Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Reexamination Certificate
2000-04-10
2002-08-27
Tsay, Frank (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
C175S343000, C175S376000
Reexamination Certificate
active
06439326
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates generally to a single roller cone bit with radial cutting elements. More specifically, the invention relates to a single roller cone bit with cutting elements arranged radially about the axis of the drill bit such that the original gage of a wellbore may be maintained after the roller cone bit inserts are worn.
2. Background Art
The most commonly used roller cone bits in the well drilling industry include three roller cones attached to a drill bit body. The three roller cones act in concert to compressively crush the rock formation that is being penetrated by the bottom hole assembly. These three-cone bits are very popular in the industry and receive widespread use.
The “cones” of the three-cone bit include the body of the cone and a plurality of cutting elements, which can be teeth or inserts. The cutting elements are typically arranged in rows and may be manufactured in several different ways. In one method the cones and the teeth are milled from one parent block of hardened steel. Various hard-coatings can then be applied to the cutting elements and the wear surfaces of the cone to resist the wear encountered during drilling operations. In another method the cutting elements are hardened inserts that are attached to the base material of the cone. These inserts are generally composed of materials such as tungsten-carbide or polycrystalline diamond. The combination of the cone body and the cutting elements produce a cutting structure.
When three-cone bits are designed for use in small diameter wellbores, the drill bits must of course use smaller cones and smaller axial and radial support structures. As the scale of a roller cone is reduced, the size of the radial bearing used to absorb radial loads generated during drilling operations is reduced as well. The smaller radial bearings have less load-bearing capacity and can wear quickly when exposed to high axial loading.
Another type of roller cone bit, the single cone bit, has proven useful when drilling small diameter wellbores. These bits use a single roller cone attached to a drill bit body generally so that the cone's drill diameter is concentric with the axis of the bit. Single roller cone bits may use a significantly larger radial bearing for the same bit diameter as a comparable three roller cone bit. The larger radial bearing enables the use of higher bit loads and may enable increases in the rate of penetration (“ROP”) of the drill bit as a result. The single cone bit typically has a hemispherical shape and drills out a “bowl” shaped bottom hole geometry.
Drill bits are rotated about an axis substantially parallel to the wellbore axis during drilling operations. The structure of the three-cone bit is such that the portions of the bit cones located nearest the center of the wellbore have linear velocities approaching zero. Therefore, the drilling efficiency of the three-cone bit at the center of the wellbore is low. The single roller bit, on the other hand, drills the center of the hole very efficiently. The structure of the single cone bit places a large portion of the cutting structure in moving contact with the formation at the center of the hole.
Moreover, the single cone bit tends to shear the formation below a reference plane that defines the top of the “bowl” shaped hole bottom. The shearing action, as opposed to the substantially compressive drilling action of three-cone bits, efficiently removes material from the formation at the center of the hole.
One of the limitations of single cone bits is that the cutting teeth or inserts used in the cone body tend to wear over time due to the shearing action. This tendency has been alleviated somewhat through the use of modern wear-resistant materials. The wear on the cutting structure does not appear to dramatically affect the ROP of the bottom hole assembly. However, as the cutting structure wears, the drilled diameter of the wellbore can be affected. As the cutting structure continues to wear, eventually the diameter of the wellbore will be reduced substantially. The reduction in wellbore diameter can be an intolerable condition and may require reaming with subsequent bits or the use of reamers or other devices designed to enlarge the wellbore diameter. Moreover, the reduced wellbore diameter will decrease the flow area available for the proper circulation of drilling fluids and bit cuttings. The use of bits, reamers, or other devices to ream the wellbore can incur substantial cost if the bottom hole assembly must be tripped in and out of the hole several times to complete the procedure.
Several types of single roller cone bits have been designed to maintain the diameter of the wellbore in the presence of worn bit inserts. For example, U.S. Pat. Nos. 2,119,618, 2,151,544, and 2,151,545 to Zublin disclose a composite single cone bit with roller reamers located above a bit structure containing a plurality of rotatable cutters. The roller reamers are designed to stabilize the bit in the bore hole. The Zublin invention, shown in prior art
FIG. 1
, uses the roller reamers to hold the bit to one side of the wellbore so that the rotating cutters are held in contact with the formation. Moreover, the roller reamers are designed to prevent excess wear on the shank that holds the rotating cutter support structure. The roller reamers also serve to absorb bit side force and, alternatively, to change the final diameter of the bore.
U.S. Pat. No. 4,140,189 to Garner discloses a rock bit with rolling cones and diamond cutters protruding from the periphery of the bit. The diamond cutters, mounted on carbide slugs, maintain the desired hole diameter when the bit is rotating.
U.S. Pat. No. 2,335,929 to Fortune discloses a roller bit that has two roller reamers located near a conical roller cutter. The roller reamers and the conical roller maintain a three point contact arrangement in the bottom of the wellbore and serve to stabilize the operation of the bit. The roller reamers serve to prevent the bit from “gyrating” within the wellbore.
Other prior art, including U.S. Pat. No. 1,322,540 to Chapman and U.S. Pat. No. 3,429,390 to Bennett disclose rollers or stand-off members for centering the drill bit within the wellbore. U.S. Pat. No. 3,424,258 to Nakayama discloses a rotary bit with scraping elements that guide the bit and produce a raised core of rock that is then drilled by the rotary member. The purpose for forming the raised core is to eliminate bit-tracking problems produced when the bit shifts radially within the wellbore.
SUMMARY OF THE INVENTION
One aspect of the invention is a drill bit that includes a roller cone and fixed cutters. The roller cone is positioned so that the drill diameter of the cone is substantially concentric with an axis of rotation of the bit, and the fixed cutters are positioned externally to the cone at a selected radius from the axis of the bit.
Another aspect of the invention is a drill bit that includes roller cones arranged circumferentially about an axis of rotation of the bit. A single roller cone is arranged so that its drill diameter is substantially concentric with the bit axis.
Another aspect of the invention is a bit that includes a bit body, a single roller cone, blades, and cutters mounted on the blades. The single roller cone is located so that its drill diameter is substantially concentric with the bit body while the blades are arranged circumferentially about the center of the bit body.
Another aspect of the invention is a bi-center bit that includes a roller cone, reaming blades, and fixed cutters located on the reaming blades. The roller cone is positioned so that the drill diameter of the cone is substantially concentric with an axis of rotation of the bit. The reaming blades and cutters are radially positioned to drill a larger diameter hole than the pass through diameter of the bit.
REFERENCES:
patent: 1322540 (1919-11-01), Chapman
patent: 1758773 (1930-05-01), Zublin
patent: 1821474 (1931-09-01), Mercer
patent: 2025261 (1935-12-01), Zublin
patent: 211961
Cawthorne Chris E.
Huang Sujian
Rosenthal & Osha L.L.P.
Smith International Inc.
Tsay Frank
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