Abstract
A drill bit for drilling a bore, the drill bit comprising: an outer housing; a primary cutting structure defining a cutting plane of a first diameter; a flow path arranged to let drilling fluid flow through the drill bit; and a deployable blade assembly at least partially located within the outer housing, the deployable blade assembly comprising a cutting structure and being arranged to be axially movable from a first position, in which the deployable cutting structure is recessed with respect to the primary cutting structure, towards the cutting plane, to a second position; wherein when the deployable blade assembly is in the second position, the deployable cutting structure defines a cutting diameter which is less than or equal to the first diameter.
Claims
1. A drill bit for drilling a bore, the drill bit comprising: an outer housing; a primary cutting structure defining a cutting plane of a first diameter; a flow path arranged to let drilling fluid flow through the drill bit; and a deployable blade assembly at least partially located within the outer housing, the deployable blade assembly comprising a deployable cutting structure and configured to be axially movable from a first position, in which the deployable cutting structure is recessed with respect to the primary cutting structure, towards the cutting plane, to a second position; wherein the deployable blade assembly is configured such that, when the deployable blade assembly is in the second position, the deployable cutting structure defines a cutting diameter which is less than or equal to the first diameter, further comprising: an actuation mechanism configured to cause the deployable blade assembly to move from the first position to the second position; wherein the actuation mechanism is a blocking assembly configured to move from a first arrangement, in which the flow path is open and fluid can flow through the flow path, to a second arrangement, in which the blocking assembly is arranged to restrict fluid flow through the flow path, in response to a change in the flow of drilling fluid through the drill bit; wherein the deployable blade assembly is configured to move from the first position to the second position under the action of fluid pressure in response to the blocking assembly moving to the second arrangement, wherein the blocking assembly comprises an occluding member and a restraint configured to hold the occluding member in the first arrangement and release the occluding member in response to the change in the flow of drilling fluid through the drill bit such that the occluding member can move from a non-occluding position in the first arrangement to an occluding position in the second arrangement in which the occluding member prevents fluid from flowing through the flow path.
2. The drill bit according to claim 1, wherein the change in the flow of drilling fluid through the drill bit increases a pressure differential across the blocking assembly to a threshold value.
3. The drill bit according to claim 1, wherein the change in the flow of drilling fluid through the drill bit is an increase in the drilling fluid flow rate.
4. The drill bit according to claim 1, further comprising a deformable release arranged between the outer housing and the deployable blade assembly; wherein a first part of the deformable release is fixed with respect to the outer housing and a second part of the deformable release is fixed with respect to the deployable blade assembly, restraining the deployable blade assembly in the first position; wherein the deformable release is configured to deform such that the deployable blade assembly can move with respect to the outer housing when a pressure differential across the deployable blade assembly reaches a deployment value.
5. The drill bit according to claim 4, wherein the deformable release is a threaded connector configured to break at a predetermined tensile load.
6. The drill bit according to claim 1, further comprising a lock arranged to hold the deployable blade assembly in the second position.
7. The drill bit according to claim 6, wherein the lock comprises: an engagement member in one of the outer housing and the deployable blade assembly, biased towards the other of the outer housing and the deployable blade assembly; and a recess arranged on the other of the outer housing and the deployable blade assembly, arranged to receive the engagement member when the deployable blade assembly is in the second position.
8. The drill bit according to claim 1, wherein the deployable blade assembly comprises: a piston located within the outer housing; and a blade connected to the piston.
9. The drill bit according to claim 8, wherein the piston and blade of the deployable blade assembly are arranged to move parallel to a longitudinal axis of the drill bit from the first position to the second position.
10. The drill bit according to claim 1, wherein the deployable cutting structure is level with, or extends out from, the primary cutting structure in an axial direction when the deployable blade assembly is in the second position.
11. The drill bit according to claim 1, wherein the occluding member is arranged to move parallel to the axis of the drill bit from the first arrangement to the second arrangement.
12. The drill bit according to claim 1, wherein the restraint comprises a breakable fastener.
13. The drill bit according to claim 12, wherein the restraint is a threaded connector configured to break at a predetermined tensile load.
14. The drill bit according to claim 1, wherein the occluding member is a rod.
15. The drill bit according to claim 1, wherein the restraint is configured to prevent the occluding member from escaping the outer housing.
16. A method of operating a drill bit, the method comprising: deploying the drill bit into a wellbore, the deployed drill bit comprising an outer housing, a primary cutting structure defining a cutting plane of a first diameter, a flow path arranged to let drilling fluid flow through the drill bit, a deployable blade assembly at least partially located within the outer housing and comprising a deployable cutting structure, and an actuation mechanism configured to cause the deployable blade assembly to move, towards the cutting plane, from a first position to a second position; operating the drill bit with the deployable blade assembly in the first position in which the deployable cutting structure is recessed with respect to the primary cutting structure to drill a bore with a first diameter; operating the actuation mechanism to cause the deployable blade assembly to move, towards the cutting plane, from the first position to the second position; wherein the actuation mechanism is a blocking assembly configured to move from a first arrangement, in which the flow path is open and fluid can flow through the flow path, to a second arrangement, in which the blocking assembly is arranged to restrict fluid flow through the flow path, in response to a change in the flow of drilling fluid through the drill bit; holding an occluding member of the blocking assembly by a restraint of the blocking assembly in the first arrangement; releasing the occluding member from the restraint in response to the change in the flow of drilling fluid through the drill bit such that the occluding member can move from a non-occluding position in the first arrangement to an occluding position in the second arrangement in which the occluding member prevents fluid from flowing through the flow path; moving the deployable blade assembly from the first position to the second position under the action of fluid pressure in response to the blocking assembly moving to the second arrangement; and operating the drill bit with the deployable blade assembly in the second position to drill a bore with a diameter equal to or less than the first diameter.
17. The method of claim 16, wherein the blocking assembly is disposed in the outer housing when the drill bit is deployed into the wellbore.
18. The method of claim 16, wherein the restraint is configured to prevent the occluding member from escaping the outer housing.
19. A whipstock milling system comprising: a whipstock; an anchor-packer; and the drill bit according to claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Examples of the present disclosure will now be described, purely by way of example, in the below figures, in which:
(2) FIG. 1 is a perspective view of a drill bit according to the disclosure in a first arrangement;
(3) FIG. 2 is a perspective view of the drill bit of FIG. 1 in a second arrangement;
(4) FIG. 3 is a cross-section of a drill bit according to the disclosure in a first arrangement;
(5) FIG. 4 is a cross-section of the drill bit of FIG. 3 in a second arrangement;
(6) FIG. 5 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(7) FIG. 6A is a cross-section of the drill bit of FIG. 5 in a second arrangement;
(8) FIG. 6B is a perspective view of the drill bit of FIG. 5 in a second arrangement;
(9) FIG. 7 is a further cross-section of the drill bit of FIG. 5 in a first arrangement;
(10) FIG. 8 is a further cross-section of the drill bit of FIG. 5 in a second arrangement;
(11) FIG. 9 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(12) FIG. 10 is a cross-section of the drill bit of FIG. 9 in a second arrangement;
(13) FIG. 11 is a further cross-section of the drill bit of FIG. 5 in a first arrangement;
(14) FIG. 12 is a further cross-section of the drill bit of FIG. 5 in a second arrangement;
(15) FIG. 13 is a cross-section of a lock pin in an unlocked arrangement;
(16) FIG. 14 is a cross-section of a lock pin in a locking arrangement;
(17) FIG. 15 is an end view of a drill bit according to the disclosure;
(18) FIGS. 16 and 17 are opposing end views of a component of a drill-bit according to the disclosure;
(19) FIGS. 18 and 19 are end views of drill bits according to the disclosure;
(20) FIG. 20 is a perspective view of a deployable blade assembly;
(21) FIG. 21 is a cross-section of a drill bit according to the disclosure;
(22) FIG. 22 is a perspective view of blades and nozzles;
(23) FIG. 23 is a cross-section of a drill bit according to the disclosure;
(24) FIGS. 24 and 25 are perspective views of blades;
(25) FIG. 26 is a perspective view of a piston;
(26) FIG. 27 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(27) FIG. 28 is a cross-section of the drill bit of FIG. 27 in a second arrangement;
(28) FIG. 29 is a further cross-section of the drill bit of FIG. 27 in a first arrangement;
(29) FIG. 30 is a further cross-section of the drill bit of FIG. 27 in a second arrangement;
(30) FIG. 31 is a further cross-section of the drill bit of FIG. 27 in a first arrangement;
(31) FIG. 32 is a further cross-section of the drill bit of FIG. 27 in a second arrangement;
(32) FIG. 33 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(33) FIGS. 34 and 35 are cross-sections of the drill bit of FIG. 33 in a second arrangement;
(34) FIG. 36 is a further cross-section of the drill bit of FIG. 33 in a first arrangement;
(35) FIG. 37 is a further cross-section of the drill bit of FIG. 33 in a second arrangement;
(36) FIG. 38 is a further cross-section of the drill bit of FIG. 33 in a first arrangement;
(37) FIG. 39 is a further cross-section of the drill bit of FIG. 33 in a second arrangement;
(38) FIGS. 40 and 41 are sleeves for use as a ratchet in a drill bit according to the disclosure;
(39) FIG. 42 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(40) FIG. 43 is a cross-section of the drill bit of FIG. 42 in a second arrangement;
(41) FIGS. 44 to 46 show a conventional whipstock milling system;
(42) FIGS. 47 to 49 are views of a whipstock milling system comprising a drill bit according to the disclosure;
(43) FIGS. 50 and 51 are end views of a drill bit according to the disclosure for use in a whipstock milling system;
(44) FIG. 52 is a perspective view of a drill bit according to the disclosure for use in a whipstock milling system in a second arrangement;
(45) FIG. 53 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(46) FIG. 54 is a cross-section of the drill bit of FIG. 53 in a second arrangement;
(47) FIG. 55 is a further cross-section of the drill bit of FIG. 53 in a first arrangement;
(48) FIG. 56 is a further cross-section of the drill bit of FIG. 53 in a second arrangement;
(49) FIG. 57 is a further cross-section of the drill bit of FIG. 53 in a first arrangement;
(50) FIG. 58 is a further cross-section of the drill bit of FIG. 53 in a second arrangement;
(51) FIG. 59 is a further cross-section of the drill bit of FIG. 53 in a first arrangement;
(52) FIG. 60 is a further cross-section of the drill bit of FIG. 53 in a second arrangement;
(53) FIG. 61 is a perspective view of a deployable blade assembly for use with the drill bit of FIG. 53;
(54) FIG. 62 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(55) FIG. 63 is a cross-section of the drill bit of FIG. 62 in a second arrangement;
(56) FIG. 64 is a cross-section of a further drill bit according to the disclosure in a first arrangement.
(57) FIG. 65 is a cross-section of the drill bit of FIG. 64 in a second arrangement;
(58) FIG. 66 is a further cross-section of the drill bit of FIG. 64 in a first arrangement;
(59) FIG. 67 is a further cross-section of the drill bit of FIG. 64 in a second arrangement;
(60) FIG. 68 is a cross-section of part of a blocking assembly;
(61) FIG. 69 is a cross-section of part of a further blocking assembly;
(62) FIG. 70 is a perspective view of a further drill bit according to the disclosure in a first arrangement;
(63) FIG. 71 is a perspective cross-section of the drill bit of FIG. 64 in a second arrangement;
(64) FIG. 72 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(65) FIG. 73 is a further cross-section of the drill bit of FIG. 72 in a first arrangement;
(66) FIG. 74 is a further cross-section of the drill bit of FIG. 72;
(67) FIG. 75 is a further cross-section of the drill bit of FIG. 72;
(68) FIG. 76 is a perspective view of a cross-section of the drill bit of FIG. 72;
(69) FIG. 77 is a further cross-section of the drill bit of FIG. 72 in a second arrangement;
(70) FIG. 78 is a further cross-section of the drill bit of FIG. 72 in a second arrangement;
(71) FIG. 79 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(72) FIG. 80 is a further cross-section of the drill bit of FIG. 78 in a second arrangement;
(73) FIG. 81 is a cross-section viewed along the axis of the drill bit of FIG. 78;
(74) FIG. 82 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(75) FIG. 83 is a further cross-section of the drill bit of FIG. 82 in a first arrangement;
(76) FIG. 84 is a further cross-section of the drill bit of FIG. 82;
(77) FIG. 85 is a further cross-section of the drill bit of FIG. 82;
(78) FIG. 86 is a further cross-section of the drill bit of FIG. 82 in a second arrangement;
(79) FIG. 87 is a further cross-section of the drill bit of FIG. 82 in a second arrangement;
(80) FIG. 88 is a perspective view of a part of the outer housing and blocking assembly in a first arrangement;
(81) FIG. 89 is a further perspective view of a part of the outer housing and blocking assembly in a second arrangement;
(82) FIG. 90 is a cross-section of a further drill bit according to the disclosure in a first arrangement;
(83) FIG. 91 is a further cross-section of the drill bit of FIG. 90;
(84) FIG. 92 is a further cross-section of the drill bit of FIG. 90 in a second arrangement;
(85) FIGS. 93A to 93C are rotationally-separated cross-sections through the drill bit of FIG. 90;
(86) FIGS. 94A to 94C are a first end view, perspective and second end view respectively of part of a blocking assembly for use in a drill bit; and
(87) FIGS. 95A to 95C are a first end view, perspective and second end view of a deployable blade assembly for use in a drill bit.
DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS
(88) In the following description, the same reference numerals will be used to refer to corresponding features in different embodiments according to the disclosure. The corresponding features need not be identical. Furthermore, it is to be understood that, unless it is explicitly stated to the contrary, features from a first embodiment of the disclosure can be combined with features of a second embodiment of the disclosure. This applies for drill bits of different diameters and different lengths—the features described as part of the present disclosure are applicable to drill bits of all sizes.
(89) Typically, the embodiments described below are either 215.9 mm (8.5 inch) drill bits or 311.15 mm (12.25 inch) drill bits. However, drill bits with diameters other than those above may be made according to this disclosure.
(90) The length of the 215.9 mm (8.5 inch) and 311.15 mm (12.25 inch) drill bits described with reference to FIGS. 1 to 43 are typically about 914.4 mm (36 inches). Using a drill bit of this length provides a highly steerable drill bit and thus drill string, as the short length of the drill bit allows tighter turning to be achieved.
(91) In a 311.15 mm (12.25 inch) drill bit for use as part of a whipstock milling system as described with reference to FIGS. 48 to 61, the length may be about 1676.4 mm (66 inches).
(92) FIG. 1 illustrates a drill bit 10. The drill bit 10 is suitable for attaching to the end of a drill string and being used to drill or mill through media located in a well bore. The drill bit 10 is substantially cylindrical and has a longitudinal axis 16 running along its central axis.
(93) In order to facilitate drilling, the drill bit 10 is configured to allow drilling fluid to flow through at least part of the drill bit 10 and to exit through ports located on the end face and/or the outer curved surface of the drill bit. The drill bit 10 therefore can be considered to have an upstream end 12 (top left in FIG. 1) and a downstream end 14 (bottom right in FIG. 1) and drilling fluid flows from the upstream end 12 towards the downstream end 14 along at least a portion of the length of the drill bit 10.
(94) A primary cutting structure 18 is located on the downstream axial end 14 of the drill bit and is used to drill or mill through material at the beginning of a drilling operation. The primary cutting structure 18 comprises a plurality of rows of cutting inserts 20 for cutting into material as the drill bit 10 is rotated. In the present drill bit, the cutting inserts 20A extend from the end surface of the drill bit 10 as well as from the curved side wall of the drill bit 10 in the vicinity of the downstream end 14. The primary cutting structure 18 therefore cuts a front face and the side walls of a bore.
(95) The drill bit 10 also has a plurality of deployable blades 22, each comprising a row of cutting inserts 20B. In FIG. 1, the deployable blades 22 are in a retracted position (i.e. a first arrangement) and the cutting inserts 20B on the deployable blades 22 do not extend from the primary cutting structure 18 and do not interfere with the material being cut by the drill bit 10.
(96) FIG. 2 shows the drill bit 10 of FIG. 1 in a second arrangement, in which the deployable blades 22 have moved towards the downstream end 14 of the drill bit 10 and are protruding from the primary cutting structure 18, forming a new, deployable, cutting structure. With the deployable blades 22 in the second arrangement, the cutting inserts 20B on the deployable blades 22 contact any material to be cut first and provide the main cutting function of the drill bit 10. Accordingly, the drill bit 10 is configured to provide two cutting structures, a first, primary cutting structure 18, and a second, deployable cutting structure, which can be selectively presented at the option of a user.
(97) The ability to effectively have a drill bit 10 with two cutting structures enables a drill bit 10 having different cutting characteristics with the deployable blades 22 in the second arrangement compared to the first arrangement and thus being geared towards cutting different materials, or cutting the same material with a different cut depth or bore profile. Alternatively, the cutting characteristics of the two cutting structures can be substantially the same and the deployable cutting structure can be engaged when the cutting inserts 20A of the primary cutting structure 18 are worn, in order to extend the service life of the drill bit 10.
(98) In order to provide different cutting characteristics, the cutting inserts 20A 20B on the primary cutting structure 18 and deployable blades 22, respectively, can be specifically selected to provide two different cutting functions. Thus the size, shape and material of the cutting inserts 20A 20B can be selected to be geared towards a specific use. Alternatively, the cutting inserts 20A 20B on the primary cutting structure 18 and deployable blades 22 can be the same type of cutting insert and the deployable blades 22 can be engaged and moved to the second arrangement when the cutting inserts 20A on the primary cutting structure 18 are worn, in order to extend the service life of the drill bit 10.
(99) Turning now to FIG. 3, a cross-section of a drill bit 10 in a first arrangement is shown. The drill bit 10 has an outer housing 24 substantially tubular in shape. The drill bit is a 215.9 mm (8.5 inch) drill bit. At the upstream end 12 of the drill bit 10, a drilling fluid inlet 26 can be seen. Drilling fluid—which flows down the drill string from the surface—enters the drill bit 10 through the drilling fluid inlet 26, flows through the outer housing 24 of the drill bit 10 and flows out through outlets 28 located downstream of the fluid inlet 26. In the drill bit 10 of FIG. 3, the outlets 28 are located on the end face of the downstream end 14 of the drill bit 10—that is, the outlets 28 are located in the primary cutting structure 18.
(100) After entering the drill bit 10 through the fluid inlet 26, the drilling fluid flows through a chamber 30 defined by the housing 25. At the end of the chamber 30 is a ball 32 located in a restraint. The restraint and ball 32 collectively form a blocking assembly, which is part of the actuation mechanism of the drill bit (discussed in more detail below).
(101) In the drill bit 10 of FIG. 3, the restraint is a support in the form of an annular ring 34 for supporting the ball 32. The inner diameter of the annular ring 34 is slightly smaller than the outer diameter of the ball 32. As such, the ball 32 is unable to pass through the annular ring 34 when the blocking assembly is in a first arrangement.
(102) The restraint and ball 32 are located in, and block off, a passage in the outer housing 24 through which drilling fluid could otherwise flow. Instead, the drilling fluid flows around the blocking assembly, through circumferentially-located nozzles 36. The restriction in the flow of the fluid around the ball 32 and annular ring 34 causes a pressure differential across the ball 32, which urges the ball 32 towards the annular ring 34 (i.e. in a downstream direction).
(103) After passing through the nozzles 36, the drilling fluid enters a deployable blade assembly 38 comprising a piston 40 and blades 22. The piston 40 is housed within the outer housing 24. The blades 22 are connected to the piston 40.
(104) A number of flow paths 42 44 are defined through the piston 40 which allow the drilling fluid to exit the drill bit 10 at the primary cutting structure 18 or through the outer housing 24, via nozzles 46 located in or adjacent the outlets 28.
(105) At a certain point during the drilling operation, a user may decide that they wish to use the deployable cutting structure—i.e. to move the blades 22 to a second position such that the second set of cutting inserts 20B are engaged.
(106) FIG. 4 shows the drill bit 10 of FIG. 3 in the second arrangement, with the deployable blade assembly 38 extended—having moved towards the downstream end of the drill bit 10 such that the end of the blades 22 and the cutting inserts 20B protrude out from the primary cutting structure 18 to form a deployable cutting structure.
(107) To move the drill bit 10 from the first arrangement to the second arrangement, a user increases the flow rate of drilling fluid through the drill bit 10. This increase in flow rate increases the pressure differential across the ball 32 to a threshold value. At the threshold value, the ball 32, the annular ring 34, or both deform sufficiently to let the ball 32 pass through the annular ring 34. At this point the blocking assembly moves from a first arrangement towards a second arrangement. This method of activation is very easy for a user to control. It is also robust and reliable, as fluid is constantly flowing through the drill string and it does not rely on a mechanical device deployed into the drill string (which can often get blocked on the way down) or an electrical connection (which can often be damaged due to the harsh environment in which such a device may be operating).
(108) In order to move the blocking assembly from the first to the second arrangement, for a 215.9 mm (8.5 inch) drill bit, the pressure drop across the blocking assembly may increase from about 689.5 kPa (100 psi) at a flow rate of 30.3 litres per second (400 gpm) to about 1550 kPa (225 psi) at a flow rate of 45.4 litres per second (600 gpm).
(109) Once the ball 32 has passed through the annular ring, the flow of drilling fluid through the drill bit 10 carries the ball 32 towards the downstream end 14 of the drill bit. The piston 40 comprises a tapered section comprising a seat 48 for holding the ball 32. Fluid flow through the piston 40 locates and holds the ball 32 in the seat 48. The seat 48 is arranged to be a constriction in, and thus form part of, one of the flow paths 44. It will typically take less than a second for the ball 32 to move from the first arrangement (supported by the annular ring 34) to the second arrangement (supported in the seat 48).
(110) When the ball 32 is located in the seat 48, one of the flow paths 44 through the piston 40 is blocked off by the ball 32, preventing drilling fluid from flowing therethrough; accordingly, the pressure differential across the piston 40 (and deployable blade assembly 38 as a whole) increases. The pressure differential across the piston 40 reaches a deployment value. When the pressure differential across the deployable blade assembly 38 reaches the deployment value, the deployable blade assembly 38 moves from a first position in which the cutting inserts 20B on the blades 22 are recessed with respect to the primary cutting structure 18, to a second position in which the cutting inserts 20B on the blades 22 protrude from the primary cutting structure 18, forming a deployable cutting structure. FIG. 4 shows the drill bit 10 in a second arrangement, with the deployable blade assembly 38 in a second position.
(111) In the 215.9 mm (8.5 inch) drill bit described, the deployable blade assembly 38 moves about 35 mm (1.375 inches) when moving from the first to the second position. However, other drill bits may move more or less than this amount.
(112) The cavity at the downstream end of the drill bit—located between the piston and the primary cutting structure—is allowed to fill with low pressure drilling fluid at all times. However, as the gaps around the blades are very small when the deployable blade assembly 38 is in the first position a lot of cuttings debris should not be able to get into these large cavities under the piston. When the deployable blade assembly 38 travels to the second position, a large gap will be created on the upstream ends of the blades (behind the piston) will allow the of ingress large debris, but this will not affect operation of the drill bit.
(113) The primary cutting structure 18 defines a bore with a first diameter. The deployable cutting structure defines a bore with the same diameter as the primary cutting structure 18. This is achieved by the deployable cutting assembly 38 (i.e. the deployable blades 22 and the cutting inserts 20B themselves) having a profile of the same diameter as the primary cutting structure 18 when viewed along the axis 16, and the deployable cutting assembly 38 (i.e. deployable blades 22) being arranged to only move parallel to the longitudinal axis 16 of the drill bit 10 when moving from the first to the second position.
(114) Providing two different cutting structures with the same bore diameter provides a number of benefits. Importantly, it provides continuity along the length of the hole. This simplifies later usage, as a change in bore diameter does not need to be considered when determining downhole components. Use of a constant bore diameter ensures that the drill bit itself can be easily extracted from the bore once drilling is complete. If a drill bit has a larger diameter in the second arrangement—i.e. the cutting inserts 20B on the blades 22 define a bore diameter which is larger than that of the primary cutting structure 18 when in the second position—it may be difficult to extract the drill bit from the completed bore as its final diameter will be larger than the diameter of the first section of the hole.
(115) In order to prevent leakages reducing the efficacy of the drill bit, a number of seals 50 are located between the outer housing 24 and internal components (e.g. the piston 40 and blocking assembly) to prevent drilling fluid from passing between components and thus reducing pressure differentials. Only one seal is used if all the flow nozzles are on the face of the primary cutting structure. Three seals are needed (as shown) if one or more nozzles are located on the outside diameter of the drill bit (as in this variant) which may have to be used if there is not enough space to locate enough flow ports on the face of a bit.
(116) FIGS. 5 and 6A illustrate a drill bit similar to that of FIGS. 3 and 4, except with the nozzles 46 of the deployable blade assembly 38 being located at a more downstream location—that is, the nozzles 46 are located much closer to the primary cutting structure 18 than in the drill bit of FIGS. 3 and 4. As with the drill bit of FIG. 3, the primary cutting structure 18 and deployable cutting structure define a bore with the same diameter.
(117) FIG. 6B is a perspective of the downstream end 14 of the drill bit in the second arrangement and the nozzles 46 can be seen, located between rows of cutting inserts 20A 20B, for ejecting drilling fluid straight into the drilling zone for facilitating cutting, in a known manner. A nozzle 46 can also be seen on the curved surface of the outer housing 24, which will be discussed further with reference to FIGS. 7 and 8.
(118) FIGS. 7 and 8 show the drill bit of FIGS. 5 and 6 rotated by approximately 45 degrees with respect to the view in FIGS. 5 and 6. FIGS. 7 and 8 show further details of the flow path 44 blocked by the ball 32 when the drill bit is in the second arrangement. This flow path 44 splits at a location downstream of the seat 48, but still within the piston 40, into two paths separated by 180 degrees. The two paths are located radially and nozzles 46 in the side wall of the outer housing 24 connect the paths to the outside and thus facilitate the radial ejection of drilling fluid. The nozzles 46 are fixed with respect to the outer housing 24.
(119) The number and location of outlets provided in a drill bit 10 can be selected to determine optimal use parameters. Reducing the number of available outlets may increase the pressure differential across the drill bit. Locating outlets upstream of the deployable blade assembly 38 may allow a higher drilling fluid input flow rate to be utilised while maintaining within certain pressure gradient parameters across the deployable blade assembly 38. Likewise, arranging a larger number of the available outlets to form part of the flow path 44 blocked by the ball 32 will maximise the increase in pressure differential across the deployable blade assembly 38 when the ball 32 moves into the second arrangement.
(120) Referring back to FIGS. 7 and 8, blades 22 can be seen located in slots of the outer housing, the slots being arranged axially to ensure the blades 22 extend axially, parallel to the longitudinal axis of the drill bit.
(121) FIGS. 7 and 8 also depict a guide pin 52 fixed with respect to the outer housing 24. The guide pin 52 extends from an internal face of the outer housing 24, into an elongated recess 54 located in the outer surface of the piston 40. The recess 54 is axially elongated, that is in a direction parallel to the longitudinal axis 16 of the drill bit. The guide pin 52 and recess 54 are arranged to help guide the piston 40 and hence the deployable blade assembly 38 as it moves from the first position to the second position. Accordingly, the elongated recess 54 has a length substantially equal to the distance between the first and second positions of the piston 40 and the guide pin 52 travels along the recess 54 from a downstream end elongated recess 54 to an upstream end of the elongated recess 54 as the piston moves from the first to the second position.
(122) FIGS. 7 and 8 also depict a shear pin 56, arranged to hold the piston 40 (and hence deployable blade assembly 38) in the first position. When the drill bit is in the first arrangement, the shear pin 56 is located in the outer housing 24 of the drill bit and extends into a receiving hole in the piston 40. Accordingly, the shear pin 56 spans the interface between the outer housing 24 and the deployable blade assembly 38 and holds the piston 40 and hence the deployable blade assembly 38 in the first position. As the flow rate of drilling fluid through the drill bit increases and the ball 32 moves through the annular ring 34 and into the seat 48 of the piston 40, the pressure differential across the piston 40 (and hence deployable blade assembly 38) increases which in turn increases the force exerted on the deployable blade assembly 38 by the drilling fluid, towards the downstream end of the drill bit. Initially, the shear pin 56 resists this movement and hence holds the piston 40 in the first position. However, when the pressure differential across the deployable blade assembly 38 reaches a deployment value, the shear pin 56 can no longer withstand the force exerted on it by the piston 40 and the shear pin 56 shears at the interface between the outer housing 24 and the piston 40. As the deployable blade assembly 38 is no longer held in the first position by the shear pin 56, the deployable blade assembly 38 moves to the second position. Accordingly, the breakage strength of the shear pin 56 determines the deployment value at which the deployable blade assembly 38 moves from the first to the second position. FIG. 8 illustrates the deployable blade assembly 38 in the second position, with the shear pin 56 broken in two parts—half in the outer housing 24 and half in the piston 40.
(123) FIGS. 9 and 10 illustrate a drill bit with an alternative arrangement for the flow path 44 which is blocked by the ball 32 when in the drill bit is in the second arrangement. The majority of the drill bit of FIGS. 9 and 10 is similar to that of FIG. 5; however, the flow path 44 which is blocked by the ball 32 when the drill bit is in the second arrangement is arranged to have an outlet in the downstream end of the drill bit—that is in the primary cutting structure 18. Such an arrangement may provide more flow out of the primary cutting structure 18 when the drill bit is in the first arrangement, as none of the flow is being directed out of the sides of the outer housing 24. The choice of where to output the drilling fluid flow may be made based on the desired cutting characteristics and environment of the specific drill bit and on the space available to locate nozzles within the passageways/flow paths of the bit face of the primary cutting structure.
(124) FIGS. 11 and 12 show the drill bit of FIGS. 5 and 6 rotated by approximately 90 degrees with respect to the view shown in FIGS. 7 and 8. Lock pins 58 are visible in FIGS. 11 and 12, for securing the piston 40 and hence holding the deployable blade assembly 38 in the second position. The lock pins 58 are located in the outer housing 24 of the drill bit and are biased inwardly—towards the centre of the drill bit. A spring 60 is located radially outwardly with respect to the lock pin and is held in place by a cap. Thus the spring 60 pushes the lock pin 58 towards the piston.
(125) Locking recesses 62 are located on the outer surface of the piston 40, arranged to receive the lock pins 58 when the deployable blade assembly 38 is in the second position.
(126) When the deployable blade assembly 38 is in the first position, the lock pins 58 abut the outer surface of the piston 40 and so are held in an outward location—entirely located within the outer housing 24. As the deployable blade assembly 38 moves from the first position to the second position, lock pins 58 slide along the outer surface of the piston 40 and, when the deployable blade assembly 38 reaches the second position and the locking recesses 62 are aligned with the lock pins 58, the lock pins 58 pop out of the inner surface of the outer housing to locate in the locking recesses 62 of the piston 40. Thus the lock pins 58 span the interface between the outer housing 24 and the piston 40 and therefore lock the piston 40 (and hence the deployable blade assembly 38) in position with respect to the outer housing 24. The lock pins 58 therefore act to hold the blades 22 and the cutting inserts 22B on the blades in position and to counter any drilling forces acting on the blades 22 which would otherwise force the deployable blade assembly 38 to move out of the second position towards the first position.
(127) FIGS. 13 and 14 show an alternative example of lock pin systems for use with any drill bit according to the disclosure in a locked and unlocked arrangement, respectively. The example of FIGS. 13 and 14 are located in holes through the outer housing 24 and comprise lock pins 58, biased by springs 60 out from the outer housing 24 towards the piston 40. The springs 60 are held in place by plugs 64 which are in turn held in place by circlips 66. A seal 68 surrounds the plug 64 and in combination with the circlip 66 prevents fluid and wellbore debris from entering or leaving the drill bit via these holes.
(128) FIGS. 15 and 16 show the downstream end 14 of a drill bit. FIG. 17 shows the internal bore of the body from the upstream end without other parts fitted.
(129) FIG. 15 shows an example arrangement of cutting inserts 20A of the primary cutting structure 18 and an example arrangement of blades 22 and cutting inserts 20B which form a deployable cutting structure. The cutting inserts 20A of the primary cutting structure can be seen to be arranged in 8 substantially radial rows with between 3 and 7 cutting inserts 20A being visible in each row. Nozzles 46 are arranged amongst the cutting inserts such that drilling fluid can be output onto the cutting structure during drilling. Blades 22 are arranged in between rows of fixed cutting inserts 20A. Each blade 22 comprises between 6 and 10 cutting inserts 20B visible from the view in FIG. 16. Three of the blades 22 comprises only a single row of cutting inserts 20B when viewed axially from the downstream end of the drill bit. One of the blades 22 is substantially L-shaped and comprises two rows of cutting inserts 20B when viewed axially from the downstream end of the drill bit. The two rows of cutting inserts are arranged substantially at 90 degrees to each other. The purpose of having such a blade 22 is to ensure that the deployable cutting structure has cutting inserts 20B provided across the entire diameter of the surface—i.e. to ensure that cutting inserts 20B are present to cut rock located substantially at the centre of the bore. The cutting inserts along one side of the L-shaped blade may be smaller than the cutting inserts along the other side of the L-shaped blade.
(130) In other embodiments (not illustrated) the deployable cutting structure may only have cutting inserts 20B located towards the outside of the drill bit face. That is, the deployable drilling structure may not provide cutting inserts 20B towards the centre of the drill bit face as shown in FIG. 15. This is because the cutting inserts 20A of the primary cutting structure located towards the outside of the drilling face (that is a larger distance from the axis 16) move much faster than those at the centre and thus wear down much quicker. Accordingly, the deployable cutting structure may be employed to replace the worn cutting inserts 20A located at large radiuses from the axis 16, rather than to provide an entirely new cutting surface.
(131) Each blade 22 comprises a key 70 in the form of an axial, semi-circular protrusion running along the length of one side of the blade 22. Each key 70 is located in a keyway formed in the housing. Each key 70 slides along its respective keyway, which ensures that each blade 22 can only move axially (i.e. parallel to the longitudinal axis of the drill bit) and not radially.
(132) In FIG. 15 the cutters 20B of the blades 22 are located behind the cutters 20A of the primary cutting structure with respect to a rotation/cutting direction. The drill bit will be rotating anti-clockwise as shown in FIG. 15 i.e. looking uphole, but clockwise looking downhole, as is normal. The cutters 20B of the deployable cutting structure are thus generally located behind corresponding cutters 20A of the primary cutting structure when viewed in terms of oncoming material to be cut. In other examples, the cutters 20B of the deployable cutting structure may be generally located behind corresponding cutters 20A of the primary cutting structure when viewed in terms of oncoming material to be cut. All blade cutter rows radiate to the centre of the bit and are designed as such if enough space is available. In the embodiment of FIG. 15, however, with 4 blades there is not enough room for the moveable blades to radiate to the centre axis (in this specific embodiment). The cutters 20B of the deployable cutting structure are generally radially-staggered compared to adjacent cutters 20A of the primary cutting structure. Furthermore, the cutters 20B of the deployable cutting structure may have an equal angular spacing.
(133) The external surface of the drill bit is hard faced in order to toughen exterior surfaces of the drill bit which may contact the formation or casing.
(134) FIG. 16 is an axial view in an upstream direction of part of the drill bit housing with the deployable blade assembly 38 removed. The profile of the slots for the blades 22 and the holes for the nozzles 46 are illustrated. FIG. 17 is a view of the component of FIG. 16 in the opposite direction (a downstream direction).
(135) FIGS. 18 and 19 depict alternative cutting structure arrangements, for example being suitable for different diameter drill bits. Similarly to with FIG. 15, FIGS. 18 and 19 depict the cutting insert 20A arrangement for the primary cutting structure 18 and the cutting inserts 20B on the blades 22 which form the deployable cutting structure. FIGS. 18 and 19 depict the cutting structures for drill bits with different diameters to that of FIG. 15. However, corresponding features are visible and corresponding comments apply.
(136) FIG. 20 shows a deployable blade assembly 38 for use with a drill bit. The deployable blade assembly 38 is located generally within the outer housing 24 of the drill bit and is arranged to move axially with respect to the outer housing, and hence drill bit.
(137) As described above, the deployable blade assembly 38 has a piston 40 to which four blades 22 are attached. Each blade 22 has a plurality of cutting inserts 20B located on its outer edge(s) and which form the cutting structure, or cutting structure, of the drill when the deployable blade assembly 38 is in the second position. The outer profile of the blades 22 and cutting inserts 20B determine the profile of the deployable cutting structure. As such, the shape of the blades 22 may vary depending on the material to be cut and the use for which the drill bit is designed.
(138) In between the blades 22 are four piston tubes 72 which connect the nozzles 46 for outputting drilling fluid to the respective flow paths 42. Also visible is the elongated recess 54 for receiving a guide pin 52 and a lock-pin receiving recess 62. Seals 50 are located in circumferential grooves on the piston in order to provide a seal between the piston 40 and the outer housing 24 to prevent drilling fluid leak. Also visible in FIG. 20 as part of the deployable blade assembly 38 is a serrated sleeve 74, for use in a ratchet locking system described in more detail below.
(139) FIG. 21 is a cross-section perpendicular to the longitudinal axis of the drill bit through the deployable blade assembly 38 and illustrates a pin 76 threaded through a hole near the base of each blade 22 to attach the blade to the piston 40. The hole projects to an outer surface of the housing 24 to provide access to the pins 76. FIG. 22 shows the arrangement of the blades 22, the pins 76 used to attach the blades and the tubes 72 which house the nozzles 46.
(140) FIG. 23 is a cross-section perpendicular to the longitudinal axis of the drill bit through the outer housing 24 and deployable blade assembly at the level of the outlets from the flow path 44 which is blocked by the ball 32, when in the deployable blade assembly 38 is in the second position. The flow path 44 and outlets blockable by the ball 32 can be seen to extend between the flow paths 42 which run axially within the drill bit 10 and have outlets on the cutting structure of the drill bit 10.
(141) FIGS. 24 and 25 are perspective views of a blade 22 for use with a drill bit.
(142) FIG. 26 is a perspective view of a piston 40 for use with a drill bit. The grooves, slots and holes for receiving the seals 50, blades 22 and tubes 72 are visible.
(143) FIGS. 27 to 32 show a further drill bit according to the present disclosure. The drill bit of FIGS. 27 to 32 is a 311.15 mm (12.25 inch) drill bit. The majority of the features of the drill bit of FIGS. 27 to 30 correspond to those of FIG. 5, albeit with slightly different dimensions and arrangements. As such, it should be assumed that features not explicitly described as being different to those of FIG. 5 operate in a corresponding manner to those of FIG. 5.
(144) With regard to the drill bit of FIG. 27, the blocking assembly and deployable blade assembly 38 operate in largely similar manners to those of FIG. 5. Drilling fluid enters the drill bit by means of drilling fluid inlet 26 and, when in the first arrangement, flows around the outside of the blocking assembly comprising a ball 32 and annular ring 34 using nozzles 36. The drilling fluid then flows through the piston 40 and out of the drill bit by means of the flow paths 42 44.
(145) When the flow rate increases a pressure gradient across the ball 32 reaches a threshold value and the ball 32 moves through the annular ring 34 and locates on the seat 48 in the piston 40, thus blocking off a flow path 44. This then causes an increase in pressure gradient across the deployable blade assembly 38 and, once the pressure differential reaches a deployment value, a shear pin 56 is broken (see FIGS. 29 and 30) and the deployable blade assembly 38 moves from the first to the second position causing the cutting inserts 20B on the edges of blades 22 to protrude from the primary cutting structure 18 and thus providing a second, deployable cutting structure. As with the drill bit of FIG. 5, a guide pin 52 assists in guiding the movement of the piston 40 and a pair of locking pins 58 engage locking recesses 62 in the piston 40 when the piston 40 is in the second position (see FIGS. 31 and 32).
(146) In order to move the blocking assembly from the first to the second arrangement, for a 311.15 mm (12.25 inch) drill bit, the pressure drop across the blocking assembly may increase from about 689.5 kPa (100 psi) at a flow rate of 54.6 litres per second (720 gpm) to about 1550 kPa (225 psi) at a flow rate of 81.8 litres per second (1080 gpm).
(147) In the 311.15 mm (12.25 inch) drill bit described, the deployable blade assembly 38 moves about 44.5 mm (1.75 inches). However, other drill bits may move more or less than this amount.
(148) The drill bit of FIG. 27 also comprises a split ratchet ring. The split ratchet ring is located between the outer housing and the deployable blade assembly 38, namely the piston 40. The split ratchet ring is configured to allow movement of the deployable blade assembly 38 towards the second position and prevent movement of the deployable blade assembly 38 away from the second position—that is the split ratchet ring is configured to only allow movement of the piston 40 towards the right in FIGS. 27 to 32.
(149) In the drill bit of FIG. 27, the ratchet ring sub-assembly comprises an inner 74 and outer serrated sleeve 78. The inner serrated sleeve 74 is fixed relative to the piston 40 with the serrations facing outwards. The outer serrated sleeve 78 is fixed relative to the outer housing 24 with the serrations facing inwards. The inner and outer serrated sleeves 74 78 are arranged such that the serrations engage when the piston 40 is located inside the outer housing 24. The inner ring has no split while the outer ring has to be split to allow it to expand when the inner ring moves downwards.
(150) In the drill bit of FIG. 27, the serrations have a first face at an oblique angle (e.g. about 45 degrees) to the longitudinal axis of the drill bit and a second face substantially perpendicular to the longitudinal axis of the drill bit. When the deployable blade assembly 38 is moving from the first position to the second position (that is, to the right in FIGS. 27 to 32), the angled surfaces of the two sleeves 74 78 engage and the inner sleeve 74 is able to slide relative to the outer sleeve 78. When the deployable blade assembly 38 is trying to move towards the first position from the second position (that is, to the left in FIGS. 27 to 32), the perpendicular faces (“straight faces”) of the two sleeves 74 78 abut and prevent movement of inner sleeve 74 relative to the outer sleeve 78 and hence prevent movement of the movably blade assembly 38 towards the first position.
(151) FIGS. 33 to 39 depict a drill bit similar to that of FIG. 27. A difference between the drill bit of FIGS. 33 to 39 and the drill bit of FIG. 27 is that the blocking assembly and the surrounding passageway arrangement is slightly modified—it can be seen that in the embodiment of FIG. 33, the ball 32 and annular ring 34 are housed in a defined central passageway, separated from the surrounding passageway(s) leading to the nozzles 36. Given that drilling fluid cannot pass through the annular ring 34 while the ball 32 is in the position shown in FIG. 33, there will be no flow of fluid in the length of passage 82 leading to the ball 32 and, as such, the ball 32 will feel a static fluid pressure. Only once the ball 32 has been released from the annular ring 34 will drilling fluid flow through the central passageway.
(152) FIGS. 40 and 41 illustrate the internal serrated sleeve 74 and external serrated sleeve 78, respectively. It can be seen that the external-facing serrations of the internal serrated sleeve 74 are arranged to engage the internal-facing serrations of the external serrated sleeve 78. On both the internal 74 and external 78 serrated sleeve the serrations are in the form of a row of equi-spaced grooves of a helix. The profile of the serrations can be seen in FIG. 40. The profile is a saw tooth with a flattened top section. The profile of the serrations may be the same in both the internal 74 and external serrated sleeve 78 (although reversed in order to engage). The external serrated sleeve 78 has an axial split in order to allow the external serrated sleeve 78 to radially expand and contract as required for installation purposes and to more easily allow it to ride over the serrations of the internal sleeve 74 when the deployable blade assembly 38 is moving from the first to the second position.
(153) FIGS. 42 and 43 illustrate a drill bit largely similar to that of FIG. 33. A difference between the drill bit of FIG. 42 and that of FIG. 33 is that the deployable blade assembly 38 is held in the first position by a shear ring 82 rather than a shear pin 56. The shear ring 82 is located between the outer housing 24 and the piston 40 of the deployable blade assembly 38. One part of the shear ring 82 is fixed with respect to the outer housing 24 and another part is attached to the piston 40 such that, as the pressure differential across the deployable blade assembly 38 increases and the deployable blade assembly 38 is urged to the right of FIG. 42, the force exerted on the shear ring 82 increases. When the force in the shear ring 82 reaches a certain value, the shear ring 82 breaks, releasing the piston 40 with respect to the outer housing 24. The shear ring 82 therefore defines a threshold pressure differential at which the deployable blade assembly 38 moves from the first to the second position, referred to herein as the deployment value.
(154) As a numerical example relating to the failure of the shear ring—when the ball 32 moves to the second arrangement and closes off one of the four flow paths through the piston, the pressure may jump up by 78% from about 4960 kPa to 8800 kPa (720 to 1280 psi). The failure pressure of the shear ring could be anywhere between 4960 kPa to 8800 kPa (720 to 1280 psi) but to give a good safety factor on the shear ring, about 6900 kPa (1000 psi) is chosen in this specific example. If the piston seal diameter is about 206 mm (8.125 inches), the piston area is about 0.033 m.sup.2 (51.85 sq. inches). The load to the shear ring will be about 23500 kg (1000 psi×51.85=51849 lbs). If the ultimate tensile strength of the shear ring is about 827400 kPa (120000 psi), the area of the breakable region needed is about 279 mm.sup.2 (0.432 sq inches). As the shear ring neck outer diameter is about 174 mm (6.85 inches), the inner diameter needed is about 173 mm (6.810 inches), to provide about a 0.5 mm (0.020 inch) wall section.
(155) FIGS. 44 to 46 depict a known whipstock milling system comprising a drill bit 90 connected to a whipstock 92 by means of a shear bolt 94. All but one of the drilling fluid outlets in the drill bit 90 are sealed by knock-off plugs 96. The one outlet that is not sealed by a knock-off plug 96 is connected to a hose 102, the far end of which is threaded through a hole in the whipstock 98 and connected to a top of anchor-packer 100 such that the flow of drilling fluid can be used to activate the anchor-packer 100 using drilling fluid at a pressure of up to about 20684 kPa (3000 psi). When the whipstock milling system reaches the desired depth in the well bore, drilling fluid is pumped through the drill string. The drilling fluid flows through the one fluid outlet which is not sealed by a knock-off plug, through the hose 102 and into the anchor packer 100. The high-pressure drilling fluid activates the anchor-packer 100 which anchors the whipstock milling system within the wellbore.
(156) Once the anchor-packer 100 sets the whipstock 92, upwards movement of the drill-string and so drill bit 90 causes the shear bolt 94 and the shearable connection between the hose 102 and the drill bit 90 to shear. The knock-off plugs 94 are knocked off once the drill bit 90 starts drilling operations.
(157) FIGS. 47 to 49 show a whipstock milling system according to the disclosure. The whipstock drilling system operates in a similar manner to the one described above. The whipstock milling system comprises a drill bit 110 connected to a whipstock 112 by a shearable bolt 120. A hose 114 extends from an outlet of the drill bit 110, through a hole in the whipstock 112 and connects to an anchor-packer 116 at the end of the whipstock 112. Knock-off plugs 118 seal the other outlets. Once drilling operations between, the knock-off plugs are knocked off from the outlets through interaction with the casing or rock face and drilling fluid flows therethrough.
(158) FIGS. 50 and 51 show an end face of the drill bit of a whipstock milling system before and after drilling operation has started. In FIG. 50 the knock-off plugs 118 are present. In FIG. 51, after drilling operations have begun, the knock-off plugs 118 have been knocked off and the outlets are open for drilling fluid flow.
(159) The drill bit for use with a whipstock milling system is largely similar to the other drill bits described above. As can be seen from FIGS. 50 to 60 (and subsequent figures), the drill bit comprises corresponding features to the drill bits described above and operates in an analogous manner. The dimensions and profile of the drill bit for use with a whipstock milling system may be different to that of the drill bits described above, for example the length of the drill bit for use with a whipstock milling system may be longer than that of the previously-described drill bits. The operation and functions carried out by equivalent parts in the drill bit for the whipstock milling system and the above-described drill bits are equivalent. Accordingly, only a brief description of the drill bit will be provided below. It is to be understood that any description made above in relation to features corresponding to those shown in the following figures, applies to the features shown in the following figures, where appropriate and adapted as appropriate.
(160) As can be seen in FIGS. 50 to 52, the drill bit comprises a primary cutting structure 18 comprising a plurality of rows of cutting inserts 20A. The drill bit also comprises blades 22 as part of a deployable blade assembly 38, each of which comprises a row of cutting inserts 20B which can form a deployable cutting structure. FIG. 52 illustrates the blades 22 protruding from the primary cutting structure to provide a deployable cutting structure.
(161) In a drill bit for use with a whipstock milling system, the cutting inserts 20A of the primary cutting structure 18 are made of a material which is suitable for drilling through steel casing located in a wellbore. The cutting inserts 20A in the primary cutting structure may therefore be tungsten carbide milling cutting inserts, for example. The cutting inserts 20B of the deployable cutting structure, attached to the blades 22, may be suitable for drilling formation. The cutting inserts 20B attached to the blades 22 may, therefore, be PDC cutting inserts, for example. This arrangement provides an advantageous system in which cutting inserts suited to the operation at hand are used at all times. Tungsten carbide cutting inserts—well suited to cutting through steel casing—can be used to mill a hole through the steel casing. Once a hole has been drilled through the steel casing, the drill bit can be activated such that the deployable blade assembly 38 moves to the second position and the deployable cutting structure is exposed. The deployable cutting structure utilises PDC cutting inserts and the drill bit is therefore now well suited to cutting through formation. The drill bit therefore has an element of adaptability. Once operations are complete, the drill string and drill bit can be drawn through the hole in the formation and steel casing, since the bores of the primary cutting structure 18 and deployable cutting structure are equal.
(162) As with the drill bits described above, the primary cutting structure 18 and the deployable cutting structure define a bore with the same diameter. Accordingly, the bore of the hole through the steel casing is the same as that through the formation behind it and the drill bit can easily be withdrawn through the formation and casing, back to the surface.
(163) FIGS. 53 to 60 are cross-sections of the drill bit. As with the drill bits described above, drilling fluid enters the drill bit by means of drilling fluid inlet 26 and, when the deployable blade assembly 38 is in the first position, the fluid flows around the outside of the blocking assembly comprising ball 32 and annular ring 34 using nozzles 36. The drilling fluid then flows through the piston 40 and out of the drill bit by means of the flow paths 42 44.
(164) When the flow rate increases a pressure gradient across the ball 32 reaches a threshold value and the ball 32 moves through the annular ring 34 and locates on the seat 48 in the piston 40, thus blocking off a flow path 44. This then causes an increase in pressure gradient across the deployable blade assembly 38 and, once the pressure differential reaches the deployment value, a shear pin 56 is broken (see FIGS. 57 and 58) and the deployable blade assembly 38 moves from the first to the second position causing the cutting inserts 20B on the edges of blades 22 to protrude from the primary cutting structure 18 and thus providing a second, deployable cutting structure. As with the drill bit of FIG. 5, a guide pin 52 assists in guiding the movement of the piston 40 and a pair of locking pins 58 engage locking recesses 62 in the piston 40 when the piston 40 is in the second position (see FIGS. 59 and 60).
(165) In a 311.15 mm (12.25 inch) drill bit for use with a whipstock milling system, the deployable blocking assembly moves about 187.3 mm (7.375 inches) from the first position to the second position.
(166) The drill bit of FIGS. 53 to 60 also comprises a ratchet ring sub-assembly. The ratchet ring sub-assembly is located between the outer housing and the deployable blade assembly 38, namely the piston 40. The ratchet ring sub-assembly is configured to allow movement of the deployable blade assembly 38 towards the second position and prevent movement of the deployable blade assembly 38 away from the second position—that is the ratchet is configured to only allow movement of the piston 40 towards the right in FIGS. 53 to 60.
(167) The ratchet ring sub-assembly comprises an inner 74 and outer serrated sleeve 78. The inner serrated sleeve 74 is fixed relative to the piston 40 with the serrations facing outwards. The outer serrated sleeve 78 is fixed relative to the outer housing 24 with the serrations facing inwards. The inner and outer serrated sleeves 74 78 are arranged such that the serrations engage when the piston 40 is located inside the outer housing 24.
(168) The serrations have a first face at an oblique angle (e.g. about 45 degrees) to the longitudinal axis of the drill bit and a second face substantially perpendicular to the longitudinal axis of the drill bit. When the deployable blade assembly 38 is moving from the first position to the second position (that is, to the right in FIGS. 53 to 60), the angled surfaces of the two sleeves 74 78 engage and the inner sleeve 74 is able to slide relative to the outer sleeve 78. When the deployable blade assembly 38 is trying to move in the direction of the first position from the second (that is, to the left in FIGS. 53 to 60), the perpendicular faces of the two sleeves 74 78 abut and prevent movement of inner sleeve 74 relative to the outer sleeve 78 and hence prevent movement of the movably blade assembly 38 towards the first position.
(169) FIG. 61 shows a deployable blade assembly 38 of the drill bit, showing the piston 40 and blades 22.
(170) Drill bits according to the disclosure may comprise blocking assemblies which vary from that described above. FIGS. 62 and 63 depict a drill bit with an outer housing 24, deployable blade assembly 39, ratchet ring sub-assembly and lock pin 58—among other features—as described above. However, the restraint of the blocking assembly comprises a hinged gate 122 and a shearable screw 124. When the blocking assembly is in a first arrangement, as shown in FIG. 62, the hinged gate 122 is in a closed position—preventing the ball 32 from passing through the central passageway 80. The hinged gate 122 is held in the closed position by a fastener, specifically a shearable screw 124, which is fixed with respect to both the hinged gate 122 and the outer housing 24.
(171) Shearable screw 124 is configured to shear when a certain force is applied to it. As such, as the flow rate through the drill bit increases, the pressure differential across the ball 32 and hinged gate 122 increases, creating a resultant force on the hinged gate 122 which is supported by the shearable screw 124. When the pressure gradient across the ball 32 and gate 122 reaches a threshold value, the shearable screw 124 fails, the hinged gate 122 opens, the ball 32 moves towards the piston and the blocking assembly moves to the second arrangement.
(172) Once the ball 32 is released, the drill bit operates in an analogous manner to the drill bits described above. The ball 32 locates in the seat 48 in the piston 40 and blocks off a flow path 44. This causes an increase in the pressure differential across the deployable blade assembly 38 and, when the pressure differential reaches a certain value—the deployment value—a shearable member (e.g. a shear pin) breaks and the deployable blade assembly moves to the second position, exposing the deployable cutting structure, as shown in FIG. 63.
(173) Example data for a 215.9 mm (8.5 inch) drill bit as described above is as follows. Ultimate load to break the shear pin holding the deployable blade assembly in the first position: diameter: about 20.5 mm (0.808 INS); area: about 329 mm.sup.2 (0.51 square inches); material: brass; ultimate shear strength: about 241320 kPa (35,000 psi); LOAD: about 8100 kg (17,850 LBS). Required pressure differential across the movable blade assembly to shear the shear pin holding the deployable blade assembly in the first position: bore diameter: about 142.9 mm (5.625 inches); piston area: about 0.016 m.sup.2 (24.9 SQ INS); pressure: about 4940 kPa (717 PSI).
(174) FIGS. 64 to 67 illustrate a further example of a blocking assembly. As before, features not forming part of the blocking assembly are as described above and comments made above relating to these features apply, where appropriate and adapted as appropriate. Similarly to the drill bit of FIG. 62, the blocking assembly of the drill bit of FIG. 64 includes a ball 32 and a gate 122 held in the first arrangement by shearable screw 124. The operation of the ball 32, gate 122 and shearable screw 124 is as previously described. Additionally, the blocking assembly of the drill bit of FIG. 64 also includes a latch 126 to hold the gate in the second arrangement once it has been released by the shearable screw 124. The latch 126 comprises an outer-housing mounted component 126A and a gate-mounted component 126B. When the gate is fully opened, the gate mounted component 126B is received by the outer housing mounted component 126A and retained, thus holding the gate 122 in the second position (i.e. open), as shown in FIGS. 65 and 67.
(175) FIGS. 68 and 69 illustrate different types of latch.
(176) In FIG. 68, the latch comprises a collet-catcher. The outer housing mounted component 128A comprises a catcher with a radially-inwardly protruding flange, arranged to receive and capture a radially-outwardly protruding flange on the gate mounted component 128B when the gate opens.
(177) In FIG. 69, the latch comprises a magnet. At least one of the outer housing mounted component 130A and the gate mounted component 130B comprises a magnet and the other of the outer housing mounted component 130A and the gate mounted component 130B comprises either a magnet or magnetic material. Accordingly, the magnetic attraction holds the gate mounted component in contact with the outer housing mounted component when the gate is open.
(178) FIGS. 70 and 71 illustrate a further example of a blocking assembly. As before, features not forming part of the blocking assembly are as described above and comments made above relating to these features apply, where appropriate and adapted as appropriate. In the drill bit of FIGS. 70 and 71, the blocking assembly comprises a ball 32 and a frangible screen 132. Frangible screen 132 is located in a central passageway through the drill bit, analogous to the location of the annular ring 34 in previous examples. The frangible ring 132 holds the ball 32 in the passageway 80 and prevents flow of drilling fluid therethrough. When the flow rate is increased and the pressure differential across the ball 32 and the frangible screen 132 increases to a threshold value, the axial force on the frangible screen 132 will cause it to break apart, releasing the ball 32 to move to the second position as in previous examples. The frangible screen 132 may be made from any material suitable for breaking apart when the pressure differential across the ball and frangible screen 132 reaches the threshold value. Suitable materials may include rubbers or plastic, for example PEEK. The frangible screen includes scores in order to encourage breakage.
(179) FIGS. 72 to 77 illustrate a further example of a drill bit. As before, the majority of features present in the drill bit of FIGS. 72 to 77 are equivalent to those in earlier-described embodiments and where a feature is not explicitly described below, it is to be assumed that the comments made above in relation to that feature apply, where appropriate and adapted as appropriate.
(180) In the drill bit of FIGS. 72 to 77, the blocking assembly comprises an occluding rod 133 and a deformable fastening—in this case a shearable screw 140. The occluding rod comprises a cylindrical body section 134 connected to a first support arm 136 and second support arm 137. The occluding rod extends substantially axially within the outer housing 24. The second support arm 137 is located on an upstream end of the cylindrical body 134 and is located in a drilling fluid passageway of the outer housing. The second support arm 137 provides a sliding engagement with a cylindrical section of the outer housing 24. A seal 142 is located between the occluding rod 133 and the cylindrical section defined by the outer housing 24 in order to prevent drilling fluid from passing between these components and reducing a pressure gradient.
(181) The first support arm 136 is located on the downstream end of the body section 134 and extends into the deployable blade assembly 38. The first support arm 136 provides a sliding engagement with a cylindrical section of the flow path (defined by the piston 40). As such, the occluding member is restricted to axial movement within the outer housing 24.
(182) A shoulder 138 is defined by a reduction in diameter of the occluding rod 133, between the cylindrical body section 134 and the first support arm 136
(183) The first support arm 136 is shaped such that, when the blocking assembly is in the first arrangement, fluid can flow around the occluding rod 133 and through all of the flow paths 42 44.
(184) Turning now to FIG. 73, a tab protrudes from the side of the cylindrical body section 134 of the occluding rod 133. When the occluding rod 133 is in the first arrangement (i.e. a non-occluding position), a shearable screw 140 extends through the tab and into a part of the outer housing 24, holding the occluding rod 133 in position. When the flow rate through the drill bit is increased and the pressure drop across the occluding rod 134 increases to a threshold value, the axial force exerted on the sharable screw 140 will cause it to fail and break, releasing the occluding rod 133 to move to the second arrangement—that is an occluding position. As the occluding rod 133 is restricted to axial movement within the outer housing 24 and the shearable screw 140 connects directly to the occluding rod 133 and the outer housing, all of the force exerted on the occluding rod 133 is transferred through the shearable screw 140. As such, the increase in tensile force exerted on the screw for a given increase in drilling fluid flow rate is larger in the drill bit of FIG. 72 than for an equivalent increase in flow rate in a drill bit as described with reference to FIG. 62.
(185) Once the shearable screw 140 breaks, as illustrated in FIGS. 74 and 75, the occluding rod 133 moves axially within the outer housing 24 towards the deployable blade assembly 38, as in previous examples, until the occluding rod 133 abuts the piston 40. In the present embodiment, the shoulder 138 of the occluding rod abuts a seat defined by a tapered section of the flow path 44 (defined by the piston 40) and seals off that flow path 44. Once the flow path 44 is closed off, the pressure gradient across the deployable blade assembly 38 increases until a deployment value is reached, at which point the shear ring 82 fails and breaks, releasing the deployable blade assembly 38, which moves under the action of the drilling fluid into the second position, as shown in FIGS. 77 and 78.
(186) FIG. 76 illustrates the upstream end of the occluding rod 133, with the second support arm 137 slidably engaged with a drilling fluid passageway of the outer housing. In FIG. 76, the occluding rod 133 has moved from the first arrangement to engage the deployable blade assembly 38, but the deployable blade assembly 38 has not yet moved from the first to the second position. As such, FIG. 76 corresponds to the drill bit arrangement of FIGS. 74 and 75. The drilling fluid passageway in which the second support arm 137 is located comprises a cylindrical section along the axis of the drill bit with a plug member 148 supporting a nozzle 146. The nozzle 146 helps control the pressure felt by the upstream end of the occluding rod 133. A ring-shaped section around the circumference of the cylindrical section comprises a series of further nozzles which allow fluid to bypass the blocking assembly. These further nozzles ensure that drilling fluid can flow from the inlet to the outlet(s) of the drill bit when the drill bit is operating in a first arrangement.
(187) FIGS. 79 to 81 illustrate a further example of a drill bit. As before, the majority of features present in the drill bit of FIGS. 78 to 80 are equivalent to those in earlier-described embodiments and where a feature is not explicitly described below, it is to be assumed that the comments made above in relation to that feature apply, where appropriate and adapted as appropriate.
(188) In the drill bit of FIGS. 79 to 81, the occluding rod 133 has a different shape, with the cylindrical body section 134 having a smaller diameter and the shoulder 138 being formed by a radial flange protruding from the occluding rod 133 between the body section 133 and the first support arm 136.
(189) Additionally, the flow path(s) 44 through which flow is restricted by the occluding rod 133 are arranged to extend radially out from the axis of the drill bit, through the curved side wall of the outer housing 24 via nozzles 144. Flow paths 42 which are not blocked by the occluding rod 133 extend axially and have outlets in the primary cutting structure—that is an axial end face of the drill bit. The inclusion of flow paths which with outlets in the curved side wall of the drill bit—i.e. outlets which are arranged remote from the primary and/or deployable cutting structure—allows a higher total number of flow paths to be implemented in the design. Higher drilling fluid flow rates can be used when flow paths with outlets remote from a drilling structure are present.
(190) FIGS. 79 and 80 illustrate the drill bit in a first and second arrangement, respectively.
(191) FIG. 81 is a view of a cross-section in a plane perpendicular to the axis of the drill bit through the flow paths 44 through which flow may be restricted by the occluding rod 133 (“blockable flow paths”). The flow paths 42 through which flow cannot be restricted by the occluding rod 133 (“open flow paths”) can be seen extending axially within the drill bit (out of the plane of the page). Three “blockable flow paths” 44 are arranged at evenly spaced intervals of 120 degrees around the circumference of the drill bit. The flow paths 44 extend from a central flow path region radially out to the curved side wall of the piston 40. Nozzles 144 are located in the flow paths 44 within the side walls of the housing 24. The nozzles 144 allow a pressure drop between the flow paths 44 and the wellbore to be controlled.
(192) FIGS. 82 to 89 illustrate a further example of a drill bit. As before, the majority of features present in the drill bit of FIGS. 72 to 77 are equivalent to those in earlier-described embodiments and where a feature is not explicitly described below, it is to be assumed that the comments made above in relation to that feature apply, where appropriate and adapted as appropriate.
(193) The blocking assembly of the drill bit of FIGS. 82 to 89 comprises a ball 32, a gate 150, a fastener in the form of a shearable screw 154 and a guide 152.
(194) As in embodiments described above, when in a first arrangement, the gate 150 is located in a fluid passageway in the outer housing and is arranged to prevent fluid flow through this passageway. The gate 150 comprises a seal 156 in this regard in order to prevent fluid from passing between the gate 150 and the passageway wall. The ball 32 is located on the upstream side of the gate 150 and is prevented from moving downstream, towards the deployable blade assembly by the gate 150.
(195) The gate 150 is in sliding engagement with the guide 152, which comprises two axially-aligned rods protruding from the outer housing (only one of which is shown in FIGS. 82 to 87). A head on the end of each rod prevents the gate 150 disengaging the guide 152.
(196) When in the first arrangement, as illustrated in FIGS. 82 and 83, the gate 150 is held in the passageway (i.e. in a first position) by the shearable screw, which extends through a part of the gate 150 and into the surrounding housing/passageway.
(197) As the flow through the drill bit increases, the pressure differential across the ball 32 and gate 150 increases and the ball 32 and gate 150 exert a force on the shearable screw 154 in the direction of the deployable blade assembly 38.
(198) When the pressure gradient across the ball 32 and gate 150 reaches a threshold value, the shearable screw breaks such that the gate 150 is no longer held in the first arrangement. The gate 150 moves in a downstream direction under the action of drilling fluid flowing through the drill bit. The guide 152 guides the gate 150 such that the gate 150 moves axially within the drill bit and is held once the gate 150 engages the heads on the end of each guide 152.
(199) The upstream side of the gate 150 (the one which is in contact with the ball 32 when in the first arrangement) has a convex surface. As such, once the gate 150 moves out of the passageway, the drilling fluid carries the ball 32 around the gate 150 and moves the ball into an occluding arrangement in the seat of the deployable blade assembly 38 as described in previous embodiments. FIGS. 84 and 85 illustrate the drill bit once the gate 150 and ball 32 have moved from the first arrangement; the ball 32 is in an occluding position, but the deployable blade assembly 38 has not yet moved from the first position.
(200) As with previous embodiments, once the ball 32 is located in an occluding arrangement—restricting flow through a flow path 44 through the deployable blade assembly—the pressure differential across the deployable blade assembly 38 increases until a deployment value is reached, at which point the shear ring 82 fails and the deployable blade assembly 38 moves towards the second position. FIGS. 86 and 87 show the drill bit in the second arrangement with the blades 22 in a deployed position.
(201) FIGS. 88 and 89 show the blocking assembly in a first and second arrangement respectively. In the first arrangement, in FIG. 88, the gate 150 is located snugly in the passageway such that the ball 32 is prevented from passing. The shearable screw 154 is intact and is holding the gate 150 in the passageway against the force created by the pressure gradient. Other passageways through the housing can be seen circumferentially surrounding the gate 150, through which the drilling fluid may flow when the drill bit is operating in a first arrangement. The guide 152 comprising two cantilevered rods can be seen on either side of the gate 150.
(202) FIG. 89 shows the blocking assembly in a second arrangement. In FIG. 89, the threshold pressure gradient has been reached and the shearable screw has failed and thus has sheared at a location between when it is attached to the gate 150 and fixed relative to the outer housing 24. The gate 150 is therefore free to move under the action of the drilling fluid, although its movement is restricted by the guide 152, which only permits axial movement. The gate 150 therefore travels along the guide from the first to a second position, at which point it abuts the heads on the guide rods. The gate 150 is held in this position by the flow of the drilling fluid. Once the gate 150 has left the central passageway, the ball 32 moves out and around the gate 150 and eventually locates in the piston 40 of the deployable blade assembly 38, as described above.
(203) FIGS. 90 to 93C illustrate a further example of a drill bit. As before, the majority of features present in the drill bit of FIGS. 90 to 93C are equivalent to those in earlier-described embodiments and where a feature is not explicitly described below, it is to be assumed that the comments made above in relation to that feature apply where appropriate and adapted as appropriate.
(204) FIG. 90 shows the drill bit with the deployable blade assembly in a first position, the drill blades 222 in a retracted position and the blocking assembly in a first arrangement (i.e. a non-blocking arrangement). FIG. 91 shows the drill bit once the blocking assembly has moved into a second arrangement (a blocking arrangement) with the deployable blade assembly still in the first position. FIG. 92 shows the drill bit once the deployable blade assembly has moved to a second position and the drill blades 222 are deployed.
(205) FIGS. 95A to 95C illustrate a deployable blade assembly suitable for use in the drill bit of FIGS. 90 to 93C. The deployable blade assembly comprises a piston 240, which can be located within the outer housing 224 of the drill bit. The piston 240 defines a plurality of flow paths therethrough. A plurality of nozzles 201 extend from the respective flow paths. The nozzles 201 are arranged to control the flow of drilling fluid out the face of the drill bit. The deployable blade assembly further comprises a plurality of blades 222 connected to the piston 240 and arranged to be extendable from the drill bit.
(206) Turning now to FIGS. 90 and 91, it can be seen that the deployable blade assembly—and in particular the piston 240—is held in a first position by a deformable release which, in the drill bit of FIGS. 90 to 93C, is a shearable screw 203—i.e. a screw configured to break when a predetermined tension load is experienced. As seen in FIG. 92, one part of the blocking assembly shearable screw 203a (e.g. the head) is fixed with respect to the outer housing 224—for example by being threaded through a support cylinder 205 which is fixed with respect to the outer housing 224. The other part 203b (e.g. the end) is fixed with respect to the piston 240—for example by screwingly engaging the piston 240.
(207) The support cylinder 205 (as shown in FIGS. 90 to 93C and in more detail in FIGS. 94A to 94C) is arranged to be fixed with respect to the outer housing 224. A plurality of axial ports 211 are arranged to allow fluid to pass from an upstream side of the support cylinder 205 and occluding member 233, to a downstream side, adjacent the deployable blade assembly piston 240, such that the fluid can pass through the flow paths arranged therein.
(208) The blocking assembly of this drill bit comprises an occluding member 233 in the form of a rod and a restraint—in this case a shearable screw 207. The occluding member 233 extends substantially axially within the outer housing 224. Part of the occluding member 233 is arranged within the support cylinder 205. A further part of the occluding member 233 is arranged within the piston 240 of the deployable blade assembly. The occluding member 233 is arranged to move axially with respect to both the support cylinder 233 and the piston 240 of the deployable blade assembly.
(209) As can be seen in FIG. 90, the blocking assembly shearable screw 207 (which may alternatively be replaced with any deformable or breakable fastening) is arranged to hold the occluding member 233 in a first arrangement. Once the blocking assembly shearable screw 207 has broken, the occluding member 233 is free to move axially under the action of fluid pressure and flow.
(210) In the drill bit of FIGS. 90 to 93C, the occluding member 233 comprises a shoulder 238 in the form of a radial protrusion. As is illustrated in FIG. 91, the shoulder 238 is configured such that it can block at least one of the plurality of flow paths 244 through the piston 240 when the blocking assembly moves to the second arrangement.
(211) In this example, a guide cylinder 209 is arranged concentrically within and fixed with respect to the support cylinder 205. The guide cylinder 209 is fixed relative to the outer housing 224. The guide cylinder 209 comprises an abutment 213 which is arranged to restrict the axial movement of the occluding member 233. As can be seen in FIG. 92, when the deployable blade assembly has moved to the second position, the abutment 213 is arranged to engage the occluding member 233 and prevent it from moving with the deployable blade assembly.
(212) In use, the drill bit will typically initially operate in a first arrangement as shown in FIG. 90. In this arrangement the deployable blade assembly is in a first position and the drill blades 222 are retracted within the outer housing 224. Drilling fluid may flow from the surface, through the ports 211 in the support cylinder 205, through the flow paths defined by the deployable blade assembly piston 240 and out of the face of the drill bit. Initially, the occluding member 233 is held in the first arrangement by the shearable screw 207.
(213) When it is desired to deploy the drill blades 222, the operator may increase the flow rate of drilling fluid through the drill bit. As the support cylinder 205 defines a restriction to the flow of drilling fluid, the increase in flow rate will increase the pressure gradient across the support cylinder 205. The pressure differential across the occluding member 233, which is arranged in parallel with the support cylinder 205, will also increase. The pressure gradient across the occluding member 233 imparts an axial force on the occluding member 233 in a downstream direction (i.e. to the right of FIGS. 90 to 93C). Once the pressure differential across the occluding member reaches a threshold value, the shearable screw 207 breaks, releasing the occluding member 233.
(214) Once the shearable screw 207 has broken the occluding member 233 is axially moved under the action of fluid pressure from a first arrangement towards a second arrangement. The occluding member 233 moves towards the deployable blade assembly (to the right in FIGS. 90 to 93C). The occluding member 233 moves to the second arrangement and, when in the second arrangement, the occluding member shoulder 238 abuts a seat defined by the piston 240 around the entry to at least one of the flow paths 244 through the piston 240. This is shown in FIG. 91.
(215) When the occluding member 233 is in the second arrangement it restricts fluid flow through the piston 240 of the deployable blade assembly (by blocking entry to at least one of the flow paths 244). This causes a sudden increase in the pressure gradient across the piston 240 and the deployable blade assembly as a whole.
(216) The increase in the pressure gradient across the piston 240 urges the deployable blade assembly from the first to the second position, against the action of the deployable blade assembly shearable screw 203. When the pressure differential across the deployable blade assembly reaches a threshold value referred to herein as the deployment value, the deployable blade assembly shearable screw 203 breaks, releasing the deployable blade assembly. The deployable blade assembly moves from the first position to the second position, deploying the drill blades 222 out of the front of the drill bit, as shown in FIG. 92.
(217) FIG. 92 shows the drill bit after the shearable screw 203 has broken and the deployable blade assembly has moved to the second position, deploying the drill blades. It can be seen that the abutment 213 of the guide cylinder 209 prevents the occluding member 233 from following the piston 240 and, as such, the flow paths 244 which were momentarily closed by the occluding member 233 are again open for drilling fluid to flow therethrough once the piston 240 has moved to the second position.
(218) FIGS. 93A to 93C are cross-sections through the axis of the drill bit at three different angular rotations, thus showing different features of the support cylinder 205 and piston 240.
(219) As in previous drill bits described herein, a plurality of lock pins 258 may be provided in the housing 224 around the circumference of the piston 240 and biased radially inwards towards the piston 240. These lock pins 258 are arranged to lock the piston 240—and hence deployable blade assembly—in the second (deployed) position by extending into recesses in the piston 240 when the deployable blade assembly enters the second position.
(220) As will be understood by the reader, a plurality of seals are employed throughout the drill bit in order to prevent fluid leakage and to ensure proper operation of the moving components.
(221) The disclosure set out above presents exemplary embodiments of the present invention, the invention being defined by the claims appended hereto below. Modifications from the disclosed exemplary embodiments may be made and fall within the scope of the claims. Furthermore, it is to be understood that the invention is in no way to be limited to the combination of features shown in the examples set out above. Features disclosed in relation to one example can be combined with features disclosed in relation to a further example.
