HELICAL CHISEL INSERT FOR ROCK BITS

Abstract

An insert for an earth boring drill bit, such as a PDC rock bit or a roller cone rock bit, is provided. The insert includes a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest.

Description

FIELD OF THE INVENTION

This invention relates in general to earth boring devices used in oil field applications, and, more particularly, to inserts for earth boring rotary cone rock bits.

BACKGROUND

Conventional earth boring rotary cone rock bits are commonly used in oil field applications. Rotational energy and weight applied to the bit by the drill pipe force the rotary cutters into earth formations. The borehole is formed as the punching and scraping action of the rotary cutters remove chips of formation. The rate at which borehole is formed is largely a result of the design of the rotary cutters. One main category of rotary cutters is tungsten carbide insert (TCI) cutters. The teeth on TCI cutters are made of tungsten carbide and are press fit (inserted) into undersize apertures on the cone. The teeth on the cutters functionally break up the formation to form new borehole by punching into it vertically and scraping horizontally. The amount of punching action is governed primarily by the weight on the bit. The horizontal scraping motion is a resultant of the position and shape of the cone cutter.

Medium and soft formation bits usually drill through varied formations in a single well. Recording devices which show instantaneous rates of penetration will often show rates as high as four feet per minute and rates as slow as one foot in ten minutes on the same bit run. As a rule, the formations tend to become harder as depth increases but there are large variations in hardness at all depths.

Bits having long inserts are typically most efficient for fast drilling in soft formations. Long inserts are relatively weak though, and are subject to breakage in the slower drilling hard formations. Short blunt inserts are better suited for the harder formations because they are less subject to breakage, but they limit a bit's penetration rate in soft formations.

Accordingly, there is a need for wear resistant inserts for drilling bits that provide a high rate of penetration in both soft and hard formations while providing resistance to insert breakage.

SUMMARY OF THE INVENTION

An insert for an earth boring drill bit is provided. The insert includes a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest.

A drill bit for boring an earth formation is provided. The drill bit includes a plurality of helical chisel inserts.

A method for drilling an earth formation is provided. The method includes the steps of providing a rotary cone cutter having a plurality of cutters, wherein each cutter has an axis of rotation for plowing the formation in a direction, and comprises an outermost heel row and a second row, positioning a first set of helical chisel inserts on the heel row, and positioning a second set of helical chisel inserts on the second row. The helical chisel inserts each include a base integrally joined to a top section, the top section having a leading flank and a trailing flank that curve in a substantially helical manner about a longitudinal axis of the insert to join an elongated crest.

The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:

FIG. 1 is a cross-sectional view of a portion of an embodiment of a TCI tri-cone rock drill bit of the present invention, showing one cone cutter rotatably mounted on a bearing pin shaft;

FIG. 2 is a front elevational view of an embodiment of the rock drill bit insert of the present invention;

FIG. 3 is a top view of the insert of FIG. 2;

FIG. 4 is a front elevational view of another embodiment of the rock drill bit insert of the present invention;

FIG. 5 is a schematic view of a bore hole bottom showing insert tracks left by an embodiment of the roller cone cutter, wherein the helical chisel inserts have been positioned for reducing insert breakage; and

FIG. 6 is a schematic view of a bore hole bottom showing insert tracks left by an embodiment of the roller cone cutter, wherein the helical chisel inserts have been positioned for increasing penetration rate.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.

As used herein, the terms “up” and “down”; “upper” and “lower”; “uphole” and “downhole” and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements of the embodiments of the invention. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point.

The present invention is directed to a helical chisel insert for a drill bit, such as a roller cone bit. The helical design of the insert provides an aggressive shape for increased penetration during drilling. In addition, the helical chisel insert is suitable for positioning the inserts in a vectored manner on the drill bit to achieve an orientation that provides increased resistance to insert breakage and/or and increased rate of penetration.

FIG. 1 shows a drill bit in accordance with an embodiment of the present invention, indicated by 2. Drill bit 2 has a threaded section 4 on its upper end for securing to the drill string (not shown). A frusto-conical roller cone cutter 8 is rotatably mounted and secured on the bearing pin shaft 16 which extends downward and inward, from the bottom of the journal segment arm 6. Cone cutter 8 has a cutting structure consisting of helical chisel inserts 22. Helical chisel inserts 22 are mounted on either heel row 10, second row 12, inner row 14, or any combination thereof Helical chisel inserts 22 may be press fit into hole 9 or otherwise positioned on cone cutter 8. Helical chisel inserts 22 may be made from any suitable material including tungsten carbide, diamond enhanced tungsten carbide, diamond or polycrystalline diamond compact (PDC). Cone cutter 8 may include conventional inserts on those rows where helical chisel inserts 22 are not mounted. The cone cutters 8 are rotatably mounted on journals with sliding bearing surfaces. The axis of rotation 18 of the cone cutter 8 extends inwardly through the center of the bearing pin shaft 16 toward and offset from the axis of rotation 20 of the drill bit 2. Although FIG. 1 depicts drill bit 2 as a roller cone bit, it will be understood by those of ordinary skill in the art that the helical chisel insert of the present invention may be used in PDC bits and other types of drill bits.

FIGS. 2 and 3 show front and top views, respectively, of an embodiment of the helical chisel insert 22a of the present invention. FIG. 4 shows the front view of another embodiment of helical chisel insert 22b of the present invention. As shown in FIGS. 2-4, helical chisel insert 22 has a cylindrical base 24 which may be inserted in hole 9 with its longitudinal axis 26 being normal to the surface 21 of cutter 8 (hole 9 and surface 21 shown in FIG. 1). A top portion 50, which is connected to cylindrical base 24, includes a cutting tip 28 and an elongated crest 36 having a length 52 along its broad side and a width 53. Top portion 50 has two faces or flanks, leading flank 30 and trailing flank 32. Flanks 30 and 32 commence at the joinder of the top portion 50 and cylindrical base 24, shown as corners 42 and 44, respectively, and curve upwards in a substantially helical manner about longitudinal axis 26, to join crest 36 at corners 38 and 40, respectively. Flanks 30 and 32 define substantially concave surfaces 46 and 48. As is apparent from FIGS. 2-4, flanks 30 and 32 define a contoured surface that is continuously twisted from the top of base 24 to the crest 36 such that iterative cross sections of top portion 50 will describe a helix at their outermost points.

The contoured surface of helical chisel insert 22 provides a more aggressive cutting surface than convention chisel inserts and may provide a greater rate of penetration than conventional chisel inserts. The shape of helical chisel insert 22 may allow insert 22 to plow through the formation, as opposed to merely striking the formation. As a result, helical chisel insert 22 may remove more rock for a given position in the drill bit than a conventional insert. For example, helical chisel inserts 22 may provide a more aggressive insert in soft formation drilling by orientating the elongated crest 36 of the cutting tip 28 preferentially with the cutting or plowing action of the drilled formation relative to the chisel rolling direction. The result may be faster rates of penetration for the drill bit 2 as a whole. Helical chisel inserts 22 may add improved plowing action to the insert over conventional inserts as helical chisel insert 22 describes its arc into, through and out of the formation being drilled.

Helical chisel insert 22 has a degree of twist θ, measured from the longest axis of the bottom cross section to the longest axis of the elongated crest 36. The degree of twist θ may be selected based on the desired characteristics including, for example, penetration rate and resistance to breakage. The embodiment of helical chisel insert 22a shown in FIGS. 2 and 3 has a degree of twist θ of about 90°, for example. The embodiment of helical chisel insert 22b shown in FIG. 4, has a degree of twist θ of about 15°, for example. Flanks 30 and 32 may curve either substantially clockwise or substantially counterclockwise. Flanks 30 and 32 may have a twist from about 90° clockwise to about 90° counterclockwise, thus describing the entire 360° radius. Flanks 30 and 32 may be selectively shaped to provide different crest 36 geometries that describe the degree of twist in variations of an “s” shape, but within the same insert diameter. Helical chisel insert 22 may incorporate timing mark 54 to assist a user with positioning helical chisel inserts 22 on drill bit 2 in a precise manner.

Although FIGS. 2-4 depict helical chisel bit 22 with two flanks, it will be understood by those of ordinary skill in the art that other embodiments of the helical chisel insert of the present invention may include only one flank, or may include more than two flanks. Similarly, while FIGS. 2-4 depict helical chisel bit 22 with an substantially elongated crest, it will be understood by those of ordinary skill in the art that other embodiments of the helical chisel insert of the present invention may include different crest formations depending on the number of flanks and the selected contour geometry, among other factors.

Helical chisel inserts 22 may be positioned on rolling cone cutter 8 in a vectored manner such that the elongated crests 36 are selectively oriented with respect to the direction of plowing action. By vectoring helical chisel inserts 22 in this manner, a drill bit 2 may be selectively configured to provide a greater rate of penetration, improved resistance to breakage, or a combination thereof. Embodiments of this vectored positioning are shown in FIGS. 5 and 6.

FIG. 5 is a schematic view of a borehole bottom showing the impression left by helical chisel inserts 22 on the two outer rows of a cone cutter, selected and positioned thereon to reduce insert breakage. The direction of bit rotation is indicated by arrow 56. By orienting (vectoring) the elongated crests 36 of the inserts 22 in line with the insert movement a helical chisel insert 22 presents a very small face to the formation. The insert 22 can withstand higher forces (or harder formations) in this situation. The helical chisel inserts 22 on the outermost heel row have a selected angle of twist θ such that crests 36 are oriented at an angle from about 30° to about 60° from the axis of rotation of the cone toward the leading side of the cone. The helical chisel inserts 22 on the second row have a selected angle of twist θ such that crests 36 are oriented at an angle from 30° to 60° from the axis of the cone toward the trailing side of the cone. Stated another way, the elongated crests on the heel row are oriented at an azimuth direction ranging from 300° to 330° from the axis of rotation of the cone with the axis being equal to 360°. The elongated crests on the second row are oriented at an azimuth direction of 30° to 60° from the axis of the cone.

With such an orientation, the insert 22 moves in formation in a direction in line with the elongated crest 36 so that a relatively small area, about width 53 of the insert 22, contacts the formation and relatively small chips are formed. The relatively thick section of tungsten carbide, for example, along the length 54 of the crest 36 provides a very high resistance to insert breakages. This type of insert orientation provides a cone cutter with much higher resistance to breakage than a similar cutter with conventional insert orientation.

The direction of bit rotation is indicated by arrow 56. The initial engagement of the elongated crests of the heel row inserts is indicated by 58. The disengagement of the elongated crests of the heel row inserts is indicated by 66 with the direction of the plowing of formation represented by arrow 62. The elongated crests of the second row inserts engage 60 and disengage 68 the formation in the direction indicated by arrow 64.

Alternatively, the angle of twist θ may be selected to orient or vector the crest 36 so that the broad side 52 of the insert crest 36 faces the direction of the plowing action. In this case, each insert 22 removes more formation, resulting in a faster penetration rate. This configuration is illustrated in FIG. 6, which is a schematic view of a borehole bottom showing insert tracks left by inserts 22 on the two outer rows of a cone cutter, where the inserts are oriented for increasing penetration rate. As shown in FIG. 6, the elongated crests 36 of the helical chisel inserts 22 are relatively perpendicular to the direction of the plowing action, indicated by arrow 88. The elongated crests 36 of the inserts 22 positioned on heel row 10 are oriented at an angle of 30° to 60° toward the trailing side of the cone. The elongated crests 36 of the inserts 22 on second row 12 are oriented at an angle of 30° to 60° toward the leading side of the cone. Stated another way, the elongated crests of the heel row inserts are oriented at an azimuth direction ranging from about 30° to 60° from the axis of rotation of the cone. The elongated crests of the second row inserts are oriented at an azimuth direction of 300° to 330° from the axis of rotation of the cone with the axis being equal to 360°. This orientation may break formation along a wider path, making more chips and larger chips than orientation of standard TCI bits, resulting in an increase penetration rate.

The direction of bit rotation is indicated by arrow 82. The initial engagement of the elongated crests of the heel row inserts is indicated by 84. The disengagement of the elongated crests of the heel row inserts is indicated by 86 with the direction of the plowing of formation represented by arrow 88. The elongated crests of the second row inserts engage 90 and disengage 92 the formation in the direction indicated by arrow 94.

The embodiments shown in FIGS. 5 and 6 show an angle of twist θ of about ±30°. Other embodiments of the helical chisel inserts of the present invention, however, may have a twist from about 90° clockwise to about 90° counterclockwise, thus describing a greater range. As a result, the helical chisel inserts allow for an increased degree of freedom in configuring the drill bit to improve resistance to insert breakage, rate of penetration, or a balance of both.

The helical chisel inserts of the present invention may provide a more aggressive cutting surface than convention chisel inserts and may provide a greater rate of penetration than conventional chisel inserts. The helical chisel inserts may add improved plowing action to the insert over conventional inserts as the helical chisel insert describes its arc into, through and out of the formation being drilled. If the insert life is given priority over the rate of penetration, the helical chisel insert may be described in reverse rotation. The helical chisel inserts also provide an insert designer with another degree of freedom to optimize chisel contour geometries to accommodate the particular stresses and wear patterns observed downhole.

From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a helical chisel insert for rock bits that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.

Claims

1. An insert for an earth boring drill bit having a base integrally joined to a top section, the top section having a first flank that curves in a substantially helical manner about a longitudinal axis of the insert to join a crest.

2. The insert of claim 1, further comprising a polycrystalline diamond compact (PDC) insert.

3. The insert of claim 2, wherein the earth boring device is a PDC rock bit.

4. The insert of claim 1, further comprising a second flank that curves in a substantially helical manner about the longitudinal axis of the insert to join the crest.

5. The insert of claim 4, further comprising a degree of twist in a range from about 0° to about 90°.

6. The insert of claim 5, wherein the flanks curve in either a substantially clockwise manner or a substantially counterclockwise manner.

7. The insert of claim 6, further comprising a tungsten carbide insert (TCI).

8. The insert of claim 6, further comprising a diamond enhanced TCI.

9. The insert of claim 6, wherein the earth boring device is a rotary cone rock bit.

10. The insert of claim 6, wherein the earth boring device is a PDC rock bit.

11. The insert of claim 5, further comprising a timing mark.

12. A drill bit for boring an earth formation, the drill bit comprising a plurality of helical chisel inserts.

13. The drill bit of claim 12, wherein the drill bit further comprises a PDC drill bit.

14. The drill bit of claim 12, further comprising a rotary cone rock bit having a plurality of cutters for plowing the formation in a selected direction, wherein each cutter has a circumferential outermost heel row with helical chisel inserts positioned thereon.

15. The drill bit of claim 14, wherein each cutter has a circumferential second row with helical chisel inserts positioned thereon

16. The drill bit of claim 15, wherein the helical chisel insert further comprises a base integrally joined to a top section, the top section having a leading flank and a trailing flank that curve in a substantially helical manner about a longitudinal axis of the insert to join an elongated crest.

17. The drill bit of claim 16, wherein the elongated crests of the helical chisel inserts positioned on the heel row are substantially in line with the direction of plowing of the formation.

18. The drill bit of claim 17, wherein the elongated crests of the helical chisel inserts positioned on the second row are substantially in line with the direction of plowing of the formation.

19. The drill bit of claim 16, wherein a broad side of the elongated crests of the helical chisel inserts positioned on the heel row substantially face the direction of plowing of the formation.

20. The drill bit of claim 19, wherein a broad side of the elongated crests of the helical chisel inserts positioned on the second row substantially face the direction of plowing of the formation.

21. A method for drilling an earth formation, comprising the steps of: providing a rotary cone cutter having a plurality of cutters, wherein each cutter has an axis of rotation for plowing the formation in a direction, and comprises an outermost heel row and a second row;positioning a first set of helical chisel inserts on the heel row; andpositioning a second set of helical chisel inserts on the second row, wherein the helical chisel inserts each comprise a base integrally joined to a top section, the top section having a leading flank and a trailing flank that curve in a substantially helical manner about a longitudinal axis of the insert to join an elongated crest.

22. The method of claim 21, further comprising the steps of: aligning the elongated crests of the first set of helical chisel inserts at an azimuth direction from about 30 degrees to about 60 degrees from the axis of rotation of the cutter; andaligning the elongated crests of the second set of helical chisel inserts at an azimuth direction from about 300 degrees to about 330 degrees from the axis of rotation of the cutter.

23. The method of claim 21, further comprising the steps of: aligning the elongated crests of the first set of helical chisel inserts at an azimuth direction from about 300 degrees to about 330 degrees from the axis of rotation of the cutter; andaligning the elongated crests of the second set of helical chisel inserts at an azimuth direction from about 30 degrees to about 60 degrees from the axis of rotation of the cutter.

24. The method of claim 21, further comprising the steps of: aligning the elongated crests of the first set of helical chisel inserts and the second set of helical inserts substantially in line with the direction of plowing of the formation.

25. The method of claim 21, further comprising the steps of: aligning the elongated crests of the first set of helical chisel inserts and the second set of helical chisel inserts substantially perpendicular to the direction of plowing of the formation.