Patent Application
20080060852
a is an assembly view, showing the intermeshing of the cutting structure of a prior art bit design.
b is a schematic drawing illustrating a composite layout of the cutting structures of
In one aspect, embodiments disclosed herein relate to drill bits having at least one roller cone having a limited number of cutting elements that contribute to the operative gage row of the drill bit. In another aspect, embodiments disclosed herein relate to drill bits having at least one roller cone having no cutting elements that contribute to the operative gage row of the drill bit.
Referring first to
Referring now to
Extending between heel surface 144 and nose 142 is a generally conical surface 146 adapted for supporting cutter elements that gouge or crush the borehole bottom 7 as the cone cutters rotate about the borehole. Conical surface 146 may include a plurality of generally frustoconical segments 148 generally referred to as “lands” which are employed to support and secure the cutter elements as described in more detail below. Grooves 149 may be formed in cone surface 146 between adjacent lands 148. Frustoconical heel surface 144 and conical surface 146 converge in a circumferential edge or shoulder 150. Although referred to herein as an “edge” or “shoulder,” it should be understood that shoulder 150 may be contoured, such as a radius, to various degrees such that shoulder 150 will define a contoured zone of convergence between frustoconical heel surface 144 and the conical surface 146.
In the embodiment shown in
Cone 114 may include a plurality of heel row inserts 160 that are secured in a circumferential row 160a in the frustoconical heel surface 144. Cone 114 may further include a circumferential row 180a of gage inserts 180 secured to cone 114 in locations along or near the circumferential shoulder 150. Cone 114 may optionally include a circumferential row 170a of wall cutting inserts 170 along or near the circumferential shoulder 150. Wall cutting inserts 170 may be interspersed or staggered between gage inserts 180. Wall cutting inserts 170 may be located such that they do not contact the hole bottom during cutting, splitting the duty of hole wall cutting and hole bottom cutting between gage inserts 180 and wall cutting inserts 170. Cone 114 may further include a plurality of inner row inserts 181, 182, and 183 secured to cone surface 146 and arranged in spaced-apart inner rows 181a, 182a, and 183a, respectively. Relieved areas or lands 178 (best shown in
As understood by those skilled in this art, heel inserts 160 generally function to scrape or ream the borehole sidewall 5 to maintain the borehole at full gage and prevent erosion and abrasion of heel surface 144. Cutter elements 181, 182 and 183 of inner rows 181a, 182a, and 183a are employed primarily to gouge and remove formation material from the borehole bottom 7. Inner rows 180a, 181a, 182a, and 183a are intermeshed, arranged and spaced on cutter 114 so as not to interfere with the inner rows on each of the other cone cutters 115, 116.
As described above, the active gage cutting elements are referred to as gage inserts, and the passive gage cutting elements are described as the heel inserts. And, typically, the gage inserts actively engage in both the hole wall and hole bottom cutting action. Since the heel inserts cut the hole wall after it has already been trimmed by the gage inserts, their cutting action is generally passive in nature
Gage inserts, or inserts that contribute to the operative gage row of a drill bit, typically account for over 30 percent of the total number of inserts that contact hole bottom for a roller cone on a drill bit. The number of inserts may also be referred to as “count,” where gage count refers to the number of gage inserts, for example. In contrast to the gage count, the total surface area for the ring of material that the gage inserts must cut is approximately 10 to 15 percent of the borehole. Reducing (minimizing or eliminating) the total gage count on a roller cone cutter may increase the penetration depth of the inserts that contact hole bottom, and thus increase the rate of penetration of the bit.
Referring now to
In some embodiments, gage cutting elements that contribute to the operative gage row of a drill bit may be 30 percent or less of the total count of cutting elements on at least one roller cone cutter of a multi-cone drill bit. In other embodiments, gage cutting elements contributing to the operative gage row may be 28 percent or less of the total count of cutting elements on at least one roller cone; 26 percent or less in other embodiments; 23 percent or less in other embodiments; and 20 percent or less, 15 percent or less, and 10 percent or less in yet other various embodiments.
In some embodiments, gage cutting elements that contribute to the operative gage row of a drill bit may be 30 percent or less of the total count of cutting elements that contact hole bottom on at least one roller cone cutter of a multi-cone drill bit. In other embodiments, gage cutting elements contributing to the operative gage row may be 28 percent or less of the total count of cutting elements that contact hole bottom; 26 percent or less in other embodiments; 23 percent or less in other embodiments; and 20 percent or less, 15 percent or less, and 10 percent or less in yet other various embodiments.
In some embodiments, a roller cone cutter may have no cutting elements contacting hole bottom contributing to the operative gage row of the drill bit. In embodiments where a roller cone does not include inserts contributing to the operative gage row, the gage inserts on the other roller cones of the drill bit may maintain the borehole diameter.
In other embodiments, gage cutting elements that contribute to the operative gage row of a drill bit may be less than 31 percent of the total count of cutting elements that contact the hole bottom and the transition region of the borehole on at least one roller cone cutter of a multi-cone drill bit. In other embodiments, gage cutting elements contributing to the operative gage row may be 28 percent or less of the total count of cutting elements that contact the hole bottom and the transition region of the borehole; 26 percent or less in other embodiments; 23 percent or less in other embodiments; and 20 percent or less, 15 percent or less, and 10 percent or less in yet other various embodiments. In other embodiments, a roller cone cutter may have no cutting elements contributing to the operative gage row of the drill bit that contact hole bottom or the transition region of the borehole on at least one roller cone cutter of a multi-cone drill bit.
Referring still to
In some embodiments, it may be desired to prevent premature contact of the off-bottom inserts with the hole bottom. For example, if the off-bottom inserts contacted hole bottom after minimal wear of cutter elements in adjacent rows, the additional cutting material contacting hole bottom could limit ROP. In some embodiments, the off-bottom elements may extend from the cone surface such that the outermost point on the cutting surface is at least 0.100 inches from contacting the bottom of the borehole prior to any wear on the bit. In other embodiments, the off-bottom elements may extend from the cone surface such that the outermost point on the cutting surface is at least 0.125 inches from contacting the bottom of the borehole prior to any wear on the bit; at least 0.150 inches in yet other embodiments.
In some embodiments, off-bottom cutting elements may be located between the heel row of cutting elements and the shoulder of the roller cone cutter, contacting and cutting along the transition region of the borehole and/or cutting the hole wall. For example, referring again to
In some embodiments, a drill bit having a limited number of gage inserts or no gage inserts contributing to the operative gage row, as described above, may include off-gage inserts. Off-gage inserts, as mentioned above, are cutting elements or inserts that are positioned so that their cutting surfaces are close to gage, but are off-gage by a small distance. The off-gage inserts do not lie on the gage curve, but are spaced from the gage curve such that they do not contribute to the operative gage row of the drill bit.
As understood by those skilled in the art of designing bits, a “gage curve” is commonly employed as a design tool to ensure that a bit made in accordance to a particular design will cut the specified hole diameter. The gage curve is a complex mathematical formulation which, based upon the parameters of bit diameter, journal angle, and journal offset, takes all the points that will cut the specified hole size, as located in three dimensional space, and projects these points into a two dimensional plane which contains the journal centerline and is parallel to the bit axis. The use of the gage curve greatly simplifies the bit design process as it allows the gage cutting elements to be accurately located in two-dimensional space, which is easier to visualize. The gage curve, however, should not be confused with the cutting path of any individual cutting element as described previously.
As known to those skilled in the art, the American Petroleum Institute (API) sets standard tolerances for bit diameters, tolerances that vary depending on the size of the bit. The term “off gage,” as used herein to describe an inner row of cutter elements, refers to the difference in distance that cutter elements radially extend into the formation and not to whether or not cutter elements extend far enough to meet an API definition for being on gage. That is, for a given size bit made in accordance with embodiments disclosed herein, cutter elements may be “off gage,” but may still extend far enough into the formation such that the cutter elements would fall within the API tolerances for being on gage for that given bit size. Nevertheless, cutter elements would be “off gage” as that term is used herein because of their relationship to the cutting path taken by inserts cutting gage. For example, a circumferential row of cutter elements may form a distinct operative row overlapping, adjacent, or proximate the operative gage row. In other embodiments, cutter elements that are “off gage” (as herein defined) may also fall outside the API tolerances for the given bit diameter.
Referring now to
Although illustrated where one cone has no gage inserts, two or three of the cones may have no gage inserts. In some embodiments, where a cone does not have gage inserts contacting hole bottom, the gage may include off-bottom inserts as described above. In other embodiments, the cone may include off-gage inserts and heel inserts. For embodiments where a cone does not have gage inserts contacting hole bottom, the gage inserts on the other roller cones may maintain the borehole diameter.
The range of off-gage distance D may range from 0.010 inches to 0.250 inches, depending upon bit diameter. In some embodiments, where the bit diameter is less than 10 inches, the off-gage distance D may range from 0.015 to 0.150 inches. In other embodiments, where the bit diameter is greater than 10 inches and less than 15 inches, the off-gage distance D may range from 0.025 to 0.200 inches. In yet other embodiments, where the bit diameter is greater than 15 inches, the off-gage distance D may range from 0.030 to 0.250 inches. In other embodiments, the off-gage distance D may be at least 0.020 inches; at least 0.050 inches in yet other embodiments.
The off-bottom and off-gage inserts described above may be of any desired geometry. For example, in one embodiment, as illustrated in
In other embodiments, the geometry of off-bottom and off-gage inserts may also be t-crested. As illustrated in
In some embodiments, a roller cone not having an operative gage row (actively cutting gage) may have a heel row spaced further up on the heel surface such that the heel row is generally aligned with the heel rows of the other cones. In this manner, the heel row does not overlap with the coverage of the off-gage row of the cone or the operative gage row of the other cones. The heel row thus functions as a reaming row, or an operative heel row, maintaining the gage previously cut by the gage inserts on the other cones. This concept is encompassed as illustrated in
In some embodiments, the roller cone not having an operative gage row may have as many passive gage cutting elements as possible, optimizing the location of off-gage inserts and heel inserts on a cone without gage inserts.
The cutting elements used in embodiments of the drill bits described above may include tungsten carbide inserts, polycrystalline diamond compacts, milled steel teeth, or any other cutting elements of materials hard and strong enough to deform or cut through the formation. Furthermore, hardfacing may also be applied to the cutting elements and other portions of the bit to reduce wear on the bit and to increase the life of the bit. In some embodiments, the cutting elements may comprise abrasive particles such as synthetic diamond, CVD coated synthetic diamond, natural diamond, CBN, TSP, or combinations thereof. In certain embodiments, the following materials may be used to form the cutting elements: tungsten carbide (WC), tungsten (W), sintered tungsten carbide/cobalt (WC—Co) (spherical or crushed), cast tungsten carbide (spherical or crushed) or combinations of these materials (all with an appropriate binder phase such as cobalt, iron, nickel, or copper to facilitate bonding of particles and diamonds), and the like. In some embodiments, sintered tungsten carbide-cobalt alloy, macrocrystalline tungsten carbide, cast tungsten carbide, reclaimed natural or synthetic diamond grit, tungsten, silicon carbide, boron carbide, aluminum oxide, tool steel, and combinations thereof, may be used. In various embodiments, the coating or hardfacing may comprise titanium-based coatings, tungsten based coatings, nickel coatings, silicon coatings, various carbides, nitrides, and other materials known to those skilled in the art.
Drill bits designed in accordance with embodiments disclosed herein deviate from typical drill bits in at least two fashions. First, as described above, the drill bit does not place as many cutting inserts as possible on the gage of the bit. Typical bits are designed to have as many inserts on gage, where the highest drilling forces are encountered, in order to prolong bit life. As detailed above, limiting the number of gage inserts may allow larger inserts, use of harder inserts may be possible, or bit life may be offset by a higher ROP.
Second, drill bits designed in accordance with embodiments disclosed herein deviate from typical drill bits by not requiring that each roller cone cutter have a gage row. In contrast, bits disclosed herein may include a roller cone cutter having no cutting elements contributing to an operative gage row.
Bits designed according to embodiments disclosed herein may be designed to maximize rate of penetration and/or to maximize wear resistance. In other embodiments, bits disclosed herein may be designed to optimize a combination of these variables to promote the desired performance. As such, bits made in accordance with embodiments disclosed herein may be designed according to the following method.
An initial bit design may first be provided. The initial bit may be tested for performance characteristics, where the testing may include modeling and/or actual testing of the bit. The initial bit design may then be iteratively adjusted to maximize rate of penetration, maximize wear resistance, or optimize a combination thereof, where the bit design is bounded by the following limitations. In some embodiments, cutting elements contributing to an operative gage row of the drill bit on at least one roller cone cutter comprises 30 percent or less of the total count of cutting elements on the at least one roller cone cutter that contact hole bottom during drilling. In other embodiments, at least one roller cone cutter does not comprise cutting elements contributing to an operative gage row of the drill bit. In other embodiments, where the at least one roller cone cutter has a limited count of cutting elements contacting hole bottom or no cutting elements contributing to an operative gage row, the at least one roller cone cutter may include off-gage and/or off-bottom inserts as described above.
Embodiments of the drill bits described herein may be employed in steel tooth bits as well as TCI bits. Advantageously, the embodiments described herein provide for roller cone drill bits having reduced gage insert count on at least one roller cone. A reduced gage count may increase the penetration depth of the gage and inner row inserts, and may increase the rate of penetration of the bit. A reduced gage count may also allow for larger gage inserts, having a larger wear surface and increased impact resistance, which may also increase the rate of penetration of the bit. Increased gage diameter may also allow a harder, more wear resistant carbide grade to be used compared to a smaller insert.
Reduced gage count may also allow for a large hole wall cutting insert to be staggered between each gage insert. This may split the duty between hole wall cutting and bottom hole cutting. The overall carbide volume contacting the hole wall may also be increased. As the hole wall cutting insert is not in contact with the hole bottom, the carbide grade may be much more wear resistant, optimally maintaining gage.
Embodiments described herein also provide a roller cone drill bit having no active gage inserts contacting hole bottom on at least one roller cone. Eliminating gage inserts may allow independent count and location of off-gage inserts. Eliminating gage inserts on at least one roller cone may also allow for deeper penetration of the off-gage inserts, improving the rate of penetration of the bit.
The differences in formations encountered while drilling and the type of drilling (straight, directional, etc.) should also be taken into account when designing or choosing a bit. In certain drilling environments, such as directional drilling, it may be preferential to use a bit that may allow a faster rate of penetration, while bit wear may not be as critical. Some formations may require a high gage count, such as when drilling a hard formation. Although the bits described herein allow for improved penetration of gage and off-gage inserts, the bits described herein may perform better in soft to medium-hard formations, where a high gage count may not be needed. Additionally, the bits described herein may advantageously be used when drilling curved sections at a higher rate of penetration.
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 be limited only by the attached claims.
All priority documents are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted. Further, all documents cited herein, including testing procedures, are herein fully incorporated by reference for all jurisdictions in which such incorporation is permitted to the extent such disclosure is consistent with the description of the present invention.
