EP2358969A1

EP2358969A1 - Hybrid drill bit with high pilot-to journal diameter ratio

Info

Publication number: EP2358969A1
Application number: EP09837870A
Authority: EP
Inventors: Don Q. Nguyen; Anton F. Zahradnik; Rudolf C. Pessier
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2008-12-19
Filing date: 2009-12-15
Publication date: 2011-08-24
Anticipated expiration: 2029-12-15
Also published as: EP2358969A4; US20100155146A1; CA2747434A1; RU2011129565A; EP2358969B1; RU2541414C2; BRPI0922569A2; WO2010080380A1; MX2011005857A

Abstract

The invention disclosed and taught herein are directed to an improved hybrid drill bit and associated elements having at least two frusto-conical cutter assemblies, each rotatable around separate axles on the bit, and at least two fixed blade cutters adjacent the frusto-conical cutter assemblies. The improved drill bit expands the pilot pin to journal diameter ratio within the body of the frusto-conical cutter assembly, but within the confines of the allowable space of the frusto-conical cutter assembly.

Description

TITLE OF THE INVENTION

Hybrid Drill Bit With High Pilot-To-Journal Diameter Ratio

PRIORITY CLAIM

5 This application claims the benefit of U.S. Patent Appl. No. 61/139,392 filed on December 19, 2008 and U.S. Patent Application No. 12/481,410 filed on June 9, 2009. The above mentioned applications are incorporated herein by reference.

to REFERENCE TO APPENDIX Not applicable.

BACKGROUND OF THE INVENTION

Field of the Invention. The disclosure described herein generally relates to is drill bits for use in drilling operations in subterranean formations. More particularly, the disclosure relates to hybrid drill bits, and apparatus and methods for increasing the strength of the support surfaces in such drill bits.

Description of the Related Art.

2« Drill bits are frequently used in the oil and gas exploration and the recovery industry to drill well bores (also referred to as "boreholes") in subterranean earth formations. There are two common classifications of drill bits used in drilling well bores known in the art as "fixed cutter" drill bits and "roller cone" drill bits. Fixed cutter type drill bits include polycrystalline diamond compact

K (PDC) and other drag-type drill bits. These drill bit typically include a bit body having an externally threaded connection at one end for connection to a drill string, and a plurality of cutting blades extending from the opposite end of the bit body. The cutting blades form the cutting surface of the drill bit. Often, a plurality of cutting elements, such as PDC cutters or other materials, which

30 are hard and strong enough to deform and/or cut through earth formations, are attached to or inserted into the blades of the bit, extending from the bit and forming the cutting profile of the bit. This plurality of cutting elements is used to cut through the subterranean formation during drilling operations when the drill bit is rotated by a motor or other rotational input device.

The other type of earth boring drill bit, referred to as a roller cone bit, typically includes a bit body with an externally threaded connection at one end, and a plurality of roller cones (typically three) attached at an offset angle to the other end of the drill bit, relative to the bit's centerline. These roller cones are able to rotate about bearings, and rotate individually with respect to the bit body.

An exemplary roller bit and cutting roller cone are illustrated in Figures 1 and 2 and described in U.S. Pat. No. 6,601 ,661, incorporated herein by reference. The roller bit 10 includes a bit body 12 having a longitudinal centerline 8 and having a threaded pin-type connector 14 at its upper end for incorporation of the bit body 12 into the lower end of a drill string (not shown). The bit body 12 has generally three downwardly depending legs (two shown at 16, 18) with a lubricant compensator 20 provided for each. Nozzles 22 (one shown) are positioned between each of the adjacent legs to dispense drilling fluid during drilling. The drilling fluid is pumped down through the drill string and into a cavity (not shown) in the bit body 12. A roller is secured to the lower end of each of the three legs. The three roller cones 24, 25, and 26 are visible in Figure 1 secured in a rolling relation to the lower ends of the legs of bit body 12.

The roller cone 24 is rotatably retained by bearings 27 on an axle 28, where the axle has an axle centerline 6 disposed at an angle to the longitudinal centerline 8 of the bit body. The axle 28 includes a journal 29 and a pilot pin 30 with a shoulder 31 formed between the journal 29 and the pilot pin 30. The diametrical surfaces of the journal 29 and pilot pin 30 are useful for supporting the roller cone in radial (bending) loading, and the surface of the shoulder, and at times the end surface of the pilot pin, is useful for supporting the roller cone in thrust (end) loading. The diameter and length of the journal, the diameter and length of the pilot pin, and size of the shoulder formed therebetween is constrained by the size and shape of the roller cone coupled thereto. For a given optimum journal diameter, a larger pilot pin diameter results in either having to shorten the overall length of the journal and/or pilot pin, or reducing the cone shell thickness, either of which can lead to failure. Similarly, too small of a surface on the shoulder may cause a failure of the axle and roller cone interface.

5 The roller cone 24 has a cutter body 32 that is typically formed of a suitably hardened steel. The cutter body 32 is substantially cone-shaped. A plurality of primary cutting elements 34, 36, 38 extend from the cutter body 32. When the cutter body 32 is rotated upon the axle 28, the primary cutting elements engage earth within a borehole and crush it. The plurality of cutting elements us may be one or a combination of milled steel teeth (called steel-tooth bits), tungsten carbide (or other hard-material) inserts (called insert bits), or a number of other formed and/or shaped cutting elements that are formed of materials having a hardness and strength suitable enough to allow for the deformation and/or cutting through of subterranean formations. In some is instances, a hard facing material is applied to the exterior of the cutting elements and/or other portions of the roller cone drill bit, to reduce the wear on the bit during operation and extend its useful working life.

These type general classes of earth boring bits have limitations, particularly with the bit life and the types of subterranean formations through which they x> can drill. Fixed cutter type bits, such as PDC bits, usually can be used with success in soft-soft to medium-hard, and medium-hard, nonabrasive formations. Hard and/or abrasive formations are generally considered unsuitable for PDC bits in that their use in such formations results in excessive wear and shortened working life. For example, mudstone and a siltstone have been drilled well; sandstones, particularly if coarse-grained and cemented, are very difficult to drill economically and are highly destructive to fixed cutter type drill bits. [See, for example, Feenstra, R., et al., "Status of Polycrystalline-Diamond-Compact Bits: Part 1 — Development" and "Part 2 — Applications", Journal of Petroleum Technology, Vol. 40 (7), pp. 675-684 and so 817-856 (1988).] Success is fully dependent on a good match between the bit, the formation to be drilled, and the operating conditions. Experience has shown that for fixed cutter bits such as PDC bits, the type of mud, the bit hydraulics, and bit design affect bit performance much more than variations in mud properties.

Repeated experience shows that a preferred practice is to develop the best bit s design for a particular field rather than to select one from a range. Increased aggressiveness in earth-boring bits is not always desirable, because of the increase torque requirements that are generally associated with it. The ability to design and/or tailor a bit to a particular subterranean operation or application can be an invaluable tool for the bit designer. Thus, in recent !3 years, attempts have been made to develop earth-boring drill bits that use a combination of one or more rolling cutters and one or more fixed blade cutters having PDC or similarly abrasive cutting elements formed or bonded thereon. Some of these combination type bits are referred to as "hybrid drill bits".

One previously described hybrid drill bit is disclosed in U.S. Patent No.

H 4,343,371 , wherein a hybrid rock bit is disclosed "wherein a pair of opposing extended nozzle drag bit legs are positioned adjacent a pair of opposed tungsten carbide roller cones. The extended nozzle face nearest the hole bottom has a multiplicity of diamond inserts mounted therein. The diamond inserts are strategically positioned to remove the ridges between the kerf rows

2ϋ in the hole bottom formed by the inserts in the roller cones." A cross section of the pilot pin and journal is not shown in the above patent, but is typically the same as a roller cone bit.

Significant stresses are placed on the journal and the pilot pin as radial (bending) and thrust (compressive) loads are applied to the drill bits during the

2s drilling operations. The journal and the pilot pin support a radial load along their respective lengths that acts transverse to the axle centerline, and the face between the journal and the pilot pin supports a thrust load that acts in parallel to the axle centerline. On a hybrid drill bit, a rotatable cutter assembly is generally smaller for a given size of bit than a corresponding roller cone bit,

ΪO because the hybrid drill bit must allow for both the rotatable cutter assemblies as well as the adjacent fixed blade cutters. The journal and pilot pin about which the rotatable cutter assembly rotates is necessarily smaller, which can result in higher stresses for the same loads with the smaller area. However, the stresses on the rotatable cutter assembly itself dictate that a minimum of material remain on the shell thickness of the cutter assembly that restricts the size and length of both the journal and pilot pin. For example, increasing the pilot pin diameter requires a shorter pin to accommodate the larger diameter within the confines of the cutter assembly, or requires a thinner wall on the cutter assembly.

There remains a need for an improved load carrying capacity for a hybrid drill bit.

BRIEF SUMMARY OF THE INVENTION

The invention disclosed and taught herein are directed to an improved hybrid drill bit and associated elements having at least two frusto-conical cutter assemblies, each rotatable around separate axles on the bit, and at least two fixed blade cutters adjacent the frusto-conical cutter assemblies. The improved drill bit expands the pilot pin to journal diameter ratio within the body of the frusto-conical cutter assembly but within the confines of the allowable space of the frusto-conical cutter assembly.

The disclosure provides a hybrid drill bit for use in drilling through subterranean formations, the hybrid drill bit comprising: a shank disposed about a longitudinal centerline and adapted to be coupled to a drilling string; at least two fixed cutter legs coupled to the shank; at least two fixed blade cutters fixedly coupled to the cutter legs distally from the shank, comprising a plurality of cutting elements extending from a surface of the blades; and at least two frusto-conical cutter assemblies coupled to the frusto-conical cutter legs distally from the shank and adjacent the fixed blade cutters and adapted to rotate relative to the shank about the axle centerline on the journal and pilot pin, the cutter assemblies comprising cutting elements extending from a surface of the assemblies. The axle of the frusto-conical cutter legs comprises a journal disposed about the axle centerline, the journal having a journal diameter; and a pilot pin coupled to the journal and extending along the axle centerline toward the longitudinal centerline, the pilot pin having a pilot pin diameter, the pilot pin diameter to journal diameter having a ratio of equal to or greater than 0.58.

The disclosure provides a hybrid drill bit for use in drilling through s subterranean formations, the hybrid drill bit comprising: a shank disposed about a longitudinal centerline and adapted to be coupled to a drilling string; at least two fixed cutter legs coupled to the shank; at least two fixed blade cutters fixedly coupled to the cutter legs distally from the shank, comprising a plurality of cutting elements extending from a surface of the blades; and at ie least two frusto-conical cutter legs coupled to the shank, comprising an axle with an axle centerline extending at an angle to the longitudinal centerline and toward the longitudinal centerline. The axle comprises a journal disposed about the axle centerline, the journal having a journal diameter; and a pilot pin coupled to the journal and extending along the axle centerline toward the

5> longitudinal centerline, the pilot pin having a pilot pin diameter, the pilot pin diameter to journal diameter having a ratio of equal to or greater than 0.58.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention so may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.

Figure 1 illustrates a side view of a typical roller cone bit.

Figure 2 illustrates a cross sectional side view of a typical roller cone bit a? journal and pilot pin configuration.

Figure 3 illustrates an exemplary side view of a hybrid drill bit. Figure 4 illustrates an exemplary bottom view of a hybrid drill bit.

Figure 5 illustrates a cross sectional side view of an exemplary enlarged pilot pin to journal diameter configuration according to the disclosure. Figure 6 illustrates a cross sectional side view of another exemplary enlarged pilot pin to journal diameter configuration according to the disclosure.

While the invention disclosed herein is susceptible to various modifications and alternative forms, only a few specific embodiments have been shown by

5 way of example in the drawings and are described in detail below. The figures and detailed descriptions of these specific embodiments are not intended to limit the breadth or scope of the inventive concepts or the appended claims in any manner. Rather, the figures and detailed written descriptions are provided to illustrate the inventive concepts to a person of io ordinary skill in the art and to enable such person to make and use the inventive concepts.

DETAILED DESCRIPTION

The Figures described above and the written description of specific structures is and functions below are not presented to limit the scope of what Applicants have invented or the scope of the appended claims. Rather, the Figures and written description are provided to teach any person skilled in the art to make and use the inventions for which patent protection is sought. Those skilled in the art will appreciate that not all features of a commercial embodiment of the

B inventions are described or shown for the sake of clarity and understanding. Persons of skill in this art will also appreciate that the development of an actual commercial embodiment incorporating aspects of the present inventions will require numerous implementation-specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such

2s implementation-specific decisions may include, and likely are not limited to, compliance with system-related, business-related, government-related and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time- consuming in an absolute sense, such efforts would be, nevertheless, a so routine undertaking for those of skill this art having benefit of this disclosure. It must be understood that the inventions disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Lastly, the use of a singular term, such as, but not limited to, "a," is not intended as limiting of the number of items. Also, the use of relational terms, such as, but not limited to, "top," "bottom," "left," "right," "upper," "lower," "down," "up," "side," and the like are used in the written description for clarity

5 in specific reference to the Figures and are not intended to limit the scope of the invention or the appended claims. The terms "couple," "coupled," "coupling," "coupler," and like terms are used broadly herein and may include any method or device for securing, binding, bonding, fastening, attaching, joining, inserting therein, forming thereon or therein, communicating, or so otherwise associating, for example, mechanically, magnetically, electrically, chemically, directly or indirectly with intermediate elements, one or more pieces of members together and may further include without limitation integrally forming one functional member with another in a unity fashion. The coupling may occur in any direction, including rotationally.

Applicants have created an improved hybrid drill bit and associated elements with an expanded pilot pin to journal diameter ratio within the body of the frusto-conical cutter assembly, where the hybrid drill bit includes at least two frusto-conical cutter assemblies, each rotatable around separate axles on the 20 bit, and at least two fixed blade cutters adjacent the frusto-conical cutter assemblies.

Figure 3 illustrates an exemplary side view of a hybrid drill bit. Figure 4 illustrates an exemplary bottom view of a hybrid drill bit. Figure 5 illustrates an exemplary enlarged pilot pin to journal diameter configuration according to 25 the disclosure. Figure 6 illustrates another exemplary enlarged pilot pin to journal diameter configuration according to the disclosure. The figures will be described in conjunction with each other.

A hybrid drill bit 50 has a longitudinal centerline 52 that defines an axial center of the hybrid drill bit. A shank 54 is formed on one end of the hybrid drill bit ^■■.ύ and is designed to be coupled to a drill string of tubular material (not shown) with threads according to standards promulgated for example by the American Petroleum Institute (API). At least two fixed cutter legs bit legs 56 extend downwardly from the shank 54 relative to a general orientation of the bit inside a borehole. The fixed cutter legs 56 transition into fixed blade cutters 58 at an end of the hybrid drill bit distal from the shank 54.

A plurality of fixed blade cutting elements 60, 62 are arranged and secured to

5 a surface 63 on each of the fixed blade cutters 58, such as at the leading edges of the hybrid drill bit relative to the direction of rotation. Generally, the fixed blade cutting elements 60, 62 comprise a polycrystalline diamond (PCD) layer or table on a rotationally leading face of a supporting substrate, the diamond layer or table providing a cutting face having a cutting edge at a vύ periphery thereof for engaging the formation. The term PCD is used broadly and includes other materials, such as thermally stable polycrystalline diamond

(TSP) wafers or tables mounted on tungsten carbide substrates, and other, similar superabrasive or super-hard materials, such as cubic boron nitride and diamond-like carbon. Fixed-blade cutting elements 60, 62 may be brazed or is otherwise secured in recesses or "pockets" on each fixed blade cutter 58 so that their peripheral or cutting edges on cutting faces are presented to the formation.

The hybrid drill bit 50 further includes at least two frusto-conical cutter legs 64 and frusto-conical cutter assemblies 72 coupled to such legs. The frusto-

20 conical cutter legs 64, in similar fashion to the fixed cutter legs 56, extend downwardly from the shank 54 relative to a general orientation of the bit inside a borehole. Each of the frusto-conical cutter legs 64 transition into an axle 66 at the legs' distal end. The axle 66 has an axle centerline 67 about which the axle is symmetrically formed. The axle centerline 67 is generally disposed at

25 an angle to the longitudinal centerline 52 (generally 51 to 59 degrees to the longitudinal centerline inclusive, that is, 31-39 degrees from a horizontal plane if the longitudinal centerline is perpendicular to the horizontal plane) and toward the longitudinal centerline. In at least one embodiment, the axle centerline 67 can intersect the longitudinal centerline 6. However, other x> angles and directions can be used including an angle pointing away from the longitudinal centerline. The axle 66 generally forms two portions — a journal 68 disposed at a base of the axle, and a pilot pin 70 adjacent the journal and extending axially along the axle centerline 67. A shoulder 71 is established as a result of the different diameters between the journal 68 and the pilot pin 70. The journal, pilot pin, ? and shoulder support a frusto-conical cutter assembly 72 rotatably disposed about the journal and pilot pin.

A frusto-conical cutter assembly 72 is generally coupled to each axle 66. The frusto-conical cutter assembly 72 generally has a truncated nose section 73 compared to a typical roller cone bit illustrated in Figure 2. The frusto-conical

& cutter assembly 72 is adapted to rotate around the axle 66 when the hybrid drill bit 50 is being rotated by the drill string through the shank 52. Generally, a plurality of cutting elements 74, 75 is coupled to a surface 77 of the cutter assembly 72. At least some of the cutting elements are generally arranged on the frusto-conical cutter assembly 72 in a circumferential row thereabout. A is minimal distance between the cutting elements will vary according to the application and bit size, and may vary from cutter assembly to cutter assembly, and/or cutting element to cutting element. Some cutting elements can be arranged "randomly" on the surface of the cutter assembly. The cutting elements can include tungsten carbide inserts, secured by interference

20 fit into bores in the surface of the cutter assembly, milled- or steel-tooth cutting elements having hard faced cutting elements integrally formed with and protruding from the surface of the cutter assembly, and other types of cutting elements. The cutting elements may also be formed of, or coated with, superabrasive or super-hard materials such as polycrystalline diamond, x cubic boron nitride, and the like. The cutting elements may be chisel-shaped as shown, conical, round, or ovoid, or other shapes and combinations of shapes depending upon the application.

In the hybrid drill bit, the cutting elements 60, 62 of the fixed blade cutter 58 and the cutting elements 74, 75 of the frusto-conical cutter assembly 72 30 combine to define a congruent cutting face in the leading portions of the hybrid drill bit profile. The cutting elements 74, 75 of the frusto-conical cutter assembly 72 crush and pre- or partially fracture subterranean materials in a formation in the highly stressed leading portions, easing the burden on the cutting elements 60, 62 of the fixed blade cutter 58.

A ball bearing 80 can assist in maintaining rotational capacity of the cutter assembly around the axle. One or more sealed or unsealed radial bearings 82, 84 provide a contact length along the axle centerline that can assist the cutter assembly 72 in being rotated about the axle 66 and support radial (bending) loading. The bearings can include sleeve bearing, roller bearings, floating bushings, shrink fit sleeves, and other bearings types and materials. In some embodiments, a thrust bearing 86 can be placed on the shoulder or an end of the pilot pin to provide thrust load capacity and facilitate the rotation of the frusto-conical cutter assembly about the axle as the cutter assembly contacts the shoulder or the end of the pilot pin.

The cutter assembly 72 generally includes a seal 88 disposed between the axle 66 and an inside cavity of the frusto-conical cutter assembly. The seal 88 can be from well-known sealing systems, such as elastomeric seals and metal face seals.

Other features of the hybrid drill bit such as back up cutters, wear resistant surfaces, nozzles that are used to direct drilling fluids, junk slots that provides a clearance for cuttings and drilling fluid, and other generally accepted features of a drill bit are deemed within the knowledge of those with ordinary skill in the art and do not need further description.

Having described the general aspects of the hybrid drill bit, the focus returns to the axle with the journal, pilot pin, and shoulder. The journal, pilot pin, and shoulder are stressed in radial and thrust loading when the hybrid drill bit is used to drill the subterranean formations. It is important to enlarge the diameters of the journal and pilot pin in relation to the shoulder, and lengthen the journal and pilot pin without compromising the integrity of the frusto- conical cutter assembly by having too thin of a shell thickness on the cutter assembly or too small of supporting surfaces on the axle. Conventional design for roller cone bits, such as shown in Figures 1 and 2, has well established certain restrictions on the size of the journal, pilot pin, and shoulder for a given size of roller cone. The size has been limited to the shape and configuration of the roller cone and minimum shell thickness to s support the loads on the roller cone. As one metric, the relative size of the pilot pin diameter to the journal diameter can be expressed as a ratio. The typical ratio is about 0.50 and is less than 0.56. Larger ratios typically compromise the bearing length for a given optimum journal diameter or cause an unwanted reduction in shell thickness.

so To the knowledge of the inventors, these same ratios have heretofore been followed on hybrid drill bits as well in keeping with standard industry practice. This following has been in spite of the need to maximize the journal and pilot pin diameters and lengths. Thus, heretofore, it has not been an obvious variation to increase the pilot pin to journal diameter ratio beyond the well- is accepted standard of up to 0.56.

The present inventors have reevaluated from ground up the journal and pilot pin diameters and resultant ratios relative to a frusto-conical cutter assembly shell thickness and have discovered that the ratios can be altered for the frusto-conical cutter assembly. This adjustment is especially important 2δ because on a hybrid drill bit, the frusto-conical cutter assembly is generally smaller for a given size of hybrid drill bit than a corresponding roller cone bit. The hybrid drill bit must allow for both the frusto-conical cutter assemblies and the adjacent fixed blade cutters, resulting in a smaller journal and pilot pin and higher stresses for the same loads.

25 The inventors have discovered that contrary to conventional wisdom, the ratio of the pilot pin diameter to the journal diameter (P: J ratio) can be increased to at least 0.58 up to and including 1.0, including P:J ratios of about 0.60, about 0.62, about 0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74, about 0.76, about 0.78, about 0.80, about 0.82, about 0.84, about 0.86, about

M 0.88, about 0.90, about 0.92, about 0.94, about 0.96, and about 0.98, as well as values within this range, for example (and without limitation), a P:J ratio ranging from about 0.71 to about 0.95, or from about 0.83 to about 0.99, inclusive. For a ratio 1.0, the pilot pin 70 becomes the same diameter as the journal 68 and the axle portions effectively merge into a continuous surface. As the pilot pin 70 increases in diameter, the shoulder 71 decreases in surface area. However, the pilot pin itself can support thrust loads on the end of the pilot pin that interfaces with the frusto-conical cutter assembly. As discussed above, a thrust bearing 86 can be included between the pilot pin 70 and the cutter assembly 72. Further, some ratios can be greater than 1.0, where the pilot pin is greater in diameter than the journal.

For calculation of the ratios, radial bearings can be included if present. Thus, if radial bearing 82 was present on the journal that had a contact surface along the axle centerline that would support a radial load, then the thickness of the bearing that supports the radial load can be calculated into the effective diameter of the journal and compared with the pilot pin diameter. Similarly, a radial bearing 84 on the pilot pin with a contact length along the axle centerline can effectively create a larger pilot pin and thus larger pilot pin diameter to be calculated in the ratio.

Other and further embodiments utilizing one or more aspects of the inventions described above can be devised without departing from the spirit of the invention. For example, various angles of the axle centerline can be used. Multiple bearings, such as two ball bearings spaced apart from each other, along the length of the journal and/or pilot pin can be used that establish an effective contact length along the axle centerline between the bearings to counter radial loads and can be used to calculate the ratios of pilot pin to journal diameters. Further, the various methods and embodiments of the hybrid drill bit can be included in combination with each other to produce variations of the disclosed methods and embodiments. Discussion of singular elements can include plural elements and vice-versa.

The order of any steps explicitly or implicitly disclosed herein can occur in a variety of sequences unless otherwise specifically limited. The various steps described herein can be combined with other steps, interlineated with the stated steps, and/or split into multiple steps. Similarly, elements have been described functionally and can be embodied as separate components or can be combined into components having multiple functions.

The invention has been described in the context of advantageous and other embodiments and not every embodiment of the invention has been described. Modifications and alterations to the described embodiments are available to those of ordinary skill in the art. The disclosed and undisclosed embodiments are not intended to limit or restrict the scope or applicability of the invention conceived of by the Applicants, but rather, in conformity with the patent laws, Applicants intend to fully protect all such modifications and improvements that come within the scope or range of equivalent of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A hybrid drill bit for use in drilling through subterranean formations, the 5 hybrid drill bit comprising: a shank disposed about a longitudinal centerline and adapted to be coupled to a drilling string; at least two fixed cutter legs coupled to the shank; at least two fixed blade cutters fixedly coupled to the cutter legs distallyo from the shank, comprising a plurality of cutting elements extending from a surface of the blades; at least two frusto-conical cutter legs coupled to the shank, comprising an axle having an axle centerline, the axle comprising: a journal disposed about the axle centerline, the journal having as journal diameter; and a pilot pin coupled to the journal and extending along the axle centerline toward the longitudinal centerline, the pilot pin having a pilot pin diameter, the pilot pin diameter to journal diameter having a ratio of equal to or greater thans 0.58; and at least two frusto-conical cutter assemblies coupled to the frusto- conical cutter legs distally from the shank and adjacent the fixed blade cutters and adapted to rotate relative to the shank about the axle centerline on the journal and pilot pin, the cutters assemblies comprising cutting elements extending from a surface of the assemblies.

2. The hybrid drill bit of claim 1, wherein the pilot pin diameter to journal diameter ratio is equal to or greater than 0.58 and less than or equal to 1.0.

3. The hybrid drill bit of claim 1, further comprising a bearing disposed around the journal, the pilot pin, or a combination thereof, the bearing having a contact length along the axle centerline with the journal, the pilot pin, or a combination thereof.

4. The hybrid drill bit of claim 3, wherein the pilot pin diameter to journal 5 diameter ratio is calculated including the bearing on the journal, pilot pin, or a combination thereof.

5. The hybrid drill bit of claim 1, wherein the frusto-conical cutter assemblies comprise a truncated nose section.

6. The hybrid drill bit of claim 1, wherein the pilot pin comprises a thrust face perpendicular to the axle centerline.

7. The hybrid drill bit of claim 1 , wherein the axle centerline is disposed at H an angle of equal to or greater than 51 degrees to less than or equal to 59 degrees relative to the longitudinal centerline of the shank portion.

8. A hybrid drill bit for use in drilling through subterranean formations, the hybrid drill bit comprising: so a shank disposed about a longitudinal centerline and adapted to be coupled to a drilling string; at least two fixed cutter legs coupled to the shank; at least two fixed blade cutters fixedly coupled to the cutter legs distally from the shank, comprising a plurality of cutting elements r> extending from a surface of the blades; and at least two frusto-conical cutter legs coupled to the shank, comprising an axle having an axle centerline, the axle comprising: a journal disposed about the axle centerline, the journal having a journal diameter; and

50 a pilot pin coupled to the journal and extending along the axle centerline toward the longitudinal centerline, the pilot pin having a pilot pin diameter, the pilot pin diameter to journal diameter having a ratio of equal to or greater than 0.58.

9. The hybrid drill bit of claim 8, wherein the pilot pin diameter to journal 5 diameter ratio is equal to or greater than 0.58 and less than or equal to 1.0.

10. The hybrid drill bit of claim 8, further comprising a bearing disposed around the journal, the pilot pin, or a combination thereof, the bearing having a contact length along the axle centerline with the journal, the pilot pin, or a io combination thereof.

11. The hybrid drill bit of claim 8, wherein the pilot pin diameter to journal diameter ratio is calculated including the bearing on the journal, pilot pin, or a combination thereof.

13

12. The hybrid drill bit of claim 8, wherein the pilot pin comprises a thrust face perpendicular to the axle centerline.

13. The hybrid drill bit of claim 8, wherein the axle centerline is disposed at an an angle of equal to or greater than 51 degrees to less than or equal to 59 degrees relative to the longitudinal centerline of the shank portion.