Downhole Tool

Abstract

A downhole tool includes a housing; a first piston arranged within the housing such that it can move axially under the action of fluid flowing through the tool; and an indexer configured to control axial movement of the first piston between a first, second and third axial position. The indexer is configured such that the first piston can be selectively moved into the third position in accordance with a variation of a flow of fluid through the tool. A second piston is movable between a closed position in which fluid flowing through the tool is restricted from communicating with an activation chamber and an open position in which fluid flowing through the tool is permitted to communicate with the activation chamber; wherein the second piston is configured to move between the closed position and the open position in response to the first piston moving to the third axial position.

Claims

1. A downhole tool comprising: a housing; a first piston within the housing configured such that the first piston can move axially under an action of fluid flowing through the tool; an indexer configured to control axial movement of the first piston between a first, second and third axial position; wherein the indexer is configured such that the first piston can be selectively moved into the third position in accordance with a variation of a flow of fluid through the tool; a second piston moveable between a closed position in which fluid flowing through the tool is restricted from communicating with an activation chamber and an open position in which fluid flowing through the tool is permitted to communicate with the activation chamber; wherein the second piston is configured to move between the closed position and the open position in response to the first piston moving to the third axial position.

2. The downhole tool according to claim 1, wherein the tool is configured such that fluid entering the activation chamber reconfigures the downhole tool between an active and an inactive arrangement.

3. The tool according to claim 1, wherein the activation chamber is arranged such that the tool is activated in response to the second piston moving to the open position.

4. The tool according to claim 1, further comprising an unobstructed axial flow path along the centre of the tool.

5. The tool according to claim 1, wherein the first piston is configured to move the second piston between the open and closed positions as the first piston goes to the third position.

6. The tool according to claim 1, wherein the second piston is moved from a closed position to an open position in response to the first piston moving to the third axial position.

7. The tool according to claim 1, wherein the second piston defines openings arranged to define an entry to the activation chamber when the second piston is in the open position, further comprising a gate member comprising a plurality of openings to the activation chamber; wherein the openings in the second piston are arranged to align with those of the gate member when the second piston is in the open position.

8. (canceled)

9. The tool according to claim 1, further comprising a tool piece configured to move between an active position and an inactive position under the action of fluid in the activation chamber, in response to the second piston moving to the open position.

10. The tool according to claim 1, further comprising a first and second biasing means, wherein the first biasing means is arranged to bias the first piston towards the first position and the second biasing means is configured to bias the second piston towards the first piston.

11. The tool according to claim 1, wherein the indexer is configured such that in order to move the first piston from the first position to the third position, a predetermined sequence of flow control actions must be undertaken, wherein the tool is configured such that the first piston is in: the first position when no fluid is flowing through the tool, the second position when fluid is flowing through the tool but the predetermined sequence of flow control actions has not been undertaken, and the third position when fluid is flowing through the tool and the predetermined sequence of flow control actions has been undertaken.

12. (canceled)

13. The tool according to claim 1, wherein the indexer is configured such that the first piston can cycle between the first position and the second position.

14. The tool according to claim 1, wherein the indexer is configured such that the first piston moves to the third position in response to a change of the rate of fluid flow through the tool during the transition from the second position to the first position.

15. The tool according to claim 1, wherein the indexer is configured such that the first piston moves to the third position in response to the flow rate through the tool being increased within a predetermined period of the flow rate being decreased.

16. The tool according to claim 1, wherein the indexer is arranged to rotate relative to both the first piston and the housing.

17. The tool according to claim 1, wherein an end surface of the indexer comprise a profile configured to abut the first piston when the first piston is in the first, second and/or third position to transfer axial loads.

18. The tool according to claim 1, wherein the indexer comprises a plurality of paths which define a pathway profile which defines the first position, the second position and the third position of the first piston, wherein the pathway profile comprises a change in depth arranged to reduce the likelihood of the first piston going straight from the first position to the third position.

19. (canceled)

20. The tool according to claim 1, wherein the first piston comprises a follower configured to damp the movement of the first piston, wherein the follower is configured to damp the movement of the first piston from the second position towards the first position.

21. (canceled)

22. The tool according to claim 17, wherein the follower is configured to engage the indexer and the follower and indexer are arranged in a chamber comprising a fluid and the follower defines a first restriction to flow for fluid flowing in one direction and a second restriction to flow for fluid flowing in the other direction.

23. (canceled)

24. A downhole tubular string comprising a downhole tool, the downhole tool comprising: a housing; a first piston within the housing configured such that the first piston can move axially under an action of fluid flowing through the tool; an indexer configured to control axial movement of the first piston between a first second and third axial position; wherein the indexer is configured such that the first piston can be selectively moved into the third position in accordance with a variation of a flow of fluid through the tool; a second piston moveable between a closed position in which fluid flowing through the tool is restricted from communication with an activation chamber and an open position in which fluid flowing through the tool is permitted to communicate with the activation chamber; wherein the second piston is configured to move between the closed position and the open position in response to the first piston moving to the third axial position.

25. A method for activating a tool, the tool comprising: a first piston; an indexer configured to control axial movement of the first piston between a first, second and third axial position; and a second piston; the method comprising moving the first piston into the third position by varying the flow of fluid through the tool, thus moving the second piston between a closed position in which fluid flowing through the tool is restricted from communicating with an activation chamber and an open position in which fluid flowing through the tool is permitted to communicate with the activation chamber.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0151] Examples of the present disclosure will now be described with reference to the figures below, in which:

[0152] FIG. 1 is a side view of a tool according to the disclosure;

[0153] FIG. 2 is a cross-sectional view of the tool of FIG. 1;

[0154] FIG. 3 is an enlarged view of part of FIG. 2;

[0155] FIG. 4 is an enlarged view of part of FIG. 3;

[0156] FIG. 5 is an enlarged view of part of FIG. 3;

[0157] FIG. 6 is a cross-sectional view of the tool of FIG. 1, with the first piston in the first position;

[0158] FIG. 7 is a cross-sectional view of the tool of FIG. 1, with the first piston in the second position;

[0159] FIG. 8 is a cross-sectional view of the tool of FIG. 1, with the first piston in the third position;

[0160] FIGS. 9A and 9B are cross-sectional views of the tool of FIG. 1 with the first piston in the second position;

[0161] FIGS. 9C and 9D are cross-sectional views of the tool of FIG. 1 with the first piston in the third position;

[0162] FIG. 10 is a perspective view of an indexer according to the disclosure;

[0163] FIG. 11 is a schematic illustration of a pathway arrangement suitable for use with an indexer according to the disclosure;

[0164] FIGS. 12A to 12K are schematic illustrations of the movement sequences of a pin in a pathway according to FIG. 11;

[0165] FIGS. 13A to 13D a illustrative views of a follower and indexer assembly for use in the tool of FIG. 1;

[0166] FIG. 14 is a graph schematically illustrating an example of the pressure of the fluid flowing through a tool according to the disclosure;

[0167] FIG. 15 is a perspective cross-sectional view of an indexer according to the present disclosure engaged with a follower;

[0168] FIG. 16 is a further perspective cross-sectional view of an indexer according to the present disclosure engaged with a follower;

[0169] FIG. 17 is a cross-sectional view of part of the tool of FIG. 1;

[0170] FIG. 18 is an enlarged view of a part of FIG. 17;

[0171] FIG. 19 is a further enlarged view of a part of FIG. 17;

[0172] FIG. 20 is a further cross-sectional view of part of the tool of FIG. 1;

[0173] FIGS. 21A to 21C are cross-sectional views of part of the tool of FIG. 1;

[0174] FIGS. 22A to 22C are cross-sectional views of a further tool according to the disclosure;

[0175] FIGS. 23A to 23C are enlarged views of part of FIGS. 22A to 22C, respectively;

[0176] FIGS. 24A and 24B are enlarged view of part of FIGS. 22B and 22C, respectively; and

[0177] FIGS. 25A and 25B are views of the tool of FIG. 22 schematically illustrating fluid pressure within the tool.

DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS

[0178] FIGS. 1 and 2 depict a tool 10 according to the disclosure. FIG. 1 is a side view and FIG. 2 is a cross-sectional view.

[0179] The tool 10 of FIGS. 1 and 2 is a string reamer. The tool 10 comprises an elongated substantially cylindrical housing 24. The housing 24 comprises a plurality of sub-sections which are assembled to form the housing 24 as shown.

[0180] The tool 10 is for use in a downhole tubular string and comprises a first and second end 12, 14 for connection with tubulars on either side thereof. The first end 12 is shown in FIGS. 1 and 2 and comprises a male connector in the form of a pin connector 16. The second end 14 is shown in FIG. 2 only and comprises a female connector in the form of a box connector 18.

[0181] Towards the centre of the tool 10 as illustrated is a cutting section 20. The cutting section 20 comprises retractable cutter blades 22. In the arrangement shown in FIG. 1, the cutter blades 22 are in an inactive state, whereby they are retracted into the housing 24 of the tool 10.

[0182] As can be seen in FIG. 2, the tool 10 comprises a tool flow path 26 which extends along the length of the tool 10 along the central axis thereof. The tool flow path 26 is configured to allow drilling mud to flow through the tool 10 during drilling operations, such that it can reach the drill bit at the end of the drill string. The tool flow path 26 comprises a cylindrical hollow of substantially constant cross section through the length of the tool 10.

[0183] FIG. 3 is a close-up of section A of the tool 10 as shown in FIG. 2. FIGS. 4 and 5 are enlarged views of FIG. 3. The following description is made with reference to FIGS. 3, 4 and 5.

[0184] The section of the tool 10 shown in FIG. 3 is configured to be selectively operable to move the cutter blades 22 between an active and inactive position.

[0185] The tool 10 comprises a first piston 28 arranged axially within the housing 24. The first piston 28 comprises a follower 30 which is fixed with respect to the first piston 28 and engages an indexer 32. The indexer 32 is configured to cooperate with the follower 30 and is configured to control axial movement of the first piston 28 between a first, second and third longitudinal position with respect to the housing 24. Towards the downhole end of the tool 10 (to the right in the figures) a second piston 34 is arranged adjacent an activation chamber 36. The second piston 34 is configured to move between a closed and an open position to restrict and permit fluid from communicating with the activation chamber 36, respectively. The fluid pressure in the activation chamber 36 is determined by whether fluid flowing through the tool flow path 26 can enter the activation chamber 36 which, in turn, is dependent on the position of the second piston 34. Increasing and decreasing the fluid pressure in the activation chamber 36 can move the cutter blades 22 between an active and inactive position.

[0186] The first piston 28 comprises a piston head 28a and a piston rod 28b. The piston head 28a and piston rod 28b both define part of the tool flow path 26 and, as such, fluid can flow through the centre of the first piston 28. The piston rod 28b of the first piston 28 extends through an annular support, the follower 30 and the indexer 32, towards the second piston 34.

[0187] The first piston 28 is configured such that it can move axially within the housing 24 in a first direction (to the right of FIG. 3) and a second direction (to the left of FIG. 3). The tool 10 comprises a first biasing means in the form of a first helical spring 44 which is arranged to bias the first piston 28 in the second direction—away from the second piston 34.

[0188] The follower 30 is fixed relative to the first piston 28. The follower 30 of the present example comprises a piston arranged to seal on an inner surface of a sleeve portion of an annular support 48. The follower 30 is arranged to move axially with the first piston 28. The follower 30 is arranged to move in a sealed chamber 46 defined by the housing 24 and the annular support 48. The chamber 46 contains oil and, as such, as the follower 30 moves within the chamber 46 the oil flows from one side of the follower 30 to the other. It should be noted, however, that fluids other than oil can be used for this purpose.

[0189] The follower 30 comprises a pin 38 which engages the indexer 32 and cooperates with paths of the indexer 32 to define the first, second and third position of the first piston 28.

[0190] It should be noted that in alternative examples, the locations of the indexer and pin may be reversed. That is, the part which is the follower in the present example may be the indexer such that it is fixed relative to the first piston 28. In such an example, the part which is the indexer in the tool of FIG. 1A may comprise a pin arranged to engage the indexer fixed relative to the first piston 28.

[0191] The indexer 32 is located adjacent and engaged with the follower 30, inside the chamber 46. The indexer 32 is a sleeve located radially-inwardly of a sleeve portion of the follower 30. The indexer 32 is mounted on an indexer support member 50. A bearing 40 located between the indexer 32 and the indexer support member 50 allows the indexer 32 to rotate relative to the housing 24. In the present example the bearing is a roller bearing, although it will be understood that any radial bearing will be suitable for such use. A thrust bearing 42 at the end of the indexer 32 axially restrains the indexer 32 while still permitting the indexer to rotate.

[0192] The second piston 34 comprises an assembly of a sealing part 34a and an activation chamber closing part 34b, as shown in FIG. 5. The second piston 34 is located in the first direction (downhole, in the present example) from the first piston 28. As with the first piston 28, the second piston 34 is configured with an internal bore such that it can form part of the tool flow path 26 to allow fluid flow therethrough.

[0193] The second piston 34 is arranged adjacent the activation chamber 36. A gate member 54 (which in the present example comprises an assembly of parts) surrounds the second piston 34 and defines a plurality of openings 55. The openings 55 in the gate member 54 provide access to the activation chamber 36. The second piston 34 comprises a series of radial ports 52 around the circumference of the second piston which are arranged to align with and communicate with the openings 55 in the gate member 54 when the second piston 34 is in an open position (as shown in FIG. 8). When the second piston 34 is in a closed position, as shown in FIGS. 2 to 6, the ports 52 are arranged adjacent a wall of the gate member 54, effectively shutting the ports 52 and restricting the flow of fluid into the activation chamber 36.

[0194] The tool 10 comprises a second biasing means in the form of a second helical spring 56 arranged to bias the second piston 34 towards the closed position—that is, in a second direction towards the first piston 28 in the present example.

[0195] FIGS. 6 to 8 depict the tool 10 with the first piston 28 in a first, second and third position, respectively.

[0196] FIG. 6 shows the tool with the first piston 28 in a first position. FIG. 7 shows the tool with the first piston 28 in the second position. FIG. 8 shows the tool with the first piston 28 in the third position. In FIG. 6, little or no fluid is flowing through the tool. In FIG. 7, fluid is flowing through the tool but the sequence of flow control actions required to move the first piston 28 to the third position have not been done. In FIG. 8, fluid is flowing through the tool and the sequence of flow control actions has been executed such that the first piston 28 can move to the third position.

[0197] In FIG. 6, the first piston 28 is in the first position, in an uphole position (i.e. as far in the second direction as the first piston 28 can go). The first piston 28 is urged in this direction by the first helical spring 44. The second piston 34 is in a closed position, which is also an uphole position (i.e. as far in the second direction as the second piston 34 can go). The second piston 34 is urged in this direction by the second helical spring 56. In the closed position, as shown in FIG. 6, the ports 52 of the second piston 34 are arranged adjacent a wall of the gate member 54. The second piston ports 52 are not in fluidic communication with the activation chamber 36.

[0198] The first piston 28 is in the first position when no fluid is flowing through the tool flow path 26.

[0199] Turning now to FIG. 7, the tool is depicted when fluid is flowing through the tool flow path 26. It can be seen that the piston has moved axially towards the second piston 34 (in the first direction—to the right of the figures) compared to the first position illustrated in FIG. 6. The first piston 28 is configured to move axially towards the second piston 34 under the action of fluid flowing through the tool. When fluid flows through the tool flow path 26, a pressure differential is provided across the first piston 28 (indicated by the arrows). This pressure differential exerts a force on the first piston 28, overcoming the biasing force and differential pressure from the tool flow path 26 to the activation chamber 36 provided by the first helical spring 44 and moving the first piston 28 towards the second piston 34.

[0200] The indexer 32 defines the first, second and third positions of the first piston 28 and, since the predetermined sequence of flow control actions has not been undertaken, the indexer 32 prevents the first piston 28 from entering the third position and instead restrains the first piston 28 at the second position via the pin 38 and follower 30, which engage the indexer 32 but are axially fixed relative to the first piston 28.

[0201] In the second position, the free end of the first piston rod 28b is adjacent the second piston 34, but has not fully engaged the second piston 34 so as to move the second piston 34 against the bias of the second helical spring 56. Accordingly, the ports 52 are still blocked by the wall of the gate member 54 and, accordingly, fluid flowing through the tool flow path 26 is restricted from entering the activation chamber 36. Differential pressure across the second piston 34 is also holding the second piston 34 in the closed position blocking the openings 55.

[0202] Turning now to FIG. 8, the tool is shown with the first piston 28 in the third position. In FIG. 8, it is assumed that fluid is flowing through the tool and the operator has undertaken the predetermined sequence of flow control actions defined by the indexer 32 such that the first piston 28 has entered the third position. In this position the first piston 28 has moved further axially towards the second piston 34 than in the second position.

[0203] The first piston 28 abuts the second piston 34 and urges the second piston 34 in the first direction (towards the right of FIGS. 6 to 8). The geometry of the first piston 28 and second piston 34, and the characteristics of the first and second helical springs 44, 56 have been selected such that, when fluid is flowing through the tool during use, the force axial force generated by the pressure gradient across the first piston 28 is sufficient to overcome the resistive forces of the first and second helical spring 44, 56 and any pressure forces acting on the second piston. As such, the first piston 28 moves the second piston 34 from the closed position (as shown in FIGS. 6 and 7) to the open arrangement.

[0204] When the second piston 34 is in the open arrangement, the ports 52 align with the openings 55 in the gate member 54 and fluid flowing through the tool can communicate with and enter the activation chamber 36 (as shown by the arrows in FIG. 8). The pressure in the activation chamber 36 therefore increases.

[0205] FIGS. 9A and 9B schematically illustrate the pressure of fluid within the tool 10 with the first piston 28 in a second position.

[0206] As can be seen in these figures, when the first piston 28 is in the second position fluid is flowing through the tool flow path 26 and the tool flow path 26 is at a comparatively high pressure.

[0207] The ports 52 of the second piston 34 are in a closed position and, as such, they are substantially closed by the gate member 54. Fluid in the activation chamber 36 is not exposed to the pressure of the fluid in the tool flow path 26. Accordingly, the fluid in the activation chamber 36 is comparatively low and the cutter blades 22 remain in an inactive (e.g. withdrawn) position.

[0208] Turning now to FIGS. 9C and 9D, the first piston 28 is now in the third position. The ports 52 of the second piston 34 are now in an open position and are aligned with the openings 55 of the gate member 54 such that fluid from the tool flow path 26 communicates with, e.g. can freely flow into, the activation chamber 36. Fluid in the activation chamber 36 is therefore exposed to the pressure of the fluid in the tool flow path 26 and thus the activation chamber 36 pressure increases. The pressure in the activation chamber 36 therefore increases and becomes a high pressure zone, as illustrated in the figure.

[0209] When the first piston 28 is in the third position and the second piston is in an open position the pressure in the activation chamber 36 is greater than that of the annulus (i.e. in the gap between the tool 10 and the wellbore). The actual pressure of the activation chamber 36 may be determined by an outer flow restriction 37, connecting the activation chamber 36 to the annulus. The outer flow restriction 37 has a cross-sectional area which is much smaller than that of the ports 52 and the openings 55 such that the pressure in the activation chamber 36 is sufficiently high to move the cutter blades 22 to an active position.

[0210] The activation chamber 36 is fluidically connected to a pressure chamber 60. When the activation chamber 36 is at a high pressure as shown in FIG. 9B, the pressure chamber exerts an axial force on a plurality of tool piece actuators in the form of wedges 58. The force caused by the fluid pressure overcomes a biasing force acting on the wedges 58 and cutter blades 22 (discuss in more detail later), and the wedges 58 move axially in a first direction (i.e. to the right—downhole in the present example). An angled face of each wedge 58 engages a cutter blade 22, causing the cutter blade 22 to extend radially outwardly from the housing 24, from an inactive position (FIG. 9A) to an active position (FIG. 9B).

[0211] FIG. 10 depicts an indexer 32 according to the disclosure.

[0212] The indexer 32 is tubular and is thus an indexer sleeve. The indexer 32 comprises an internal radius configured to be mounted on roller bearings surrounding a cylindrical mounting surface within the housing, such that the indexer can rotate relative to the housing. A first end 62 of the indexer 32 comprises a flat surface which is arranged to engage a thrust bearing located between the first end 62 of the indexer 32 and the housing 24, or a support fixed with respect to the housing 24. The indexer 32 is therefore configured to rotate relative to the housing 24 but is axially restrained such that it cannot move in the first direction with respect to the housing 24.

[0213] A second end 64 comprises a castellated profile. The castellated profile may be configured to engage a similarly castellated profile on the inside of the follower 30 (discussed in more detail below) to support axial loads when the first piston is in the second and third positions.

[0214] On the outer curved surface of the indexer 32 a pathway profile 74 comprising a plurality of paths is defined in the form of channels cut into the thickness of the indexer sleeve. The channels are arranged to mate with the follower pin 38. The paths cooperate with the pin 38 of the follower 30 to define the first position, second position and third position of the first piston 28. The paths comprise corresponding locations for the pin 38 when the first piston is in the first position 66, second position 68 and the third position 72.

[0215] In the example shown, the paths also comprise a location for the pin 38 which define an intermediate position 70 of the first piston 28, to be entered between the second position and the third position. When in the intermediate position, the first piston is at the same axial position as the second position (i.e. the second piston has not been urged to move between the closed and open position). The provision of an intermediate position for the first piston 28 increases the length of the sequence of flow control actions required to enter the third position and, as such, reduces the likelihood that the first piston 28 will enter the third position by mistake.

[0216] The indexer 32 and pin 38 are configured such that the pin 38 can travel along the paths as the first piston 28 moves axially within the housing 24. The indexer 32 is configured to rotate relative to the first piston 28 as the pin 38 traverses a path which extends circumferentially around the indexer 32.

[0217] The pathway profile 74 comprises a change in depth in the form of a step 75. The step 75 is located at a position to prevent a pin 38, following the paths defined by the pathway profile 74 from entering the paths in an incorrect sequence and hence going straight from the first position to an intermediate position or the third position without first going to the second position. The step is discussed further with reference to FIG. 11.

[0218] FIG. 11 schematically illustrates an example pathway profile 77 for use on an indexer 32 according to the disclosure. The pathway profile 77 of FIG. 11 and FIG. 12 is similar, but slightly different, to that shown in FIG. 10. The function of both pathway profiles 74, 77 however, are essentially the same—that is, both profiles define a first, second and third position of the first piston. Both pathway profiles 74, 77 are suitable for use in a tool 10 according to the disclosure.

[0219] The pathway profile 77 includes a position for the pin 38 when the first piston 28 is in the first position 66, second position 68, an intermediate position 70 and the third position 72.

[0220] The pathway profile 77 comprises a first path 76 along which the pin 38 may travel when the first piston 28 moves axially towards the second piston 34 in response to fluid flowing through the tool 10, thus producing a pressure differential across the first piston 28. The first path 76 guides the first piston 28 from the first position to the second position.

[0221] If the pressure across the first piston 28 is reduced, for example because the flow through the tool flow path 26 has been reduced, the first piston 28 moves in the second direction and the pin 38 traverses the second path 78, which leads from the pin location for the second position 68 to that for the first position 66.

[0222] If the pressure in the tool flow path 26 remains low, the first piston 28 reaches the first position and the pin 38 reaches the corresponding location for the first position 66.

[0223] If, however, during the return stroke—i.e. as the first piston 28 moves from the second position towards the first position and the pin moves from the corresponding location for the second position 68 towards that for the first position 66—the pressure in the tool flow path 26 again increases, the first piston 28 moves back in the first direction. The pin 38 will therefore follow the first intermediate path 80, which branches off from the second path 78 and leads to a pin location corresponding to the intermediate position 70.

[0224] In the intermediate position the first piston is at the same axial location as in the second position and as such, the arrangement of tool is as shown in FIGS. 7 and 9A.

[0225] When the pressure in the tool 10 is again reduced, the first piston 28 moves in the second direction again and the pin 38 follows the second intermediate path 82 towards the location for the first position 66.

[0226] If the pressure in the tool flow path 26 remains low, the first piston 28 reaches the first position and the pin 38 reaches the corresponding location for the first position 66.

[0227] If, however, the pressure in the tool flow path 26 is again increased before the first piston 28 reaches the first position (and hence before the pin 38 reaches the corresponding location 66), the first piston 26 again moves in the first direction and the pin 38 follows the third path 84. The third path 84 leads the corresponding pin location for the third position 72. Accordingly, the first piston enters the third position.

[0228] The time during which the flow rate can be increased to enter the ‘next’ path (e.g. the first intermediate path 80 from the second path 78, or the third path 84 from the second intermediate path 82) is determined by the location of the intersections 85. The intersections 85 are configured such that once the pin 38 is located at, or has traversed, the intersection 85, reversal of the movement of the pin 38 results in the pin 38 entering the next path rather than the one from which it came. Therefore, the pin 38 must have traversed, or be located at, the intersection 85 before the flow rate is increased in order for the pin 38 to enter the ‘next’ path. The time that it takes for the pin 38 to travel from the location corresponding to the second position 68 (or intermediate position 70) to the intersection 85 may be referred to as a “predetermined period”.

[0229] Once the pin 38 has traversed the intersections the first piston will not be able to advance to the ‘next’ position, even if the flow rate is again increased. Instead, the first piston 28 will go to the first position. The section in which this is the case extends between the intersections 75 and the location corresponding to the first position 66.

[0230] Given knowledge of the characteristics of the tool 10, the time that it takes for the pin 38 to move from the location corresponding to the second position 68 (or intermediate position 70) to the intersection 85 may be calculated. Alternatively, it may be measured.

[0231] Likewise, the time it takes for the first piston 28 to travel from the second position to the first position can be calculated or measured.

[0232] These two times will allow a user to determine a window of time after reducing the flow through the tool during which the flow needs to be increased in order to move the first piston 28 into the ‘next’ position (e.g. intermediate position or third position). This window of time is schematically represented in FIG. 11 by reference numeral 86.

[0233] Although not visible in FIG. 11, the location of the change in depth of the paths—i.e. steps 75—are indicated. A first step 75 is located at the intersection between the first path 76 and the second path 78 at the end closest to that corresponding to the first position 66. A second step 75 is located at the end of the third path 84 and second intermediate path 82 at the end closest to the location corresponding to the first position 66. The steps 75 are defined as a step down when travelling along the second path 78 or third path 84 towards the location corresponding to the first position 66 of the piston 68. The steps 75 are arranged to prevent a pin from inadvertently entering the second path 78 or third path 84 from the first path 76, without first going to the location corresponding to the second position 68. This prevents the tool 10 from inadvertently going straight from no-flow to the third position, activating the tool, unintentionally.

[0234] As can be seen from the schematic pathway profile 77, the third position corresponds to an axial location of the first piston further towards the second piston (i.e. in the first direction) than the second and intermediate positions.

[0235] Turning now to FIGS. 12A to 12K a movement sequence of the pin 38 in the pathway profile 77 of FIG. 11 is shown.

[0236] In FIG. 12A the pin 38 is at the location corresponding to the first position 66 of the first piston 28.

[0237] In FIG. 12B, the pin 38 is shown moving from the location corresponding to the first position 66 to that of the second position 68 along the first path 76. This movement is caused by fluid starting to flow through the tool 10, thus introducing a pressure differential across the first piston 28 and moving the first piston 28 to the second position.

[0238] In FIG. 12C, the flow of fluid through the tool 10 has been reduced causing the first piston 28 to be urged towards the first position by the first helical spring 44. The pin 38 therefore travels towards the location corresponding to the first position 66 along the second path 78.

[0239] In FIG. 12D the pin 38 continues along the second path 78, until it reaches the location corresponding to the first position 66 of the first piston 28, in FIG. 12E.

[0240] In FIG. 12F, movement is shown corresponding to a movement of the first piston 28 towards the second piston 34 occurring after the period shown in FIG. 12D but before the period shown in FIG. 12E. That is, the flow rate through the tool 10 is increased during the transition from the first position to the second position (i.e. at some point while the pin 38 is traversing the second path 78). FIG. 12F shows the pin moving up the second path 78, towards the intermediate position 70.

[0241] In FIG. 12G, the flow rate is maintained and so the pin 38 continues to travel to the intermediate position 70, via the first intermediate path 80.

[0242] In FIG. 12H, the flow rate through the tool 10 is reduced such that the first piston 28 is biased in the second direction and the pin 38 moves along the second intermediate path 82 towards the location corresponding to the first position 66.

[0243] In FIGS. 121 and 12J the flow rate is maintained at a low level (e.g. off) and the first piston 28 continues to move in the second direction and the pin 38 therefore travels along the second intermediate path 82 to the location corresponding to the first position 66.

[0244] In FIG. 12K, however, the flow rate through the tool 10 is increased before the first piston reaches the first position (and hence before the pin 38 reaches the corresponding location 66). The first piston 28 is therefore moved in a first direction and moves to the third position; the pin follows the third path 84 and moves to the location corresponding to the third position 72. The flow rate is increased at a time after the period shown in FIG. 12H but before that shown in FIGS. 121 and 12J (although it is to be noted that the first piston 28 would still enter the third position if the flow rate was increased after the period shown in 121 but before that of 12J).

[0245] FIGS. 13A to 13D depict an assembly of the follower 30 and indexer 32 in configurations corresponding to the first piston 28 being in the first position, second piston, an intermediate position and the third position.

[0246] The follower 30 has six pins 38 equally spaced around the circumference of the sleeve portion of the follower 30 which engage the pathway profile of the indexer 32. The pathway profile defines ramps 79 which provide a change in depth of the corresponding path. Ramps 79 are located in the first path, leading from the location first position to the second position, and the path leading from the third position back to the first position. The ramps 79 are provided such that step 75 can be included and the pathway profile can still provide a continuous pathway profile around the indexer 32.

[0247] In FIG. 13A, the pins 38 are located in a position corresponding to the first piston 28 being in the first position 66.

[0248] In FIG. 13B the first piston 28 has moved to the second position and the pin 38 has advanced to the corresponding second position 68. The follower 30 has moved axially, the indexer 32 has rotated relative to the housing 24 and follower 30.

[0249] In FIG. 13C the pin 38 is in an intermediate position 70. Accordingly, the flow through the tool 10 has been reduced and then increased before the first piston 28 reached the first position. Again, the follower 30 has moved axially while the indexer 32 rotates.

[0250] In FIG. 13D the first piston 28 is in the third position and the pin 38 is in the corresponding position.

[0251] FIG. 14 is a graph showing an exemplar sequence of flow control actions for use with a tool according to the disclosure. In the tool according to the graph of FIG. 14, the indexer 32 comprises a pathway profile including an intermediate position. As such, two cycles of a reducing in pressure shortly followed by an increase in pressure are required in order for the first piston 28 to move to the third position to activate the tool. In this example, the predetermined time period (i.e. the time period during which the flow rate must be increased for the first piston to move to the ‘next’ position) has been calculated or measured at 2 minutes.

[0252] The tool starts with little or no fluid flowing therethrough. Thus the first piston is in the first position. During the time period t1 the flow rate is increased and thus the pressure increases causing the piston to move into the second position 68. In t2 the flow rate is reduced and the pressure drops. Before the first piston 28 reaches the first position, however, the flow rate is increased at the start of t3—this moves the piston to the intermediate position 70. The flow rate is again reduced and the pressure drops during t4. Before the first piston reaches the first position, the flow rate is again increased and the pressure rises during t5. This causes the first piston to move to the third position (t5), activating the tool.

[0253] Time periods t6 and t7 illustrate that the flow rate can be reduced and provided it is increased within the predetermined time period (2 minutes in the present example) ensuring that the first piston 28 does not reach the first position, the first piston will go back to the third position. In t6 the flow rate is reduced such that the first piston 28 leaves the third position and the tool is deactivated. However, the flow rate is increased before the first piston 28 reaches the first position and, as such, the first piston 28 moves back to the third position, reactivating the tool (t7).

[0254] In time period t8 the flow rate is reduced for longer than the predetermined time period such that the first piston 28 reaches the first position. Accordingly, when the flow rate is again increased in period t9, the first piston 28 moves to the second position and the tool fails to reactivate immediately, unlike in time period t7.

[0255] The graph of FIG. 14 also illustrates that there is a drop in the peak pressure of the fluid flowing through the tool when the first piston 28 is in the third position. This allows a user to easily and reliably confirm from the surface whether the tool is in an active or inactive position.

[0256] FIG. 15 illustrates an assembly of a follower 30 and an indexer 32 according to the disclosure.

[0257] The indexer 32 comprises is as described with reference to FIG. 10. The assembly includes a pair of needle roller bearing 88 and needle thrust bearing 90 on the inner circumferential surface and first end 62 of the indexer 32. The bearings 88, 90 allow the indexer 32 to rotate relative to the housing 24 or cylindrical support member 100 (see FIG. 16) on which it is mounted.

[0258] The indexer 32 comprises a plurality of sets of identical pathway profiles which repeat around the circumference of the indexer 32. In the present example there are six sets of identical pathway profiles repeated around the outer surface of the indexer 32.

[0259] The second end 64 of the indexer 32 comprises a castellated profile, as discussed above. The end profile of the second end 64 is configured to be complementary to, and engage, a corresponding profile on a surface of the follower 30 such that the axial load is transferred between the follower 30 and the indexer 32 via the castellated profile rather than the pin 38. Accordingly, a first set of surfaces of the second end 64 of the indexer 32 and of the follower 30 are arranged to abut when the first piston 28 is in a second position. A further set of surfaces of the second end 64 of the indexer 32 and of the follower 30 are arranged to abut when the first piston 28 is in an intermediate position. A further set of surfaces of the second end 64 of the indexer 32 and of the follower 30 are arranged to abut when the first piston 28 is in the third position.

[0260] The follower 30 is arranged to seal with a tubular member in which it is located, for example the housing 24. The follower comprises a sleeve section 94 which is arranged to surround the indexer 32 when the first piston 28 is in the third position. The follower 30 and indexer 32 are therefore arranged such that the indexer 32 can move into and out of the follower 30 as the first piston moves between the first, second and third positions.

[0261] The follower 30 comprises six pins 38 arranged around the internal circumference of the sleeve section 94 to engage the channels of the six sets of pathway profiles 74 of the indexer 32. The follower 32 comprises a wave spring 92 arranged to bias each pin 38 away from the follower 32, into the path/pathway profile 74 of the indexer 32.

[0262] The wave spring 92 biases the pin 38 towards the bottom of the corresponding path. This ensures that, if the pin 38 encounters a step 75 arranged in the pathway profile 74, it does not inadvertently traverse the step 75 due to a poor contact between the path and the pin 38. The wave spring 92 ensures the pin 38 is always in contact with the bottom of the path such that the step 75 efficiently prevents the pin 38 from entering the corresponding path.

[0263] As discussed previously, the pathway profile 74 comprises ramps in order to return the pin 38 to the ‘correct’ height after traversing a step 75, these are seen in FIG. 13A. This ensures a continuous pathway profile 74 can be provided.

[0264] The follower 30 and indexer 32 are arranged within a sealed chamber containing fluid. The follower 30 provides a seal with support 48 (shown in FIG. 3). The indexer 32 is axially fixed within the housing 24. As the follower 30 moves axially with the first piston 28, fluid within the chamber moves from one side of the follower 30 to the other. The follower 30 comprises a flow control valve 96 and a check valve 98 for defining a restricting to fluid flow in both directions. However, in other examples the check valve 98 may be omitted and the fluid may flow through just the control valve 96 in both directions. Alternatively, the control valve 96 and check valve 98 may be replaced with a high bulk modulus oil (e.g. silicone oil) flowing through a flow restriction defined by the follower 30.

[0265] The check valve 98 is configured such that, when the follower 30 is moving in a first direction (i.e. the first piston 28 is moving towards the second position and the second piston 34), the check valve 98 permits fluid flow therethrough. The check valve 98 is configured such that, when the follower 30 is moving in a second direction (i.e. the first piston 28 is moving towards the first position and away from the second piston 34), the check valve 98 restricts fluid flow therethrough. Accordingly, the overall restriction to fluid flow defined by the follower 30 is greater when the follower 30 (and hence first piston 28) is moving in a second direction (i.e. towards the first position and away from the second piston 34) than when the follower 30 is moving in the opposite direction.

[0266] The restriction to fluid flow determines the predetermined time period. That is, the restriction to fluid flow determines the speed at which the first piston 28 moves between the first, second and third positions. By increasing the restriction to fluid flow when the first piston 28 is moving towards the first position from the second, third or an intermediate position, the transition from the second/intermediate/third position to the first position lasts a longer time and it is easier for an operator to increase the flow rate to move the first piston on to the ‘next’ position, if required.

[0267] FIG. 16 illustrates the follower 30 and indexer 32 assembly of FIG. 15 mounted on a first piston 28 and cylindrical support member 100. In both FIG. 16 and FIG. 17, the first piston 28 is in the first position.

[0268] FIG. 17 is an enlarged view of a part of FIG. 2. FIG. 18 depicts detail E of FIG. 17. FIG. 19 depicts detail F of FIG. 17. In all of these figures, the first piston 28 is in the first position and, accordingly, the tool 10 is in a deactivated state with the cutter blades 22 in an inactive position. FIG. 20 depicts part of the tool 10 of FIG. 1, in an activated state.

[0269] The tool 10 is configured to be activated to extend cutter blades 22 radially out from the housing 24 to engage the side walls of a wellbore. As described above, the tool 10 is configured to allow a user to selectively increase and decrease the pressure in the activation chamber 38. The activation chamber 38 is fluidically connected to a pressure chamber 60 arranged within the housing 24. Axially-slidable wedges 58 are located adjacent or within the pressure chamber 60. As will be described below with reference to FIGS. 21A to 21B, the wedges 58 are biased in a second direction towards the second piston 34, which corresponds to an inactive position of the cutter blades 22.

[0270] When the second piston 34 is moved to the open position, the pressure in the activation chamber 38 and hence pressure chamber 60 increases. The pressure in the pressure chamber 60 creates a pressure differential across the wedges 58 which causes the wedges 58 to move axially within the housing 24 towards the first direction (to the right in FIGS. 17 to 20). As the wedges 58 move to the right, the angled surface 58a of the wedges engage the cutter blades 22—which also comprise an angled surface 22a—and force the cutter blades 22 radially outwards, thus entering an active position as shown in FIG. 20.

[0271] When flow through the tool 10 stops, the second piston 34 is moved to the closed position, the pressure in the activation chamber 38 drops and the pressure differential across the wedges 58 reduces. The biasing force is reasserted on the wedges 58 (as described below) and the wedges 58 move in the second direction. Without the wedges 58 holding the cutter blades 22 in an active position, the cutter blades 22 retract into the housing 24, either due to a biasing force provided within the tool or due to the forces inherent in the operation of the tool—e.g. the forces exerted onto the blades 22 by the wellbore.

[0272] FIGS. 21A to 21C depict a biasing assembly arranged to bias the wedges 58 in the second direction in a first, second and third configuration.

[0273] The biasing assembly is connected to the wedges by means of a connector 102, which it in turn connected to a rod 104.

[0274] The rod 104 is threaded through and engages a wedge-biasing spring 106, which is fixed at either end to first and second spring-pistons 108 110.

[0275] In FIG. 21A there is no fluid flowing through the tool 10. The wedge-biasing spring 106 biases the wedges 58 in the second direction by engaging a protrusion 114 on the rod 104 and urging the rod 104 and connector 102 to the left of FIG. 21A.

[0276] Whenever fluid flows though the tool, a port 116 in rod 104 allows high-pressure fluid to act on one side of the first spring-piston 108; the other side of the first spring-piston 108 is exposed to annulus pressure and, as such, the first spring-piston 108 compresses the wedge-biasing spring 106. This arrangement is shown in FIG. 21B. In this arrangement the wedge-biasing spring 106 no longer acts on the rod 104 and connector 102 (and hence the wedges 58) since the first spring-piston 108 no longer contacts the protrusion 114 on the rod 104. In this arrangement, wedges 58 are biased in the second direction by the pressure differential across the second spring-piston 110 caused by the fluid. The second spring-piston 110 is connected to the rod 104, which in turn is connected to the connector 102 and hence the wedges 58; as such, the wedges 58 are biased in the second direction by the fluid pressure.

[0277] FIG. 21C shows the biasing assembly when the first piston 28 is in the third position. When the first piston 28 enters the third position and the second piston 34 moves to an open position, the pressure in the activation chamber 34 and pressure chamber 60 (see FIG. 20) increases. The increase in pressure urges the wedges 58 in the first direction. This pressure force is larger than that of the second spring-piston 110 and, as such, the biasing force is overcome and the wedges 58 are urged in the first direction. The connector 102 and rod 104 move with the wedges 58 until the protrusion 114 of the rod abuts the first spring-piston 108 or the second spring-piston abuts the housing 24. When the second spring-piston abuts the housing 24, no, or a low, biasing force is applied to the wedges 58 by wedge-biasing spring 106 or a pressure gradient (as the right hand surface of the second spring-piston is not exposed to fluid flow).

[0278] FIGS. 22A to 25B illustrate a further tool 210 according to the disclosure. The tool 210 of FIGS. 22A to 25B is a near-bit reamer. The majority of the features of the tool 10 according to FIGS. 1 to 21C are replicated in the tool 210 of FIGS. 22A to 25B. Accordingly, discussion of the features and operation of this tool 210 is largely identical to that of the previous tool 10 and the discussion provided above applies, mutatis mutandis. Where corresponding components are included in both examples, the reference numerals used for the tool 210 of FIGS. 22A to 24B are equal to those of the tool 10 of FIGS. 1 to 21C advanced by 200. Given the similarity between the examples, detailed comments will not be provided on the tool 210 of FIGS. 22A to 25B.

[0279] As illustrated in FIGS. 22A to 22C, the tool 210 comprises a substantially cylindrical housing 224 which houses a first piston 228 and associated follower 230, an indexer 232 and a second piston 234. All of the description provided above for corresponding features of the previous example apply, mutatis mutandis, to the features of this example.

[0280] The tool 210 is configured to selectively actuate, thus moving a plurality of cutter blades 222 from an inactive to an inactive position. The tool 210 is further configured to selectively deactivate, thus moving the cutter blades 222 from an active position to an inactive position in which they are withdrawn into the housing 226.

[0281] In order to move the cutter blades 222 between an active and inactive position, the tool 210 is configured to selectively increase the pressure in an activation chamber 236 by means of moving the second piston between an open and closed position. When fluid pressure in the activation chamber 236 increases, the cutter blades 222 are urged outward, to an active position.

[0282] The first piston 228 is configured to move between a first, second and third position, relative to the housing. The first, second and third positions are defined by the indexer 232 which cooperates with a pin 238 of the follower 230, which in turn is fixed with respect to the first piston 228.

[0283] The first position corresponds to an inactive state of the tool 210, when no fluid is flowing through the tool 210. This arrangement is shown in FIGS. 22A and 23A. As can be seen, the first piston 228 is to the left of the figure. The second piston 234 is in a closed position. The second piston 234 is surrounded by a gate member 254 and, when the second piston 234 is in the closed position, the gate member 254 prevents or restricts fluid from flowing from the tool flow path 226 through a series of ports 252 arranged around the second piston 234.

[0284] When fluid flows through the tool flow path 226 of the tool 210, the first piston 228 moves to the second position under the action of a pressure differential across the piston to the position shown in FIGS. 22B, 23B and 24A. As can be seen from these figures, the first piston 228 has moved towards the second piston 234 to move from the first to the second position. However, the first piston 228 has not moved axially far enough to engage and move the second piston 234 to the open position. As such, the second piston 234 is still located in a closed position and, as such, the pressure in the activation chamber 236 is low and the cutter blades 222 are located in an inactive position.

[0285] FIGS. 22C, 23C and 24B depict the tool 210 in an activate state, with the cutter blades 222 in an active position (e.g. extended radially outwards from the housing).

[0286] The first piston 228 moves to the third position (that shown in FIGS. 22C, 23C and 24B) after a predetermined sequence of flow control operations have been undertaken. The required sequence of actions is determined by the indexer 230, as described above. Once these actions have been undertaken, the first piston 228 moves to the third position which, in turn, moves the second piston 234 to the open position. In the open position, ports 252 of the second piston 234 align with openings 255 in the gate member 254 such that the tool flow path 226 is fluidically connected to the activation chamber 236. Fluid flowing through the tool flow path can now enter the activation chamber 236 and the pressure in the activation chamber 236 increases. The activation chamber 236 is arranged to flow between a gap 312 formed between two opposing surfaces of the second piston 234 and gate member 254. Flow from the tool flow path 226 flows radially outwards through the ports 252, openings 255 and the gap 312 and into a pressure chamber 260 located radially inwards of the cutter blades 222. A pressure chamber 260 fluidically connected to, or formed as part of, the activation chamber 236 exerts a driving force on the blades 222, which are moved to an active position against the action of a blade spring 112 arranged to urge the cutter blades 222 to an inactive position.

[0287] When the flow through the tool 210 stops, the pressure gradient across the first piston 228 reduces and the first helical spring 244 urges the first piston 228 away from the second piston 228. The second helical spring 256 urges the second piston 234 in the second direction, closing the ports 252. The pressure thus drops in the activation chamber 236 and the blade spring 112 urges the cutter blades 222 to an inactive position.

[0288] FIGS. 25A and 25B show the tool in an inactive and active state, respectively, with the cutter blades 222 in an inactive and active position. FIGS. 25A and 25B show the distribution of high pressure fluid (shaded) in both the active and inactive arrangement. As can be seen, when the first piston 228 is in the third arrangement, high pressure fluid from the tool flow path has access to the activation chamber 236 and pressure chamber 260, thus urging the cutter blade 222 radially outwards to an active position.