EARTH BORING BIT FOR SOFT TO HARD FORMATIONS

Abstract: A drill bit having thermally stable PCD cutting elements (10, 11) includes a matrix body element (14) having a plurality of spaced cutting elements (10, 11) supported in a body (12) of matrix material such that a substantial portion of the cutter (10) is above the body matrix (14) and a minor portion (15) is received within the body matrix (14). The cutters (10) have side surfaces (10b, 11b) exposed and are so positioned that at least in some of the cutters (10, 11) more surface area (10b, 11b) of one side face (10a, 11a) is exposed as compared to the other side faces. The cutter support (12) may include a small pad (30) of matrix material to reduce the loading directly on the PCD. In a preferred form the PCD elements (10) are mounted on pads (30) or blades formed by spaced channels (32). The hydraulics are straight radial flow and improved hydraulic flow is achieved through the use of waterways which concentrate the fluid flow near the face of the cutters (10). In one form, improved hydraulics are obtained by having one fluid discharge port for each of the radially disposed fluid channels (32).

Description: The present invention relates to the field of earth boring bits, and more particularly to an improved earth boring bit having temperature stable polycrystalline diamond elements as the cutting elements, and adapted to be used in soft to medium hard formations and typically those which aree more abrasive than pure shale and pure mudstone, for example. Document US-A-4,098,363 discloses a diamond drill bit for soft and medium hard formations, including all the features set forth in the preamble of the independent claim 1. From document EP-A-0 121 802 it is known to provide a trailing support behind the polycrystalline diamond cutting elements, said trailing support being integrally formed from the matrix material of the rotary bit, the polycrystalline diamond element being thus securily retained on the bit face. It is desirable to provide a drilling tool, especially an earth boring tool, having thermally stable PCD cutting elements in which the exposure of the cutting element above the body matrix and the exposed surface area is at the maximum while still proving sufficient anchoring of the cutting element such that it is effectively retained in the tool and the resulting structure is relatively stable with respect to impact loads. It is also desirable to provide a drilling tool of the type described in which the cutting elements are arranged such that a large and exposed cutting face is provided which extends an appreciable distance beyond the adjacent matrix material which forms the bit body and wherein adequate provisions are made for support of the cutter to avoid the vibration and impact damage. In accordance with this invention an improved drilling tool especially adapted for oil and gas drilling and the like is provided in which there is maximum exposure of the cutting elements which are preferably temperature stable PCD elements, as described, and which are located and fixed in the body matrix during formation of the body matrix. The earth boring bit may be a mining bit or any of the bits used in drilling for oil or gas, for example, and includes a matrix body member having a curved surface portion which includes a gage, shoulder, flank, nose, and apex, the curved surface forming the cutting surface of the bit. Above the shoulder is the usual gage. The matrix body member may be a relatively thin surface layer on a suitable backing support, as is know in the art, rather than the thicker body matrix which is well known and usually used in bits of the type to which the present invention relates. The cutting surface of the bit includes a plurality of channels which form spaced pad elements between the adjacent channels. Located in each pad are a plurality of spaced synthetic PCD elements, as described, which are mounted in the matrix body during formation of the body. The cutting elements are of a predetermined geometrical shape and are temperature stable to at least about 1,200 degrees C. Thus, while the PCD elements are temperature stable, as previously described, there is the generation of relatively high local heats during a drilling operation with possible thermal degradation of the cutting elements, especially in the harder formations. By this invention, the extensive exposure of the surfaces of the cutting elements permits the drilling fluid to contact the same over a substantial portion of the exposed surface area in order to effect more efficient cooling of the same during use. This is of practical importance since the heat conductivity through the PCD is three to five times greater than the heat conductivity of the matrix body material. Accordingly, while some of the prior art designs have adequate flow of fluid across the matrix body components of the bit, the comparatively low heat conductivity of the matrix body material does not offer a good heat sink for dissipation of heat in comparison to direct contact with the PCD itself. The cutting elements, of a geometry to be described, include a front face which has a predetermined surface area and a longitudinal axis which is arranged generally parallel to the axis of rotation of the bit. The cutting elements include portions adjacent to the front face and generally to the side thereof, as well a a rear portion. A minor portion of the cutting elements is received in the matrix of the pad, with a substantial portion of the cutting element exposed over the surface of the pad. Thus, the cutting elements are so positioned in the matrix material of the pad such that the front face extends above the pad to form the cutting face while the adjacent portions of the cutting element are disposed such that one is adjacent to the pad and the other is spaced from the pad, with the adjacent cutters along the nose and flank being spaced from each other such that there is some minor flow circumferentially between adjacent cutters of each pad. By positioning the cutting elements as described, those located in the flank and shoulder have an exposed cutting face whose surface area is greater than a majority of the predetermined surface area of the front face thereof. A large front cutting face is thereby provided for cutting and which may be effectively cooled. The side portions of the cutters are also exposed, the side portion spaced from the pad being essentially fully exposed and being of a greater surface are than the portion adjacent to the pad which is also partly exposed, with fluid flowing between adjacent cutters as mentioned. The cutters may be arranged with a five to twenty degree back rake and a tilt of between about zero to five degrees from the vertical axis, depending upon the geometry of the cutter and the location on the bit. In some cases, especially for drilling in hard rock formations, the tilt angle may be ninety degrees to the bit surface. Regardless of the location of the cutting element, more than 0.5mm of the cutting element is exposed above the matrix of the pad and the rear portion of the cutting element is supported by matrix material. In a preferred form, the drill bit of this invention includes cutting elements, as described, whose side exposure is somewhat unique. For example, all of the cutters, regardless of position on the cutting face have at least the same minimal side exposure which is greater than 0.5mm. In some cases, the side exposure of that side of the cutter away from the pad is somewhat greater than the other side of the same cutter, depending upon location of the cutters in the bit face. The side exposure of those cutters at the nose is the same as the side exposure of one side of the cutters located along the flank and shoulder, but in either case, the exposure is more than 0.5mm above the surface of the associated pad. Even with a somewhat lesser exposure, there is adequate direct cooling because of the radial nature of the flow, i.e., the amount of fluid flow over the cutters is greater per cutter along the nose than along the flank and shoulder. However, the amount of total exposed surface area per cutter, including the side surfaces, is greater at the flank and shoulder than at the nose, as will be explained in detail. Overall, the bit is a stepped bit in configuration with blades or pads and the cutters arranged on the bit face in a redundancy pattern such that the bottom of the hole is traversed by one and preferably at least four cutters. In such a case the cutting action of the cutter elements is that of a chisel, with a shearing action in cutting, with some kerfing action, with the result that the torque is somewhat lower than the prior art bits in certain formations. The bit of the present invention is intended for use in formations of shale with hard stringers and sandstone or limestone with shale sections. One further aspect of this invention is the nature of the cutting action in which that the portion of the formation between a preceding and trailing cutter is relieved of the confining stress and as the cutters pass, the confining stress is partially released and the formation tends to fracture even though not directly contacted by a cutting surface. Due to the relatively large surface area of the cutting face, the bit of the present invention tends to perform well in soft formations as compared to some of the bits previously discussed. More specifically, shale tends to ball up less when cut by the bit of this invention and the present bit cuts well in soft to hard sandstone formations as well as some harder rock. Another aspect of this invention is the provision of an improved mounting for each of the cutters which reduces the potential for cutter damage due to impact loads. From a view of dynamics of cutting, it is desired to have a sharp exposed and pointed cutting edge. However, such an arrangement is prone to impact damage due to high unit impact forces. To reduce the tendency for damage due to impact loads, the cutter-matrix support is constructed to provide a flat upper suface, i.e., the surface which faces the formation, whose length is less than the length of the supporting matrix to the rear of the the rear surface of the cutter. The flat or planar top surface of the cutter-matrix assembly may be achieved through the use of a cutter having a broad upper exposed surface, such as a split cylinder, or the use of a triangular element set such that there is a short trailing support which forms a short pad to the rear of the cutting face. In this way, a large bearing surface is avoided since that tends to inhibit the cutter from biting into the formation, but sufficient upper surface is provided to distribute the impact shock loads over a greater surface area, while providing sufficient support to the rear of the cutter to prevent vibration and to provide back support during cutting. The present invention possesses many other advantages and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are illustrated in the drawings accompanying and forming part of the present specification. The forms described in detail are for the purpose of illustrating the general principles of the present invention; but it is to be understood that such detailed description is not to be taken in a limiting sense. Referring to the drawings: Figure 1 is a view in perspective of one form of mounting a PCD cutting element in accordance with the present invention; Figure 2 is a view in perspective of the mounting shown in Figure 1 as seen from the front cutting face of the PCD; Figure 3 is a view partly in section and partly in elevation taken along the line 3-3 of Figure 1; Figure 4 is a view partly in section and partly in elevation taken along the line 4-4 of Figure 3; Figure 5 is a view partly in section and partly in elevation taken along the line 5-5 of Figure 3; Figure 6 is a view in perspective of another form of mounting for the PCD in accordance with the present invention; Figure 7 is a view in perspective of the mounting arrangement as shown in Figure 6 as viewed from the front of the cutting face; Figure 8 is a view in perspective of a mounting arrangement of a half-cylinder PCD cutting element in accordance with the present invention; Figure 9 is a view in perspective of the mounting arrangement as shown in Figure 8 as viewed from the front of the cutting face; Figure 10 is a diagrammatic view of a portion of the mold used in fabricating bits in accordance with this invention and illustrating the position of a rectangular PCD element; Figure 11 is a view similar to that of Figure 10 but illustrating the position of a half-cylinder PCD element; Figure 12 is a diagrammatic view of a drill bit in accordance with the present invention illustrating the general orientation of the cutting elements; Figure 13 is a fragmentary somewhat enlarged view in perspective of a portion of the bit of Figure 12 and illustrating the mounting of the PCD elements in accordance with this invention; Figure 13a is a view similar to that of Figure 13, illustrating a modified form of mounting for the PCD elements; The drill bit of this invention tends to perform better than the prior art drilling bits in the formations mentioned, especially in formations of mixed shale and sandstone, limestone and which include portions of hard and abrasive stringers, major sections of sandstone, or mixed shale and sandstone. The drill bit of this invention is not as effective in soft, sticky formations. Thus, referring to the drawings which illustrate preferred forms of the present invention, Figures 1-5 illustrate one form of mounting a PCD cutting element 10 (and 11) in a matrix body support generally designated 12. The matrix support is part of the body matrix 14, both the body and support being formed by the procedures already mentioned, infiltration or diffusion bonding, or the like, and the matrix is preferably of a tungsten carbide type for erosion and abrasion resistance. The PCD is mounted directly in the matrix, during matrix formation, and is preferably a temperature stable PCD, as already described. In the form illustrated in Figure 1, the PCD element 10 is triangular in shape and may be of the dimensions previously described and of the size already noted. Other geometrical shapes may be used, as will be described. As shown, a minor problem 15, shown in dotted form, of the PCD is below the surface 16 of the body matrix, while a majority of the cutting element extends above the surface. As shown, the PCD 10 includes a front face 10a, side portions adjacent to the front face in the form of side faces 10b and a rear portion 10c, with 10d indicating the top of the PCD. In this form and in the other forms to be described, the front face 10a of the cutting element has a predetermined surface area, calculable from the illustrative dimensions already given, and a longitudinal axis 17. It is apparent from the drawings, which are not to exact scale, that a major portion of the surface area of the front face 10a, which forms the cutting face, is above the body matrix surface 16, i.e., the exposure of the PCD above the surrounding body matrix is far greater than 0.5mm, as will be explained in detail later. To the rear of the rear portion 10c of the cutting element 10 is a matrix backing 20 which slopes from the top 21 of a top pad element to the rear, joining with the body matrix 14. The matrix backing 20 operates to provide a backing support to support the cutter with respect to front face loading during the cutting action. Since the cutters have such a large exposed cutting face, the loads from the front to the rear of the cutting elements are significant. Between the top 10d of the cutting element 10 and the sloping rear surface 22 of the backing is a top pad element 25, again of matrix material and which served as a short pad to absorb the axial shock and bouncing loads rather than allowing these loads to be absorbed directly on the top surface 10d of the of the PCD element 10. This pad, though relatively small as measured from the front face of the cutting element, extends across the full width of the cutting element and is sufficient to impart significant axial load resistance to the cutter 10 as compared to the same structure without the pad 25. To assist retention of the PCD 10 in the matrix support, the body matrix 14 includes a front portion 27, at essentially the same level as surface 16, to lock in place the forward corner 27a of front face 10a of the cutter 10. Preferably not more than about one-third of the front face 10a of the PCD is positioned below the surface of the matrix material. Referring now to Figures 1-5, the PCD cutters 10 and 11, and many of the other PCD cutters which make up the drill bit, are mounted on body pads 30 which are located between adjacent spaced channels 32 through which fluid flows for the purposes of cooling and cutting face 10a and to remove cuttings. The channel includes a side wall 33 which intersects the body pad at 35, the PCD cutting elements being set adjacent to the intersection, but spaced rearwardly therefrom by a distance which represents the circumferential dimension of the front portion 27, i.e., the dimension from the junction 35 to the front face 10a of the cutter at the region where the cutter intersects the body pad 30. This is apparent from cutter 11, shown in perspective, which is offset with respect to cutter 10, the latter being shown in section. In a preferred form, the rear surface or wall 22 of the matrix support 12 is sloped as shown and intersects the side wall of the channel. To improve the cutting efficiency of the cutters 10-11 and the other cutters, they are mounted in the support 12 with a small back rake, less than about 25 degrees and in the range of 5 degrees to 20 degrees with a preferred back rake being 15 degrees, as seen in Figure 3. As mentioned, a substantial portion of the front face 10a of each cutter is exposed above the surface 16 of the body pad in which it is received, as seen in Figure 4, and there is a significant portion of the front face which extends above that surface. Further, a minor portion 15 of the cutter is located in the body pad. In the case of triangular cutting elements, the rectangular face is the cutting face and the setting is referred to as a tangential setting. It has been discovered that a tangential setting and the relatively large exposure of the front face enables good performance in the softer formations. Thus, as seen in Figure 4, assuming a one-third carat PCD cutter having rectangular face of 4mm by 2.6mm, the front exposed face 10a of the cutter extends far greater than 0.5mm above the surface 16 and may extend as much as between about 2.0mm and 2.5mm above the level of the front portion 27, i.e. more than 50% of the front face is exposed. The exposed surface area is between 5.27 sq.mm and 6.6 sq.mm. In the case of a one carat PCD elements, the exposure above the level of the front portion 27 may be between 3.3mm to 4.5mm with an exposed front face surface area of between 12.21 sq. mm to 16.65 sq. mm. Again, more than 50% of the front face is exposed. These relatively large exposed front faces, in addition to providing a large surface area available for cutting, also provides a large surface area which may be cooled by the fluid. It is also clear from Figures 4 and 5 that the side portions 10b of the PCD cutters are fully exposed. The advantage of full side exposure and large surface area full face exposure is that there is better overall cooling of the PCD cutters which tend to develop localized high heats at the cutting regions of the PCD cutting elements. In general, it is far better to cool the cutters directly than to cool the cutter by cooling the matrix within which they are supported, especially since the matrix material is not as good a conductor of heat as compared to the PCD. The heat conductivity of the PCD may be as much as 3 to 5 times that of the matrix, depending upon matrix composition. The drill bits of the present invention are more aggressive drilling bits, in that they cut more rock, faster and with less energy than the prior drill bits already discussed. It is also true that the drill bits according to the present invention are capable of withstanding higher point loading per cutter than may have been the case the prior art devices. Higher point loading, in effect, means better drilling performance, while effective cooling tends to extend cutter life. Figure 4 also shows that the top front surface 34 of the cutter is free of matrix material, in the preferred form, so that there is no "run-in" required for the effective cutting surface to engage the formation at the initial start of the use of the drill bit. In effect, the bit may be lowered into the borehole and may start cutting as soon as the cutters contact the opposed surface of the formation without the necessity to abrade away matrix material to expose the cutting surface. This is apparent from Figure 4, which is a view as one would see if it were possible to look directly at the front face of a cutter during drilling. In the view seen in Figure 5, it is apparent that the support body for the cutter preferably extends from the junction 35 of one body pad and channel wall 33 to the junction 35a of an adjacent body pad and channel wall of the adjacent channel. It is to be understood that the PCD cutting elements are mounted on a surface of the bit which may be curved, as will be described. In the form of mounting arrangement for the PCD cutting element illustrated in Figures 6 and 7, in which the same reference numerals have been applied to the same elements previously illustrated, a prepad 40 which assists in retention of the PCD includes a flat front face 43 located along the intersection 35 of the channel wall 33 and surface 16 and which extends along the full width of the front face 10a of the PCD. The prepad 40 may be used where more abrasive formations are contemplated to assure that the front support is not abraded away during drilling. Figures 8 and 9 illustrate the use of a thermally stable PCD element of the type previously described in the form of a half cylinder 50. In this particular instance, the cutting element includes a rather broad upper surface 52 and is thus better able to withstand high axial loads since the point loads are distributed over a larger surface area as compared to a triangular cutting element. Nonetheless, it is preferred to use a top surface pad 25a, as shown, and which extends the full width of the cutting face. The advantage of this type of cutter is that there is a greater amount of depth of PCD at the top of the cutting element. Again the PCD cutting element includes a longitudinal axis 54 and a relatively large surface are front face 55. The rear portion 57 is cylindrical and the exposed side face 55a is of a relatively small dimension due to the curvature. Again there is a prepad 40a which may also be of the type shown in Figures 6 and 7. The matrix support 12 is sloped as described, while the cutter 50 and the matrix support are positioned with respect to the channels 32 as already described. As noted, the half cylinder cutters may be of various sizes. In each case however, the amount of front face exposure above the matrix adjacent to the cutter is more than the portion which is received in the matrix. As shown only a minor portion 58 is received within the matrix body pad 14 and below its surface 16, such that the cutter extends more than 0.5mm above the surface of the body pad. The half cylinders may be formed by cutting cylindrical elements in half along the long axis thereof. A 4mm by 6mm cylinder provides two PCD elements having a flat front cutting face which is 4mm by 6mm, and a 6mm by 8mm provides two half cylinders of a flat front cutting face dimension of 6mm by 8mm. Other sizes may be used but in each case the half cylinder is mounted such that more that about 50% is exposed above the body pad surface. In some instances, one end of the cylinder is in the form of a cone. In that instance the point of the cone may be imbeded in the matrix or may be the upper surface. It is preferred to use the flat end face as the upper exposed cutting face. With this geometry of cutter it has been noted that the tilt may be eliminated, if desired. It is preferred that there be a back rake in the amount indicated. To facilitate understanding of the manner in which the PCD is mounted, reference is made to Figure 10 which illustrates diagrammatically a portion 60 of the mold used to form the bit. For purposes of explanation, reference will be made to a one carat PCD of the dimensions previously described. The mold includes a cavity 62 having a sloped wall 63 which corresponds to the sloped wall 22 of the back support. The angle of the wall 63, as indicated at 64 is 31 degrees, although angles between 15 and fourty degrees may be used. This angle is measured between wall 63 and surface 65, the latter corresponding in position to the surface height of surface 16. Wall 68 is angled in an amount of 15 degrees, as indicated at 69, for example, and represents the back rake angle of the front face 10a of the cutter. Angles 64 and 69 may be other than that as shown for purposes of illustration. The mold also includes a lower flat surface 70 which forms the top surface pad 25. From Figure 10, it can be seen that a substantial portion of the PCD is above the surface 16, the portion above that surface being represented by the portion of the PCD 10 which is below the surface 65 of the mold. In the form shown, the dimension at 71 is about 3.81mm and thus the exposure of the front face is slightly greater than that dimension. In processing, the mold is filled with matrix powder such that the cavity 62 is filled as well as that portion above surface 65, and processed, with the result that the finished product is as illustrated in Figures 1 and 2. The mold portion 75 illustrated in Figure 11 is used to produce the mounting of the PCD as illustrated in Figures 8 and 9. Again, the mold includes a cavity 76 having bottom wall portions 77 and 78. Wall portion 77 forms the top surface pad 25a and is angled at 15 degrees as indicated at 81 while wall portion 78 forms the rear surface 22 and is angled at 30 degrees, as indicated at 82. The dimension of the wall portion 77 is about 4.42mm, assuming a half-cylinder whose radius is 3mm. The axial strength of the half-cylinder is 6mm thereby providing a front face exposure of slightly greater than 3.125mm. Surface 85 of the mold is inclined at about 15 degrees to provide a back rake, the front flat face of the half-cylinder being positioned in facing relation with surface 85. After processing, the resulting mounting is as shown in Figures 8 and 9. Figure 12 illustrates in somewhat diagrammatic form the position of the cutting elements and the relative tilt and general orientation of the cutters with respect to the center axis of the bit. Thus a plurality of cutters are shown located in the cone generally designated 90, the nose generally designated 92, the flank generally designated 95 and the shoulder generally designated 97. The gage 99 is vertically above the shoulder 97. As will be seen from this illustration, the cutters are arranged such that their longitudinal axes are in general alignment with the axis of rotation 100 of the bit. Some of the cutters are provided with a tilt, for example cutters 102a near the shoulder 97 and cutters 102b from the flank 95 and along the flank all have a tilt of about 5 degrees. The cutters 102c in the area between the flank and the nose have a tilt of about 3 degrees, while those 102d in the nose have no tilt. In the transition from the nose to the cone, the cutters 102e have a tilt of negative 3 degrees while those 102f in the cone have a tilt of 5 negative degrees. The different tilts of from 5 degrees to a negative 5 degrees of the cutters located in different portions of the bit are used to provide a smooth transition across the bit face and to reduce high side loads. It is also apparent from this Figure that side exposure of the cutters is at least that of the cutters 102d, with side exposure of one side of the cutters increasing as will be described. As will be described further below, the cutters are set in a redundant pattern so that at least two or more cutters traverse the formation. In the view of Figure 12, the second set of cutters 103a, 103b, 103c, 103d, 103e and 103f have a tilt as described for the series 102 cutters. It is to be noted, however, that the side exposure of some of the cutters varies, depending upon the location of the cutter. Thus, in each case the cutters 102a, 102b and 102c each include one side face 105 whose exposure, measure axially from the matrix surface 106, is less than that of the opposite side face 107, i.e., the radially outward face has a greater exposure than the face of the corresponding cutter adjacent to the matrix body 106. The same is true of the corresponding 103 series cutters. The side faces of cutters 102d and those of the 103d cutters have essentially the same side face exposure on each cutter. In the case of the cutters 102e and 102f and the corresponding 103 cutters, the situation is the reverse, in that the radially inward face 114 has a greater exposure than the radially outward face. As can be seen from Figure 12, the general appearance of the bit is that of a stepped bit, which is of importance with respect to the nature of the cutting action. For the cutters along the shoulder and flank, the radially outward region 120 is the primary cutting region. For those cutters in the cone and the transition from the nose to the cone, the primary cutting region is the radially inward region 122. The principal cutting action, according to theory, is that of a kerfing-like cutting action, as may be understood with respect to the following illustration. The portion of the formation between the side face 107 of cutter 102b and vertically above the cutting region 120 and that portion of the formation along the top exposed surface of the cutter 103a is effectively unsupported. Thus as the pairs of cutters pass, the formation between two cutting regions is relaxed. As the trailing cutters contact the relaxed formation, it is easier for the trailing cutters to cut the relaxed formation. This type of cutting action tends to cause the unsupported portion of the formation to crumble or weaken such that during the pass of subsequent cutters, the formation is more easily cut. This cutting theory is in accord with actual field experience which has demonstrated that the more irregular and sharper the cutting profile, the faster the cutting action. Moreover, assuming uniform wear on the cutters, they should be operative until the cutters are worn to the line "A" of Figure 12.. In the form illustrated in Figure 12, the flank angle, as measured between lines F and F1 is between 35 and 50 degrees, while the cone angle is between 110 and 130 degrees, as indicated at C which shows half of the cone angle. As seen in Figure 12, the flank angle and tilt and relative position on the cutter face have an affect on the amount of change in the side exposure of the PCD cutters from the nose to the general area of the gage. As seen in Figure 13, (wherein the same reference numerals have been used where applicable) and with respect to the cutters in the flank area and the region from the nose to the flank, a greater amount of the side face 10b is exposed than is the case with the side face 10d and a minor portion of the front face 10a is below the matrix body. As one proceeds towards the gage, essentially the entire side face may be exposed, see cutter 106 of Figure 12, for example. In the case of the cutters located at the nose, the side exposure is essentially the same on each side and is in the amount previously specified. Accordingly, there is at least one side of each cutter that has the same side face exposure while the remaining side faces of the remaining cutters have either the same exposure or a greater exposure, as is seen in Figure 12. Figure 13 also illustrates the fact that the prepad 40c and the back support surface 22 may include portions 40d and 22a whicha are at the same level as the body pad 30 while portions 40e and 22b are positioned above the body pad portion 30a. In the view of Figure 13, the width of the tooth is essentially equal to the width of the pad. The form illustrated in Figure 13a is similar to that of Figure 13, except that the width of the pad 30 is wider than the width of the tooth, the latter including a curved rear surface 22d. The bit of this invention has demonstrated good performance in mixed formations such as shale with hard stringers and sandstone or limestone with shale sections. The large area of the front cutting face, to some extent, acts as a chisel in cutting. In general, it is preferred to use triangular PCD elements of one carat size for resistance to balling in shale type formations, although any predetermined geometrical shape may be used. While reference has been made to drill bits, it is understood that within that term is included core bits and the like. In crab orchard sandstone with a point loading of 50 lbs per cutter and at 150 RPM, the ROP was better than some of the prior art bits and about 24 feet per hour. As point loading per cutter was increased to 75 lbs, the ROP increased in the same formation and at the same RPM to 38 feet per hour. It will also be apparent that even though the invention has been described principally with reference to drill bits, the present invention may also be used in core bits and the like.

Claims: A bit for use in earth boring, said bit being rotatable along an axis and including a body member (14) having a metal matrix curved surface (16), a plurality of spaced synthetic polycrystalline diamond cutting elements (10, 11, 50) mounted directly in the matrix, each of said cutting elements (10, 11, 50) being of a predetermined geometrical shape and temperature stable to at least about 1200 degrees C, and each of said cutting elements (10, 11, 50) including a front face (10a, 11a, 55) having a predetermined surface area and portions (10b, 11b, 55a) adjacent to said front face (10a, 11a, 55),at least some of said cutting elements (10, 11, 50) including a minor portion (15, 58) received within the matrix material and being so positioned that said front face (10a, 11a, 55) extends above the surface (16) of said matrix material to form an exposed cutting face of said cutting element (10, 11, 50),the exposed cutting face of at least some of the cutting elements (10, 11, 50) having a surface area which is greater than one-half of said predetermined surface area of said front face (10a, 11a, 55), each of said cutting elements (10, 11, 50) including a surface portion (10, 11c, 57) generally to the rear of said cutting face, matrix material contacting at least a portion of said surface portion (10c,11c,57) to the rear of said cutting face to form a matrix backing (20) to support said cutting element (10,11,50), the exposed surface area of the side portion (10b,11b,55a) of at least some of the cutting elements (10,11,50) spaced from said matrix being greater than the exposed surface area of the portion of said corresponding cutting element (10,11,50) which is adjacent to said matrix, each of said plurality of cutting elements (10,11,50) being spaced apart from adjacent ones of said cutting elements (10,11, 50) to allow substantially free hydraulic access to substantially all of said exposed surfaces, the improvement in said bit characterized in that: said diamond cutting elements (10,11,50) are mounted in the matrix during matrix formation and include a flat, rectangular front face (10a,11a,55) having a longitudinal axis (17,54) generally parallel to the axis of rotation of the bit and a top edge (10d,52) extending perpendicular to said longitudinal axis (17,54) and parallel to said flat, rectangular front face (10a,11a,55), said matrix backing (20) extending up to at least the level (21) of said top edge (10d,52) and providing a flat top pad element (25,25a) of matrix metal extending across the full width of said top edge (10d) and perpendicular to said longitudinal axis (17,54) for absorbing shock and impact loads imposed on said cutting elements (10,11,50) in a direction generally parallel to the bit axis. The bit of claim 1, further including a trailing and downwardly sloping support (22) to the rear of said flat pad (25,25a). The bit of Claim 1 or 2, wherein said polycrystalline diamond cutting elements are triangular prismatic diamond elements (10, 11) including two opposing triangular sides (10b) and three rectangular sides, said front face (10a, 11a) being defined by a portion of one of said rectangular sides. The bit of Claim 1 or 2, wherein said polycrystalline diamond cutting elements are of a half cylindrical geometric shape (50), said front face (55) being defined by a portion of the diametrically extending flat surface of said half cylindrical geometric shape (50). The bit of Claim 4, wherein said matrix backing (20) extends forwardly around the rear cylindrical portion (57) of said half cylindrical geometric shape (50) to the edge of said front face (55). The bit of Claims 1 through 5, wherein said pad (25, 25a) extends across the full width of said cutting elements (10, 11, 50). The bit of claim 1 wherein the plurality or spaced synthetic polycrystalline diamond cutting elements (10, 11, 50) are prismatic and have at least one major surface and one minor surface, said major surface having an area substantially greater than the area of said minor surface, each of said cutting elements (10, 11, 50) including an exposed front face which includes said minor surface having a predetermined surface area and a longitudinal axis (17, 54) and portions adjacent to said exposed front face, and at least some of said cutting elements (10, 11, 50) including a small portion (15, 58) received within the matrix material and being so positioned that said front face (10a, 11a, 55) extends above the matrix surface (15, 106) to form a cutting face of said cutting element (10, 11, 50) while at least two adjacent side portions (10b, 11b, 55a, 105, 107), which include said major surface, are disposed such that one (105) is adjacent to said matrix and the other (107) is spaced from said matrix, said two adjacent side portions (10b, 11b, 55a, 105, 107) being substantially exposed, the total exposed cutting surface of at least some of the cutting elements (10, 11, 50) having an exposed surface area which is greater than one-half of the total surface area of the diamond prismatic cutting element (10, 11, 50), at least some of said cutting elements (10, 11, 50) being arranged in an orientation in which the longitudinal axis (17, 54) of said cutting face is generally parallel to the axis of rotation (100) of said bit, said plurality of cutting elements (10, 11, 50) being arranged and configured in at least two radially distributed sequences, namely a first plurality of said cutting elements (10, 11, 50) disposed in a first series (102a-f) of radially spaced-apart positions and a second plurality of said cutting elements (10, 11, 50) disposed in a second series (103a-f) of radially spaced-apart positions, said first (102a-f) and second (103a-f) series of cutting elements (10, 11, 50) being radially offset one from the other so that at least one cutting element (10, 11, 50) of said second series (103a-f) radially overlaps and is disposed azimuthally behind and radially between two corresponding cutting elements (10, 11, 50) of said first series (102a-f) of cutting elements (10, 11, 50). The bit of claim 1 wherein the plurality of spaced synthetic polycrystalline diamond cutting elements (10, 11, 50) are prismatic and mounted directly in the matrix in a stepped arrangement, each prismatic element characterized by a prismatic axis, said element (10, 11, 50) having a major surface and a minor surface, said major surface having an area greater than the area of said minor surface and being substantially perpendicular to said prismatic axis, and each of said cutting elements (10, 11, 50) including an exposed front face including said minor surface having a predetermined surface area and portions adjacent to said front face, and at least some of said cutting elements (10, 11, 50) including a small portion (15, 58) received within the matrix material and being so positioned that said front face (10a, 11a, 55) extends above the matrix surface (16, 106) to form a cutting face of said cutting element (10, 11, 50) while at least two adjacent side portions (10b, 11b, 55a, 105, 107) including said major surface are disposed such that one (105) is adjacent to said matrix and the other (107) is spaced from said matrix, said prismatic axis of said diamond cutting element being generally radial, and said two adjacent side portions (10b, 11b, 55a, 105, 107) being exposed. The bit of claim 8 wherein said matrix backing support means (20) includes a pad means (25, 25a) on the upper surface (22) thereof which contacts the cutter element (10, 11, 50) along the top portion (10d, 52) thereof and to the rear (10c, 11c, 57) thereof, said pad (25, 25a) extending across the full width of said cutting element (10, 11, 50). The bit of claim 8 wherein said matrix backing support means (20) includes an upper surface (21), at least a portion of which is inclined, said upper surface (22) including a pad (25, 25a) to the rear of the cutter (10, 11, 50) and an inclined portion to the rear of said pad (25, 25a). The bit of claim 1 wherein said polycrystalline diamond elements (10, 11, 50) are mounted in a plurality of cutting teeth forming part of said surface (16), said plurality of teeth being provided with hydraulic fluid, each cutting tooth including at least one said synthetic polycrystalline diamond prismatic element (10, 11, 50), said element (10, 11, 50) having at least one major surface and at least one minor surface, said major surface having an area greater than the area of said minor surface, wherein a tooth structure (30) comprises said cutting tooth, said prismatic diamond element (10, 11, 50) having said minor surface (10a) disposed within said tooth structure (30) as a leading exposed cutting surface as defined by rotation of said bit, said minor surface (10a) including one edge embedded into said tooth structure (30), at least a portion of said tooth structure (30) overlying said minor surface (10a), adjacent surfaces (10b, 10d) to said minor surface (10a) including said major surface, said adjacent surfaces (10b, 10d) being substantially exposed and substantially freely accessible to thermal contact with said hydraulic fluid, a rear minor surface opposing said minor surface (10a) forming said leading cutting face being in contact with and backed by said tooth structure (30), and less than 40 percent of the total surface area of said synthetic polycrystalline diamond element (10, 11, 50) being in contact with said tooth structure (30), the remaining portion of said diamond element (10, 11, 50) being exposed. The bit of claim 11 wherein said prismatic diamond element is a triangular prismatic diamond element (10, 11) and said major surfaces being said triangular faces of said triangular prismatic element (10, 11), said triangular prismatic element (10, 11) being disposed within said tooth structure (30) with said triangular faces radial-most and exposed. The bit of claim 12 wherein said triangular prismatic element (10, 11) includes two opposing triangular faces (10b, 10d) and three side faces therebetween, said tooth structure (30) completely contacting only two of said side faces. The bit of claim 13 wherein one of said side faces (10a) comprises said leading cutting face, only a lower edge portion of said side face (10a) being in contact with said tooth structure (30), said tooth structure (30) overlying said portion of said side face (10a) comprising said leading cutting face. The bit of claim 11 wherein more than 70 percent of synthetic polycrystalline diamond element (10, 11, 50) within said tooth structure (30) is exposed. The bit of claim 11 wherein said plurality of cutting elements (170) are arranged and configured in at least two radially distributed sequences, namely a first plurality of said cutting elements disposed in a first series (102a-f) of radially spaced-apart positions, and a second plurality of said cutting elements disposed in a second series (103a-f) of radially spaced-apart positions, said first (102a-f) and second (103a-f) series of cutting elements (170) being radially offset one from the other so that at least one cutting element (170) of said second series (103a-f) radially overlaps and is disposed azimuthally behind and radially between two corresponding cutting elements (170) of said first series (102a-f) of cutting elements (170). The bit of claim 11 wherein said body member (300) includes a plurality of raised lands (305), each said cutting tooth being disposed on one of said raised lands (305) in said tooth structure (30), said diamond element being disposed entirely above said one raised land (305). The bit of claim 17 wherein said plurality of cutting elements (310) are arranged and configured in at least two radially distributed sequences, namely a first plurality of said cutting elements (310) disposed in a first series (102a-f) of radially spaced-apart positions, and a second plurality of said cutting elements (310) disposed in a second series (103a-f) of radially spaced-apart positions, said first (102a-f) and second (103a-f) series of cutting elements (310) being radially offset one from the other so that at least one cutting element (310) of said second series (103a-f) radially overlaps and is disposed azimuthally behind and radially between two corresponding cutting elements (310) of said first series (102a-f) of cutting elements (310).

Inventors: BIGELOW, LOUIS K., GRAPPENDOFF, RICHARD H., MESKI, ALEXANDER K.
Applicants: EASTMAN TELECO COMPANY
Application year: 1987
Main classification: E21B10
IPC codes: E21B10