FIXED CUTTER DRILL BIT HAVING CORE RECEPTACLE WITH CONCAVE CORE CUTTER

Abstract

A drill bit includes a shank having a threaded coupling formed at an upper end thereof; a bit body mounted to a lower end of the shank and having a plenum; a gage section forming an outer portion of the drill bit; a cutting face forming a lower end of the drill bit and including: a core receptacle formed at a center of the cutting face, operable to receive a core of earth, and including: a concave core cutter mounted to a bottom of the bit body; and a core port extending from the plenum through the bottom of the bit body and operable to discharge drilling fluid onto the core and core cutter; a plurality of blades protruding from a bottom of the bit body and extending from a periphery of the core receptacle to the gage section; and a plurality of leading cutters mounted along each blade.

Claims

1. A drill bit, comprising: a shank having a threaded coupling formed at an upper end thereof; a bit body mounted to a lower end of the shank and having a plenum; a gage section forming an outer portion of the drill bit; and a cutting face forming a lower end of the drill bit and comprising: a core receptacle formed at a center of the cutting face, operable to receive a core of earth, and comprising: a concave core cutter mounted to a bottom of the bit body; and a core port extending from the plenum through the bottom of the bit body and operable to discharge drilling fluid onto the core and core cutter; a plurality of blades protruding from a bottom of the bit body and extending from a periphery of the core receptacle to the gage section; and a plurality of leading cutters mounted along each blade.

2. The bit of claim 1, wherein an innermost one of the leading cutters is positioned such that a diameter of the core ranges from four to seventeen percent of an outer diameter of the drill bit.

3. The bit of claim 1, wherein the concave core cutter overlaps with a portion of a diameter of the core ranging between one-quarter and one-half thereof.

4. The bit of claim 1, wherein the concave core cutter is tilted relative to a centerline of the drill bit by an angle ranging between ten and fifty degrees.

5. The bit of claim 1, wherein a diameter of the concave core cutter ranges between one-half and three-halves of a diameter of the core.

6. The bit of claim 1, wherein a bottom of the concave core cutter is sub-flush with a midline of the blades.

7. The bit of claim 1, wherein a depth of the concavity ranges between four percent and eighteen percent of a diameter of the concave core cutter.

8. The bit of claim 1, wherein the drill bit comprises only one concave core cutter.

9. The bit of claim 1, wherein: the core cutter is a first core cutter, and the bit further comprises a second concave core cutter mounted to the bottom of the bit body.

10. The bit of claim 9, wherein the core cutters are angularly spaced from each other about the core receptacle ranging between thirty and one hundred eighty degrees.

11. The bit of claim 9, wherein: the first core cutter is an in inner core cutter, the second core cutter is an outer core cutter, a bottom of each core cutter may be sub-flush with a bottom of the blades, the outer core cutter extends from the bottom of the bit body at a height greater than a height that the inner core cutter extends from the bottom of the bit body, and a cutting table of the outer core cutter overlaps with an outer portion of the core and a cutting table of the inner core cutter overlaps with an inner portion of the core such that the core cutters are operable to cut the core in two stages.

12. The bit of claim 1, wherein: the bit has at least three blades, and the bit has a number of concave cutters greater than or equal to a number of the blades.

13. The bit of claim 1, wherein the bit body is made from a ceramic and/or cermet powder infiltrated by a metallic binder.

14. The bit of claim 1, wherein: lower tips of the blades are impregnated with a superhard material, and the bit further comprises one or more superhard wear elements mounted to a bottom of each blade adjacent an inner end thereof.

15. A method of drilling a wellbore using the drill bit of claim 1, comprising: connecting the drill bit to a bottom of a pipe string, thereby forming a drill string; lowering the drill string into the wellbore until the drill bit is proximate a bottom thereof; rotating the drill bit and injecting drilling fluid through the drill string; and exerting weight on the drill bit, wherein the concave core cutter smoothly crushes the core utilizing both shear forces and lateral forces in order to break the core apart and crush it.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0018] FIG. 1 illustrates drilling of a wellbore with a drill bit having a core cutter, according to one embodiment of the present disclosure.

[0019] FIGS. 2A, 2B, and 3A-3C illustrate the drill bit having the core cutter engaged with the core. FIG. 3D illustrates a tilt angle of the core cutter.

[0020] FIG. 4A illustrates a cutting face of the drill bit. FIG. 4B illustrates a core receptacle of the drill bit.

[0021] FIGS. 5A and 5B illustrate the core cutter of the drill bit.

[0022] FIG. 6 illustrates an alternative drill bit having a dual cutter receptacle, according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

[0023] FIG. 1 illustrates drilling of a wellbore 1 with a drill bit 2 having a core cutter 3, according to one embodiment of the present invention. The drill bit 2 may be assembled as part of a bottomhole assembly (BHA) 4. The BHA 4 may be connected to a bottom of a pipe string 5, such as drill pipe or coiled tubing, and deployed into the wellbore 1, thereby forming a drill string. The BHA 4 may further include one or more drill collars 6 connected to the drill bit 2, such as by threaded couplings. The drill bit 2 may be rotated, such as by rotation of the drill string from a rig (not shown) and/or by a drilling motor (not shown) of the BHA 4, while drilling fluid 7, such as mud, may be pumped down the drill string. Weight of the drill string may be set on the drill bit 2. The drilling fluid 7 may be discharged by the drill bit 2 and carry cuttings up an annulus 8 formed between the drill string and the wellbore 1 and/or between the drill string and a casing string and/or liner string 9. As the wellbore 1 is being drilled, a cylindrical core 10 of earth is formed and is received by a center of the drill bit 2. A top of the core 10 is ground and broken apart by the core cutter 3 and the core cuttings are also carried up the annulus 8 by the discharged drilling fluid 7. The drilling fluid and cuttings are collectively referred to as returns 11.

[0024] FIGS. 2A, 2B, and 3A-3C illustrate the drill bit 2 having the core cutter 3 engaged with the core 10. FIG. 3D illustrates a tilt angle 26 of the core cutter 3. FIG. 4A illustrates a cutting face of the drill bit 2. FIG. 4B illustrates a core receptacle of the drill bit 2. The drill bit 2 may include a bit body 12, a shank 13, a cutting face, and a gage section. The shank 13 may be tubular and include an upper piece and a lower piece connected to the upper piece, such as by threaded couplings secured by a weld. The bit body 12 may be made from a composite material, such as a ceramic and/or cermet body powder infiltrated by a metallic binder. The bit body 12 may be mounted to the lower shank piece during molding thereof. The shank 13 may be made from a metal or alloy, such as steel, and have a coupling, such as a threaded pin, formed at an upper end thereof for connection of the drill bit 2 to the drill collar 6. The shank 13 may have a flow bore formed therethrough and the flow bore may extend into the bit body 12 to a plenum thereof. The cutting face may form a lower end of the drill bit 2 and the gage section may form at an outer portion thereof.

[0025] Alternatively, the bit body 12 may be metallic, such as being made from steel, and may be hardfaced. The metallic bit body may be connected to a modified shank by threaded couplings and then secured by a weld.

[0026] The cutting face may include one or more (three shown) primary blades 14p, one or more (four shown) secondary blades 14s, fluid courses formed between the blades, leading cutters 15a, backup cutters 15b, and a core receptacle 16. The core receptacle 16 may be a bladeless region formed at a center 17 of the cutting face. The core receptacle 16 may be configured to receive the core 10 having a diameter ranging between four to seventeen percent of an outer diameter of the drill bit 2. The diameter of the core 10 may be controlled by a position of an innermost one 15n of the leading cutters 15a.

[0027] The core receptacle 16 may be defined between inner ends of the primary blades 14p and include the core cutter 3 and a core port 18. The core cutter 3 may be mounted in a pocket formed in the bottom of the bit body 12, such as by brazing. The core port 18 may be formed in the bit body 12 and may extend from the plenum and through the bottom of the bit body to discharge drilling fluid onto the core 10 and core cutter 3, thereby facilitating crushing of the core by the core cutter and washing cuttings therefrom. The core port 18 may include a nozzle (not shown) fastened to the bit body 12 or be nozzle-less (shown). A diameter of the core cutter 3 may be selected and the core cutter may be tilted 26 relative to the longitudinal centerline 17 of the drill bit 2 such that a cutting table 3t thereof overlaps a portion of the core diameter, such as ranging between one-quarter to one-half of the core diameter, thereby ensuring complete crushing thereof as the core cutter rotates with the drill bit 2. The tilt angle 26 may range between ten and fifty degrees. The diameter of the core cutter 3 may range between one-half and three-halves of the diameter of the core 10. The core cutter 3 may be slightly offset from the center 17 of the cutter face such that a bottom of the cutting table 3t is adjacent to an outer surface of the core 10 and/or an edge of the core cutter pocket may intersect the center 17 of the cutter face. The core receptacle 16 may be in fluid communication with the fluid courses. A bottom of the core cutter 3 may be sub-flush with a bottom of the primary blades 14p and may be substantially sub-flush therewith, such as being sub-flush with a mid-line of the primary blades.

[0028] The blades 14p,s may be disposed around the cutting face and each blade may be formed during molding of the bit body 12 and may protrude from the bottom of the bit body. The primary blades 14p may each extend from a periphery of the core receptacle 16 to the gage section. One or more (seven shown) blade ports may be formed in the bit body 12 and each blade port may extend from the plenum and through the bottom of the bit body to discharge drilling fluid along the fluid courses. A nozzle 19 may be disposed in each blade port and fastened to the bit body 12. An inner set of one or more (three shown) of the blade ports may be disposed adjacent to respective inner ends of the primary blades 14p. The secondary blades 14s may extend from a location on the cutting face adjacent to the inner set of blade ports to the gage section. Each blade 14p,s may extend generally radially from the cutting face to the gage section with a slight spiral curvature.

[0029] A base of each blade 14p,s and a mid-portion of each blade may be made from the same material as the bit body 12. A lower tip 20 of each blade 14p,s may impregnated with a superhard material, such as diamond, to enhance abrasion resistance. The leading cutters 15a may be mounted in pockets formed along leading edges of the blades 14p,s, such as by brazing. The backup cutters 15b may be mounted in pockets formed along bottoms of the blades 14p,s, such as by brazing. Each backup cutter 15b may be aligned or slightly offset from a respective leading cutter 15a. The backup cutters 15b may or may not fully extend to the gage section. Each cutter 15a,b may include a superhard cutting table, such as polycrystalline diamond, attached to a hard substrate, such as a cermet, thereby forming a compact, such as a polycrystalline diamond compact. The innermost pocket or pair of pockets of each primary blade 14p in the bottom thereof may have wear segments 21 instead of backup cutters 15b. Each wear segment 21 may be impregnated with a superhard material, such as diamond, to enhance abrasion resistance.

[0030] The gage section may include a plurality of gage pads 22 and junk slots formed between the gage pads. The junk slots may be in fluid communication with the fluid courses formed between the blades 14p,s. The gage pads 22 may be disposed around the gage section and each pad may be formed during molding of the bit body 12 and may protrude from the outer portion of the bit body. Each gage pad 22 may be made from the same material as the bit body and each gage pad may be formed integrally with a respective blade 14p,s.

[0031] FIGS. 5A and 5B illustrate the core cutter 3. The core cutter 3 may include the concave cutting table 3t attached to a cylindrical substrate 3s. The concave cutting table 3t may be circular and the substrate 3s may be a circular cylinder. The cutting table 3t may be made from a superhard material, such as polycrystalline diamond, attached to a hard substrate, such as a cermet, thereby forming a compact, such as a polycrystalline diamond compact. The cermet may be a cemented carbide, such as cobalt (or group VIII metal)-tungsten carbide. The cutting table 3t may have an interface 23 with the substrate 3s and a cutting face 24 opposite to the interface. The cutting face 24 may have an outer chamfered edge 24e, a planar rim 24r adjacent to the chamfered edge, a conical surface 24n adjacent to the rim, and a central crater 24c adjacent to the conical surface 24c. The interface 23 may have a planar outer rim 23r and an inner parabolic surface 23p. The thickness of the cutting table 3t may be a minimum at the crater 24c and increase outwardly therefrom until reaching a maximum at the rim 23r. A depth 25 of the concavity may range between four percent and eighteen percent of a diameter of the core cutter 3.

[0032] Alternatively, the cutting table 3t and substrate 3s may each be elliptical.

[0033] Cutting efficiency may be problematic at the center of fixed-cutter bits due to the low linear speed. Advantageously, the concave core cutter 3 will smoothly crush the core 10 utilizing both shear forces and lateral forces in order to break the core apart and crush it. This dual action cutting is superior to any of the prior art solutions, discussed above. Also, to be clear, even though the core 10 is created during drilling, the drill bit 2 is not a coring bit, as the core is destroyed by the core cutter 3 and cuttings therefrom are washed along the fluid courses and junk slots.

[0034] FIG. 6 illustrates an alternative drill bit 27 having a dual cutter receptacle 27r, according to another embodiment of the present disclosure. The alternative drill bit 27 may be similar to the drill bit 2 except for having the dual cutter receptacle 27r instead of the core receptacle 16 and having a modified bit body 27b for accommodating the dual cutter receptacle. The dual cutter receptacle 27r may include an outer core cutter 28o, an inner core cutter 28n, and the core port (not shown). Each core cutter 28n,o may be similar to the core cutter 3. Each core cutter 28n,o may be mounted in a respective pocket formed in the bottom of the modified bit body 27b. The core cutters 28n,o may be angularly spaced from each other about the alternative core receptacle 27r, such as by a spacing ranging between thirty and one hundred eighty degrees. A bottom of each core cutter 28n,o may be sub-flush with a bottom of the primary blades (not shown). The outer core cutter 28o may extend from the bottom of the modified bit body 27b at a height greater than a height that the inner core cutter 28n extends from the bottom of the modified bit body. A cutting table of the outer core cutter 28o may overlap with an outer portion of the core 10 and a cutting table of the inner core cutter 28n may overlap with an inner portion of the core such that the core is cut in two stages. The two-stage cut may give the core 10 a tiered shape within the alternative core receptacle 27r.

[0035] Alternatively, the alternative drill bit 27 may have more than two core cutters 28n,o, such as a number of core cutters greater than or equal to the number of primary blades, such as three, or greater than or equal to the number of total blades (primary+secondary), such as seven.

[0036] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope of the invention is determined by the claims that follow.