Cutter having shaped working surface with varying edge chamfer

A cutter for a drill bit used for drilling wells in a geological formation includes an ultra hard working surface and a chamfer along an edge of the working surface, wherein the chamfer has a varied geometry along the edge. The average geometry of the chamfer varies with cutting depth. A depression in the shaped working surface is oriented with the varied chamfer and facilitates forming the varied chamfer. A non-planar interface has depressions oriented with depressions in the shaped working surface to provide support to loads on the working surface of the cutter when used.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to drill bits in the oil and gas industry, particularly to drill bits having cutters or inserts having hard and ultra hard cutting surfaces or tables and to cutters or inserts for drill bit such as drag bits and more particularly to cutters and inserts with ultra hard working surfaces made from materials such as diamond material, polycrystalline diamond material, or other ultra hard material bonded to a substrate and/or to a support stud.

2. Background Art

Rotary drill bits with no moving elements on them are typically referred to as “drag” bits. Drag bits are often used to drill very hard or abrasive formations. Drag bits include those having cutters (sometimes referred to as cutter elements, cutting elements or inserts) attached to the bit body. For example the cutters may be formed having a substrate or support stud made of cemented carbide, for example tungsten carbide, and an ultra hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate at an interface surface.

An example of a prior art drag bit having a plurality of cutters with ultra hard working surfaces is shown inFIG. 1. The drill bit10includes a bit body12and a plurality of blades14that are formed in the bit body12. The blades14are separated by channels or gaps16that enable drilling fluid to flow between and both clean and cool the blades14. Cutters18are held in the blades14at predetermined angular orientations to present working surfaces20with a desired rake angle against a formation to be drilled. Typically, the working surfaces20are generally perpendicular to the axis19and side surface21of a cylindrical cutter18. Thus the working surface20and the side surface21form a circumferential cutting edge22. Nozzles23are typically formed in the drill bit body12and positioned in the gaps16so that fluid can be pumped to discharge drilling fluid in selected directions and at selected rates of flow between the cutting blades14for lubricating and cooling the drill bit10, the blades14and the cutters18. The drilling fluid also cleans and removes the cuttings as the drill bit rotates and penetrates the formation. The gaps16, which may be referred to as “fluid courses,” are positioned to provide additional flow channels for drilling fluid and to provide a passage for formation cuttings to travel past the drill bit10toward the surface of a wellbore (not shown).

The drill bit10includes a shank24and a crown26. Shank24is typically formed of steel or a matrix material and includes a threaded pin28for attachment to a drill string. Crown26has a cutting face30and outer side surface32. The particular materials used to form drill bit bodies are selected to provide adequate toughness, while providing good resistance to abrasive and erosive wear. For example, in the case where an ultra hard cutter is to be used, the bit body12may be made from powdered tungsten carbide (WC) infiltrated with a binder alloy within a suitable mold form. In one manufacturing process the crown26includes a plurality of holes or sockets34that are sized and shaped to receive a corresponding plurality of cutters18. The combined plurality of cutting edges22of the cutters18effectively forms the cutting face of the drill bit10. Once the crown26is formed, the cutters18are mounted in the sockets34and affixed by any suitable method, such as brazing, adhesive, mechanical means such as interference fit, or the like. The design depicted provides the sockets34inclined with respect to the surface of the crown26. The sockets are inclined such that cutters18are oriented with the working face20generally perpendicular to the axis19of the cutter18and at a desired rake angle in the direction of rotation of the bit10, so as to enhance cutting. It will be understood that in an alternative construction, the sockets can each be substantially perpendicular to the surface of the crown, while an ultra hard surface36is affixed to a substrate38at an angle on the cutter body or stud40so that a desired rake angle is achieved at the working surface.

A typical cutter18is shown inFIG. 2. The typical cutter has a cylindrical cemented carbide substrate body38having an end face or upper surface54referred to herein as the “interface surface”54. An ultra hard material layer44, such as polycrystalline diamond or polycrystalline cubic boron nitride layer, forms the working surface20and the cutting edge22. A bottom surface52of the cutting layer44is bonded on to the upper surface54of the substrate38. The joining surfaces are herein referred to as the interface46. The top exposed surface or working surface20of the cutting layer44is opposite the bonded surface52. The cutting layer44typically has a flat or planar working surface20, but may also have a curved exposed surface, that meets the side surface21at a cutting edge22.

Cutters may be made, for example, according to the teachings of U.S. Pat. No. 3,745,623, whereby a relatively small volume of ultra hard particles such as diamond or cubic boron nitride is sintered as a thin layer onto a cemented tungsten carbide substrate. Flat top surface cutters as shown inFIG. 2are generally the most common and convenient to manufacture with an ultra hard layer according to known techniques. It has been found that cutter chipping, spalling and delaminating is common for ultra hard flat top surface cutters.

Generally speaking, the process for making a cutter18employs a body of cemented tungsten carbide as the substrate38where the tungsten carbide particles are cemented together with cobalt. The carbide body is placed adjacent to a layer of ultra hard material particles such as diamond or cubic boron nitride particles and the combination is subjected to high temperature at a pressure where the ultra hard material particles are thermodynamically stable. This results in recrystallization and formation of a polycrystalline ultra hard material layer, such as a polycrystalline diamond or polycrystalline cubic boron nitride layer, directly onto the upper surface54of the cemented tungsten carbide substrate38.

It has been found by applicants that many cutters develop cracking, spalling, chipping and partial fracturing of the ultra hard material cutting layer at a region of cutting layer subjected to the highest loading during drilling. This region is referred to herein as the “critical region”56. The critical region56encompasses the portion of the cutting layer44that makes contact with the earth formations during drilling. The critical region56is subjected to the generation of peak (high magnitude) stresses form normal loading, shear force loading and impact loading imposed on the ultra hard material layer44during drilling. Because the cutters are typically inserted into a drag bit at a rake angle, the critical region includes a portion of the ultra hard material layer near and including a portion of the layer's circumferential edge22that makes contact with the earth formations during drilling. The peak stresses at the critical region alone or in combination with other factors, such as residual thermal stresses, can result in the initiation and growth of cracks58across the ultra hard layer44of the cutter18. Cracks of sufficient length may cause the separation of a sufficiently large piece of ultra hard material, rendering the cutter18ineffective or resulting in the failure of the cutter18. When this happens, drilling operations may have to be ceased to allow for recovery of the drag bit and replacement of the ineffective or failed cutter. The high stresses, particularly shear stresses, can also result in delamination of the ultra hard layer44at the interface46.

One type of ultra hard working surface20for fixed cutter drill bits is formed as described above with polycrystalline diamond on the substrate of tungsten carbide, typically known as a polycrystalline diamond compact (PDC), PDC cutters, PDC cutting elements or PDC inserts. Drill bits made using such PDC cutters18are known generally as PDC bits. While the cutter or cutter insert18is typically formed using a cylindrical tungsten carbide “blank” or substrate38which is sufficiently long to act as a mounting stud40, the substrate38may also be an intermediate layer bonded at another interface to another metallic mounting stud40. The ultra hard working surface20is formed of the polycrystalline diamond material, in the form of a layer44(sometimes referred to as a “table”) bonded to the substrate38at an interface46. The top of the ultra hard layer44provides a working surface20and the bottom of the ultra hard layer44is affixed to the tungsten carbide substrate38at the interface46. The substrate38or stud40is brazed or otherwise bonded in a selected position on the crown of the drill bit body12. As discussed above with reference toFIG. 1, the PDC cutters18are typically held and brazed into sockets34formed in the drill bit body at predetermined positions for the purpose of receiving the cutters18and presenting them to the formation at a rake angle.

In order for the body of a drill bit to also be resistant to wear, hard and wear resistant materials such as tungsten carbide are typically used to form drill bit body for holding the PDC cutters. Such a drill bit body is very hard and difficult to machine. Therefore, the selected positions at which the PDC cutters18are to be affixed to the bit body12are typically formed substantially to their final shape during the bit body molding process. A common practice in molding the drill bit body is to include in the mold, at each of the to-be-formed PDC cutter mounting positions, a shaping element called a “displacement.” A displacement is generally a small cylinder made from graphite or other heat resistant material which is affixed to the inside of the mold at each of the places where a PDC cutter is to be located on the finished drill bit. The displacement forms the shape of the cutter mounting positions during the bit body molding process. See, for example, U.S. Pat. No. 5,662,183 issued to Fang for a description of the infiltration molding process using displacements.

It has been found by applicants that cutters with sharp cutting edges or small back rake angles provide good drilling rate of penetration, but are often subject to instability and are susceptible to chipping, cracking or partial fracturing when subjected to high forces normal to the working surface. For example, large forces can be generated when the cutter “digs” or “gouges” deep into the formation or when sudden changes in formation hardness produce sudden impact loads. Small back rake angles also have less delamination resistance when subjected to shear load. Cutters with large back rake angles are often subjected to heavy wear, abrasion and shear forces resulting in chipping, spalling, and delaminating due to excessive WOB required to obtain reasonable ROP. Thick ultra hard layers that might be good for abrasion wear are often susceptible to cracking, spalling, and delaminating as a result of residual thermal stresses associated with formation of thick ultra hard layers. The susceptibility to such deterioration and failure mechanisms is accelerated when combined with excessive load stresses.

FIG. 3shows a prior art PDC cutter held at an angle in a drill bit10for cutting into a formation. The cutter18includes a diamond material table44affixed to a tungsten carbide substrate38that is bonded into the socket34formed in a drill bit blade14. The drill bit10(seeFIG. 1) will be rotated for cutting the inside surface of a cylindrical well bore. Generally speaking, the back rake angle “A” is used to describe the working angle of the working surface20, and it also corresponds generally to the attack angle “B” made between the working surface20and an imaginary tangent line at the point of contact with the well bore. It will be understood that the “point” of contact is actually an edge or region of contact that corresponds to critical region56of maximum stress on the cutter18. Typically, the geometry of the cutter18relative to the well bore is described in terms of the back rake angle “A.”

Different types of bits are generally selected based on the nature of the formation to be drilled. Drag bits are typically selected for relatively soft formations such as sands, clays and some soft rock formations that are not excessively hard or excessively abrasive. However selecting the best bit is not always practical because many formations have mixed characteristics (i.e., the formation may include both hard and soft zones), depending on the location and depth of the well bore. Changes in the formation can affect the desired type of bit, the desired rate of penetration (ROP) of a bit, the desired rotation speed, and the desired downward force or weight on the bit (WOB). Where a drill bit is operating outside the desired ranges of operation, the bit can be damaged or the life of the bit can be severely reduced. For example, a drill bit normally operated in one general type of formation may penetrate into a different formation too rapidly or too slowly subjecting it to too little load or too much load. For another example, a drill bit rotating and penetrating at a desired speed may encounter an unexpectedly hard material, possibly subjecting the bit to surprise impact force. A material that is softer than expected may result in a high rate of rotation, a high rate of penetration (ROP), or both, that can cause the cutters to shear too deeply or to gouge into the formation. This can place greater loading, excessive shear forces and added heat on the working surface of the cutters. Rotation speeds that are too high without sufficient WOB, for a particular drill bit design in a given formation, can also result in detrimental instability and chattering because the drill bit cuts too deeply, intermittently bites into the formation or leaves too much clearance following the bit. Cutter chipping, spalling, and delaminating, in these and other situations, are common for ultra hard flat top surface cutters.

Dome cutters have provided certain benefits against gouging and the resultant excessive impact loading and instability. This approach for reducing adverse effects of flat surface cutters is described in U.S. Pat. No. 5,332,051. An example of such a dome cutter in operation is depicted inFIG. 4. The prior art cutter60has a dome shaped top or working surface62that is formed with an ultra hard layer64bonded to a substrate66. The substrate66is bonded to a metallic stud68. The cutter60is held in a blade70of a drill bit72(shown in partial section) and engaged with a geological formation74(also shown in partial section) in a cutting operation. The dome shaped working surface62effectively modifies the rake angle A that would be produced by the orientation of the cutter60. It has been found by applicants that chipping at the edge of the working surface continues to be associated with some dome cutters.

Scoop cutters, as shown inFIG. 5(U.S. Pat. No. 6,550,556), have also provided some benefits against the adverse effects of impact loading. This type of prior art cutter80is made with a scoop top working surface82formed in an ultra hard layer84that is bonded to a substrate86at an interface88. A depression90sometimes referred to as a “scoop” is formed in the critical region56. The substrate upper surface92has a depression94corresponding to the depression90, such that the depression90does not make the ultra hard layer84too thin. The interface88may be referred to as a non-planar interface (NPI). It has been found by applicants that while scoop cutters provide some benefits against the adverse effects of impact loading, additional improvement is desirable.

Diamond cutters provided with single or multiple chamfers with constant chamfer geometry (U.S. Pat. No. 5,437,343) have been proposed for reduction of chipping and cracking at the edge of the cutter. In these designs the size and the angle of each chamfer are constant circumferentially around the cutting edge. It has been found by applicants that constant chamfer geometry can provide some additional strength and support to the contact edge, yet the cutting efficiency can be reduced at all cutting depths and amount of support to the ultra hard layer and the strength of the edge is uniform with changing depth of cut. It has been found by applicants that increased strength due to a constant size and shape chamfer and does not necessarily counter act the extra proportional increase of loading associated with changes in cutting depth when using cylindrically shaped cutters. It has been found that without appropriately designed NPI, multiple stepped chamfer top surfaces can also result in extra thickness toward the center of the cutter. This can result in a corresponding increase in residual thermal stress and associated cracking, crack propagation, chipping and spalling.

Thus, cutters are desired that can better withstand high loading at the critical region imposed during drilling so as to have an enhanced operating life. Cutters that cut efficiently at designed speed and loading conditions and that regulate the amount of cutting load in changing formations are also desired. In addition, cutting elements that variably increase the strength of the cutter edges in response to increased cutting depth are further desired.

SUMMARY OF INVENTION

One aspect of the present invention relates to an ultra hard cutter having a shaped working surface that includes a varying geometry chamfer that is useful for drill bits used for drilling various types of geological formations. In certain embodiments, the ultra hard layer forms or is formed to provide a shaped working surface that has, at the cutting edge, a chamfer that varies in geometry with cutting depth. According to this aspect of the invention the varied geometry of the chamfer acts to reduce certain adverse consequences of sudden increased loading due to changes in the geological formation or in the manner of drill bit operation.

According to another aspect of the invention, a shaped working surface cutter also includes one or more depressions in the shaped working surface that facilitate formation of a desired varied geometry chamfer and that can also provide other useful cutter characteristics.

According to another aspect of the invention, a non-planer interface is formed between the ultra hard cutter layer and the substrate in a configuration oriented to the shaped working surface to provide increased thickness at the cutting edge of the shaped working surface in the critical region.

According to another aspect of the invention, a shaped working surface cutter has been discovered to provide reduced shear forces and also to provide additional strength against adverse effects of shear such as reduced susceptibility to spalling and delaminating.

According to another aspect of the invention, a cutter provides a useful combination taking into consideration the shape of the working surface, variations in chamfer geometry (including variations in cutting edge width, cutting edge angle or both) and/or the shape of the NPI to achieve improved toughness, reduced residual thermal stress, reduced cracking, reduced spalling, and reduced delamination.

According to another aspect of the invention a drill bit is formed using cutters with variable chamfers to obtain a desired “effective” back rake angle provided by the combined effect of the angle of the top working surface of the cutter and the angle and depth of the chamfers at the critical areas at which the cutters engage the formation during drilling.

According to another aspect of the invention the chamfer of a cutter is varied depending upon the position on a drill bit and the predicted shape and depth of cut of the cutter during drilling. Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

Embodiments of the present invention relate to cutters having shaped working surfaces with a varied geometry chamfer. By using such a structure, the present inventors have discovered that such cutters can better withstand high loading at the critical region imposed during drilling so as to have an enhanced operating life. According to certain aspects of the invention, cutters with shaped working surfaces with variable chamfer can cut efficiently at designed speed, penetration and loading conditions and can compensate for the amount of cutting load in changing formations. Such varied chamfer geometry has been found to variably increase the strength of the cutter edges in response to increased cutting depth, and according to certain aspects of the invention, to increase the strength of the cutter edges proportionally to the increased load associated with increased depth of cutting.

FIG. 6Ashows an ultra hard top layer100for a cutter that has a shaped working surface102including a varied geometry chamfer104circumferentially around the cutting edge106. The shaped working surface102is depicted as generally flat except for the shape of the chamfer104. The chamfer104is varied in size circumferentially around the cutting edge106according to one embodiment of the present invention. The change in the size or the width of the chamfer is demonstrated in the elevation section views ofFIGS. 6B and 6Ctaken along section lines B-B and C-C ofFIG. 6A, respectively. In this embodiment the width108inFIG. 6Bis smaller that the width110inFIG. 6C. The angle112of the chamfer at section B-B,FIG. 6B, is the same as angle114at section line C-C,FIG. 6C. In this embodiment, the chamfer geometry varies in terms of varied width and the angle does not change.

FIG. 7Ashows another embodiment of an ultra hard top layer120for a cutter having an alternative design of a shaped working surface122including a varied geometry chamfer124wherein the angle of the chamfer124is varied circumferentially around the cutting edge126according to another aspect of the invention. The change in the angle of the chamfer is illustrated inFIGS. 7B and 7C. In this embodiment, the angle128inFIG. 7Bis smaller than the angle130inFIG. 7C. The width132of the chamfer124at section B-B,FIG. 7B, is the same as the width134of the chamfer124at section line C-C,FIG. 7C. In this embodiment, the chamfer geometry varies in terms of varied angle and the width or size of the chamfer124does not change.

It will be understood that a varied geometry of a chamfer according to the invention could also be provided as a combination of varied size and varied angle. For purposes of convenience and clarity, the depictions in the drawing figures will primarily indicate varied chamfer geometry with change in size so that the variable nature of the chamfer geometry is discernable in the drawings.

FIG. 8shows an alternative embodiment of an ultra hard top layer140for a cutter with a shaped working surface142and having a varied geometry chamfer144circumferentially around a cutting edge146at the intersection of the shaped working surface142and a side surface148. The shaped working surface142includes one or more depressions150a,150b, and150cextending radially outwardly to the cutting edge146. While three depressions150a-care depicted uniformly spaced around the shaped working surface142, fewer or a greater number with uniform or non-uniform spacing may be formed without departing from certain aspects of the invention. For example, one or more depressions150a-ccan be formed as one or more planar surfaces or facets in a face154. Depending upon the embodiment, the face154may be a planar shaped surface, a dome shaped surface or a surface having another shape. The depressions150a-cin this embodiment comprise planar surfaces or facets each at an obtuse angle relative to a central axis152of the cylindrical ultra hard top layer. The obtuse angle is different from the angle of other portions of the working surface, such that a relative depressed area defining the depressions150a-cis formed the face154. Where the surrounding portions of the face154are planar and at a 90-degree angle with respect to the axis of the cutter, the obtuse angle is generally greater than 90 degrees with respect to the axis152of the cutter. However, according to alternative embodiments of the invention, the obtuse angle may be less than 90 degrees. It will also be understood that in other alternative embodiments, each of the depressions150a-ccan be multi-faceted or comprised of multiple planar surfaces. Alternatively, the depressions150a-ccan also be formed with simple curved surfaces that may be concave or convex or can be formed with a plurality of curved surfaces or with a smooth complex curve.

The depressions150a-cmay be formed and shaped during the initial compaction of the ultra hard layer140or can be shaped after the ultra hard layer is formed, for example by Electro Discharge Machining (EDM) or by Electro Discharge Grinding (EDG). The ultra hard layer140may, for example, be formed as a polycrystalline diamond compact or a polycrystalline cubic boron nitride compact. Also, in selected embodiments, the ultra-hard layer may comprise a “thermally stable” layer. One type of thermally stable layer that may be used in embodiments of the present invention may be a TSP element or partially or fully leached polycrystalline diamond. The depressions150a-cextend generally at an angle relative to the face154outward to the edge of the cutter. It has been found that a varied chamfer144can be conveniently made with a fixed angle and fixed depth EDM or EDG device. For example, a EDM device will typically cut deepest into the edge146where the raise areas of face154extend to the edge146and will cut less deep where the depressions150a-cextend to the edge146. The chamfer144is cut the least at the lowest edge point in each depression150a-cand progressively deeper on either side of the lowest edge point. A varied width or size chamfer is conveniently formed circumferentially around the edge146of the ultra hard cutter layer140. Alternatively, variable or programmable angle and depth EDM or EGM can be used to form the variable geometry chamfer.

During use, depending upon the embodiment of the invention, the average amount of chamfer, the angle of the chamfer, or both the amount and the angle of the chamfer will vary with different cutting depth. For example, a cutter in accordance with embodiments of the invention may have a region on the cutting surface with increasing chamfer contacting the formation when engaging in a deeper cut. The increased chamfer helps to “shoulder” the increased stress with the deeper cut.

FIG. 9shows a graphical comparison of Average Chamfer Size vs. Cutting Depth, for a 16 mm cutter having the varied chamfer geometry according to a cutter formed with the ultra hard top layer ofFIG. 8. A cutter with a small chamfer generally has good cutting efficiency. The varied chamfer cutter has a small average amount of chamfer toward the middle of the critical region (the area of the cutter surface or cutter surfaces engaged with the geological formation and under load). When using a varied chamfer cutter under normal drilling conditions, the cutting depth is confined or limited within a specified range and does not generally engage the formation beyond the depth at which the average chamfer is relatively small. Therefore, the variable chamfer on a cutting tool provides good cutting efficiency within the range of normal cutting depths. Under severe loading, such as impact with hard formation features or such as excessive tool pressure or weight on bit (WOB), the cutting depth increases beyond the range of normal cutting depths. The geometry of the chamfer is varied along the edge in the critical region so that the average chamfer size also varies with the depth of the cut.

In the embodiment considered with reference toFIG. 9, the chamfer is formed so that its size increases progressively on either side of the point of maximum contact and around the arc of the cutting edge in contact with the geological formation. The graph ofFIG. 9indicates that the average amount of the variable size chamfer in contact with the formation increases with the depth of the cut. The size of the variable chamfer is increased along the edge as the distance from the point of contact increases. Thus, when the cutter digs into the formation, a greater portion of the cutting edge has a larger chamfer to give more protection against chipping and spalling. The increased chamfer corresponds to and is encountered with the increased depth of cut so the chamfered portion of the cutter better shoulders the increased loading and therefore provides better protection to the cutter when greater protection is needed.

Similarly, the cutting characteristics change with the angle of the chamfer of a cutter. Where characteristics associated with different chamfer angles are desired under different loading conditions the chamfer angle can be varied on either side of the point of contact. For example, if a larger angle chamfer is desired under high loading conditions associated with deeper cutting depths, the angles of the chamfer can be made larger. Thus, the average angle of the chamfer will be larger when the cutting depth increases. Where the characteristics, of the chamfer associated with a smaller angle, as for example greater stability of a drill bit, are desired for deeper cutting depth, the angle of the chamfer can be varied to be a smaller angle on either side of the point of contact in the critical region. A combination of characteristics associated with varied width of chamfer and varied angle of chamfer can be obtained by varying the geometry of the chamfer with both changes in width and changes in the angle.

It should be understood that while the chamfer described herein is depicted as a straight angle truncated conical chamfer (i.e., a straight angled edge in cross-section); a radius chamfer (i.e., a curved edge in cross-section profile) is also contemplated within the scope of the invention.

FIG. 10shows a three-dimensional model of a cutter160having an ultra hard layer162with a shaped working surface164. The ultra hard layer162is bonded to a substrate166at a non-planar interface168according to one embodiment of the invention.

FIG. 11shows a three dimensional model, of the cutter160ofFIG. 10showing the contours170a-cand another set of contours171a-cof a non-planar interface168according to one embodiment of the invention. Each set of contours170a-cand171a-cis oriented with one of a plurality of depressions174and175at the intended critical regions176and178respectively. It will be understood with reference toFIG. 11that where there are additional depressions, such as a third depression173, a corresponding third set of contours172a-c(not fully shown inFIG. 11) will be provided. The deepest contours170aand171aare oriented with the deepest portion of the depressions174and175along the cutting edge and at the point of maximum cutting contact in the critical regions. The presence of contours170a-c,171a-cand172a-cprovide additional bonding surface area that resists shear forces and delamination at the interface. The contours also provide a peak and valley geometry at the NPI168that also resists shear forces and delamination at the interface. The contours further serve to interrupt potential crack propagation through the ultra hard layer. Horizontal cracks initiated in the ultra hard layer in the valleys will generally stop propagating when the crack encounters the substrate at the peaks. The deep contours170aand171a(and173anot shown) of each set of contours in the substrate166also are deepest toward the outer circumference of the substrate166. This forms an angled support surface for the ultra hard layer that is oriented with the point of maximum loading contact. The angled support surface is at an angle that is more nearly perpendicular to the primary force vector caused by cutting load. Thus, increased portion of the load is supported by the substrate with compaction strength and a decreased portion of the load is supported by the substrate with shear strength. Further, it has been discovered that with the increased surface area and the deepest part of the contours at the point of maximum loading, thermal distribution and heat dissipation is facilitated.

FIG. 12shows an assembly view of another embodiment of a cutter180having an ultra hard layer182with a shaped working surface184including a varied chamfer geometry186and an alternative configuration of a non-planar interface188. This cutter180is formed with a plurality of depressions190a,190b, and190c(190cnot shown), each corresponding to a potential critical cutting region191a-b. Only one depression190a(or190bor190c), corresponding to one critical region191a(or191bor191c), will be oriented for cutting a geological formation when the cutter180is brazed to a drill bit (not shown inFIG. 12). When a sufficient number of cutters180are damaged in the selected depression190aso that the effectiveness of the drill bit is diminished, the drill bit can be run out of the hole and the cutters180can be removed, rotated, and re-brazed to the drill bit with an undamaged depression190b(or190c) oriented in proper cutting position. Thus, in many instances the drill bit can be refurbished by reusing some or all of the same cutters180.

According to other aspects of the invention, the non-planar interface188is formed with depressed areas192a-bin the upper surface193of the substrate196, and oriented with the depressions190a-bthat are formed in the shaped working surface182. According to these alternative aspects of the invention, the average depth of the depressed area192at the outer periphery194of the cutter body196is greater than the average depth of the depressed areas192of the non-planar interface188at locations away from the point of maximum load in the critical region191. In the alternative embodiment depicted inFIG. 12, a plurality of depressed areas192a-bare formed in the non-planar interface188and the maximum depth of each depressed area192in the non-planer interface188corresponds to the position of the maximum edge depth of each of the plurality of working surface depressions190a-b. This results in varied thickness of the ultra hard layer, with the thickest portion200of the ultra hard layer184positioned adjacent the critical area191of the shaped working surface182. It has also been found to be useful, according to alternative embodiments of the invention, to provide the ultra hard layer with a minimum thickness202of about 0.040 inch and the maximum thickness at the thickest portion200of about 0.160 inch. This maintains residual thermal stress in the ultra hard layer within acceptable limits

FIG. 13shows a varied thickness of the ultra hard layer184oriented on the non-planar interface of the cutter180ofFIG. 12. There is an increased thickness at each depression190a-bof the shaped working surface182. It can be understood that the depressions190a-bin the working surface182result in an easy-to-form varied chamfer186and also provides an increased angle “G” greater than 90 degrees between the side of the cutter body197and the shaped working182surface. To provide back rake angles on existing drill bits within certain acceptable ranges, it has also been found to be useful to form the angle G within a range of about 91 degrees to about 130 degrees. By having the non-planar interface188also deeper at the outer periphery194and in the critical region191, the ultra hard layer184is also thicker at the periphery edge in the critical region191. Moreover, the upper surface193of the substrate196effectively provides support to the ultra hard layer184at an increased angle relative to the load caused by cutting contact with the formation (i.e. at the maximum load point, the upper surface193is at an angle that is more nearly normal to the vector of the load force). Thus, during use, a greater portion of the cutting force or load is supported by compression on the angled surface193of the substrate196and tangential shear forces support a smaller portion of the load. Reduction in tangential shearing forces has been found to reduce spalling and delaminating. The shaped working surface also has a larger area for convective cooling such that the adverse effects of heavy loading are reduced.

Finite element analysis shows that the varying chamfer can reduce the stress at the cutting edge and the outer diameter of the ultra hard layer or diamond table.

FIG. 14shows a diagram of maximum principle stress plotted along the “z” axis of a cutter and comparing the results for a cutter with no chamfer (curve210), a cutter with a dome shaped working surface (curve212), and a cutter with side chamfer (curve214), compared to a cutter with top chamfer (curve216) according to the present invention. It is clear from this comparison that top chamfer provides very effective relief of the maximum principle stress ODR.

FIG. 15shows a diagram of maximum principle stress on the top surface plotted along the “x” axis of a cutter with no chamfer (curve220) and a cutter with side chamfer (curve222), compared to a cutter with top chamfer (curve224) according to the present invention. It is clear from this comparison that both top chamfer and side chamfer provide significant relief of the maximum principle stress on the top surface.

The comparisons illustrated inFIGS. 14 and 15, show that the cutter according to this example has resistance to chipping and spalling.

Also, increasing chamfer size can prevent the bit from drilling too aggressively when the cutter cuts an excessive depth (e.g., when encountering a soft formation), hence, drilling stability for the whole bit is improved. In accordance with embodiments of the invention, the chamfer with or angle varies in the critical region. The variable chamfer can be established during manufacture. The variable chamfer in the cutting region can be appropriately adjusted, as it would be with a constant size chamfer. Increasing the size or angle of the chamfer outside the center of the critical region does not interfere with the drilling efficiency in standard drilling. In situations where the formation changes with depth or location, the variable chamfer provides protection to the cutters under various drilling conditions, and the overall efficiency of the cutters with a variable chamfer can remain substantially the same. Thus, a variable chamfer can have a minimum influence on drilling efficiency or normal energy consumption, while increasing drilling stability and improving the endurance and useful life of the ultra hard cutter.

FIG. 16shows another alternative embodiment of a cutter240having a shaped working surface242with varied chamfer geometry244and an alternative configuration of a non-planar interface246according to aspects of the invention.

FIG. 17shows another alternative embodiment of a cutter250having a shaped working surface252with varied chamfer geometry254and an alternative configuration of a non-planar interface256according to aspects of the invention.

FIG. 18shows another alternative embodiment of a cutter260having an alternative design of a shaped working surface262with varied chamfer geometry264according to aspects of the invention.

FIG. 19shows another alternative embodiment of a cutter270having an alternative design of a shaped working surface272with varied chamfer geometry274according to an alternative embodiment of the invention of the invention.

FIG. 20shows another alternative embodiment of a cutter280having an alternative design of a shaped working surface282with varied chamfer geometry284according to certain aspects of the invention as depicted.

FIG. 21schematically shows an example of a hypothetical drill bit300with selected cutters302,304,306,308,310and312at selected radial positions r1and r2on blades314,316,318,320,322, and324, respectively. The blades are schematically represented by lines tracing the blade profile in this end view. Cutters302and304are at the same radial positions r1from the center of the drill bit face, such that cutters302and304demonstrate opposed dual set cutters. Assuming the blade profile shape is the same for opposed blades314and316, the opposed dual set cutters302and304will each cut in spiral paths having the same shape and at the same depth depending upon the ROP and RPM of the drill bit. Cutters306and308are similarly opposed dual set cutters each at a position defined by radius r1and the profile shape of the blades318and320respectively. In this example cutters306and308are also leading cutters because they are followed during drilling by trailing cutters310and312, each at the same radius r2on the blades322and324. Trailing blades322and324follow leading blades318and320, respectively, in the direction of cutting326. Thus, assuming the blades have the same profile shape, the trailing dual set cutter310will follow in the same spiral path as the leading cutter306and the trailing cutter312will follow in the same spiral path as leading cutter308. Because the leading cutters306and308traverses a greater cutting distance as they cut into the formation, compared to the cutting distance traversed by the trailing cutters310and312, the leading cutters306and308will have a greater depth of cut than the trailing cutters310and312. It has been found by the inventors to be useful according to one embodiment of the invention that varying the chamfer and having a different geometry chamfer for a leading cutter and a trailing cutter. For example, a leading cutter that cuts deeper than a corresponding trailing cutter may benefit from a larger chamfer that can effectively increase the back rake angle to help protect the working surface from delaminating, chipping, and spalling as discussed above.

FIG. 22shows an example of a predicted partial bottom hole cutting pattern340for a hypothetical drill bit with repeated dual set cutter placement similar to the placement shown inFIG. 21. For example, cutter302ofFIG. 21at radius r1produces a cutting path342. The cutting path342traveled by cutter302is offset from a trough354formed by cutter306so that the ridge346between adjacent cutting paths354and358is engaged by a central portion of cutter302. Cutter306ofFIG. 21produces a cutting path344at radius r2and trailing cutter310follows along the cutting path at radius r2cutting only slightly deeper than leading cutter306. A cut engagement shape348shows the interface between the cutter302and the formation. Similarly the engagement shape350shows the cutter/formation engagement interface formed by the leading cutter306. shape350is predicted in this embodiment to have a deep central area and shallower sides. A more uniform arc shape cutter/formation interface would be encountered by the trailing cutter310ofFIG. 21. One reason for a trailing dual set cutter is to retain a sharp cutting edge in the event the leading cutter is damaged or in the event that an unexpected increase in depth of cut or ROP occurs while drilling. The shallow depth of cut therefore reduces that stress and wear on the trailing cutter so that it remains sharp.

FIG. 23shows an example of a cutter360with a variable size chamfer362. A portion364of the chamfer362is engaged in drilling a formation74at a bottom hole with a depth of cut366. The working face368defines a back rake angle370relative to a perpendicular372to the formation surface. It has been found by the inventors that the chamfer forms a chamfer back rake angle374that is larger than the faced back rake angle370. The percentage the face engaged with the formation74, as may be indicated by the depth376relative to the total depth366, and the percentage of the chamfer362that is engage with formation74, as may be indicated by the depth378depth relative to the total depth366, gives an effective back rake angle380. The effective back rake angle can be considered for purposes of approximating the cutting forces on the cutter and the stress and wear. It will be understood by those skilled in the art based upon this disclosure that specific calculations of the areas and back rake angles of the face component and the chamfer component can also be made and the calculated results combined to give the effective forces and the effective stress with very similar results in most cases. The theoretical effective back rake angle produced by the combined working face and the portion of a variable chamfer engaged in the formation is further helpful for understanding the usefulness of a variable chamfer designed, selected, or otherwise provided in accordance with the shape of the cutter/formation interface, or for purposes of matching the desired back rake angle to the depth cut along any portion of the cutter.

FIG. 24shows a predicted cutter/formation engagement pattern350or shape (as shown inFIG. 22) for a leading cutter306in an example dual set drill bit300(shown inFIG. 21). There are depths at350A,350B,350C and350D along the interface pattern350.

FIG. 25is a top view of an example of the face368and a variable chamfer362for a cutter360according to one embodiment of the invention. The cutter may correspond to or may usefully replace a leading cutter306in a dual set drill bit. In this embodiment the size of the chamfer is made to vary in width. A width362A is relatively narrow to correspond to the shallow depth350A. Widths362B and362C are relatively wider to correspond to the deep cut depths350B and350C. A width362D is relatively narrow corresponding to the shallow depth350D. (The depths are shown inFIG. 24).

FIG. 26A-Dshows a series of side views of the cutter360ofFIG. 25each at different points around the engaged cutter edge so that various portions362A,362B,362C, and362D of the chamfer362and the face368are shown engaged at different depths350A,350B,350C, and350D as predicted for the cutter/formation engagement pattern350ofFIG. 24.

FIG. 27shows an alternatively predicted cutter/formation engagement pattern352for a trailing cutter in a dual set drill bit. The shape of the pattern352is characterized by shallow depth of cut along the entire engaged critical area. For example depth352A,352B, and352C are all about equal in this embodiment.

FIG. 28shows an example of a variable chamfer cutter390for a trailing cutter in a dual set drill bit similar to the cutter310inFIG. 21that is useful for the cutter/formation pattern352ofFIG. 27according to one embodiment of the invention. A face392is circumscribed by a chamfer392. The chamfer has substantially constant widths392A,392B, and392C in the area corresponding to the predicted cut pattern350. Those skilled in the art will understand based upon the entire disclosure that chamfer widths392D and392E may usefully vary for other purposes, for example so that unexpected deeper cuts are met with increased chamfer size as described above and as further indicated in connection withFIG. 29Dbelow.

FIG. 29A-Cshows a series of side views of the trailing cutter390ofFIG. 28with various portions of the chamfer392A,392B, and392C, respectively, engaged at different depths352A,352B, and352C as predicted for the cutter/formation engagement pattern352ofFIG. 27.

FIG. 29Dis a side view of the cutter390having a variable chamfer392engaged at a depth394greater than the typically predicted depths352A-C for the expected cutter/formation engagement pattern352ofFIG. 27under normal conditions. Thus, for example, a wider chamfer portion392D may act to reduce the effective back rake angle when unexpected deep cutting occurs. This can helps to reduce gouging into the formation, it can direct the flow of formation cuttings, and it can reduce the impact of a sudden deeper cut, and can help limit the further increase in depth of cut.

FIG. 30shows an example of a predicted cutter/formation engagement pattern356or shape (as shown inFIG. 22) for a cutter, similar to cutter302as in an example drill bit300(shown inFIG. 21), that might be offset radially from a preceding cutter. The pattern356shows varying depths at356A,356B,356C and356D along the critical area of engagement with a formation.

FIG. 31is a top view of an example of the face408and a variable chamfer402for a cutter400according to one embodiment of the invention. The cutter400may correspond to or may usefully replace an offset cutter302in an opposed cutter dual set drill bit or might be any cutter that is offset from the path of a preceding cutter. In this embodiment the size of the chamfer402is made to vary in width. A width402A is relatively narrow to correspond to the shallow depth356A. Widths402B and402C are relatively wider to correspond to the deep cut depths356B and356C. A width402D is relatively narrow corresponding to the shallow depth356D. (The depths are shown inFIG. 30).

FIGS. 32A-Dshow a series of side views of the cutter400ofFIG. 32each at different points around the engaged cutter edge so that various portions402A,402B,402C, and402D of the chamfer402and the face408are shown engaged at different depths356A,356B,356C, and356D as predicted for the cutter/formation engagement pattern356ofFIG. 30.

FIG. 33shows an example of a drill bit410having a plurality of cutters411,412,413,414,415,416,417, and418. The cutters are variously provided with varied geometry chamfers and are positioned along the profile420with the chamfers421,422,424,423,424,425,426,427, and428oriented to provide vector forces431,432,433,434,435,436,437, and438on the cutters, respectively, in directions at angled with respect to the normal to the engaged formation surface along the profile420. When drilling with the drill bit410, the varied chamfers (larger inward and smaller outward) the of cutters411,412,413, and414along the cone419of the drill bit410produce greater combined outward directed side force than the combined inward directed side force produced by cutters415,416,417, and418. A total outward directed side force440can therefore be made using the variable chamfer cutters according to one embodiment of the invention. Such an outward directed side force440can be useful for designing and making a drill bit that has controlled walking characteristics, as for example for purposes of directional drilling. It will be understood by those skilled in the art based upon this disclosure that the varied chamfer geometry according to other embodiments of the invention may be arranged to provide any number of possible resultant total forces on a drill bit.

Thus, what has been disclosed includes a variable chamfer ultra hard cutter that can be costs effectively formed in combination with the forming one or more depressions or other shaping of the ultra hard working surface of the cutter. For example, a working surface can be formed with one or a plurality of depressions in the intended critical region and extending radially to the cutting edge. With little if any modification, a process of forming a chamfer that would have been a constant size around the edge of a flat top cutter will result in forming a variable size chamfer along the edge at the working surface depression. Rotating a cylindrical cutter about its axis with a fixed angled chamfering tool will cut a chamfer that varies in size circumferentially around the edge of the cutter. The chamfer will be smaller where the depression is deep along the cutting edge and the chamfer will be larger at the edges where the depression is shallow.

The shaped working surface also provides other useful characteristics for ultra hard cutters that cooperate with the useful characteristics of a variable chamfer. For example, one embodiment of a shaped working surface shown in (FIG. 12) provides a section angle of greater than 90 degrees for the cutting edge. It can strengthen the cutting edge and reduce edge chipping and spalling. At the same cutting depth, the shaped working surface has a larger area and a longer portion of cutting edge in contact with the formation than flat top surface. This can reduce the stress from cutting and hence reduce chipping and spalling. The shaped working surface enables a larger angle between the interface and the cutting load direction (FIG. 13impact loading). The increased angle can reduce shear stress at the interface and hence increase delamination resistance. Combined design of the shaped working surface and the non-planar interface can reduce harmful components of thermal residual stress. The shaped cutting edge features a varying chamfer or radius. The chamfer varies with different cutting depth. Under normal drilling condition, the cutting depth is confined. The average chamfer is small and the cutter has good cutting efficiency. Under severe loading such as impact and excessive WOB, the cutting depth increases, and so does the average chamfer size. Increased chamfer size gives more protection to the cutting edge from chipping or spalling. Also, the increase of chamfer size with excessive cutting depth can prevent the bit from drilling too aggressively, hence drilling stability is increased for the whole bit. According to certain embodiments of the invention, a varied chamfer cutter can have a minimum influence on drilling efficiency, while increasing drilling stability and improving the endurance of the diamond cutter.

According to one embodiment a drill bit is formed using cutters with variable chamfers to obtain a desired “effective” back rake angle provided by the combined effect of the angle of the top working surface of the cutter and the angle and depth of the chamfers at the critical areas at which the cutters engage the formation during drilling. The chamfer of the cutter can be varied according to the position on a drill bit and the predicted shape and depth of cut of the cutter during drilling so that wider chamfer is provided to correspond to deeper expected cut areas.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should include not only the embodiments disclosed but also such combinations of features now known or later discovered, or equivalents within the scope of the concepts disclosed and the full scope of the claims to which applicants are entitled to patent protection.