CN1304719C

CN1304719C - Drill bit

Info

Publication number: CN1304719C
Application number: CNB018151892A
Authority: CN
Inventors: 弗雷德里克·丹姆豪夫; 朱勒·H·齐斯玲
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 2000-09-08
Filing date: 2001-09-06
Publication date: 2007-03-14
Anticipated expiration: 2021-09-06
Also published as: NO20031055D0; WO2002020936A2; AU1222102A; OA12369A; BR0113687A; GB0304377D0; WO2002020936A3; US20040020693A1; GC0000369A; GB2384505B; CN1452685A; NO20031055L; EG22664A; CA2421288A1; AU2002212221B2; AR030606A1; MXPA03001924A; GB2384505A

Abstract

The invention relates to a rotary drill bit for drilling a borehole in an earth formation, the drill bit comprising a first and a second disc cutter, each disc cutter being arranged to roll along the borehole bottom during rotation of the drill bit and thereby to cut respective first and second substantially circular, radially spaced cuts in the borehole bottom so that a body of rock material is defined between said cuts. The second disc cutter is arranged to cut into the bottom of the borehole at a selected rotational interval of the drill bit behind the first disc cutter and to shear-off said body of rock material in the direction of the first cut. Each disc cutter includes a set of mutually spaced cutting members arranged to create, during a turn of the drill bit, a corresponding set of cut sections of the cut created by the disc cutter, and wherein the cutting members are arranged so that the sets of cut sections created during subsequent drill bit turns are staggered relative to each other.

Description

Drill bit

Technical Field

The present invention relates to a rotary drill bit for drilling a borehole in an earth formation.

Background

There are many types of drill bits that are used in the prior art, such as gear bits or jet cutting bits. These bits are typically provided with a plurality of wear resistant cutting elements made of a material that is highly wear resistant, such as diamond or tungsten carbide. The cutting action of these cutting elements is mainly produced by grinding of these elements along the bottom of the bore hole. The progress of the drill bit in the borehole is determined by a number of factors, such as the amount of wear of the cutting elements, the hardness of the rock and the weight of the drill bit. Since the cost of drilling a well accounts for a large portion of the overall wellbore cost, there is a need to reduce drilling time, i.e., increase drilling rate.

WO99/11900 discloses a rotary drill bit comprising a plurality of disc cutters arranged on tapered rollers and capable of cutting a plurality of substantially circular and radially spaced-apart kerfs in the bottom of a bore hole. The set of cutters on each roller is moved radially relative to the set of cutters on the other roller so that for each pair of radially adjacent cutters, the second cutter of the pair cuts into the bottom of the borehole at a location behind the first cutter. A body of rock material is defined between the respective kerfs, which body will be sheared off by the second cutting member in the direction of the kerfs formed by the first cutting member.

It has been found that: it is known that the rate of penetration (ROP) of a drill bit into a formation is relatively low in certain rock formations, particularly hard rock formations, because it is difficult to shear a body of rock material along the upper end of a kerf formed by a first cutting member.

Disclosure of Invention

It is therefore an object of the present invention to provide an improved drill bit capable of increasing the rate of penetration ROP in these types of rocks.

According to the present invention there is provided a rotary drill bit for drilling a borehole in an earth formation, the drill bit comprising: a first disc-shaped cutting member and a second disc-shaped cutting member, each disc-shaped cutting member being configured to roll along the bottom of the borehole during rotation of the drill bit, so as to sever circular, radially spaced cutting slots at the bottom of the borehole, thereby confining a body of rock material between said cutting slots; the second disc-shaped cutting members being designed to cut into the borehole bottom at a selected rotational distance of the drill bit behind the first disc-shaped cutting members and to cut away the rock material body in the direction of the first grooving, each disc-shaped cutting member comprising a set of mutually spaced cutting elements arranged such that during one rotation of the drill bit a set of corresponding grooving portions is formed by the disc-shaped cutting members, characterized in that the cutting elements are further arranged such that sets of grooving portions formed during further rotation of the drill bit are in a mutually staggered configuration.

By the following features: each disc-shaped cutting member is formed of a set of discrete cutting elements which replace the continuous disc-shaped cutting elements of the prior art, thus reducing the instantaneous contact surface of the cutting elements with the bottom of the borehole and thereby allowing a greater depth of penetration of the drill bit into the rock formation for a given weight. In this way, the cutting slot formed by the cutting members is also deeper, so that more rock material bodies are sheared off in the direction of the lower end of the first cutting slot than in the direction of the upper end of the first cutting slot, compared to the prior art.

It should be noted that: since the disc-shaped cutting member is no longer continuous, a complete circumferential cut must be made after several revolutions of the drill. This can be achieved by dimensioning the drill bit in the following way: so that rock material interposed between the cutting groove portions formed by the cutting members during a previous rotation of the drill bit can be cut into by the cutting members during a subsequent rotation of the drill bit.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a bottom view of a drill bit according to the present invention;

FIG. 2 schematically illustrates a partial side view of the drill bit shown in FIG. 1;

FIG. 3 schematically illustrates a bottom view of tapered rollers of the drill bit shown in FIG. 1;

fig. 4 schematically shows a transverse cross-sectional view of the bottom of a borehole at various stages of drilling with the drill bit shown in fig. 1.

Detailed Description

In the drawings, like reference numerals denote like parts.

In fig. 1, a bottom view of a drill bit 1 is shown, the drill bit 1 being provided with a bit body 3 and three tapered rollers 4, 5, 6 arranged at an angular spacing of 120 ° with respect to the rotational axis 7 of the drill bit. The tapered rollers are rotatably connected to the bit body 3. The tapered roller 4 is provided with a set of disc-shaped cutting means 4a, 4b and 4c, the tapered roller 5 is provided with a set of disc-shaped cutting means 5a, 5b and 5c, the tapered roller 6 is provided with a set of disc-shaped cutting means 6a, 6b and 6c, each disc-shaped cutting means 4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b and 6c extending along the circumference of the respective tapered roller in a plane substantially perpendicular to the axis of rotation of the tapered roller. Each

disc cutting element

4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b and 6c is designed to cut a substantially circular slot in the bottom of the borehole as the respective roller 4, 5 and 6 rolls along the bottom of the borehole during rotation of the drill bit 1.

Referring to fig. 2, a partial side view of the drill bit 1 and tapered rollers 4 is shown. For the sake of simplicity, the tapered rollers 5 and 6 are not shown in the figures, but the parts of the

cutting members

5b, 5c, 6b and 6c that are in contact with the bottom of the bore hole at the respective points of contact are shown in dashed lines. The radially outermost cutting members 4a, 5a and 6a are designed to cut into the bottom of the borehole at equal radii relative to the axis 7, i.e. they are arranged at the same axial position on each tapered roller 4, 5 and 6. The

internal cutting members

4b, 4c, 5b, 5c, 6b and 6c are arranged on the tapered rollers 4, 5 and 6 in an axially (relative to the axis of rotation of the tapered rollers) staggered with respect to each other. In other words, the cutting member 5b cuts into the bottom of the borehole at a radius between the radii of the

cutting members

4a and 4b cutting into the bottom of the borehole; the cutting member 5c cuts into the bottom of the borehole at a radius between the radii of the

cutting members

4b and 4c cutting into the bottom of the borehole; the cutting member 6b also cuts into the bottom of the borehole at a radius between the radii of the

cutting members

4a and 5b cutting into the bottom of the borehole; the cutting member 6c also cuts into the bottom of the borehole at a radius that is between the radii of the cutting members 4b and 5c cutting into the bottom of the borehole.

Each disc cutting element is provided with two

side walls

10, 12, of which only the

respective side walls

10, 12 of the

cutting elements

4a, 4b and 4c are shown for clarity in fig. 2. Each pair of

sides

10, 12 defines a wedge-shaped cutting edge 14. Furthermore, each side 12 extends perpendicularly to the axis of rotation of the respective taper roller 4, 5 and 6 (indicated by reference numeral 16 on the taper roller 4), so that during drilling the side 12 is pressed against the rock in the direction of the axis of rotation 16. The side surface 20 extends parallel to the axis of rotation 7 of the drill bit 1 at a point where it contacts the bottom of the borehole.

As shown in fig. 2, each of the

disc cutting elements

4a, 4b, 4c, 5a, 5b, 5c, 6a, 6b, 6c is formed by a set of mutually spaced recesses 20, so that the remaining parts of the disc cutting elements correspondingly define a set of mutually spaced cutting members 22. For each tapered roller 4, 5 and 6, the groups of cutting elements 22 on adjacent cutting units are staggered with respect to one another.

Each tapered roller 4, 5, 6 is dimensioned such that the cutting members 22 of each disc cutting assembly on the tapered roller are able to form a set of cutback portions (not shown) at the bottom of the borehole during one revolution of the drill bit 1 and to allow relative rotation of the sets of cutback portions formed as the drill bit continues to rotate. In other words, during the next rotation of the drill bit 1, the cutting members 22 of the disc cutting members cut into the bottom of the borehole in a position not cut by the preceding cutting member 22. This is illustrated as follows: the complete circular cutting groove is formed by the disc cutting members after a number of revolutions of the drill bit 1.

In the case of cutting elements 22 spaced apart from one another at equal distances along the circumference of the respective circular disc cutting element, i.e. in the case of the embodiment shown, the desired dimensioning can be achieved if it is desired to avoid cutting the cutting elements 22 exactly into the same slots formed in the previous turn during the next turn of the drill bit. One approach is to do this by avoiding the occurrence of the following conditions: l is i × T, where L is the circumference of the slot, i is the integer 1, 2, 3.

Since T ═ pi × D/n and L ═ pi × D, where D is the rolling diameter of the disk cutting unit, n is the number of cutters of the disk cutting unit, and D is the diameter of the flutes formed by the cutting unit, this yields: if D/D is (i + f)/n, wherein: f is a coefficient, 0 < f < 1, then the dimensions can be correctly designed.

Preferably, f is 0.3 < 0.7. For example, f may be about 0.5, which may allow a complete undercut to be formed in about two revolutions of the bit.

The values of D and D may be chosen in such a way that 1.5 < D/D < 2.0 is satisfied.

In fig. 3, a bottom view of the tapered rollers 4 is shown, showing the angular part a of the extension of the cutting members of the disc cutting unit, and the angle β of the extension of the grooves between the cutting members, the angles α and β satisfying the relation α ═ β + δ, where 0 ° < δ < 4 °. Also shown are the values for the angular ranges of the cutters and recesses (32 for cutters and 28 for recesses) for one embodiment. The figure also shows a situation where the cutting elements of the circular cutting element 4a and the circular cutting element 4b overlap each other by 2 deg.. There is also a similar angular overlap of the cutting elements in the

respective cutting elements

4b, 4 c.

The taper rollers 4, 5, 6 are furthermore provided with conventional hard cutting inserts 26 on the outermost cutting parts 4a, 5a, 6a and on the inner parts of the taper rollers.

During normal operation, the drill bit 1 rotates in the borehole, which causes the tapered rollers 4, 5, 6 to roll and cut along the bottom of the borehole. The cutting operation will be described below only with respect to the

cutting members

4b, 5b and 6b, since the operation of the other cutting members is similar to the cutting members described above.

Referring to fig. 4, the

cutting members

4b, 5b and 6b

form cutting flutes

32, 34 and 36 adjacent to each other at the bottom of the bore. These slots are indicated by straight lines, but in practice the shape of the slots corresponds to a different extent to the shape of the part of the cutting member that penetrates the bottom of the bore hole. The lines f, g, h, I, j represent the envelope of the lower ends of the disc-

shaped cutting members

4b, 5b and 5c as a function of the drill rotation angle. Thus, the drill bit starts rotating in the borehole from 0 of rotation at depth f, line g represents the height level at which the drill bit rotates 120, line h represents the height level at which the drill bit rotates 240, line I represents the height level at which the drill bit rotates 360, and line j represents the height level at which the drill bit rotates 480.

At a rotation angle of 120 deg., the cutting portion 4b has located the incision 36 at a height g. At a rotation angle of 240 °, the cutting member 5b positions the cutting slot 34 at a height h. In this way, the body of rock material 38a is defined between the cutting slot 36 at a height level h and the cutting slot 34 at a height level g, while the body of rock material 38a is sheared by the side 12 of the cutting element 5b along a line s1 extending between the cutting

slots

36 and 34.

At a 360 deg. angle of rotation, the cutting element 6b has formed a cutting groove 32 at a height i, whereby a body 38b of rock material is confined between the cutting groove 34 at a height level g and the cutting groove at a height level i, while the body 38b of rock material is sheared off by the side 12 of the cutting element 6b along a line s2 extending between the cutting grooves 34 and 32.

At a corner of 480 deg., the cutting element 5b has formed a cutting slot 34 at a height j, so that a body 38c of rock material is defined between the cutting slot 36 at a height level i and the cutting slot 34 at a height level j, the body 38c of rock material being sheared by the side of the cutting element 5b along a line s3 extending between the cutting

slots

36 and 34.

Similarly, after a further rotation of 120, a rock material body 38d is confined between the cutting slot 34 at the height level j and the deeper lying cutting slot 32, while the rock material body 38d is sheared by the side of the cutting element 6b along a line s4 extending between the cutting

slots

36 and 34.

The outer cutting members 4a, 5a and 6a will cut and shear off rock material located between the cutting slot (not shown) formed by the cutting members and the cutting slot 32 formed in a similar manner by the cutting portion 5 b. The cutting action of the cutting members 4c, 5c, 6c is similar to the cutting action of the cutting

members

4b, 5b, 6 b.

The discrete cutting portions formed by the cutting members 22 will extend to a greater depth into the bottom of the borehole than the flutes formed by the continuous disk cutting members (i.e., cutting members without flutes) of the same weight on the drill bit. The body of rock material between adjacent cutting flutes is thus relatively large in the direction of drilling by the drill bit, so that superficial cutting of the surface layer only when performing drilling operations in hard earth formations can be avoided, and drilling efficiency can thus be improved.

Claims

1. A rotary drill bit for drilling a borehole in an earth formation, the drill bit comprising: a first disc-shaped cutting member and a second disc-shaped cutting member, each disc-shaped cutting member being configured to roll along the bottom of the borehole during rotation of the drill bit, so as to sever circular, radially spaced cutting slots at the bottom of the borehole, thereby confining a body of rock material between said cutting slots; the second disc-shaped cutting members being designed to cut into the borehole bottom at a selected rotational distance of the drill bit behind the first disc-shaped cutting members and to cut away the rock material body in the direction of the first grooving, each disc-shaped cutting member comprising a set of mutually spaced cutting elements arranged such that during one rotation of the drill bit a set of corresponding grooving portions is formed by the disc-shaped cutting members, characterized in that the cutting elements are further arranged such that sets of grooving portions formed during further rotation of the drill bit are in a mutually staggered configuration.

2. The rotary drill bit of claim 1, wherein: the cutting pieces are distributed on the cutting part at basically same intervals; the drill bit is dimensioned in such a way that it satisfies the following formula: D/D ═ i + f)/n,

wherein,

d is the diameter of the cut made by the cutting member;

n is the number of cutting pieces of the cutting part;

d is a rolling member of the cutting member;

i ═ integer 1, 2, 3,. et al;

f is a coefficient, 0 < f < 1.

3. The rotary drill bit of claim 2, wherein: f is more than 0.3 and less than 0.7.

4. The rotary drill bit of claim 3, wherein: f is 0.5.

5. The rotary drill bit of any one of claims 2 to 4, wherein: D/D is more than 1.5 and less than 2.

6. The rotary drill bit of any one of claims 1 to 4, wherein: the drill bit comprises a bit body and a plurality of tapered rollers interconnected with the bit body such that they can roll within the bore substantially along the bottom of the bore and be positioned in different radial orientations during rotation of the drill bit, wherein a first tapered roller is provided with a first disc-shaped cutting member and a second tapered roller is provided with a second disc-shaped cutting member.

7. The rotary drill bit of claim 6, wherein: each tapered roller is provided with a plurality of disc-shaped cutting components which are positioned at intervals along the axial direction of the tapered roller; the cutting parts of adjacent cutting parts on the tapered rollers are staggered.

8. The rotary drill bit of any one of claims 1 to 4, wherein: angles α and β are defined for each disc-shaped cutting member, angle α being the angular portion over which each cutting piece of the disc-shaped cutting member extends, angle β being the angular portion over which the spacing between adjacent cutting pieces of the disc-shaped cutting member extends, wherein α ═ β + δ, and 0 ° < δ < 4 °.

9. The rotary drill bit of claim 8, wherein: delta is more than 1 degree and less than 3 degrees.

10. The rotary drill bit of claim 9, wherein: δ is 2 °.

11. The rotary drill bit of any one of claims 1 to 4, wherein: each group of cutting parts is defined by a group of grooves which are arranged on the disk-shaped cutting part and are positioned at intervals, and a plurality of groups of cutting parts are arranged on the disk-shaped cutting part.