Patent Grant
8678111
1. Technical Field
The present invention relates in general to earth-boring bits and, in particular, to an improved bit having a combination of rolling-cutters and fixed cutters and cutting elements and a method of design and operation of such bits.
2. Description of the Related Art
The success of rotary drilling enabled the discovery of deep oil and gas reservoirs and production of enormous quantities of oil. The rotary rock bit was an important invention that made the success of rotary drilling possible. Only soft earthen formations could be penetrated commercially with the earlier drag bit and cable tool, but the two-cone rock bit, invented by Howard R. Hughes, U.S. Pat. No. 930,759, drilled the caprock at the Spindletop field near Beaumont, Tex., with relative ease. That venerable invention, within the first decade of the last century, could drill a scant fraction of the depth and speed of the modern rotary rock bit. The original Hughes bit drilled for hours; the modern bit now drills for days. Modern bits sometimes drill for thousands of feet instead of merely a few feet. Many advances have contributed to the impressive improvements in rotary rock bits.
In drilling boreholes in earthen formations using rolling-cone or rolling-cutter bits, rock bits having one, two, or three rolling cutters rotatably mounted thereon are employed. The bit is secured to the lower end of a drill string that is rotated from the surface or by downhole motors or turbines. The cutters mounted on the bit roll and slide upon the bottom of the borehole as the drill string is rotated, thereby engaging and disintegrating the formation material to be removed. The rolling-cutters are provided with cutting elements or teeth that are forced to penetrate and gouge the bottom of the borehole by weight from the drill string. The cuttings from the bottom and sides of the borehole are washed away and disposed by drilling fluid that is pumped down from the surface through the hollow, rotating drill string, and the nozzles as orifices on the drill bit. Eventually the cuttings are carried in suspension in the drilling fluid to the surface up the exterior of the drill string.
Rolling-cutter bits dominated petroleum drilling for the greater part of the 20th century. With improvements in synthetic diamond technology that occurred in the 1970s and 1980s, the fixed blade cutter bit or drag bit became popular again in the latter part of the 20th century. Modern fixed blade cutter bits are often referred to as “diamond” or “PDC” (polycrystalline diamond cutter bits) bits and are far removed from the original fixed bladecutter bits of the 19th and early 20th centuries. Diamond or PDC bits carry cutting elements comprising polycrystalline diamond compact layers or “tables” formed on and bonded to a supporting substrate, conventionally of cemented tungsten carbide, the cutting element being arranged in selected location on blades or other structures on the bit body with the diamond tables facing generally in the direction of bit rotation. Fixed blade cutter bits have the advantage of being much more aggressive during drilling and therefore drill much faster at equivalent weight-on-bit levels (WOB) than, for instance, a rolling-cutter bit. In addition, they have no moving parts, which make their design less complex and more robust. The drilling mechanics and dynamics of fixed blade cutter bits are different from those of rolling-cutter bits precisely because they are more aggressive in cutting and require more torque to rotate during drilling. During a drilling operation, fixed blade cutter bits are used in a manner similar to that for rolling-cutter bits, the fixed blade cutter bits also being rotated against a formation being drilled under applied weight-on-bit to remove formation material. The cutting elements on the fixed blade cutters are continuously engaged as they scrape material from the formation, while in a rolling-cutter bit the cutting elements on each rolling cutter indent the formation intermittently with little or no relative motion (scraping) between the cutting element and the formation. A rolling-cutter bit and a fixed blade cutter bit each have particular applications for which they are more suitable than the other. The much more aggressive fixed blade cutter bit is superior in drilling in a softer formation to a medium hard formation while the rolling-cutter bit excels in drilling hard formations, abrasive formations, or any combination thereof.
In the prior art, some earth-boring bits use a combination of one or more rolling cutters and one or more fixed blade cutters. Some of these combination-type drill bits are referred to as hybrid bits. Previous designs of hybrid bits, such as U.S. Pat. No. 4,343,371, to Baker, III, have used rolling-cutters to do most of the formation cutting, especially in the center of the hole or bit. Another type of hybrid bit is described in U.S. Pat. No. 4,444,281, to Schumacher, has equal numbers of fixed blade cutters and rolling-cutters in essentially symmetrical arrangements. In such bits, the rolling-cutters do most of the cutting of the formation while the fixed blade cutters act as scrapers to remove uncut formation indentations left by the rolling-cutters as well as cuttings left behind by the rolling-cutters. While such a hybrid bit improves the cutting efficiency of the hybrid bit over that of a rolling-cutter bit in softer formations, it has only a small or marginal effect on improving the overall performance in harder formations. When comparing a fixed blade cutter bit to a rolling-cutter bit, the high cutting aggressiveness of a fixed blade cutter bit frequently causes such bit to reach the torque capacity or limit of a conventional rotary table drilling systems or motors, even at a moderate level of weight-on-bit during drilling, particularly on larger diameter drill bits. The reduced cutting aggressiveness of a rolling-cutter bit, on the other hand, frequently causes the rolling-cutter bit to exceed the weight-on-bit limits of the drill string before reaching the full torque capacity of a conventional rotary table drive drilling system.
None of the prior art addresses the large difference in cutting aggressiveness between rolling-cutter bits and fixed blade cutter bits. Accordingly, an improved hybrid bit with adjustable cutting aggressiveness that falls between or midway between the cutting aggressiveness of a rolling-cutter bit and a fixed blade cutter bit would be desirable.
A hybrid earth-boring bit comprising a bit body having a central axis, at least one, preferably three fixed blade cutters, depending downwardly from the bit body, each fixed blade cutter having a leading edge, and at least one rolling-cutter, preferably three rolling-cutters, mounted for rotation on the bit body. A fixed blade cutter and a rolling-cutter forming a pair of cutters on the hybrid bit body. When there are three rolling-cutters, each rolling-cutter is located between two fixed blade cutters.
A plurality of cutting elements is arranged on the leading edge of each fixed blade cutter and a plurality of cutting elements is arranged on each of the rolling-cutters. The rolling-cutters each have cutting elements arranged to engage formation in the same swath or kerf or groove as a matching cutting element on a fixed blade cutter. In the pair of cutters, the matching fixed blade cutter being arranged to be either trailing, leading, or opposite the rolling-cutter to adapt the hybrid bit to the application by modifying the cutting aggressiveness thereof to get the best balance between the rate-of penetration of the bit and the durability of the bit for the pair of cutters.
A method for designing a hybrid earth-boring bit of the present invention permits or allows the cutting aggressiveness of a hybrid bit to be adjusted or selected based on the relationship of at least a pair of cutters comprising a fixed blade cutter and a rolling-cutter, of a plurality of fixed blade cutters and rolling-cutters, wherein the relationship includes a fixed blade cutter leading a rolling-cutter in a pair of cutters, a rolling cutter leading a fixed blade cutter in a pair of cutters, a rolling-cutter being located opposite a fixed blade cutter in a pair of cutters on the bit, and the angular relationship of a fixed blade cutter and a rolling-cutter of a pair of cutters regarding the amount of leading or trailing of the cutter from an associated cutter of the pair of cutters. The cutting aggressiveness of a hybrid bit of the present invention being achieved by defining a cutting aggressiveness of a hybrid drill bit and the various combinations of pairs of a fixed blade cutters and a rolling-cutters, when compared to each other and to different types of drill bits, such as a rolling-cutter drill bit and a fixed blade cutter drill bit, either as the ratio of torque to weight-on-bit or as the ratio of penetration rate to weight-on-bit. The cutting aggressiveness for a hybrid bit of the present invention being adjusted by performing at least one of the following steps:
Other features and advantages of the present invention become apparent with reference to the drawings and detailed description of the invention.
Turning now to the drawing figures, and particularly to
The graph shows the performance characteristics of three different types of earth-boring bits: a three rolling-cutter bit (three roller cones), a six blade fixed cutter bit having PDC cutting elements, and a “hybrid” bit having both (three) rolling-cutters and (three) fixed blade cutters. As shown, each type of bit has a characteristic line. The six fixed blade cutter bit having PDC cutting elements has the highest ROP for a given WOB resulting in a line having the steepest slope of the line showing cutting performance of the bit. However, the PDC bit could not be run at high weight on bit because of high vibrations of the bit. The three rolling-cutter bit (three roller cone bit) has the lowest ROP for a given WOB resulting in a line having the shallowest slope of the line showing cutting performance of the bit. The hybrid bit in the three embodiments of the present invention exhibits intermediate ROP for a given WOB resulting in lines having an intermediate slopes of the lines showing cutting performance of the bit between the lines for the fixed blade cutter bit and the three rolling-cutter bit.
The slope of the line (curve) plotted for ROP versus WOB for a given bit can be termed or defined as the bit's cutting aggressiveness or simply “Aggressiveness” as used herein. “Aggressiveness,” for purposes of this application and the inventions described herein, is defined as follows:
Aggressiveness=Rate of Penetration (ROP)/Weight on Bit (WOB) (1)
Thus aggressiveness, as the mathematical slope of a line, has a value greater than zero. Measured purely in terms of aggressiveness, it would seem that fixed blade cutter bits would be selected in all instances for drilling. However, other factors come into play. For example, there are limits on the amount of WOB and torque to turn the bit that can be applied, generally based on either the drilling application or the capacity of the drill string and drilling rig. For example, as WOB on a fixed blade cutter bit increases the drill string torque requirement increase rapidly, especially with fixed blade cutter bits, and erratic torque can cause harmful vibrations. Rolling-cutter bits, on the other hand, require high WOB which, in the extreme, may buckle a bottom hole assembly or exceed the load bearing capacity of the cutter bearings of the rolling-cutters of the rolling-cutter bit. Accordingly, different types of bits, whether a fixed blade cutter bit, a rolling-cutter bit, or a hybrid bit, have different advantages in different situations. One aspect of the present invention is to provide a method for the design of a hybrid earth-boring bit so that its aggressiveness characteristics can be tailored or varied to the drilling application.
Illustrated in
A rolling cutter 29, 31, 33 is mounted for rotation (typically on a journal bearing, but rolling-element or other bearings may be used as well) on each bit leg 17, 19, 21. Each rolling-cutter 29, 31, 33 has a plurality of cutting elements 35, 37, 39 arranged in generally circumferential rows thereon. In the illustrated embodiment, cutting elements 35, 37, 39 are tungsten carbide inserts, each insert having an interference fit into bores or apertures formed in each rolling cutter 29, 31, 33. Alternatively, cutting elements 35, 37, 39 can be integrally formed with the cutter and hardfaced, as in the case of steel- or milled-tooth cutters. Materials other than tungsten carbide, such as polycrystalline diamond or other super-hard or super-abrasive materials, can also be used for rolling-cutter cutting elements 35, 37, 39 on rolling-cutters 29, 31, 33.
A plurality of cutting elements 41, 43, 45 are arranged in a row on the leading edge of each fixed blade cutter 23, 25, 27. Each cutting element 41, 43, 45 is a circular disc of polycrystalline diamond mounted to a stud of tungsten carbide or other hard metal, which is in turn soldered, brazed or otherwise secured to the leading edge of each fixed blade cutter. Thermally stable polycrystalline diamond (TSP) or other conventional fixed-blade cutting element materials may also be used. Each row of cutting elements 41, 43, 45 on each of the fixed blade cutters 23, 25, 27 extends from the central portion of bit body 13 to the radially outermost or gage portion or surface of bit body 13. On at least one of the rows on one of the fixed blade cutters 23, 25, 27, a cutting element 41 on a fixed-blade cutter 23 is located at or near the central axis or centerline 15 of bit body 13 (“at or near” meaning some part of the fixed cutter is at or within about 0.040 inch of the centerline 15). In the illustrated embodiment, the radially innermost cutting element 41 in the row on fixed blade cutter 23 has its circumference tangent to the axial center or centerline 15 of the bit body 13 and hybrid bit 1.
A plurality of flat-topped, wear-resistant inserts 51 formed of tungsten carbide or similar hard metal with a polycrystalline diamond cutter attached thereto are provided on the radially outermost or gage surface of each fixed blade cutter 23, 25, 27. These serve to protect this portion of the bit from abrasive wear encountered at the sidewall of the borehole. Also, a row or any desired number of rows of back-up cutters 53 is provided on each fixed blade cutter 23, 25, 27 between the leading and trailing edges thereof. Back-up cutters 53 may be aligned with the main or primary cutting elements 41, 43, 45 on their respective fixed blade cutters 23, 25, 27 so that they cut in the same swath or kerf or groove as the main or primary cutting elements on a fixed blade cutter. Alternatively, they may be radially spaced apart from the main fixed-blade cutting elements so that they cut in the same swath or kerf or groove or between the same swaths or kerfs or grooves formed by the main or primary cutting elements on their respective fixed blade cutters. Additionally, back-up cutters 53 provide additional points of contact or engagement between the bit 11 and the formation being drilled, thus enhancing the stability of hybrid bit 11.
In the embodiments of the inventions illustrated in
In
Illustrated in
Illustrated in
Illustrated in
When considering a pair of cutters of the hybrid bit 11 including a rolling cutter and a fixed blade cutter, each having cutting elements thereon, having the same exposure of cut, and located at the same radial location from the axial center of the hybrid bit 11 cutting the same swath or kerf or groove, adjusting the angular spacing between rolling cutters 29, 31, 33, and fixed blade cutters 23, 25, 27 is one way in which to adjust the cutting aggressiveness or aggressiveness of a hybrid bit 11 according to the present invention. When considering a pair of cutters having cutting elements thereon having the same exposure of cut and located at the same radial location from the axial center of the hybrid bit 11 cutting the same swath or kerf or groove on the hybrid bit 11, the closer a rolling cutter 29 is to a fixed blade cutter 23 of the pair of cutters of the hybrid bit 11, the rolling-cutter 29 is the primary cutter of the pair with the fixed blade cutter 23 cutting less of the pair. Spacing a rolling cutter 29 closer to a fixed blade cutter 23 of a pair of cutters on the hybrid bit 11 causes the rolling cutter 29 to have a more dominate cutting action of the pair of cutters thereby causing the hybrid bit 11 to have less cutting aggressiveness or aggressiveness. Spacing a rolling-cutter 29 farther away from a fixed blade cutter 23 of a pair of cutters on the hybrid bit 11 allows or causes the cutting elements of the fixed blade cutter 23 to dominate the cutting action of the pair of cutters thereby increasing the cutting aggressiveness or aggressiveness of the hybrid bit 11.
Another way of altering the cutting aggressiveness of a hybrid bit 11 is by having a rolling cutter to lead a trailing fixed blade cutter of a pair of cutters (including one of each type of cutter) or to have a fixed blade cutter lead a trailing rolling cutter of a pair of cutters (including one of each type of cutter). As illustrated in drawing
In the illustrated hybrid bit 11 of
Also, in the embodiments of
The hybrid bit 111 of
Still another way to adjust or vary the aggressiveness of the hybrid bit 11 is to arrange the cutting elements 35, 37, 39 on the rolling-cutters 29, 31, 33 so that they project deeper into the formation being drilled than the cutting elements 41, 43, 45 on the fixed blade cutters 23, 25, 27. The simplest way to do this is to adjust the projection of some or all of the cutting elements 35, 37, 39 on the rolling-cutters 29, 31, 33 from the surface of each rolling cutter 29, 31, 33 so that they project in the axial direction (parallel to the bit axis 15) further than some or all of the cutting elements 41, 43, 45 on fixed blades cutters 23, 25, 27. In theory, the extra axial projection of a cutting element of the cutting elements on the rolling cutters causes the cutting element to bear more load and protects an associated cutting element of the fixed blade cutter.
In practice, it is a combination of the projection of each cutting element of a rolling-cutter from the surface of its rolling cutter, combined with its angular spacing (pitch) from adjacent cutting elements that governs whether the cutting elements of a rolling-cutter actually bear more of the cutting load than an associated cutting element on a fixed blade cutter. This combination is referred to herein as “effective projection,” and is illustrated in
From the exemplary embodiment described above, a method for designing a hybrid earth-boring bit of the present invention permits or allows the cutting aggressiveness of a hybrid bit to be adjusted or selected based on the relationship of at least a pair of cutters comprising a fixed blade cutter and a rolling-cutter, of a plurality of fixed blade cutters and rolling-cutters, wherein the relationship includes a fixed blade cutter leading a rolling-cutter in a pair of cutters, a rolling-cutter leading a fixed blade cutter in a pair of cutters, a rolling-cutter being located opposite a fixed blade cutter in a pair of cutters on the bit, and the angular relationship of a fixed blade cutter and a rolling-cutter of a pair of cutters regarding the amount of leading or trailing of the cutter from an associated cutter of the pair of cutters. The cutting aggressiveness of a hybrid bit of the present invention being achieved by defining a cutting aggressiveness of a hybrid drill bit and the various combinations of pair of a fixed blade cutter and a rolling-cutter, when compared to each other and to different types of drill bits, such as a rolling-cutter drill bit and a fixed blade cutter drill bit, either as the ratio of torque to weight-on-bit or as the ratio of penetration rate to weight-on-bit. The cutting aggressiveness for a hybrid bit of the present invention being adjusted by performing at least one of the following steps:
As described above, decreasing the angular distance between a leading rolling-cutter and fixed blade cutter decreases aggressiveness of the pair of cutters, while increasing the distance therebetween increases aggressiveness of the pair of cutters. Increasing the effective projection on cutting elements of a rolling-cutter by taking into account the pitch between them increases the aggressiveness and the converse is true. Finally, designing the cutting elements on a fixed blade to lead the cutting elements on the trailing rolling-cutter increases aggressiveness, while having a rolling-cutter leading its trailing fixed blade cutter has the opposite effect. According to this method, aggressiveness is increased, generally, by causing the scraping action of the cutting elements and fixed blades and to dominate over the crushing action of the cutting elements and the rolling-cutters.
Increased aggressiveness is not always desirable because of the erratic torque responses that generally come along with it. The ability to tailor a hybrid bit to the particular application can be an invaluable tool to the bit designer.
The invention has been described with reference to preferred or illustrative embodiments thereof. It is thus not limited, but is susceptible to variation and modification without departing from the scope of the invention.
This application claims the benefit of U.S. provisional patent application Ser. No. 60/988,718, filed Nov. 16, 2007, which is incorporated herein in its entirety. This application is related to application Ser. No. 12/061,536, filed Apr. 2, 2008, which is incorporated herein in its entirety.
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