Milling cutter having undulating chip breaker

A cutting element includes a front face and leading face extending between a first and second sides. A leading cutting edge is located at an intersection of the front face and the leading face, and an undulating back-up cutting edge is formed in the front face and extends from the first side to the second side, and defines a leading surface and a trailing surface. A method includes cutting with a tool having a blade coupled to a tool body, and a cutting element coupled to a forward surface of the blade. The cutting element has a leading cutting edge formed at an intersection of front and leading faces, and an undulating back-up cutting edge formed in the front face and defining leading and trailing surfaces. The leading cutting edge of the cutting element contacts and cuts a work piece.

BACKGROUND

Downhole milling tools may be used to, for example, form casing windows or remove entire sections of downhole casing. Downhole milling tools may also be used to remove metallic debris—known as “junk”—that has fallen into the wellbore.

Downhole milling tools may include a tubular body having a plurality of equi-azimuthally spaced cutting blades coupled to the body. Each cutting blade has a forward surface facing the direction of rotation of the tool which is dressed with a cutting material (e.g., one or more cutting elements disposed in an outer surface of the cutting blade). The cutting material may include or define a protruding ridge or chip breaker, which is a projection that limits the length of swarf or chip cut by the leading cutting edge of the element.

Chip breakers are used to prevent or reduce “birdnesting,” which is the term given to the long spirals of swarf that are cut from a tubular member (e.g., casing), that form into a conglomerate mass, which may restrict the flow of drilling mud about a tool, reduce the rate of penetration of the tool, and reduce the ability to carry cuttings back to the surface. Chip breakers may control the size of chips formed by the cutting element to increase the speed and efficiency of milling.

SUMMARY

In one aspect, embodiments disclosed herein relate to a cutting element including front and leading faces extending between first and second sides of the cutting element. A leading cutting edge is formed at an intersection of the front face and the leading face. An undulating back-up cutting edge is formed on the front face and extends from the first side to the second side. The undulating back-up cutting edge includes a leading surface and a trailing surface.

In another aspect, embodiments disclosed herein relate to a downhole tool including a tool body and a blade coupled to the tool body. The blade includes a forward surface and a cutting element is coupled to the forward surface. The cutting element includes a front and leading faces extending between first and second sides of the cutting element. A leading cutting edge formed at an intersection of the front face and the leading face. An undulating back-up cutting edge is formed in the front face and forms a leading surface and a trailing surface extending from the first side to the second side.

In yet another aspect, embodiments disclosed herein relate to a method of cutting with a downhole tool including deploying a downhole tool to a downhole position in a borehole. The downhole tool includes a tool body and a blade coupled to the tool body. The blade has a forward surface and a cutting element coupled to the forward surface. The cutting element includes a leading cutting edge formed at an intersection of a front face and a leading face of the cutting element. The cutting element also includes an undulating back-up cutting edge formed in the front face extending from a first side to a second side of the cutting element and forming a leading surface and a trailing surface. The leading cutting edge of the cutting element is contacted with a work piece and the downhole tool is rotated and translated.

DETAILED DESCRIPTION

In one aspect, one or more embodiments disclosed herein relate to a cutting element for a milling tool which incorporates an undulating back-up cutting edge which may act as a chip breaker. In another aspect, one or more embodiments disclosed herein relate to a downhole milling tool which includes a cutting element having an undulating back-up cutting edge. In yet another aspect, one or more embodiments disclosed herein relate to a method of cutting with a milling tool which includes a cutting element having an undulating back-up cutting edge.

Referring toFIG. 1, a partial cross-sectional view of a downhole milling tool100is shown in accordance with embodiments disclosed herein. The downhole milling tool100may have a tubular, substantially circular body101extending in a longitudinal direction from an upper end portion104to a lower end portion106. The downhole milling tool100may include an axial passage103therethrough for the circulation of fluid. The upper end portion104of the body101may include an internal screw thread105for connecting the body101to a drill string (not shown). A lower end portion106of the body101may have a “bull nose”108positioned to stabilize the milling tool within the borehole. The body101may have three, equi-azimuthally spaced longitudinal blades (two shown)107,109. One of ordinary skill in the art will appreciate that the downhole milling tool100may have fewer or more than three blades and that the blades may or may not be equally spaced about tool100. A plurality of cutting elements113may be disposed on a forward surface111of each blade107,109(i.e., facing forwardly in the direction of rotation of the downhole milling tool100). The cutting elements113may be coupled to each blade107,109by any convenient means known in the art such as by brazing, welding, soldering, mechanical fastening, or any combination of the foregoing.

Referring now toFIGS. 1-3, the cutting elements113may be positioned in radial rows115-118. The cutting elements113may be disposed in a “brickwork” pattern. In other words, by using cutting elements113of varying widths and/or offsetting some of the cutting elements113, the interface of radially adjacent cutting elements113may not be aligned with an interface of the cutting elements113of an adjacent longitudinal row. Now referring toFIG. 2, the cutting elements113may have differing widths so that some cutting elements are wider than others. For example, inFIG. 2, wide cutting element121is wider than intermediate cutting element123, which is in turn wider than narrow cutting element125. In one embodiment, the odd numbered rows115,117, as counted from a lower edge119of the blade107, may include one wide cutting element121. Rows116and118(both even numbered rows as counted from lower edge119of blade107) may include an intermediate cutting element123and a narrow cutting element125. Alternating rows116,118may alternate the positions of the intermediate cutting element123and narrow cutting element125. In other embodiments, other layouts of the cutting elements113are contemplated. For instance, even numbered rows may include wide cutting elements121, and odd numbered rows may include one narrow cutting element125and one intermediate cutting element123. In still other embodiments, some odd and even numbered rows may include wide cutting elements121, intermediate cutting elements123, or narrow cutting elements125, or some combination of the foregoing. In still other embodiments, rather than, or in addition to, the horizontal configuration of the rows115-118shown inFIG. 2, the rows115-118may be angled across the blade107, or may be vertically aligned.

In the embodiment ofFIGS. 1-3, the cutting elements113may be placed in an abutting radial and longitudinal relationship relative to one another, though one having ordinary skill in the an will understand in view of the disclosure herein that the cutting elements113may be spaced apart from one another longitudinally, radially, or both longitudinally and radially. Likewise, the blades107,109of the downhole tool100may be illustrated as having a zero or neutral rake angle and/or a zero or neutral lead angle, though one having ordinary skill in the art will understand in view of the disclosure herein that the downhole tool may be designed to position the blades to include a positive or negative rake and/or lead angle. Furthermore although the cutting elements113shown are rectangular and described in rectangular terms, one having ordinary skill in the art would understand that the cutting elements could comprise any shape such as, for example, a rectangle, triangle, rhomboid, star-shape, etc. Other shaped-cutting elements may also be used to form a brickwork pattern in some embodiments. In some embodiments, the cutting elements113may be formed as wafers having a rectangular, triangular, rhomboidal, star-shaped, circular, cylindrical, etc. shape. In such an embodiment, and as shown and described herein, cutting edges may extend side-to-side along the wafer (e.g., in an undulating pattern). Such cutting edge may be contrasted with a helical cutting edge extending between a top and bottom of a drill bit or other cutting element.

Referring now toFIGS. 2 and 3, each cutting element113may have a first side131, a second side133, a leading face130, and a front face132. The intersection of the leading face130and the front face132forms a leading cutting edge127. A plurality of undulating back-up cutting edges129may be formed in the front face132. Each undulating back-up cutting edge129may extend from the first side131to the second side133of the cutting element113. As illustrated inFIG. 4, each undulating back-up cutting edge129may vary in distance from the leading cutting edge127across the front face132of cutting element113(i.e., from the first side131to the second side133), forming a series of one or more high points134and one or more low points136. Each undulating back-up cutting edge129-1may be longitudinally spaced from an adjacent undulating back-up cutting edge129-2by a selected distance135. The high points134and low points136of each undulating back-up cutting edge129may substantially align, so that adjacent undulating back-up cutting edges129remain the selected distance135apart across the front face132of the cutting element113, although in other embodiments the selected distance135may vary across the front face132of the cutting element113. Each undulating back-up cutting edge129may have a period137. The period137may be measurable from, for example, a high point134to an adjacent high point (or a low point136to an adjacent low point, or as shown inFIG. 4, from a midpoint to a midpoint) on the same undulating back-up cutting edge129. Period137may relate to a width150of the cutting element113so that the undulating back-up cutting edges129of radially adjacent cutting elements113form a continuous edge profile across the interface between cutting elements113. Likewise, the selected distance135may relate to a height151of the cutting element113so that the undulating back-up cutting edges129of longitudinally adjacent cutting elements113may also form a continuous edge profile across the interface between cutting elements113. Optionally, the selected distance135may relate to an amplitude142, measured between the high points134and low points136of an undulating back-up cutting edge129. In some embodiments, the high point134-1of one undulating back-up cutting edge129-1may be farther from the leading cutting edge127than the low point136-1of the next adjacent undulating back-up cutting edge129-2. In other embodiments, the high point134-1of one undulating back-up cutting edge129-1may near or about the same distance from the leading cutting edge127relative to the low point136-1of the next adjacent undulating back-up cutting edge179-2.

Referring toFIG. 5, each undulating back-up cutting edge129may form a leading surface138and a trailing surface139. The leading surface138of each undulating back-up cutting edge129may intersect the trailing surface139of the adjacent undulating back-up cutting edge129. Each trailing surface139may then intersect the leading surface138of the next undulating back-up cutting edge129. The leading surface138of each undulating back-up cutting edge129may face the leading cutting edge127of the cutting element113. The leading surface138and the trailing surface139may define a recessed portion140between the adjacent undulating back-up cutting edges129.

One of ordinary skill in the art will appreciate in view of the disclosure herein that the dimensions of a cutting element113—including width150, height151, a depth152, selected distance135, period137, and amplitude142—may vary. For example, the height151may be between 0.1 inch (2.5 mm) and 3 inches (76 mm) and the width150may be between 0.1 inch (3 mm) and 6 inches (152 mm). In other embodiments, the height151may be between 0.3 inch (8 mm) and 0.5 inches (13 mm), and the width150may be between 0.3 inch (8 mm) and 1.5 inches (38 mm). In still other embodiments, where more than one cutting element113is used, one cutting element113may have a width150different from the width150of a second cutting element113. One of ordinary skill in the art will appreciate in view of the disclosure herein that the various dimensions of the cutting elements113may vary independent of other dimensions. For example, the width150may vary independently of the period137. Additionally, one of ordinary skill in the art will appreciate in view of the disclosure herein that the depth152may be between 0.05 inch (1 mm) and 1 inch (25 mm). In other embodiments, the depth152may be between 0.2 inch (5 mm) and 0.5 inch (13 mm). It will be understood that these dimension values are meant as examples and do not limit the scope of embodiments disclosed herein.

In some embodiments, the selected distance135may be between 0.03 inch (1 mm) and 0.15 inch (4 mm), the amplitude142may be between 0.03 inch (1 mm) and 0.15 inch (4 mm), and the period137may be between 0.25 inch (6 mm) and 1.5 inch (38 mm). In other embodiments, the selected distance135may be between 0.07 inch (1.8 mm) and 0.09 inch (2.3 mm), the amplitude142may be between 0.075 inch (1.9 mm) and 0.095 inch (2.4 mm), and the period137may be between 0.3 inch (8 mm) and 0.5 inch (13 mm). It will be understood that these dimension values are meant as examples and do not limit the scope of embodiments disclosed herein. Furthermore, will be understood that the selected distance135, amplitude142, and period137may each vary independently of any one or more of the width150, height151, or depth152. The number of undulating back-up cutting edges129may vary. In some embodiments, there may be between two and ten (or more) undulating back-up cutting edges129. In other embodiments, there may be between three and seven undulating back-up cutting edges129. In still other embodiments, there may be between four and six undulating back-up cutting edges129. Moreover, due to the undulating nature of the back-up cutting edges129, there may be different numbers of undulating back-up cutting edges129at different positions along the width150of the cutting element113. The number of undulating back-up cutting edges129may also vary as the cutting element113is eroded as discussed in more detail herein.

FIG. 6illustrates a detail view at6ofFIG. 5. As shown, the leading cutting edge127may define an axial rake angle141between the first trailing surface139and a line perpendicular to the leading face130of cutting element113(or parallel to the axis of the cutting tool and/or borehole). In some embodiments, the axial rake angle may be between about 0° and about 30°, though one having ordinary skill in the art will appreciate in view of the disclosure herein that this angle may vary. Additionally, each of the undulating back-up cutting edges129may define a land angle143as measured between leading surface138of the undulating back-up cutting edge129and a line perpendicular to the front face132of cutting element113. In some embodiments, the land angle143may be between about 0.1° and about 15°. The leading surface138may extend from the trailing surface139by distance145. In some embodiments, the distance145may be between about 0.005 inch (0.1 mm) and 0.25 inch (6 mm). It will be understood that these dimensions are meant as examples and do not limit the scope of embodiments disclosed herein. Cutting elements113may be formed from any material known in the art, for example, tungsten carbide, diamond (e.g., synthetic, natural, polycrystalline), tool steel, high speed steel, titanium carbide, cubic boron nitride, etc.

The undulating back-up cutting edges129so far depicted have had curvilinear undulations. For example, in some embodiments, the undulating back-up cutting edges129may be in the shape of sinusoidal curves extending from the first side131to the second side133as shown inFIGS. 1-4. The undulating back-up cutting edges129may, however, have other shapes that fall within the scope of this disclosure. For example,FIGS. 7 and 8depict a further embodiment of a cutting element213having undulating back-up cutting edges229formed in a front face232of cutting element213. The undulating back-up cutting edges229may vary in distance from the leading cutting edge227, forming sets of one or more high points234and sets of one or more low points236. Here, the undulating back-up cutting edges229may have non-smooth, or abrupt undulations, and the high points234and low points236may be located at abrupt transitions. InFIGS. 7 and 8, the abrupt transitions at the high points234and low points236may include intersections of straight line segments. As used herein, cutting edges with abrupt or non-smooth undulations refer to cutting edges that do not have a curvilinear profile. For example, the undulating back-up cutting edges229may be in the shape of a triangular waveform producing triangular undulations. In other embodiments, however, the undulating back-up cutting edges may have other forms or profiles. For instance,FIG. 9illustrates a cutting element313having undulating back-up cutting edges329in the shape of a sawtooth waveform such that the undulating back-up cutting edges329produce sawtooth undulations.FIG. 10illustrates another example cutting element414having undulating back-up cutting edges429in the shape of a square waveform such that the undulating back-up cutting edges429produce square undulations.

With continued reference toFIGS. 7 and 8, the cutting element213may have a leading cutting edge227. The leading cutting edge227and the undulating back-up cutting edges229may extend from a first side231to a second side233of the cutting element213. Each undulating back-up cutting edge229may be longitudinally spaced from an adjacent undulating back-up cutting edge229by a selected distance235. The high points234and low points236of each undulating back-up cutting edge229may substantially align, so that adjacent undulating back-up cutting edges229remain the selected distance235apart across the front face232of the cutting element213(i.e., from the first side231to the second side233). Each undulating back-up cutting edge229may have a period237, measured from, for example, a high point234to an adjacent high point, a low point236to an adjacent low point, or a middle point to an adjacent middle point on the same undulating back-up cutting edge229.

Referring toFIG. 8, each undulating back-up cutting edge229may form a leading surface238and a trailing surface239. The leading surface238of each undulating back-up cutting edge229may intersect the trailing surface239of the next adjacent undulating back-up cutting edge229. Each trailing surface239may then intersect the leading surface238of the next undulating back-up cutting edge229. The leading surface238of each undulating back-up cutting edge229may face the leading cutting edge227of the cutting element213. The leading surface238and the trailing surface239may define a recessed portion240between adjacent undulating back-up cutting edges229.

Depending on the work piece to be cut, for example, a downhole milling tool may have different configurations with different blade geometries and varying cutting element placement so that a leading cutting edge is aligned with the work piece. Work pieces may include, for example, plugs (e.g., bridge plugs), tubulars (e.g., other tools, casing, liners, etc.), downhole restrictions, broken tool components (e.g., roller cones and hand tools dropped down a borehole from the surface), and the like. One or more embodiments of a downhole milling tool may include a pilot mill, an expandable section mill, a taper mill, a junk mill, a follow mill, a dress mill, or a lead mill depending on the desired use. One or more embodiments may include, for example, the downhole milling tool100inFIG. 1arranged and designed to cut downhole casing in a longitudinal direction with a planar cut orthogonal to the longitudinal direction. Therefore, the lower end portion119of the blades109,111may extend substantially radially from the tool body101, about perpendicular to the longitudinal axis of the borehole. The cutting elements113may be mounted so that the leading cutting edge127also extends substantially radially from the tool body101, about perpendicular to the longitudinal axis of the borehole.

Referring toFIG. 11, during operation of a downhole milling tool (e.g., downhole milling tool100ofFIG. 1), the downhole milling tool may be lowered into a borehole on a drill string. The cutting element513may be placed in contact with a work piece550.FIG. 11depicts the cutting element513having a positive rake angle α, but one skilled in the art will understand in view of the disclosure herein that a negative or neutral rake angle may also be used and remain within the scope of this disclosure. The tool may then be rotated, also causing the cutting element513to rotate. The leading cutting edge527contacts the work piece550, and shaves a chip552from a top layer or exposed surface of the work piece550. The chip552continues to grow (i.e., lengthen) as more material from the work piece550is removed. When the chip552grows to a certain length, the chip552contacts the leading face537of the next undulating back-up cutting edge529. This contact may cause additional stress within the chip552, eventually causing the chip552to break from the work piece550. The distance535between the leading cutting edge527and the undulating back-up cutting edge529may determine the size of the chip552when it is broken off from the work piece550.

Without the undulating back-up cutting edge529, the chip552may grow unbounded into a long, tangled strand. Such a strand may wrap around the drill string, clog the borehole around the drill string, or even cut casing around the rotating drill string. This birdnesting may reduce the effectiveness and/or efficiency of a milling operation. As chips552are removed from the work piece550, the corresponding downhole milling tool may be steadily lowered or translated further into the borehole.

Referring toFIG. 12, a front elevation view of a cutting element613is shown. Because of the varying distances661,662of the leading cutting edge627to high points636and low points634of the undulating back-up cutting edge629-1, chips cut by the cutting edge629-1are broken off at different lengths depending on where along the width of the leading cutting edge627they are formed. For instance, the distance661from the leading cutting edge627to the undulating back-up cutting edge629-1is less at a point near the low point634than the distance662at a point near the high point636. Thus, a chip cut at661would be smaller than a chip cut at662. Because the undulating back-up cutting edge629-1is periodic, chips are broken at a designed average chip length. This average chip length may be controlled by the selected distance635between the undulating back-up cutting edges629-1,629-2.

Referring back toFIG. 11, as the cutting element513slidingly contacts the work piece550, a leading face547of the cutting element513may be eroded away, lowering the overall height535of the cutting element513. As this occurs, the leading cutting edge527may continuously move up the face of cutting element513. When the leading cutting edge527meets the leading surface537, the undulating back-up cutting edge529becomes the new leading cutting edge.

Referring toFIG. 13, the cutting element613is shown after the leading cutting edge627has been eroded back to a new leading cutting edge627-1. As the undulating back-up cutting edge629-1is eroded, the next adjacent undulating back-up cutting edge629-2may act as a chip breaker for portions671of the leading cutting edge627-1, while the undulating back-up cutting edge629-1continues to act as chip breaker for other portions672of the leading cutting edge627-1. Because the undulating back-up cutting edges629-1,629-2are spaced a distance635apart, the average chip length may remain substantially the same as the cutting element613is eroded. By maintaining a substantially stable average chip length throughout milling operations, the milling operation may proceed more expediently, as, for example, a feed rate—defined as the amount of the work piece550(FIG. 11) milled in a given amount of time—does not have to be varied in response to changing chip tenths resulting from erosion of the cutting element613.

In other embodiments, a downhole milling tool may be a taper mill. In a taper mill, the blades may be positioned to cut away a casing at an angle relative to the longitudinal axis of the borehole and the downhole trajectory of the mill. In such a mill,FIG. 14illustrates that the leading cutting edge727of a cutting element713may be oriented at an angle β relative to the trajectory799of the mill. A chip cut by the cutting element713therefore may not travel perpendicularly from the leading cutting edge727to the next undulating back-up cutting edge (e.g.,729-1,729-2). Instead, as shown inFIG. 14, a chip may follow an oblique path752-1to contact the undulating back-up cutting edge729-1at an angle. As the cutting element713wears and undulating hack-up cutting edge729-1is eroded, the next adjacent undulating back-up cutting edge729-2may act as a chip breaker for portion771of the leading cutting edge727, while the undulating back-up cutting edge729-1may continue to act as a chip breaker for one or more other portions772of the leading cutting edge727. Because a high point734of undulating back-up cutting edge729-1may be substantially the same distance from the leading cutting edge727as a low point736of the undulating back-up cutting edge729-2, there may be little or no gap across the leading cutting edge for unrestrained chip growth, also known as birdnesting, as even a very oblique chip path752-2may still contact the next adjacent undulating back-up cutting edge729-2. One having ordinary skill in the art will recognize in view of the disclosure herein that the high point734could be nearer to, or farther from, the leading cutting edge727than the low point736and still effect the disclosures herein. In an embodiment where a chip may pass through a gap between a high point734and a low point736, the chip may grow into a very long strand which may lead to birdnesting and resulting damage.

Those of ordinary skill in the art will also appreciate in view of the disclosure herein that while the high points734and low points736of adjacent undulating back-up cutting edges729-1,729-2may be generally aligned along the cutting element713(e.g., in a linear direction parallel the height of the cutting element713, in a direction offset at an angle β relative to the trajectory799of the mill, etc); however, other embodiments are contemplated. For instance, a line drawn between high points734and/or low points736of adjacent undulating back-up cutting edges729-1,729-2may be otherwise oriented. In some embodiments, for instance, a line drawn between high points734and/or low points736of the adjacent undulating back-up cutting edges729-1,729-2may be about parallel to the trajectory799of the mill. In such an embodiment, the selected distance between the undulating back-up cutting edges729-1,729-2may vary along the width of the cutting element713when measured in a direction parallel to the height of the cutting element713, but may be constant when measured along one or more of the oblique chip paths752-1,752-2.

Select embodiments may reduce the length of cuttings shaved from the surface of a work piece and restrict and potentially eliminate birdnesting. In certain embodiments, an undulating back-up cutting edge may provide for a relatively stable average chip length throughout the operation of the downhole milling tool even as the cutting element is eroded.

In other embodiments, a method of cutting with a downhole tool is described, and may include providing a downhole milling tool. A blade for multiple blades) may be coupled to the body of the downhole milling tool may have a forward surface. One or more cutting elements may be coupled to the forward surface of the blade. The cutting element can include a front face extending between a first side and a second side, a leading face extending between the first and second side, and a leading cutting edge formed at an intersection of the front face and the leading face. Additionally, the cutting element may have an undulating back-up cutting edge formed in the front face extending from the first side to the second side, forming a leading surface and a trailing surface. The method may also include contacting the leading cutting edge of the cutting element with a work piece. The method may also include rotating and/or translating the downhole tool.

In some embodiments, a method may also include shaving a chip from the work piece, contacting the chip with the leading surface of the undulating back-up cutting edge, and breaking the chip from the work piece. The chip may be broken from the workpiece by a leading face of a next undulating back-up cutting edge. In some embodiments, the method may also include eroding the leading face of the cutting element, the eroding forming a second leading face of the cutting element and a second leading cutting edge formed at an intersection of the front face and the second leading face of the cutting element. The second leading cutting edge may be located at the next undulating back-up cutting edge.

In some embodiments, the method may also include eroding a portion of the undulating back-up cutting edge, shaving a second chip from the work piece with the second cutting edge, contacting the second chip with a second leading surface of a second undulating back-up cutting edge, and breaking the chip from the work piece. The second undulating back-up cutting edge may also be formed in the front face a selected distance from the undulating back-up cutting edge. In some embodiments, the method may also include determining a selected distance to optimize an average chip size.