BACKGROUND
Historically, there have been two main types of drill bits used for drilling earth formations, drag bits and roller cone bits. The term “drag bits” refers to those rotary drill bits with no moving elements. Drag bits include those having cutting elements attached to the bit body, which predominantly cut the formation by a shearing action. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled.
Bit type may be selected based on the primary nature of the formation to be drilled. However, many formations have mixed characteristics (i.e., the formation may include both hard and soft zones), which may reduce the rate of penetration of a bit (or, reduce the life of a selected bit) because the selected bit is not as desirable for certain zones. For example, both milled tooth roller cone bits and PDC bits can efficiently drill soft formations, but PDC bits will often have a rate of penetration several times higher than roller cone bits.
PDC Drill Bits
Drag bits, often referred to as “fixed cutter drill bits,” include bits that have cutting elements attached to the bit body, which may be a steel bit body or a matrix bit body formed from a matrix material such as tungsten carbide surrounded by a binder material. Drag bits may generally be defined as bits that have no moving parts. However, there are different types and methods of forming drag bits that are known in the art. For example, drag bits having abrasive material, such as diamond, impregnated into the surface of the material which forms the bit body are commonly referred to as “impreg” bits. Drag bits having cutting elements made of an ultra hard cutting surface layer or “table” (often made of polycrystalline diamond material or polycrystalline boron nitride material) deposited onto or otherwise bonded to a substrate are known in the art as polycrystalline diamond compact (“PDC”) bits.
PDC bits drill soft formations easily, but they may frequently be used to drill moderately hard or abrasive formations. They cut rock formations with a shearing action using small cutters that do not penetrate deeply into the formation. Because the penetration depth is shallow, high rates of penetration are achieved through relatively high bit rotational velocities.
Roller Cone Drill Bits
Roller cone drill bits may be used to drill formations that fail more efficiently by crushing and gouging as opposed to shearing. Roller cone drill bits are also used for heterogeneous formations that initiate vibration in drag bits. Roller cone drill bits include milled tooth bits and insert bits. Milled tooth roller cone bits may be used to dill relatively soft formations, while insert roller cone bits are suitable for medium or hard formations. Roller cone drill bits include a bit body with a threaded pin formed on the upper end of the bit body for connecting to a drill string, and one or more legs extending from the lower end of the bit body. The threaded pin end is adapted for assembly onto a drill string for drilling oil wells or the like. Roller cone bits, on the other hand, may have better steerability when building curve section of a wellbore.
Hybrid Drill Bits
Both roller cone and PDC bits have their own advantages. Due to the difference in cutting mechanisms and cutting element materials, they are best suited for different drilling conditions. Roller cone bits predominantly use a crushing mechanism in drilling, which gives roller cone bits overall durability and strong cutting ability (particularly when compared to previous bit designs, including disc bits). PDC bits use a shearing mechanism for cutting, which allows higher performance in soft formation drilling than roller cone bits are able to achieve.
Thus, in drilling operations facing mixed formations, using one type of drill bit over the other may not be adequate for the entire operation. Hybrid drill bits that use a combination of one or more crushing mechanisms and one or more shearing mechanisms have been proposed previously. However, problems arise during the design of these hybrid bits in trying to combine rolling cutters and fixed blades within a limited amount of space.
SUMMARY OF DISCLOSURE
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
In one aspect, embodiments disclosed herein relate to a drill bit including a bit body having a longitudinal bit axis extending there through, a plurality of journals extending from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body center and extending radially outward to less than an outer diameter of the drill bit.
In another aspect, embodiments disclosed herein relate to a drill bit including a bit body having a longitudinal bit axis extending there through, a plurality of journals, extending from the bit body, and a roller cone rotatably mounted to each of the journals, wherein at least one roller cone having a different outer diameter than the others, wherein an offset angle ranging from about 0 degrees to about 90 degrees is formed between a line perpendicular to the bit axis and extending through the bit axis and a center of a backface of the roller cone.
In yet another aspect, embodiments disclosed herein relate to a drill bit including a bit body having a longitudinal bit axis extending there through, a plurality of journals, extending from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the plurality of journals extend from the bit body such that an acute angle ranging from about 15 degrees to about 25 degrees is formed between the journal axis and the bit axis. The drill bit further includes a roller cone rotatably mounted to each of the journals, wherein at least one roller cone comprises a plurality of roller cone cutting elements having planar cutting faces and at least one roller cone comprises a plurality of roller cone cutting elements having non-planar cutting faces, wherein the roller cone cutting elements comprise a roller cone cutting profile.
Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of a bit according to embodiments of the present disclosure.
FIG. 2 shows a side view of the Cartesian coordinate system and roller cone orientation according to one embodiment of the present disclosure.
FIG. 3 shows a top view of the Cartesian coordinate system and roller cone orientation according to one embodiment of the present disclosure.
FIG. 4 is a schematic of a roller cone retained on a journal according to one embodiment of the present disclosure.
FIG. 5 is a schematic side view of a roller cone cutting element having back rake according to embodiments of the present disclosure.
FIG. 6 is a schematic top view of a roller cone cutting element having side rake according to embodiments of the present disclosure.
FIG. 7 is a perspective view of a bit according to embodiments of the present disclosure.
FIG. 8 is a top view of roller cones according to embodiments of the present disclosure.
FIG. 9 is a perspective view of a bit according to embodiments of the present disclosure.
DETAILED DESCRIPTION
Embodiments disclosed herein relate generally to drill bits. In particular, embodiments disclosed herein relate to roller cone drill bits having radially offset journals such that the roller cones engage and cut different regions of a borehole.
Referring to FIG. 1, a perspective view of a roller cone drill bit according to one embodiment of the present disclosure is shown. As shown in FIG. 1, a roller cone drill bit 130 includes a bit body 139 having a longitudinal axis 110 extending axially there through. At one end of the bit 130 is a threaded pin end (not shown) for coupling bit 130 to a drill string (not shown). At the other end of the bit (generally oriented as the lower end when the bit is installed on a drill string within a well) is the cutting end of bit 130, the side of the bit substantially facing the direction of drilling and that may engage the bottom hole of the wellbore being drilled. In particular, bit body 139 terminates at its cutting end with at least one blade 126 protruding from the bit body center and a plurality of journals 135. Each journal 135 may be integral with the rest of bit body 139, or in other embodiments, may have separately formed and attached to the bit body 139. Each journal 135 has a journal axis extending from the base of the journal through the length of the journal. On each journal 135, a roller cone 136 having a frustoconical shape is rotatably mounted. Each roller cone 136 has disposed thereon a plurality of rows of roller cone cutting elements 137: at least two rows of cutting elements 137 in some embodiments or at least four or five rows of cutting elements in other embodiments. The at least one blade protruding from the bit body center has disposed thereon a plurality of blade cutting elements 127.
In this embodiment, the rolling cone cutting elements 137 and the blade cutting elements 127 have planar cutting faces. However, different types of cutting elements may be used on the blades 126 and roller cones 136. For example, as shown in FIG. 11 (which is discussed below), some of the rolling cone cutting elements may have non-planar cutting faces. Rolling cones having cutting elements with planar cutting faces are also known as shearing rolling cones since the cutting elements shear the formation. Alternatively, rolling cones having cutting elements with non-planar cutting faces are also known as crushing rolling cones since the cutting elements crush/fracture the formation. Cutting elements used with hybrid drill bits of the present disclosure may include polycrystalline diamond compacts (PDCs), diamond grit impregnated inserts (“grit hot-pressed inserts” (GHIs), natural diamond, milled steel teeth, tungsten carbide inserts (TCIs), diamond enhanced inserts (DEIs), or conical shaped (or other substantially pointed) cutting elements.
As discussed above, a roller cone may be rotatably mounted to journals extending from a bit body. Roller cones may include bodies having rounded, conical, or disc shape and a plurality of cutting elements disposed thereon. For example, referring again to FIG. 1, a roller cone 136 has a frustoconical shaped body with a plurality of cutting elements 137 disposed thereon. Roller cone sizes may differ with respect to one or more of a roller cone's outer radius, nose projection, radius of curvature, etc. As shown, the roller cone 136 has three circumferential rows of cutting elements 137. However, other embodiments may have more or less than three rows of cutting elements. Further, roller cones may have cutting elements disposed thereon in arrangements other than in rows.
Further, according to some embodiments, the plurality of roller cones 136 may be arranged in such a manner that they engage with and cut the nose and shoulder regions of a bottom hole, but do not engage with the center of a bottom hole whereas the at least one blade 126 may engage and cut the center of a bottom hole. The blade cutting elements 127 form a blade cutting profile, and the roller cone cutting elements 137 form a roller cone cutting profile. As used herein, a cutting profile (e.g., a blade cutting profile and a roller cone cutting profile) refers to the profile or outline of cutting elements as they would appear in rotated view, i.e., when the bit rotated about its longitudinal axis and the roller cones are rotated about their rotational axes. The extent of overlap between roller cone 136 cutting profile and blade 126 cutting profile depends on the radial extension of the at least one blade 126, each blade 126 extending to less than an outer diameter of the drill bit 130.
Further, journals may extend from the bit body at different angles with respect to the longitudinal axis of the bit, as compared to a conventional roller cone bit. Specifically, as shown in FIG. 1, in addition to being pointed axially downward (away from the pin end of the bit), the cones 136 may also be pivoted such that the tip or nose of the cone is pointing radially outward of the bit center. For example, greater details of the orientation are shown in FIGS. 2 and 3, which show a side view of the Cartesian coordinate system and cone orientation and a top view, respectively, where the z-axis is the bit axis, the y-axis extends from the bit axis through the center of the backface of the cone (represented with a circled “x”), and the x-axis extends from the bit axis perpendicular to the y axis and z-axis. Referring to FIG. 2, a cone 136 is mounted on a journal (not shown). The journal extends downward and at an angle β, which may be referred to as the journal angle, with respect to the bit or z-axis. In one or more embodiments, angle β may range from about −90 degrees to about 90 degrees. In more specific embodiments, angle β may have a lower limit of any of at least −90, −60, −30, 0, or 30 degrees, and an upper limit of any of −30, 0, 30, 60, or 90 degrees, where any lower limit can be used in combination with any upper limit. As also shown in FIGS. 1 and 2, the cones (and journals) may extend from a leg (139 in FIG. 1) that extends from the bit body 139. The extension of the legs is represented in FIG. 2 as length S (the length between point B and point C), which may extend, for example, a distance ranging from about ¼ of the radius of drill bit 130 to about ¾ of the radius of drill bit 130. Further, cone radius (the length between point C and point D) may range from about ¼ of the radius of drill bit 130 to about a full radius of drill bit 130.
FIG. 3 shows a top view of the coordinate system in FIG. 2, where points A, B, C, and D shown in FIG. 2 are also shown in FIG. 3 based on their location in the Cartesian coordinate system. As shown in FIG. 3, the leg 140 (extending from B to C) also has a horizontal offset Rb from the bit or z-axis to the cone axis 140 (illustrated as the length between point O on the z-axis and point A on the cone axis 140), according to an embodiment. In one or more embodiments, such horizontal offset may range from about ¼ of the radius of drill bit 130 to about ½ of the radius of drill bit 130. In addition, as mentioned above, the cones 136 are pivoted relative to the bit axis Z to form a cone offset angle. The cone offset angle may be defined as the angle a that is between the backface of the cone 136 and the y axis, which, as mentioned above, is defined as the axis (perpendicular to the bit axis) that extends through the bit axis and the center of the backface of the cone 136. In one or more embodiments, the cone offset angle, as defined herein, may range from about 0 to about 180 degrees. In more specific embodiments, cone offset angle may have a lower limit of any of at least 0, 15, 30, 45, or 60 degrees, and an upper limit of any of 60, 90, 120, 150, or 180 degrees, where any lower limit can be used in combination with any upper limit.
Additionally in accordance with various embodiments of the present disclosure, as shown in FIGS. 4-5 together, roller cone 136 may be retained on journal 135 through a ball bearing retainer system. In an embodiment, a plurality of bearing balls 440 are fitted into complementary ball races 437, 439 in the journal 135 and cone 136, respectively, to retain cone 136 on journal 135. A cone 136 is first fitted on the journal 135, and then the bearing balls 440 are inserted through ball passage (not shown) to fit in the space between ball races 437 and 439. Balls 440 are retained in ball races 437 and 439 by a ball retainer, which is inserted into passage (not shown) after balls 440, and then secured in place (such as by a plug welded in place). The balls 440 carry any thrust loads tending to remove the cone 136 from the journal 135 and thereby retain the cone 136 on the journal 135. Lubricant or grease is retained in the bearing structure by a resilient seal 452 within a seal gland formed between the cone 136 and journal 135.
Due to the orientation of the cone 136, disclosed above, the cutting elements used on roller cones may have a unique orientation for roller cone cutting elements so as to enable the cutting elements to shear the formation. Specifically, cutting elements may be oriented or installed on the cones with a particular back rake and/or side rake. For example, referring now to FIG. 5, a schematic side view of a roller cone cutting element 501 having back rake is shown within the Cartesian coordinate system defined above in FIGS. 2 and 3. The roller cone cutting element 501 has a cutter axis 502 extending therethrough where the installation back rake 511 angle is defined as the angle with respect to the roller cone surface, or the angle subtended between the cutter axis 502 and a line parallel to the axis of the roller cone 503. In one or more embodiments, the installation back rake angle, as defined herein, may range from about 0 degrees to about 180 degrees. In more specific embodiments, the installation back rake angle may have a lower limit of any of at least 0, 15, 30, 45, or 60 degrees, and an upper limit of any of 60, 90, 120, 150, or 180 degrees, where any lower limit can be used in combination with any upper limit.
Equivalent back rake 520 is defined as the resultant of installation back rake angle with the combination of journal angle, and measured by the journal angle β less the installation back rake 511 angle. As previously discussed, the journal angle forms an angle β, between a longitudinal axis 510 of the bit and the center of roller cone back surface 509. According to some embodiments, the equivalent back rake angle, as defined herein, may range from about 10 degrees to about 30 degrees. In more specific embodiments, the equivalent back rake angle may range from about 15 to about 25 degrees.
Referring now to FIG. 6, a schematic top view of a roller cone cutting element 501 having side rake is shown in the Cartesian coordinate system set forth in FIG. 3 above, according to an embodiment. The roller cone cutting element 501 has a cutter axis 502 extending therethrough where installation side rake angle 605 is defined with respect to the roller cone axis, or the angle subtended between the cutter axis 502 and the roller cone axis 603 (extending through the center of roller cone back surface 509). The engage point velocity 607 is defined as the velocity of the lowest, engaged point of the roller cone to the formation. In one or more embodiments, the installation side rake angle, as defined herein, may range from about 0 degrees to about 60 degrees. In more specific embodiments, the installation side rake angle may range from about 15 degrees to about 45 degrees.
Equivalent side rake 609 is defined as the resultant of installation side rake angle with the combination of journal offset, and measured by the angle formed between the engage point velocity 607 and the roller cone axis 603 less the installation side rake 605 angle. As previously discussed and shown in FIG. 4, journal offset forms an angle α, between the backface of the cone 136 and the y axis. According to some embodiments, the equivalent side rake angle, as defined herein, may range from about 0 degrees to about 45 degrees. In more specific embodiments, the equivalent side rake angle may range from about 15 degrees to about 25 degrees. When viewed along the longitudinal axis of the bit, a negative side rake results from counterclockwise rotation of a cutting element, and a positive side rake, from clockwise rotation.
Referring to FIG. 7, a perspective view of a roller cone drill bit according to another embodiment of the present disclosure is shown. As shown in FIG. 7, a roller cone drill bit 730 includes a bit body 732 having a longitudinal axis 710 extending axially there through. In particular, bit body 732 terminates at its upper end into a plurality of journals 735, each having a journal axis extending from the base of the journal through the length of the journal. In an embodiment, each journal is integral with the rest of bit body 732. On each journal 735, a roller cone 736A/B having a frustoconical shape is rotatably mounted. Each roller cone 736A/B has disposed thereon a plurality of rows of roller cone cutting elements 737: at least two rows of cutting elements 737 in some embodiments or at least four or five rows of cutting elements in other embodiments.
In such embodiments, the rolling cone cutting elements 737 have planar cutting faces, such as those conventionally referred to as polycrystalline diamond compact (PDC) cutters. As discussed above, rolling cones having cutting elements with planar cutting faces are also known as shearing rolling cones since the cutting elements shear the formation. Alternatively, rolling cones having cutting elements with non-planar cutting faces are also known as crushing rolling cones since the cutting elements crush/fracture the formation. For example, in some embodiments, rolling cones having cutting elements with non-planar cutting faces may have a pointed, or conical shaped, dome shaped, chisel shaped, and/or saddle shaped cutting face geometry. In some embodiments, rolling cones may have a combination of cutting elements with planar and non-planar cutting faces. Cutting elements used with hybrid drill bits of the present disclosure may include polycrystalline diamond compacts (PDCs), diamond grit impregnated inserts (“grit hot-pressed inserts” (GHIs), natural diamond, milled steel teeth, tungsten carbide inserts (TCIs), diamond enhanced inserts (DEIs), or conical shaped (or other substantially pointed) cutting elements.
According to various embodiments of the present disclosure, roller cone drill bit 730 may include a plurality of gauge cutters 740 disposed on the bit body 732 and along a gauge region of the bit which extends parallel to bit axis 710 at the outer radial periphery of the overall bit cutting profile. In such embodiments, gauge cutters 740 are arranged to engage a side wall of the formation. The plurality of gauge cutters 740 may include rotatable and non-rotatable cutting elements having planar and non-planar cutting faces. In some embodiments, gauge cutters 740 may be substantially similar in material, shape, and size as roller cone cutting elements 737. Further, gauge cutters may be oriented or installed on the bit body 732 with a particular back rake and/or side rake angle.
Additionally in accordance with various embodiments of the present disclosure, at least one roller cone has a different outer diameter than the others. As shown in FIGS. 7-9, roller cones 736A have a larger outer diameter than roller cones 736B, according to an embodiment. In some embodiments, the cutting profile of the smallest roller cone may radially overlap with the cutting profile of the largest roller cone cutting. In such embodiments, the cutting profile of the smallest roller cone may extend an axial distance greater than the cutting profile of the largest roller cone. For example, the cutting profile of the smallest roller cone may extend an axial distance ranging from about ¼ of the radius of drill bit 730 to about ¾ of the radius of drill bit 730 further from the bit body than the cutting profile of the largest roller cone.
One of ordinary skill in the art will appreciate that a roller cone may be characterized by its diameter to height ratio. Referring to FIGS. 7 and 9, embodiments of the present disclosure may include roller cones 736A/B having a diameter to height ratio ranging from about 4:1 to about 2:1.
Referring to FIG. 8, a top view of two roller cones with different outer diameters is shown. As shown in FIG. 8, smaller roller cone 836B has outer diameter A and cone height B whereas larger roller cone 836A has outer diameter C and cone height D. However, in particular embodiments, the diameter to height ratio of C:D may be about 1 to about 2 times that of the diameter to height ratio of A:B (not shown). Further, the plurality of roller cones 836A and 836B may be arranged in such a manner that roller cone 836B engages with and cuts the nose and shoulder regions of a bottom hole whereas roller cone 836A engages with and cuts the center of a bottom hole.
Referring to FIG. 9, a perspective view of a roller cone drill bit according to yet another embodiment of the present disclosure is shown. This embodiment is similar to the embodiment disclosed previously and illustrated in FIG. 7; however, at least one roller cone has cutting elements with planar cutting faces while the other roller cones have non-planar cutting faces disposed thereon.
As shown in FIG. 9, a roller cone drill bit 930 includes a bit body 932 having a longitudinal axis 910 extending axially there through. In particular, bit body 932 terminates at its upper end into a plurality of journals 935, each having a journal axis extending from the base of the journal through the length of the journal. In an embodiment, each journal is integral with the rest of bit body 932 On each journal 935, a roller cone 936A/B having a frustoconical shape is rotatably mounted. At least one roller cone 936A/B has a different outer diameter than the others. Each roller cone 936AB has disposed thereon a plurality of rows of roller cone cutting elements 937A/B: at least two rows of cutting elements 937A/B in some embodiments or at least four or five rows of cutting elements in other embodiments. In this embodiment, at least one roller cone 936A has cutting elements 937A with planar cutting faces. In an embodiment, at least one roller cone 936B has cutting elements 937B with non-planar cutting faces. The planar cutting elements 937A on larger roller cones 936A shear the formation, while the non-planar cutting elements 937B on smaller roller cones 936B crush the formation, according to an embodiment. The combined shearing and crushing action may improve bit performance under certain conditions.
Though two sizes of roller cone are illustrated in each of FIGS. 7 and 9, the drill bit may have more than two sizes of roller cones. The differently-sized roller cones may have a variety of configurations. In an embodiment, there are an even number of each different size of roller cone, so that pairs of each size of roller cone may be configured in a symmetric manner with respect to the bit axis in order to balance the bit and minimize bit vibrations while drilling. In addition, each roller cone may have a variety of orientations in order to target different portions of the formation. For example, a roller cone may be oriented so that its cutting elements contact at least one of: the nose region, the shoulder region, or the center region of the bottom hole.
While FIG. 9 shows planar cutting elements 937A on larger roller cones 936A and non-planar cutting elements 937B on smaller roller cones 936B, in other embodiments a variety of cutting element arrangements may be used. For example, one or more larger roller cones may have non-planar cutting elements, while one or more smaller roller cones may have planar cutting elements. In another embodiment, one or more roller cones may each have a combination of non-planar and planar cutting elements. As described above with respect to FIGS. 5 and 6, the cutting elements—whether planar or non-planar—may have a variety of back rake and side rake orientations. In an embodiment, bit 932 includes gauge cutting elements (not shown), similar to that shown and described with respect to gauge cutters 740 in FIG. 7.
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.
Patent Application
20160348440
