. As will be described in more detail below, the first indexing sleeve 746a is configured to operate the valve sleeve 740 to be moved to an open position following the passage of a predetermined number of balls 748.

(135) The tool 718 further includes a catching sleeve 741, which includes a plurality of fingers 804 and associated seat member 806, wherein the catching sleeve 741 is arranged adjacent a release sleeve 824, in a similar manner as defined above. In the arrangement shown in FIG. 17A, the catching sleeve 741 is positioned within a free configuration, such that any balls are free to pass therethrough, wherein the catching sleeve 741 is capable of being reconfigured into a catching configuration in which any passing balls may become caught. The precise form and operation of the catching sleeve 741 is similar to that described in connection with other embodiments, and as such no further detailed description will be given.

(136) A second indexing sleeve 746b is arranged within the housing 734 relative to the second indexing profile 742b and uphole of the catching sleeve 741. As will be described in more detail below, the second indexing sleeve 746b is configured to operate the catching sleeve 741 to move to its catching configuration following the passage of a number of balls 748.

(137) In the arrangement shown in FIG. 17A, each indexing sleeve 746a, 746b is initially arranged to be moved in the same number of discrete movement steps before reaching an actuation site. Thus, as illustrated in FIG. 17B, when a predetermined number of balls 748 have passed, the first indexing sleeve 746a will have moved to actuate and move the valve sleeve 740 to open the fluid ports 720, and the second indexing sleeve 746b will have moved to actuate and move the catching sleeve 741 to radially collapse the seat members 806 to permit the ball 748 to become caught. The ball 748 may then function to block the central bore 735 of the tool 718, allowing substantially all flow to be diverted through the open ports 720.

(138) Reference is now made to FIGS. 18A and 18B which show different stages of operation of a downhole tool, generally identified by reference numeral 818, in accordance with an alternative embodiment of the present invention. Tool 818 is similar in many respects to tool 18 shown in FIG. 2, and as such like features share like reference numerals.

(139) Tool 818 includes a housing 834 which includes first, second and third sets of ports 820a, 820b, 820c through a wall thereof. The tool 818 includes first, second and third valve sleeves 740 each arranged within the housing 834, and each positioned relative to a respective set of ports 820a, 820b, 820c, wherein the sleeves 840a, 840b, 840c are illustrated in FIG. 18A in a closed position, such that the ports 820a, 820b, 820c in the housing 834 are initially closed.

(140) The housing 834 defines first, second and third indexing profiles 842a, 842b, 842c which each include a plurality of annular recesses 844. A first indexing sleeve 846a is arranged within the housing 834 relative to the first indexing profile 842a and uphole of the first valve sleeve 840a. A second indexing sleeve 846b is arranged within the housing 834 relative to the second indexing profile 842b and uphole of the second valve sleeve 840b. Similarly, a third valve sleeve 840c is arranged within the housing 834 relative to the third indexing profile 842c and uphole of the third valve sleeve 840b. As will be described in more detail below, the indexing sleeves 846a, 846b, 846c are each configured to operate the respective valve sleeve 840a, 840b, 840c to be moved to an open position following the passage of a predetermined number of balls 848.

(141) The tool 818 includes a single catching sleeve 841 located downhole of the third valve sleeve 840c, wherein the catching sleeve 841 includes a plurality of fingers 904 and associated seat members 906, and is arranged adjacent a release sleeve 924, in a similar manner as defined above. In the arrangement shown in FIG. 18A, the catching sleeve 841 is positioned within a free configuration, such that any balls are free to pass therethrough, wherein the catching sleeve 841 is capable of being reconfigured into a catching configuration in which any passing balls may become caught. The precise form and operation of the catching sleeve 841 is similar to that described in connection with other embodiments, and as such no further detailed description will be given.

(142) In use, each passing ball 848 will cause each indexing sleeve 846a, 846b, 846c to progress in discrete steps of movement towards their associated valve sleeves 840a, 840b, 840c. When a predetermined number of objects have passed the valve sleeves 840a, 840b, 840c will be actuated to move towards their open positions to open the respective ports 820a, 820b, 820c, as illustrated in FIG. 18B. Further, actuation of the third valve sleeve 840c will cause the catching sleeve 841 to become configured into its catching configuration, such that a passing object 848 becomes caught. In such an arrangement the central bore 835 may become blocked, such that substantially all flow is diverted through the open ports 820a, 820b, 820c.

(143) Although the embodiment shown in FIG. 18A has three valve members, it will be appreciated that any number may be used, for example two or more.

(144) In the embodiments described above the present invention provides for actuation of either a valve sleeve and/or a catching sleeve. However, it will be appreciated that in alternative embodiments features of the present invention may be utilised to operate any type of downhole tool, in any downhole operation and in any required sequence. An example of one such alternative embodiment is schematically illustrated in FIGS. 19A to 19D, which show the sequential operation of a downhole system, generally identified by reference numeral 900.

(145) Referring initially to FIG. 19A, the downhole system 900 includes a tubing string 901 which is shown positioned within a wellbore 902. The tubing string 901 includes a number of tools and tool components along its length.

(146) More specifically, the tubing string 901 includes first, second and third axially arranged packers 910a, 910b, 910c. Each packer 910a, 910b, 910c includes an associated actuator, which each includes an indexing sleeve 912a, 912b, 912c. The indexing sleeves 912a, 912b, 912c are provided in a similar form to indexing sleeve 46 first shown in FIG. 2, and as such no further detailed description will be give. Each indexing sleeve 912a, 912b, 912c is arranged within the tubing string 901 to cooperate with respective indexing profiles (not illustrated) on the inner surface of the tubing string 901, to be moved in a number of discrete steps of movement towards an actuation site upon passage of a corresponding number of objects, such as balls. Upon reaching the respective actuation sites, the indexing sleeves 912a, 912b, 912c actuate the respective packers 910a, 910b, 910c, as will be described in more detail below.

(147) A first valve assembly 932a is positioned between the first and second packers 910a, 910b, and a second valve assembly 932b is positioned between the second and third packers 910b, 910c. Each valve assembly 932a, 932b is configured in the same manner as tool portion 32 first shown in FIG. 2, and as such no further detailed description will be given. Thus, each valve assembly 932a, 932b includes a valve member 940a, 940b initially arranged in FIG. 19A to block fluid ports 920a, 920b through a wall of the tubing string 901. Further, each valve assembly 932a, 932b includes a catching sleeve 941a, 941b which is configurable from a free configuration in which an object may freely pass therethrough, to a catching configuration in which an object may be caught.

(148) Each valve assembly 932a, 932b includes an associated actuator, which each includes an indexing sleeve 946a, 946b. The indexing sleeves 946a, 946b are provided in a similar form to indexing sleeve 46 first shown in FIG. 2, and as such no further detailed description will be give. Each indexing sleeve 946a, 946b is arranged within the tubing string 901 to cooperate with respective indexing profiles (not illustrated) on the inner surface of the tubing string 901, to be moved in a number of discrete steps of movement towards an actuation site upon passage of a corresponding number of objects, such as balls. Upon reaching the respective actuation sites, the indexing sleeves 946a, 946b actuate the respective valve assemblies 932a, 932b to move the valve members 940a, 940b to open the respective ports 920a, 920b, and to reconfigured the respective catching sleeves 941a, 941b to their catching configurations.

(149) In a similar manner to the embodiments described above, the required number of passing objects to cause the various indexing sleeves 912a, 912b, 912c, 946a, 946b to reach their respective actuation sites is determined by the initial positioning of said indexing sleeves. In this respect, a significant advantage of the present invention is the ability to provide an operator with significant flexibility in terms of setting any desired sequence of operation of downhole tools. However, in the present exemplary embodiments, the various indexing sleeves 912a, 912b, 912c, 946a, 946b are initially arranged such that the packers 910a, 910b are caused to be set upon passage of a first object, the second valve assembly 932b is actuated upon passage of a second object, and the first valve assembly 932a is actuated upon passage of a third object. Such operation will now be described with reference to FIGS. 19B, 19C and 19D.

(150) Referring first to FIG. 19B, a first object, specifically a first ball 948a is passed along the tubing string 901, moving each indexing sleeve 912a, 912b, 912c, 946a, 946b a single discrete step. This single discrete step is sufficient to cause the indexing sleeves 912a, 912b, 912c to actuate the respective packers 910a, 910b, 910c, to establish sealing engagement with a wall 903 of the wellbore 903 and achieve zonal isolation. The indexing sleeves 912a, 912b, 912c may provide any suitable actuation of the packers 910a, 910b, 910c. For example, the indexing sleeves 912a, 912b, 912c may axially compress the respective packers 910a, 910b, 910c. Alternatively, the indexing sleeves 912a, 912b, 912c may establish fluid communication with a source of hydraulic power which may be used to actuate the packers 910a, 910b, 910c. For example, the indexing sleeves 912a, 912b, 912c may open one or more ports which provide fluid communication with hydrostatic pressure within the annulus 904 between the tubing string 901 and the wall 903 of the wellbore 902.

(151) Upon passage of a second ball 948b, as shown in FIG. 19C, indexing sleeves 946a, 946b are each caused to move a further single discrete step. Such movement is sufficient to cause indexing sleeve 946b to drive the valve member 940b of the second valve assembly 932b to open the ports 920b, and also reconfigure the catching sleeve 941b so that the ball 948b may become caught. In such a configuration a fluid, such as a fracturing fluid, flowing along the tubing string 901 may be diverted outwardly through the opened ports 920b to treat a surrounding formation in the zone defined between the second and third packers 910b, 910c. In a similar manner to that described above in other embodiments, the catching sleeve 941b may eventually be configured to release the ball 948b, again allowing full bore access along the tubing string 901.

(152) Upon passage of a third ball 948c, as shown in FIG. 19D, indexing sleeve 946a is caused to move a further single discrete step, to now engage and drive the valve member 940a of the first valve assembly 932a to open the ports 920a, and also reconfigure the catching sleeve 941a so that the ball 948c may become caught. In such a configuration a fluid, such as a fracturing fluid, flowing along the tubing string 901 may be diverted outwardly through the opened ports 920c to treat a surrounding formation in the zone defined between the first and second packers 910a, 910b. In a similar manner to that described above in other embodiments, the catching sleeve 941c may eventually be configured to release the ball 948c, again allowing full bore access along the tubing string 901.

(153) As noted above, the present invention can permit downhole tools to be actuated in any desired sequence. In the system 900 of FIG. 19A, the indexing sleeves 912a, 912b, 912c are initially arranged to set the associated packers 910a, 910b, 910c upon passage of a single actuation object. However, in a modified embodiment indexing sleeve 912c may be arranged to set packer 910c upon passage of a first object, indexing sleeve 912b may be arranged to set packer 910b upon passage of a second object, and indexing sleeve 912a may be arranged to set packer 910a upon passage of a third object. In such an arrangement a passing object may only be required to actuate a single packer. This may provide advantages, in terms of maximising the available energy of an object for actuating a single packer, rather than requiring the object to have sufficient energy to actuate a number of downhole tools. In such an arrangement there might be the possibility that the available actuation energy of an object is dissipated before all target tools or packers are actuated.

(154) Reference is now made to FIG. 20A in which there is shown a downhole system, generally identified by reference numeral 1000, in accordance with an embodiment of the present invention. The downhole system 1000 includes a tubing string 1001 which is shown positioned within a wellbore 1002. The tubing string 1001 includes a number of tools and tool components along its length.

(155) More specifically, the tubing string 901 includes first and second valve assemblies 1032a, 1032b, wherein each valve assembly 1032a, 1032b is configured in the same manner as tool portion 32 first shown in FIG. 2, and as such no further detailed description will be given. Thus, each valve assembly 1032a, 1032b includes a valve member 1040a, 1040b initially arranged in FIG. 20A to block fluid ports 1020a, 1020b through a wall of the tubing string 1001. Further, each valve assembly 1032a, 1032b includes a catching sleeve 1041a, 1041b which is configurable from a free configuration in which an object may freely pass therethrough, to a catching configuration in which an object may be caught.

(156) Each valve assembly 1032a, 1032b includes an associated actuator, which each includes an indexing sleeve 1046a, 1046b. The indexing sleeves 1046a, 1046b are provided in a similar form to indexing sleeve 46 first shown in FIG. 2, and as such no further detailed description will be give. Each indexing sleeve 1046a, 1046b is arranged within the tubing string 1001 to cooperate with respective indexing profiles (not illustrated) on the inner surface of the tubing string 1001, to be moved in a number of discrete steps of movement towards an actuation site upon passage of a corresponding number of objects, such as balls. Upon reaching the respective actuation sites, the indexing sleeves 1046a, 1046b actuate the respective valve assemblies 1032a, 1032b to move the valve members 1040a, 1040b to open the respective ports 1020a, 1020b, and to reconfigured the respective catching sleeves 1041a, 1041b to their catching configurations.

(157) In a similar manner to the embodiments described above, the required number of passing objects to cause the indexing sleeves 1046a, 1046b to reach their respective actuation sites is determined by the initial positioning of said indexing sleeves.

(158) A conduit 1004 runs alongside the tubing string 1001. The conduit may be of any suitable form and provide any required function. For example, the conduit 1004 may be configured to provide fluid, electrical, optical communication or the like along the tubing string 1001.

(159) In the present embodiment illustrated, the conduit 1004 extends along the outer surface of tubing string 1001 at a circumferential location which is absent from any fluid ports, as illustrated in FIG. 20B, which is a sectional view of the system 1000 of FIG. 20A, taken through line B-B. In this respect, the ports 1020a are evenly circumferentially distributed around the tubing string 1001, with the exception that a port is absent from the circumferential region (the 12 o'clock position in the illustrated embodiment) at which the conduit 1004 is located. Accordingly, the conduit 1004 may be protected from direct exposure to any fluids, such as a fracturing fluid, exiting the ports 1020a.

(160) It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention.