This invention relates to a cutting insert for use in a wellbore milling tool and to a wellbore milling tool provided with such a cutting insert. Milling tools are used, inter alia to cut out windows or pockets from a tubular, e.g. for directional drilling and sidetracking; and to remove material in a wellbore, for example redundant or jammed pipe, casing liners, tubing and jammed tools. The shape and configuration of the cutting inserts significantly effect the performance of the wellbore milling tool.

According to one aspect of the present invention there is provided a cutting insert for use in a wellbore milling tool, said cutting insert comprising a body having a base which can be mounted on a surface of said wellbore milling tool, and at least two cutting sur¬ faces, wherein each cutting surface is defined by linear boundaries which are substantially parallel to one another and which extend from a first edge of the cut¬ ting insert to a second edge of the cutting insert.

Further features of the invention are set out in Claims 2 to 16.

The present invention also provides a wellbore cutting tool provided with a cutting insert in accor¬ dance with the present invention.

By providing linear boundaries cuttings are sheared into multiple streams; i.e., rather than producing a single relatively wide cutting, the cutting insert produces narrower cuttings, one for each cutting sur¬ face.

The body of the cutting insert, as viewed from above or below, may be generally circular, square, oval, rectangular, or triangular in shape. For a better understanding of the present invention

reference will now be made, by way of example, to the accompanying drawings, in which:-

Fig. IA is a perspective view of a first embodiment of a cutting insert according to the present invention; Fig. IB is a top plan view of the cutting insert of Fig. IA;

Fig. IC is a partial side view of the cutting insert of Fig. IA;

Fig. ID is a front view of the cutting insert of Fig. IA;

Fig. IE is a bottom view of the cutting insert of Fig. IA;

Fig. IF is a rear view of the cutting insert of Fig. IA; Fig. 2A is a perspective view of a second embodi¬ ment of a cutting insert according to the present inven¬ tion;

Fig. 2B is a top view of the cutting insert of Fig. 2A (the bottom view is a plain square); Fig. 2C is a side view of the cutting insert of Fig. 2B;

Fig. 2D is a cross-sectional view taken along line 2D-2D of Fig. 2B;

Fig. 2E is an enlargement of a portion of the cutting insert encircled and identified by reference 2E in Fig. 2B;

Fig. 2F is a cross-sectional view of a chipbreaker in a central portion of the cutting insert as shown in Fig. 2D; Fig. 2G is a cross-sectional view of a chipbreaker in a side portion of the cutting insert as shown in Fig. 2D;

Fig. 2H is a cross-sectional view taken along line 2H-2H of Fig. 2E; Fig. 3A is a perspective view of a third embodiment

of a cutting insert according to the present invention;

Fig. 3B is a top view of the cutting insert of Fig. 3A;

Fig. 3C is a bottom view of the cutting insert of Fig. 3A;

Fig. 3D is a front view of the cutting insert of Fig. 3A;

Fig. 3E is a rear view of the cutting insert of Fig. 3A; Fig. 4A is a top view of a fourth embodiment of a cutting insert according to the present invention;

Fig. 4B is a cross-sectional view taken along line 4B-4B of Fig. 4A;

Fig. 4C is a cross-sectional view along line 4C-4C of Fig. 4A;

Fig. 5A is a perspective view of a fifth embodiment of a cutting insert according to the present invention;

Fig. 5B is a perspective view of the cutting insert of Fig. 5A shown producing multiple cuttings from a casing;

Fig. 6A shows one embodiment of a wellbore milling tool provided with cutting inserts according to the present invention;

Fig. 6B shows, to an enlarged scale, a portion of the wellbore milling tool of Fig. 6A;

Fig. 7 shows another embodiment of a wellbore milling tool provided with cutting inserts according to the present invention;

Fig. 8 is a plan view of a sixth embodiment of a cutting insert according to the present invention; and

Fig. 9 is a perspective view of a seventh embodi¬ ment of a cutting insert according to the present inven¬ tion.

Referring now to Figs. IA - IF, there is shown a cutting insert which is generally identified by refer-

ence numeral 10. The cutting insert 10 has a body 20 with four sides 21, 22, 23, 24. The body 20 is shown as square, but it may be rectangular, circular, oval, triangular or any desired shape. The top surface of the body 20 has three cutting surfaces 25, 26, and 27. The cutting surfaces 25 and 27 have a height t as shown in Fig. IA. The surface 26 (disposed between the cutting surfaces 25 and 27) has a height t + h as shown in Fig. IA. Each cutting surface 25, 26, 27 has a plurality of chipbreaker indentations 28 formed therein with a ridge 29 between each pair of chipbreakers. As viewed from the side the side 21 is like the side 23.

The body 20 has a width w and a length 1 (equal to each other in the square embodiment of Fig. IA). Each of the cutting surfaces 25, 26, 27 has a width a, three times which equals the width w. Sides 16 and 18 extend upwardly from the cutting surfaces 25 and 27 to the cutting surface 26. It is within the scope of this invention for the three cutting surfaces 25, 26, 27 to have different widths or for any two of the cutting surfaces to have the same width (either less than or greater than the width of the third cutting surface).

In certain preferred embodiments t + h ranges between about 5mm (3/16") and about 7mm (1/4"); and h ranges between about 0.8mm (.03") and about 2.3mm (.09"). In one embodiment 1 and w are about 13mm (.5"); t is about 2.3mm (.187"); a is about 4.2mm (.166"); and h is about 1.5mm (.06"). T is the angle between the surface of the ridges 29 and the sides of the cutting surface 26. In certain preferred embodiments T is ninety degrees or between eighty and ninety degrees. In certain preferred embodiments of such cutting inserts, or tools with such cutting inserts, cuttings are pro¬ duced which range in thickness between about 0.38mm (.015") and about 0.64mm (.025"), in length between

about 13mm (.5") and about 38mm (1.5"); and in width between about 3.2mm (.125") and about 4.3mm (.170"). In one embodiment cuttings about 0.4mm (.015") thick, about 4.3mm (.170") wide, and about 38mm (1.5") long are produced.

Fig. IC shows one of the chipbreaker indentations 28 and ridges 29. S is a distance from an edge of the ridge 29 to the center of the indentation 28. L is the width of the ridge 29. d is the depth of the indenta- tion 28. f is an angle between a portion of the inden¬ tation 28 and a vertical line drawn from an edge of a ridge 29 (not shown in Fig. IC). g is an angle between a portion of the indentation 28 and a vertical line drawn through the inner edge of the ridge 29 (Fig. IC). R is a radius of curvature of the angle V. V is an angle between ninety and one hundred and ten degrees..

In one preferred embodiment L ranges between 0.13mm (.005") and 0.38mm (.015"). In one particular embodi¬ ment L is 0.25mm (.01"); V is 102 degrees; f is 33 de- grees; g is 45 degrees; R is 0.76mm (.03"); S is 1.12mm (.044"); and d is 0.56mm (.022").

Fig. 2A shows a cutting insert which is generally identified by the reference numeral 40. The cutting insert 40 has a body 49; four sides 41, 42, 43, 44; cutting surfaces 45, 46, and 47; and a plurality of chipbreaking indentations 48. Angled interior side walls 39 in middle of the insert 40 extend from the side cutting surfaces 45, 47 down to the middle cutting surface 46. In certain embodiments of the cutting insert 40 (Figs. 2A-2H) the labelled features have the following preferred dimensional ranges:

A ( to 13mm) ( " to %" ) B (6.5mm to 8.7mm) (.25" to .335") C (3.2mm to 4.3mm) (.125" to .167")

D (4.8mm to ) (3/16" to " )

E ( 1.5mm to 2.9mm) ( .06" to . ,115")

F (0.1mm to 0.5mm) (.005" to .020" )

G (4.9mm to 6.7mm) (3/16" to %")

H (0.8mm to 2.34mm) (.030" to .090")

K 0° to 10°

L 0 ^β to 45 ^β

M 0° to 45°

N 0" to .2"

P 0 ^β to 45°

Q 25° to 45'

R .02" to .04"

S 0° to 45°

T 0 ^β to 45°

V 0° to 45°

W 0" to .2"

Letters N, W, R, in Figs. 2F, 2G, 2H, respectively indicate radii of chipbreaking recesses.

As shown in Fig. 2A the cutting insert 40 has the three cutting surfaces 45, 46, and 47 which are defined by linear boundaries running from one edge of the cut¬ ting insert to another edge of the cutting insert. The cutting surfaces each lie in a plane and the planes as shown are not coincident. The planes of the outside cutting surfaces 45 and 47 are at angle to the plane of the middle cutting surface 46 which is greater than 180°. The streams of cuttings produced by the two outside cutting surfaces 45 and 47 will diverge from the cuttings stream produced by the middle cutting surface 46. In another embodiment the angle of the outside planes with respect to the middle plane is less than 180" and the streams of cuttings produced by the outside cutting surfaces will converge on and be directed toward the cuttings stream produced by the middle cutting surface. It is within the scope of this invention to

provide a cutting insert with only two cutting surfaces (e.g. any two of the cutting surfaces of any cutting insert shown or described herein).

Fig. 3A shows a cutting insert 60 according to the present invention which has a body 19; four sides 61, 62, 63, 64; cutting surfaces 65, 66 and 67; and a plur¬ ality of chipbreaking indentations 68 with ridges 69 therebetween. The two sides of the insert 60, one shown in Fig. 3A, look the same. Figs. 4A - 4C shows a cutting insert 70 with a four sided body 75 with a plurality of ramps 76 in rows 71, 72, 73, and 74. Peaks 79 of ramps in one row are offset from those in another row.

Figs. 5A and 5B show inserts 80 and 81 designed by Mr. Robert Taylor and co-owned with the present inven¬ tion. The cutting insert 80 has a plurality of criss¬ crossing ridges 82, 83 between which are formed chip- breakers 84. The cutting insert 81 has a plurality of criss-crossing ridges 85, 86 between which are formed chipbreakers 87. As shown in Fig. 5B the insert 81 cuts a casing 88 to form three cuttings 89.

It will be noted that in the embodiments shown in Figs. 4A, 4B, 4C, 5A and 5B all the cutting surfaces lie in the same plane. However, the width of the chips is kept small by the boundaries of the cutting surfaces.

Fig. 6A and 6B show a pilot mill 110 according to the present invention which is similar to a prior art A- 1 TDS Pilot Mill; but provided with cutting inserts 102 according to the present invention (like any insert described and/or claimed herein) on blades 104 on a mill body 106 with an upper threaded end 108 and a lower pilot mill end 112.

Fig. 7 shows a pilot mill 150 according to the present invention (e.g. similar to that as referred to in U.S. Patent 4,984,488) with inserts 100 according to

the present invention (like any insert described and/or claimed herein) on blades 151 thereof. Such inserts may also be used on the bottom ends of the mills shown in Fig. 6A and in Fig 7. Fig. 8 shows a cutting insert 200 according to the present invention with an elliptical base 205 and an upper cutting surface that has an array of chipbreaker indentations 202 (like the array in Fig. 2B; like the indentations in Figs. IA and IC). The base 205 when viewed from below is like the top view of Fig. 8, but without any indentations. The middle cutting surface is lower than the two side cutting surfaces.

Fig 9 shows a cutting insert 250 according to the present invention with a circular base 255 and three cutting surfaces 256, 257, and 258. The cutting surfaces each are covered with chipbreaker indentations 252 separated by ridges 259.