Mill-drill cutter and drill bit

Abstract

A mill-drill cutter for an earth boring bit includes a cutting structure secured to a substrate. The cutting structure has a drilling edge, and the substrate has a milling edge. The substrate is configured to be received in a cutter pocket of the earth boring bit. The drilling edge of the cutting structure is disposed radially internal to the milling edge of the substrate.

Claims

1. A cutter for an earth boring bit, comprising: a cutting structure having a drilling edge and made from a superabrasive material; and a substrate secured to the cutting structure, made from a softer material than the superabrasive material, and having a milling edge, the softer material of the substrate configured to be received by a cutter pocket of the earth boring bit, the drilling edge of the cutting structure disposed radially internal to the milling edge of the substrate, wherein: the substrate is delimited on an end adjacent to the milling edge by a flat face, the cutting structure is secured to the flat face, a portion of the flat face extending outward of the cutting structure is an exposed milling surface, the milling edge and surface are operable to engage with a casing or associated component thereof, and the milling edge is operable to create a clearance distance between the casing or associated component thereof and the cutting structure while the milling edge and surface mill therethrough, and the milling edge, the flat face, and the milling surface are also made from the softer material.

2. The cutter of claim 1 wherein softer material is tungsten carbide.

3. The cutter of claim 2 wherein the superabrasive material is polycrystalline diamond compact and the cutting structure comprises a diamond table layer.

4. The cutter of claim 3 wherein the drilling edge is disposed at a perimeter of the diamond table layer.

5. The cutter of claim 2 wherein the superabrasive material is cubic boron nitride.

6. The bit of claim 2, wherein the tungsten carbide is low cobalt type machining grade with cobalt in the 3% to 10% range.

7. The cutter of claim 1 wherein the cutting structure is disposed coaxial with the substrate.

8. The cutter of claim 1 wherein: the flat face is circular, and the milling edge is disposed at a perimeter of the milling surface.

9. The cutter of claim 1 wherein the cutter is axisymmetric.

10. The cutter of claim 1 wherein the substrate comprises a rounded rear surface configured to be received by the cutter pocket.

11. The cutter of claim 1 wherein the substrate comprises a flat, circular surface configured to be received by the cutter pocket.

12. The cutter of claim 1 wherein the cutting structure is long substrate bonded to the substrate.

13. The bit of claim 1, wherein: the milling edge and face are part of a cylindrical enlarged diameter portion of the substrate, and the diameter of the enlarged diameter portion is 10%-50% larger than a diameter of the cutting structure.

14. The bit of claim 1, wherein the cutting structure is brazed to the substrate.

15. An earth boring bit, comprising: a plurality of blades, each blade having a plurality of cutter pockets; and the cutter of claim 1 secured within each cutter pocket.

16. The bit of claim 15 wherein each substrate defines an annular portion extending beyond the respective cutting structure, the annular portion secured within a recess of the respective cutter pocket.

17. The bit of claim 15 wherein each cutter is disposed at a rake angle of 5°-25° and a lesser rake angle corresponds to a greater clearance distance.

18. A method of drilling a wellbore, comprising: deploying a mill-drill bit into a wellbore, the mill-drill bit comprising a plurality of blades and a plurality cutters disposed in pockets of the blades, each cutter comprising: a cutting structure having a drilling edge and made from a superabrasive material; and a substrate secured to the cutting structure, made from a softer material than the superabrasive material, and having a milling edge, the softer material of the substrate configured to be received by a cutter pocket of the earth boring bit, the drilling edge of the cutting structure disposed radially internal to the milling edge of the substrate, wherein: the substrate is delimited on an end adjacent to the milling edge by a flat face, the cutting structure is secured to the flat face, a portion of the flat face extending outward of the cutting structure is an exposed milling surface, and the milling edge, the flat face, and the milling surface are also made from the softer material; milling through a casing or associated component thereof using the mill-drill bit, wherein: the milling edges and surfaces engage with the casing or associated component thereof, and engagement of the milling edges with the casing or associated component thereof creates a clearance distance between the casing or associated component thereof and the cutting structure; and after milling, drilling through an earth formation with the mill-drill bit, wherein the milling edges are abraded by the formation, thereby resulting in contact of the drilling edges with the formation.

19. The method of claim 18, wherein the softer material is tungsten carbide and the superabrasive material is polycrystalline diamond compact or cubic boron nitride.

20. The method of claim 19, wherein the tungsten carbide is low cobalt type machining grade with cobalt in the 3% to 10% range.

21. The method of claim 18, wherein: each milling edge and face are part of a cylindrical enlarged diameter portion of the respective substrate, and each diameter of the enlarged diameter portion is 10%-50% larger than a diameter of the respective cutting structure.

22. The method of claim 18, wherein each cutting structure is brazed to the respective substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which:

(2) FIG. 1 illustrates a perspective view of a mill-drill bit according to the teachings of the present disclosure;

(3) FIGS. 2A and 2B are cross-sections of a mill-drill cutter in a milling and a drilling operation, respectively;

(4) FIG. 3 illustrates a mill-drill cutter exploded from a cutter pocket;

(5) FIG. 4 illustrates an alternate embodiment of a mill-drill cutter exploded from a cutter pocket; and

(6) FIGS. 5A-5D illustrate different rake angles that may be employed with the mill-drill cutter according to the teachings of the present disclosure.

DETAILED DESCRIPTION

(7) A cutter for a drill bit according to the present disclosure includes a cutting element with combined polycrystalline diamond compact (“PDC”) and tungsten carbide cutting structures in a single cutter to perform dual-purpose drilling. The cutter effectively mills out a steel well casing and once through the casing, the cutter is configured to continue drilling into the rock formation. The mill-drill bit of the present disclosure includes a plurality of blades where each blade supports a plurality of dual-purpose or mill-drill cutters.

(8) The dual-purpose cutter includes two separate cutting edges to perform two different tasks. The dual-edge cutter is manufactured in two parts, a tungsten carbide substrate and a PDC diamond layer that is LS (long substrate) bonded to the tungsten carbide substrate. The tungsten carbide substrate is manufactured to a larger diameter than the PDC layer. It is on this tungsten carbide substrate that a prepared cutting edge is machined or otherwise formed to mill a steel casing or other hard material. And, since the diameter of the cutting edge on the carbide substrate is larger the PDC layer, the tungsten carbide cutting structure protects the PDC layer from damage that would otherwise result from contact between the PDC layer and the steel of the casing-associated component.

(9) Reference is made to FIG. 1, which illustrates a mill-drill bit 10 according to the teachings of the present disclosure. The mill-drill bit 10 is a fixed cutter bit. It includes a bit face 12 defining a plurality of radially extending blades 14. The blades 14 may be straight or spiral blades or any other configuration known in the art to support fixed cutters. The blades 14 are separated from each other by junk slots 16. A drilling fluid nozzle 18 is also disposed between the blades 14. Threads 20 formed in an attaching portion of the bit 10 allows the bit 10 to be attached to a drill string and rotated such that the cutters perform either milling a casing-associated component or drilling through a rock formation to form a borehole. The bit 10 may be cast from a matrix material, or it may be machined from steel. In certain embodiments, the bit 10 is formed by a casting process, and then additional details are machined in the bit 10. For example, the blades 14 may be primarily formed by casting, and then the threads 20 may be machined.

(10) Each of the blades 14 supports a plurality of cutters. The cutters are secured into pockets that are formed in the blades 14. The bit 10 employs a variety of cutters. For example, the bit employs mill-drill cutters 22 according to the teachings of the present disclosure that are disposed radially inward of a gage 26 to cut an inner portion of a casing or a borehole. Each blade 14 of the bit 10 also employs conventional PDC cutters 24 that are disposed proximate the gage 26 of the bit 10. In certain embodiments, all of the cutters of a particular blade 14 or all of the cutters of the mill-drill bit 10 may be mill-drill cutters 22 and be configured to cut a steel casing with one portion of the cutter and configured to cut an earth formation with a different portion of the same cutter 22. As described further below, the mill-drill cutter 22 includes an enlarged diameter milling portion 28 and a PDC diamond table surface 30. In milling a steel casing and through contact with a rock formation, a portion of the milling surface will wear away and expose the PDC diamond table drilling surface 30 to cut the earth formation.

(11) Reference is made to FIG. 2A, which is a cross-section of the mill-drill cutter 22 in a pocket 32 formed in a blade 14. The mill-drill cutter 22 is illustrated as cutting a metal casing 34. According to certain embodiments, the mill-drill cutter 22 is secured within the cutter pocket 32 by brazing, although other methods may be used. The braze material used to secure the mill-drill cutter 22 within the pocket 32 typically has a melting point in a range of 1300 degrees Fahrenheit to 1330 degrees Fahrenheit.

(12) The mill-drill cutter 22 includes a substrate 36 and a PDC cutting structure 38 secured to the substrate 38. The substrate 36 is delimited on one end by a flat, circular face 40 and on an opposite end by a rounded rear surface 42. The substrate 36 is formed from tungsten carbide or any other suitable material. In certain embodiments, the tungsten carbide may have a percentage of cobalt to facilitate machining the features describe herein. For example, the substrate 36 can be made of “low cobalt” type machining grade with cobalt in the 3% to 10% range, where conventional PDC cutters typically use tungsten carbide in the 11% to 14% cobalt range.

(13) A front portion of the substrate 36 includes the enlarged diameter portion 28, which is a generally cylindrical portion of the substrate 36. The enlarged diameter portion 28 extends radially outward with respect to a longitudinal axis 44 of the cutter 22, beyond the PDC cutting structure 38. A rear portion of the generally cylindrical enlarged diameter portion 28 includes a beveled surface 46. The enlarged diameter portion 28 is delimited on one end by the flat, circular face 40 and on the other end by the beveled surface 46. An exposed portion of an annular portion of the face 40 extending outward beyond the PDC cutting structure 38 is the milling surface 48. A perimeter of the milling surface 48 is a milling edge 50. A drilling edge 54 of the PDC cutting structure 38 is disposed radially internal to the milling edge 50. The diameter of the enlarged diameter portion 28 may be 10%-50% larger than the diameter of the PDC cutting structure 38. According to one embodiment, a diameter of the face 40 of the enlarged diameter portion 28 is approximately 14.17 millimeters. A diameter of a face of the PDC diamond table surface 30 is approximately 11 millimeters.

(14) The PDC cutting structure 38 is secured to the face 40 to be coaxial with the substrate 36. The PDC cutting structure 38 includes the diamond table layer 30, which functions as the primary drilling surface for drilling the rock formation. The diamond table layer 30 may be non-leached, shallow leached, deep leached, or resubstrated fully leached, as desired. In other embodiments, the diamond table layer 30 may be replaced with cubic boron nitride, or other hard material.

(15) The enlarged diameter portion 28 performs multiple functions. For example, the enlarged diameter portion 28 provides the face surface 40 on which a PDC cutting structure 38 is secured. The PDC structure 38 may be brazed to the face 40 of the substrate or otherwise secured using joining methods that are known in the art of earth boring drill bits. For example, the PDC cutting structure 38 may be secured to the substrate 36 using a high temperature/high strength braze joint or LS (long substrate bond) as is known in the art. The braze joint may be created using an induction brazing process performed in a controlled atmosphere to produce a high quality, high strength braze joint or bond.

(16) As described above, the portion of the enlarged diameter portion 28 that extends radially beyond the PDC cutting structure 28 provides the milling surface 48. A milling edge 50 is prepared at a perimeter of the milling surface 48. As shown in FIG. 2A, the milling surface 48 engages the metal casing 34 and tears, cuts, shears, and rips apart the metal casing 34.

(17) Because it extends beyond the PDC cutting structure 38, the enlarged diameter portion 28 protects the PDC cutting structure 38 from contact with the metal casing 34. As shown in FIG. 2A, there is a clearance distance 52 between the casing-associated component 34 and the PDC cutting structure 38. The clearance distance 52 is provided by the engagement of the milling edge 50 and/or the milling surface 48 with the casing 34. The clearance distance 52 decreases as the enlarged diameter portion 28 wears away due to abrasion and wear caused by milling the casing 34 and abrasion resulting from contact with the subterranean rock formation encountered after milling through the casing-associated component 34. Ultimately, the clearance distance 52 reduces to zero and the PDC cutting structure 38 will be engaged and perform the cutting function. Preferably, the milling action wears away the enlarged diameter portion 28 and reduces the clearance distance to zero once the milling is complete or shortly thereafter. In this manner, a fresh drilling surface and drilling edge 54 of the PDC diamond table 30 that has not been degraded due to contact with the casing 34 is exposed to drill the rock formation.

(18) Reference is made to FIG. 2B, which illustrates the mill-drill cutter 22 of FIG. 2A performing a drilling operation. Once the milling operation is completed, and the mill-drill bit 10 begins formation drilling, the enlarged diameter portion 38 of the substrate 36 wears or breaks away so as to allow the diamond table 30 to function as the primary cutting structure to drill a subterranean rock formation 56. In this way, the drill bit 10 can be first used for milling (with the milling surface 48 and milling edge 50) and then used for drilling (with the diamond table 30 and the drilling edge 54 of the PDC cutting structure 38), thus obviating the need to use and then pull a specialized milling bit from the hole.

(19) FIG. 2B does not show a clearance distance, as shown in FIG. 2A (reference number 52) because it has been reduced to zero by the wearing away of the milling portion of the enlarged diameter portion 38 of the substrate 36 that includes the milling surface 48. In the earth drilling (rock formation drilling) operation, the drilling surface of the PDC diamond table layer 30 and the drilling edge 54 engage the formation 56 to rip, cut, and break apart the formation. The original milling edge 50 and has worn away at least in part due to abrasion and other wear mechanisms resulting from milling through the casing 34. Because it has worn away, the enlarged diameter portion 28 no longer creates a clearance distance between the drilling edge 54 and the formation 56.

(20) The mill-drill cutter 22 is axisymmetric about its longitudinal axis 44. As such, the mill-drill cutter 22 can be removed from the pocket 32, rotated, and re-secured within the pocket 32. Methods, typically involving heating to break down the brazing material, and separate cutters from cutter pockets are known in the art. The pocket 32 may be cleaned or otherwise prepared to receive a rotated mill-drill cutter 22. Then, the mill-drill cutter 22 may be rotated approximately 180 degrees about its longitudinal axis 44 and re-brazed into the pocket 32. Thus, the portion of the enlarged diameter portion 28 that was secured in a groove formed in the pocket 32 is now in a milling position and is configured to cut and break apart casing. Similarly, the portion of the PDC cutting structure 38 that was furthest from and had the least exposure to the materials being milled or drilled is now in a position to have the greatest exposure to the materials being milled or drilled.

(21) Reference is made to FIG. 3, which is a cross section of the blade 14 and the pocket 32 with the mill-drill cutter 22 exploded from the pocket 32. The contours of the pocket 32 correspond to the shape of the mill drill cutter 22. For example, the pocket 32 includes a rounded rear surface 58 that corresponds to the rounded rear surface 42 of the substrate 36 of the mill-drill cutter 22. Similarly, the pocket includes a recess or groove 60 that corresponds to the enlarged diameter portion 28 of the substrate 36. The recess 60 is configured to accommodate the enlarged diameter of the outer cutting structure of the increased diameter portion 28. The recess may have a flat faced surface 62 in the drilling direction of cut and beveled surface 64 at the opposite trailing side. According to an embodiment, a depth of the groove corresponds to the portion of the enlarged diameter portion 28 that extends beyond the PDC cutting structure 38.

(22) The pocket 32 may be partially or completely formed using a graphite displacement disposed in the location of the pocket 32 during casting of the body of the mill-drill bit 10. Subsequent machining operations may be performed on the cast pocket. The cutter pocket 32 including the groove 60 provides an increased surface area for retention of the mill-drill cutter 22.

(23) The bit may be formed from steel, a matrix material, or other materials known in the art. A steel mill-drill bit may be machined to form the pocket 32 including the rounded rear surface 58 and the recess 60 corresponding to the increased diameter portion 28 of the mill-drill cutter 10.

(24) Reference is now made to FIG. 4, which illustrates an alternate embodiment of a cutter pocket 68 and a mill-drill cutter 70. FIG. 4 is a cross section of a blade 14 with the cutter pocket 68 and a flat back mill-drill cutter 70 exploded from the pocket 68. The mill-drill cutter 70 includes a generally flat, circular rear surface 72 of the substrate. A perimeter 74 of the flat rear surface 72 is beveled. Similarly, the pocket 68 formed in the blade 14 includes a generally flat rear surface 76 with a beveled perimeter 78 corresponding to the flat rear surface 72 and beveled perimeter 74 of the substrate of the flat back mill drill cutter 70. Similar to the rounded rear surface pocket 32 embodiment shown in FIG. 3, the pocket 68 includes a recess or groove 80 shaped to receive the enlarged diameter portion of the substrate. The mill-drill cutter 70 is brazed to secure it in the pocket 68 as described above with respect to FIG. 3.

(25) Reference is now made to FIGS. 5A-5D, which illustrate the mill-drill cutter 22 at different rake angles. The pocket 32 (or pocket 68) is formed to accommodate the desired rake angle of the mill-drill cutter 22 (or mill-drill cutter 70). FIG. 5A shows a rake angle of 5 degrees. Also, the less the rake angle the greater the clearance distance 52, which means more of the enlarged diameter portion 28 of the substrate 36 is exposed to the material. As such, the mill-drill cutters 22 at shallower rake angles can be used for increased milling before wearing to a clearance distance 52 of zero and exposure of the PDC cutting structure 38 and the drilling surface 30. FIG. 5B illustrates a rake angle of 10 degrees. FIG. 5C illustrates a rake angle of 15 degrees, and FIG. 5D illustrates a rake angle of 20 degrees. Any suitable rake angle may be employed according to the teachings of the present disclosure.

(26) A mill-drill bit 10 that employs mill-drill cutters 22, 70 according to the teachings of the present disclosure can mill through casing, or drill out through a casing bit or frac plug and then drill ahead into formation. Mill-drill cutters and bits including dual purpose (i.e. mill/drill) cutters may be used in connection with casing window mills, mill-drills, and PDC casing bit drill out bits. In addition, reamers may include mill-drill cutters and be used in conjunction with window milling.

(27) The mill-drill cutters 22 are robust enough to accomplish the milling tasks asked of them while being structurally predisposed to disintegration and shedding when milling is completed and the bit moves forward for drilling the formation. Mill-drill bits according to the teachings of the present disclosure can be used to drill out steel bodied casing shoe bits or casing shoe bits constructed from other materials extending the casing shoe bit choices of casing drilling operations. Bits of the current disclosure can also be used in one trip mill drill systems where the bit is attached at the top of a whipstock for running in the hole.

(28) The mill-drill bit as described herein can be advantageously used in combined milling and formation drilling operations. In accordance therewith, a mill-drill bit 10 with certain ones of the cutters being mill-drill cutters is provided for attachment to a drill string or other drilling equipment. The milling surface 48 is configured for milling operations on a casing-associated component located in the hole but is not optimal for earth formation drilling operations. The drill bit is rotated and the milling surface 48 of the mill-drill cutters 22 perform a down hole milling operation on the casing-associated component. Drilling with the mill-drill bit 10 continues after milling of the casing-associated component to drill an underlying earth formation. Importantly, the same drill bit is being used, and thus there is no need to pull a milling bit from the hole before resuming formation drilling. The drilling of the earth formation causes a portion of the milling surfaces of the mill-drill cutters to be destroyed and thus expose the drilling surface of the diamond table to engage the subterranean earth formation.

(29) It will be understood that the mill-drill bit described herein is equally applicable to any downhole tool that might otherwise use conventional PDC cutters. For example, the mill-drill cutters could be used in connection with downhole tools comprising: bi-center bits, casing shoe bits, PDC reamers, PDC hole openers, expandable reamers, PDC set stabilizers, PDC set guide shoes and reaming guide shoes. More generally, the mill-drill cutters are applicable to downhole tools expected to engage or come in contact with any “casing” or “casing-associated component” as previously described.

(30) The foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.