DRILL BIT

Abstract

There is described a drill bit comprising: a body portion comprising at least one chamber, the drill bit further comprising at least one cutting element, the at least one cutting element comprising a cutting edge and a retention member; wherein the retention member is removably held within the chamber to retain the cutting edge at a first surface of the body portion; wherein the retention member comprises a material with a higher coefficient of thermal expansion than the material of the body portion. There is also described a kit of parts for a drill bit and a cutting element for use in a drill bit or kit of parts.

Description

FIELD OF THE INVENTION

The present invention relates to a drill bit. The invention also relates to kit of parts for a drill bit and a cutting element for use in a drill bit or kit of parts.

BACKGROUND TO THE INVENTION

Drills can be used to drill holes and are used in the oil and gas industries to form oil, gas and geothermal wells in the ground. Drill bits comprise the cutting edge of the drill, the cutting edge being the portion of the drill which cuts into the ground to remove material. The cutting edge of the drill bit can wear down with use and may require regular replacement and/or maintenance.

Fixed drill bits or fixed cutter bits are a type of drill bit having a cutting element integrated to the body of the drill bit. Fixed drill bits do not have moving parts and are designed to excavate holes by shearing formations rather than chipping or gouging formations. One example of fixed drill bit uses polycrystalline diamond compact (PDC) cutters.

It is known in the art to use brazing to secure the cutting edge of the drill bit to a steel body or matrix (tungsten carbide) body of the drill bit. However, when the cutting edge becomes blunt or damaged, it can be cumbersome and expensive to remove, repair or replace the cutting edge. In particular, the specialist nature of the brazing manufacturing step can require the drill bit to be sent to specialist for the repair work to be carried out.

Objects and aspects of the present claimed invention seek to alleviate at least these problems with the prior art.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a drill bit comprising: a body portion comprising at least one chamber, the drill bit further comprising at least one cutting element, the at least one cutting element comprising a cutting edge and a retention member; wherein the retention member is removably held within the chamber to retain the cutting edge at a first surface of the body portion; wherein the retention member comprises a material with a higher coefficient of thermal expansion than the material of the body portion.

In this way there is provided a drill bit which can easily be assembled and disassembled, and which securely retains the cutting edge on the first surface. The retention member can be removably held within the chamber of the body portion without the requirement for any special tooling. Further, the retention member provides a ‘bridge’ of material with a thermal expansion greater than the body portion, such that upon heating, the retention member expands to a greater extent than the body portion, thereby causing the retention member to fill the chamber and/or provide a greater force against the walls of the chamber. As such, a more secure retention of the cutting edge on the first surface is provided, with a greater force required to remove the retention member from the chamber.

During drilling into the ground, the temperature experienced by the drill bit increases due to the temperature downhole and/or due to mechanical failure of rock within the ground. When heated, the retention member expands to fill the chamber and/or provide a greater force against the walls of the chamber. The additional heat generated during drilling serves to further expand the retention member relative to the body portion and ensure the cutting edge is firmly retained at the first surface.

In some embodiments, the drill bit comprises a plurality of chambers and a plurality of cutting elements. Preferably, the number of chambers is equal to the number of cutting elements. In this way, the drill bit contains more than one cutting element and more than one cutting edge configured to cut or drill into the ground.

Preferably, the coefficient of thermal expansion of the retention member is at least 15×10⁻⁶° C.-1 at 20° C. More preferably, the coefficient of thermal expansion of the retention member is at least 50×10⁻⁶° C.-1 at 20° C.

Preferably, the coefficient of thermal expansion of the body portion is no more than 10×10⁻⁶° C.-1 at 20° C. More preferably, the coefficient of thermal expansion of the body portion is no more than 6×10⁻⁶° C.-1 at 20° C. In some embodiments, the coefficient of thermal expansion of the body portion is a negative value.

Preferably, the coefficient of thermal expansion of the retention member and the coefficient of thermal expansion of the body portion are substantially identical at temperatures above 200° C. In this way, the retention member is configured to be tightly housed within the chamber of the body portion at temperatures above 200° C. When the coefficient of thermal expansions of the retention member and body portion are substantially identical at temperatures above 200° C., excessive expansion of the retention member is also prevented. Excessive expansion of the retention member can cause part failure and damage to the drill bit, in particular damage to the retention member and body portion.

In some embodiments, the body portion further comprises an aperture, wherein the aperture intersects a second surface of the body portion and the aperture is connected to the chamber. The aperture may act as vent hole, providing a fluid connection between the second surface and the chamber.

Preferably, the first surface of the body portion and second surface of the body portion are different surfaces. Preferably, the first surface of the body portion and second surface of the body portion are adjacent surfaces. In this way, the cutting element can be located distal the location where the aperture intersects the second surface.

In some embodiments, the drill bit further comprises at least one seal configured to maintain a minimum pressure within the chamber. Preferably, the at least one seal is an airtight seal. In this way, the retention member can be better held within the chamber as the at least one seal maintains a minimum pressure within the chamber which provides a retaining force on the retaining member. Such a feature is particularly advantageous when the drill bit is at ground level or is not subjected to additional heat, such as heat generated during drilling. In such cases, the relative thermal expansion between the retention member and the body portion is lower than when the drill bit is subjected to heat, and so the retaining force between the retention member and the walls of the chamber is improved by the presence of a seal.

Preferably, the at least one seal comprises a blocking member located in the aperture, the blocking member configured to inhibit airflow between the second surface of the body portion and the chamber. Preferably, the blocking member is a grub screw or other stopper for sealing the aperture.

Preferably, at least one seal is located between the retention member and the body portion, the at least one seal configured to inhibit airflow between the first surface of the body portion and the chamber. Preferably, the at least one seal comprises a pair of seals located about the perimeter of the retention member. For example, the pair of seals may comprise O-ring seals.

A configuration wherein both a blocking member located in the aperture and a seal located between the retention member and the body portion ensure the portion of the chamber between the two seals is sealed in an airtight matter, thereby providing a retaining force on the retention member to hold the retention member in the chamber. Preferably, the drill bit comprises a vacuum located between at least two seals of the at least one seal. In this way, removal of the retention member from the chamber will be resisted by the vacuum between the retention member and the seal.

Preferably, the longitudinal axis of the aperture is substantially perpendicular to the longitudinal axis of the chamber. In this way, the cutting element can be located distal the location where the aperture intersects the second surface. Preferably, the cutting edge is configured to be located concentrically on the retention member. Such a configuration is advantageous when the cutting edge is configured to rotate. Alternatively, the cutting edge is configured to be located non-concentrically on the retention member.

Preferably, the retention member is configured to be removably held within the chamber with a clearance fit or a transition fit. In this way, the retention member can be easily inserted and removed from the chamber without specialist tools, thereby improving ease of manufacture and maintenance. Further, a transition fits aids retention of the retention member within the chamber.

Preferably, the body portion comprises chromium molybdenum alloy steel or a material with a cast tungsten carbide matrix. An example of chromium molybdenum alloy steel is AISI 4145 Alloy Steel (UNS G41450). A table of compositions of AISI 4145 Alloy Steel is provided below.

Element     % composition
Carbon      0.43-0.49
Manganese   0.85-1.10
Molybdenum  0.15-0.25
Sulphur     At most 0.040
Silicon     0.10-0.35
Chromium    0.80-1.10
Nickel      At most 0.25
Phosphorous At most 0.035

Preferably, the retention member comprises aluminium and/or a nickel-iron-chromium alloy. An example of a suitable nickel-iron-chromium alloy is Incoloy® 800 (UNS N08800/W. Nr. 1.4876). A table of compositions of Incoloy 800 is provided below.

Element             % composition
Nickel              30.0-35.0
Chromium            19.0-23.0
Iron                At least 39.5
Carbon              At most 0.10
Aluminium           0.15-0.60
Titanium            0.15-0.60
Aluminum + Titanium 0.30-1.20

Preferably, the cutting edge comprises synthetic diamond. In some embodiments, the cutting edge consists of synthetic diamond.

In some embodiments, the retention member is fixed to the cutting edge. In this way, greater security between the cutting edge and the retention member is provided as the permanent connection reduces the risk of accidently removal of the cutting edge from the retention member.

In some embodiments, the retention member is substantially cylindrical. In some embodiments, the retention member is substantially a rectangular prism. It is envisaged that the retention member may be any suitable shape to retain the cutting edge at the first surface of the body portion. In some embodiments, the aperture is substantially cylindrical.

In some embodiments, the body portion comprises a collar defining at least one wall of the chamber. Preferably, the collar defines substantially the entire internal circumference of the chamber. Preferably, at least the collar of the body portion comprises material with a lower coefficient of thermal expansion than the material of the retention portion. In this way, the collar is the portion of the body surrounding the retention member and the relative expansion of the collar and retention member during heating of the drill bit improve retention of the retention member within the chamber.

In some embodiments, the body portion is not formed from one integral part. In this way, the collar can be manufactured separately from the remainder of the body portion. In some embodiments, the collar is fixed relative to the non-collar portion/s of the body portion. For example, the collar may be attached to the remainder of the body portion via adhesive or screws. In some embodiments, the collar is free to move relative to the non-collar portion/s of the body portion.

Preferably, the collar comprises an iron-nickel alloy containing 42% wt. % nickel (Alloy 42). In some embodiments, the collar consists of an iron-nickel alloy containing 42% wt. % nickel (Alloy 42).

Preferably, the drill bit further comprises a bolting member configured to bolt the body portion to the retention member. Preferably, the bolting member is configured to be housed in a bolt aperture, the bolt aperture extending through at least a portion of the retention member and at least a portion of the body portion. In embodiments comprising a collar, preferably, the bolt aperture extends through at least a portion of the retention member, at least a portion of the collar and at least a portion of the body portion. In this way, the collar is better retained to the remainder of the body portion.

Preferably, the bolting member comprises an external thread. Preferably, the bolting member comprises a bolt or grub screw. The bolting member further improves retention of the retention member within the chamber by locking the retention member to the body portion. The bolt aperture additionally performs the function of the aperture detailed above, namely to act as a vent hole for reducing unwanted pressure within the chamber. It is understood that preferred embodiments of the invention comprise either an aperture and at least one seal, or a bolt and a bolt aperture.

Preferably, the longitudinal axis of the bolt aperture intersects the longitudinal axis of the chamber. In some embodiments, the longitudinal axis of the bolt aperture is offset from the longitudinal axis of the chamber. Namely, the axes do not intersect. In some embodiments, the longitudinal axis of the bolt aperture is perpendicular to the longitudinal axis of the chamber.

It is understood that a bolting member and bolt aperture may be present in embodiments of the invention which do not comprise a collar. Additionally, a collar may be present in embodiments of the invention which do not comprise a bolting member and bolt aperture.

Preferably, the drill bit is a fixed drill bit. Namely, the drill bit does not have moving parts and is configured to excavate holes by shearing formations rather than chipping or gouging formations. Preferably, the drill bit comprises a polycrystalline diamond compact (PDC) cutter.

According to a second aspect of the invention there is provided a kit of parts for a drill bit, the kit of parts comprising: a body portion comprising at least one chamber, and at least one cutting element, the at least one cutting element comprising a cutting edge and a retention member; wherein the retention member is configured to be held within the chamber and retain the cutting edge at the first surface of the body portion; wherein the retention member comprises a material with a higher coefficient of thermal expansion than the material of the body portion.

Preferably, the body portion comprises a plurality of chambers, and the kit of parts comprises a plurality of cutting elements. In this way, a drill bit with multiple cutting edges is provided.

According to a third aspect of the invention there is provided a cutting element for use in the drill bit of the first aspect of the invention or kit of parts of the second aspect of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 depicts a drill bit in accordance with the first aspect of the invention;

FIG. 2 depicts a second embodiment of a drill bit in accordance with the first aspect of the invention, the drill bit comprising at plurality of seals;

FIG. 3 depicts an alternative embodiment of a drill bit according to the first aspect of the invention, wherein no aperture intersecting the second surface of the body portion or connected to the chamber is present; and

FIG. 4 depicts a further view of the drill bit of FIG. 3.

With reference to FIG. 1, a drill bit 100 is illustrated. The drill bit 100 comprises a body portion 105 comprising a chamber 110 and an aperture 115. The drill bit 100 further comprises a cutting element 120 comprising a cutting edge 125 and a retention member 130. The retention member 130 is removably held within the chamber 110 to retain the cutting edge 125 at a first surface 135 of the body portion 105.

As shown in FIG. 1, a first portion 145 of the retention member 130 is located outside of the chamber 130 and is configured to be held within the cutting edge 125. The first portion 145 is about one third of the total length of the retention member 130. The first portion 145 is fixed to the cutting edge 125 to increase security.

In this embodiment, the cutting edge 125 comprises synthetic diamond. In this way, the cutting element 120 comprises a polycrystaline diamond compact (PDC) cutter.

The chamber 110 has substantially the same cross-sectional shape as the retention member 130, such that the chamber 110 complements the cross-sectional shape of the retention member 130. In this embodiment, the retention member 130 is configured to be held within the chamber with a transition fit, such that any gap between the retention member 130 and the internal walls 140 of the chamber 110 is very small.

The retention member 130 comprises a material with a higher coefficient of thermal expansion than the material of the body portion 105. In this way, when the drill bit 100 is subjected to heat, such as during drilling and/or due to pressure the drill bit 100 experiences underground, the retention member 130 expands a greater amount relative to the body portion 105. As such, any gap or space between the retention member 110 and the internal walls 140 of the chamber 110 is filled by the expanded retention member 110 and/or the pressure exerted by the retention member 130 on the walls 140 of the chamber 110 increases. Such a force increases the friction between the walls 140 and the retention member 130, such that it is harder for the retention member to be pulled out or otherwise dislodged from the chamber 110.

In this embodiment, the coefficient of thermal expansion of the retention member is greater than 15×10⁻⁶° C.-1 at 20° C. and the coefficient of thermal expansion of the body portion is less than 6×10⁻⁶° C.-1 at 20° C. It is understood that some materials falling within the scope of the present invention have a negative coefficient of thermal expansion.

In this embodiment, the body portion 105 comprises AISI 4145 Alloy Steel and the retention member comprises Incoloy® 800. AISI 4145 Steel has a low thermal expansion coefficient relative to Incoloy® 800. AISI 4145 Steel has a coefficient of thermal expansion of around 12×10⁻⁶ and Incoloy® 800 has a coefficient of thermal expansion of 6×10⁻⁶.

The aperture 115 intersects a second surface 150 of the body portion and is connected to the chamber 110. In this way, the first surface 135 is fluidly connected to the second surface 150. The aperture 115 acts as a vent hole to allow air within the chamber 110, such as air heated during drilling, to exit the chamber 110. Additionally, without removal of the air from the chamber 110, the pressure within the chamber may increase to a level which would prevent or inhibit accurate connection and alignment of the retention member 130 within the chamber 110. The first surface 135 is a neighbouring perimeter surface of the body portion 105 to the second surface 150. The aperture 115 is substantially straight and the chamber 115 has a constant cross-section across its length. The longitudinal axis A of the aperture 115 is substantially perpendicular to the longitudinal axis B of the chamber 110.

The cutting edge 125 is located non-concentrically on the retention member 130, such that the longitudinal axis B of the chamber 110 does not intersect the central axis C of the cutting edge 125. In some embodiments, it is envisaged that the longitudinal axis B of the chamber 110 intersects the central axis C of the cutting edge 125 such that the cutting edge 125 is located concentrically on the retention member 130.

With reference to FIG. 2, a second embodiment of a drill bit 200 is illustrated. The drill bit 200 of the second embodiment is substantially identical to the drill bit 100 of the first embodiment with the following differences.

The drill bit 200 comprises three seals 255, 260, 265. A first airtight seal comprising a blocking member 255 is located within the aperture 215. The blocking member 255 comprises a grub screw and the aperture 215 comprises a complementary thread configured to retain the grub screw. The blocking member 255 inhibits air flow in both directions between the chamber 210 and the second surface 250.

A second airtight seal 260 and third airtight seal 265 comprise O-ring seals and are located concentrically about the perimeter of the retention member 230. The second seal 260 and third seal 265 are configured to inhibit airflow between the first surface 235 and the chamber 230 in both directions. In this way, a minimum pressure can be maintained within a portion of the chamber 210.

With reference to FIGS. 3 and 4, a drill bit 300 is illustrated. The drill bit 300 comprises a body portion 305 comprising a chamber 310. The drill bit 300 further comprises a cutting element 320 comprising a cutting edge 325 and a retention member 330. The retention member 330 is removably held within the chamber 310 to retain the cutting edge 325 at a first surface 335 of the body portion 305. As shown in FIG. 3, a first portion 345 of the retention member 130 is located outside of the chamber 330 and is configured to be held within the cutting edge 325.

The embodiment of FIGS. 3 and 4 is substantially identical to the embodiment of FIGS. 1 and 2, with the following differences.

The body portion 305 comprises a collar 370 defining the inner walls of chamber 310. In this way, the collar 370 acts as a sleeve defining the internal walls of the chamber 310 within the body portion 305. The retention member 330 is configured to be housed in the chamber 310 such that the collar 370 substantially surrounds the retention member 330, as illustrated in FIG. 3.

In this embodiment, the body portion 305 is not formed from a single part and the collar 370 is attached to the rest of the body portion 305 via any suitable means, for example adhesive. In this embodiment, the collar comprises an iron-nickel alloy containing 42% wt. % nickel (Alloy 42).

The drill bit 300 further comprises a bolting member 375 comprising a bolt. The bolting member 375 is configured to be housed in a bolt aperture 380. The bolting member 375 and bolt aperture 380 comprise complementary threads, such that the bolting member 375 can be securely screwed into the bolt aperture 380.

The bolt aperture 380 is located in the body portion 305, with a portion of the bolt aperture 380 passing through the collar 370. The bolt aperture 380 comprises a portion located in the retention member 330, such that when the retention member 330 is housed in the chamber 310, ready for use, the bolt aperture 380 forms a substantially uninterrupted path in which the bolting member 375 can be housed.

The bolting member 375 provides a retaining force thereby ‘locking’ the body portion 305 to the retention member 330, and further fixing the collar 370 to the remainder of the body portion 305.

The longitudinal axis of the bolt aperture 380 is perpendicular to, and intersects the longitudinal axis B′ of the chamber 310.

Claims

1. A drill bit comprising:

a body portion comprising at least one chamber,

the drill bit further comprising at least one cutting element, the at least one cutting element comprising a cutting edge and a retention member;

wherein the retention member is removably held within the chamber to retain the cutting edge at a first surface of the body portion;

wherein the retention member comprises a material with a higher coefficient of thermal expansion than the material of the body portion.

2. The drill bit of claim 1, wherein the coefficient of thermal expansion of the retention member is at least 15×10−6° C.-1 at 20° C.

3. The drill bit of claim 1, wherein the coefficient of thermal expansion of the body portion is no more than 6×10−6° C.-1 at 20° C.

4. The drill bit of claim 1, wherein the body portion further comprises an aperture, wherein the aperture intersects a second surface of the body portion and the aperture is connected to the chamber.

5. The drill bit of claim 4, wherein the first surface of the body portion and second surface of the body portion are different surfaces.

6. The drill bit of claim 4, wherein the drill bit further comprises at least one seal configured to maintain a minimum pressure within the chamber.

7. The drill bit of claim 6, wherein the at least one seal comprises a blocking member located in the aperture, the blocking member configured to inhibit airflow between the second surface of the body portion and the chamber.

8. The drill bit of claim 6, wherein at least one seal is located between the retention member and the body portion, the at least one seal configured to inhibit airflow between the first surface of the body portion and the chamber.

9. The drill bit of claim 8, wherein the at least one seal comprises a pair of seals located about the perimeter of the retention member.

10. The drill bit of claim 4, wherein the longitudinal axis of the aperture is substantially perpendicular to the longitudinal axis of the chamber.

11. The drill bit of claim 1, wherein the cutting edge is configured to be located concentrically on the retention member.

12. The drill bit of claim 1, wherein the cutting edge is configured to be located non-concentrically on the retention member

13. The drill bit of claim 1, wherein the retention member is configured to be removably held within the chamber with a clearance fit or a transition fit.

14. The drill bit of claim 1, wherein the body portion comprises chromium molybdenum alloy steel or a material with a cast tungsten carbide matrix.

15. The drill bit of claim 1, wherein the retention member comprises aluminium and/or a nickel-iron-chromium alloy.

16. The drill bit of claim 1, wherein the cutting edge comprises polycrystaline diamond compact, PDC.

17. The drill bit of claim 1, wherein the retention member is fixed to the cutting edge.

18. A kit of parts for a drill bit, the kit of parts comprising:

a body portion comprising at least one chamber, and

at least one cutting element, the at least one cutting element comprising a cutting edge and a retention member;

wherein the retention member is configured to be held within the chamber and retain the cutting edge at the first surface of the body portion;

wherein the retention member comprises a material with a higher coefficient of thermal expansion than the material of the body portion.

19. The kit of parts of claim 18, wherein the body portion comprises a plurality of chambers, and the kit of parts comprises a plurality of cutting elements.

20. A cutting element for use in the drill bit of claim 1.