The present invention relates generally to bits for drilling a wellbore, and more particularly to a hybrid rotary cone drill bit for use in conditioning a wellbore and drilling out hydraulic fracture equipment (e.g. frac plugs) or bridge plugs.
A roller cone rock bit is a cutting tool used in oil, gas, and mining fields to break through earth formations to shape a wellbore. In shaping the wellbore, the roller cone bit drills through different geological materials making up different rock formations. Although the drill bit encounters different formations at different depths in drilling through rock, generally speaking all parts of the drill bit are drilling the same type of rock formation at the same time.
In hydraulic fracturing operations, a frac plug is secured to a casing that lines the borehole. The frac plug is something of a disposable tool because after the frac plug has performed its function, it is drilled out using a roller cone rock bit manufactured to International Association of Drilling Contractors (IADC) standards, and the drilled out pieces of the plug are flushed up the wellbore by the drilling mud. A frac plug is a generally cylindrical component formed of different materials disposed at different radial positions moving from a generally hollow center. In contrast to drilling through rock formations, when drilling out a frac plug, the drill bit simultaneously drills through different materials. The different materials create different penetration efficiencies and wear characteristics on different parts of the bit.
Reference is made to U.S. Pat. No. 5,131,480 to Lockstedt (the disclosure of which is incorporated by reference), which discloses a milled tooth rotary cone rock bit where a heel row of each cone is relieved and tungsten carbide chisel inserts are inserted in the relieved heel row.
The heel row inserts cooperate with the gage row milled teeth and progressively cut more of the gage row of the bore hole as the gage row milled teeth wear.
In an embodiment, a hybrid rotary cone drill bit includes a plurality of legs. A bearing shaft extends from each leg, and a rotary cone is rotationally coupled to each bearing shaft. At least one rotary cone includes a nose row of cutting structures, an inner row of cutting structures, and a gage row of cutting structures. The nose row and the inner row of cutting structures include milled teeth. The gage row of cutting structures includes cutter inserts.
In certain embodiments, the cutter inserts are tungsten carbide inserts and the milled teeth are formed of steel. The cutter inserts may be conical-shaped or chisel-shaped.
The hybrid rotary cone drill bit of the present disclosure is employed to drill out different materials of a plug simultaneously. The location of the cutter inserts and the milled teeth on the rotary cones allows the different materials of the plug to be effectively drilled out. Specifically, the relatively harder material of a plug slip disposed on an outer diameter of the plug is effectively drilled out by the cutter inserts disposed on an outer diameter of the bit, while the relatively softer material of the plug body is effectively drilled out by milled teeth disposed radially inward of the cutter inserts.
Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which:
Reference is now made to
The hybrid drill bit 10 is configured to drill out the entirety of a borehole and/or a frac plug secured within a borehole. Thus, the hybrid drill bit 10 is configured to drill out either rock formation or portions of a frac plug from the centerline of the borehole and extending to the full radius of the borehole. The hybrid drill bit 10 differs from a reamer in that a reamer is not configured to drill out a central portion of a borehole proximate the centerline. Rather, a reamer is configured to ream a hole that has already been at least partially formed.
In certain borehole operations, such as hydraulic fracturing or fracking, a plug 14, such as a frac plug, is used to isolate a portion of a wellbore 12 to be fracked. The plug 14 acts as a one-way valve and allows a specific section of the borehole to be isolated and pressurized for the hydraulic fracking operation. After the plug 14 has performed its function, it is drilled out in a drill out operation using the hybrid rotary cone drill bit 10 according to the teachings of the present disclosure. In a drill out operation, the hybrid rotary cone drill bit 10 is attached to a drill string and is rotated such that its cutting elements crush, rip, and break apart the plug 14. Drilling fluid pumped through the bit 10 flushes the pieces of the plug 14 back to the surface. Plugs other than frac plugs may be secured in a borehole and may be drilled out with a hybrid rotary cone drill bit 10 according to the teachings of the present disclosure. For example, the hybrid rotary cone drill bit 10 may be used to drill out bridge plugs and other types of plugs that engage a casing 16.
In preparation for fracking, the plug 14 is positioned at the desired location in the borehole 12 such that an outer diameter portion of the plug 14 grips the casing 16 and secures or sets the plug 14 in position. Once set, the plug 14 will withstand pressurization of the zone in the borehole without moving or slipping. To set the plug 14, a slip 26 that is generally in the form of a ring surrounding a portion of a plug body 28 is caused to engage the casing 16 and create a type of seal. For purposes of this disclosure, the plug body 28 includes any portion of the plug not formed of relatively harder material that is engaged with the casing 16 to set the plug in position and create a seal. Although the plug body 28 is primarily disposed radially internal to the slip 26, some portions of the plug body 28 may be disposed above or below and aligned with the slips 26.
In the embodiment illustrated in
In certain embodiments, the slip 26 may include tungsten carbide or ceramic inserts that embed into the casing 16 for a better grip. A plug including such inserts is disclosed in U.S. Pat. No. 5,984,007 to Yuan (the disclosure of which is incorporated by reference). In contrast to the very hard material of the slip 26, the plug body 28 is generally formed of softer material than the slip 26 and/or any inserts that are included in the slip 26. For example, the plug body 26 is often formed of a composite material, a thermoplastic, or a softer metal, such as brass.
Because the plug 14 includes relatively softer materials in its inner portions and relatively harder materials in its outer portions, during drill out the hybrid rotary cone drill bit 10 simultaneously contacts and breaks apart both relatively harder and relatively softer materials. As such, during the drill out using the hybrid bit 10, the cutter inserts 22 engage the slip 26 and/or the plug inserts that are adjacent, contacting, or embedded into the casing 16. This is because the inserts cutters 22 are disposed on the outer diameter of the bit 10, which in operation are closest to the casing 16. For example, the cutter inserts 22 may be disposed on the outer one inch diameter of the cutting face of the bit 10. Thus, a hybrid rotary cone drill bit 10 with a face defining a twelve inch outer diameter may have milled teeth from its center to an approximately 10 inch diameter while the outer one inch radius (two inch diameter) of the face is where the cutter inserts 22 are disposed.
The softer bit body 28 is drilled out by the milled teeth 24, but the milled teeth are generally not subjected to the hard material of the slip 26, which increases the overall durability of the bit 10. The milled teeth 24 are more aggressive, efficient, and better suited for penetrating, gripping, and cutting the softer material of the plug body 28. In contrast, the cutter inserts 22 are less efficient in cutting and ripping the material of the plug body 28. Moreover, if the cutter inserts 22 are used to drill out the plug body 28, the steel substrate of the rotary cone 20 is subject to wear, which often results in expensive cutter inserts separating from the rotary cone 20 and being lost in the borehole.
The cutter inserts 22 are typically formed of very hard material, such as tungsten carbide. The cutter inserts 22 may alternatively be other very hard material incorporated into a cutting structure, such as a polycrystalline diamond compact, an impregnated diamond segment, a polycrystalline cubic boron nitride compact, or the cutter inserts 22 may be formed of any of the material in the family of ceramic materials. The hard material incorporated into the cutter inserts 22 does not wear as fast as the steel substrate when it drills through or otherwise contacts the substantially equally hard material of the slip 26 and or slip inserts. Thus, the cutter inserts 22 wear less than the milled teeth 24 when drilling out the hard material of the slip 26 and or slip inserts of the plug 14.
Reference is made to
According to the teachings of the present disclosure, the nose row milled teeth 36a are disposed in a central portion of the bit to drill through the corresponding softer material center portion of a plug, referred to as the plug body. The nose row milled teeth 36a efficiently drill through this softer material at a higher rate of penetration than other types of cutting structures, including cutter inserts 22. Each of rotary cones two and three also include nose rows of milled teeth 36b, 36c. The relative drilling positions among the nose rows of milled teeth are shown in
Disposed from the nose row milled teeth toward a base 38 of the rotary cone 32 is an inner row of cutting structures. The cutting structures forming the inner row are milled teeth 42a formed similarly to the nose row milled teeth 36a. Each of rotary cones one, two, and three have one inner row of milled teeth 42a, 42b, 42c. Similar to the nose row milled teeth 36a, 36b, 36c, the inner row milled teeth 42a, 42b, 42c are also disposed to drill through the inner portion of the plug 14 or plug body 28, which generally is formed from softer materials, such as composites, thermoplastics, or softer metals. The relative drilling positions among the inner rows of milled teeth 42a, 42b, 42c for each rotary cone 32a, 32b, 32c are illustrated in
A gage row of cutter inserts 46 is disposed closest to the base of the rotary cone 32. The gage row of cutter inserts 46 extend from the generally conical surface 33 of the rotary cone 32. Each of rotary cones one, two, and three includes gage rows of cutter inserts 46a, 46b, 46c. In the embodiment shown in
As shown in
As seen in the cross section of
Disposed between the gage row 44 and the base 38 is a heel 56 of the rotary cone 32. The heel 56 and the base 38 are not considered part of the generally conical surface 33 of the rotary cone 32. There are generally no cutting elements, milled tooth or cutter inserts, on the base 38 or the heel 54 of the rotary cone 32.
The milled teeth 36a, 36b, 36c of the nose rows (especially the nose row milled teeth 36a of cone one 32a) provide a penetrating cutting structure to drill out the center portion of the plug. In addition, the tooth profile of the milled teeth is better suited to penetrate the softer material of the bit body. Together, these characteristics of the milled teeth allow the cutter to penetrate and “chew” up the softer material of the plug body while simultaneously the harder cutter inserts 46, for example tungsten carbide inserts, dislodge the slip 26 from the casing and break the slip apart into chunks to be flushed up the borehole.
Reference is now made to
Similar to the embodiment of
Each of the three cones 62 include a gage row of cutter inserts 76a, 76b, 76c (represented by reference number 76 in
As shown in
The foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.