Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Reexamination Certificate
2000-07-21
2002-09-17
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
C175S425000, C076S108200
Reexamination Certificate
active
06450271
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to drill bits for drilling into subterranean formations and methods of manufacturing the same, wherein such bits include at least one surface to which formation material exhibits relatively low-adhesion, the low-adhesion surface being effected by coating, plating, or otherwise treating that portion of the bit such as by mechanical or thermal processing.
2. State of the Art
Rotary-type drill bits include both rotary drag bits and roller-cone bits. Typically, in a rotary drag bit, fixed cutting elements made of natural diamond or polycrystalline diamond in the form of polycrystalline diamond compacts (PDCs) are attached to the face of the drill bit, either as freestanding, unbacked cutters or, where suitably configured, mounted or a stud, cylinder or other carrier. The cutters on the bit face are typically adjacent to waterways or fluid courses extending to passageways or “junk slots” formed in the side or gage surface of the bit body above the bit face (as the bit is oriented for drilling) to allow drilling fluid with entrained material (cuttings) that has been cut from the formation to pass upwardly around the bit and into the borehole thereabove.
In a roller-cone arrangement, the bit typically has three cones, each independently rotatable with respect to the bit body supporting the cones through bearing assemblies. The cones carry either integrally formed teeth or separately formed inserts that provide the cutting action of the bit. The spaces between the teeth or inserts on the cones and between the legs of the bit to which the cones are mounted provide a passage for drilling fluid and formation cuttings to enter the borehole above the bit.
When drilling a hole with prior art drill bits, the cuttings may adhere to, or “ball up” on, the surface of the drill bit. The cuttings thus tend to accumulate on the cutting elements and the surfaces of the drill bit and collect in any void, gap or recess created between the various structural components of the bit. This phenomenon is particularly enhanced in formations that fail plastically, such as certain shales, mudstones, siltstones, limestones and other ductile formations, the cuttings from which may become mechanically packed in the aforementioned voids, gaps or recesses on the drill bit exterior. In other cases, such as when drilling certain shale formations, the adhesion between a bit surface and the formation cuttings is most probably, or in many instances, caused by a chemical bond. When the surface of a bit becomes water wet in such formations, the bit surface and clay layers of the shale share common hydrogen electrons. A similar sharing of electrons is present between the individual sheets of the shale itself A result of this sharing of electrons is an adhesive-type bond between the shale and the bit surface. Adhesion between the formation cuttings and the bit surface may also occur when the charge of the bit face is opposite the charge of the formation, the oppositely charged formation particles tending to adhere to the surface of the bit. Moreover, particles of the formation may actually be compacted onto exterior surfaces of the bit or mechanically bonded into pits or trenches etched into the bit by erosion and abrasion during the drilling process.
Attempts have been made to alleviate the aforementioned electrical charge-induced adhesion tendencies as disclosed in U.S. Pat. Nos. 5,330,016 and 5,509,490 and in two IADE/SPE papers respectively referenced as IADC/SPE 23870, Roy et al., “Prevention of Bit Balling in Shales; Some Preliminary Results” and IADC/SPE 35110, Smith et al., “Successful Field Application of an Electro-Negative ‘Coating’ to Reduce Bit Balling Tendencies in Water Based Mud.”
If cuttings become stuck to the surface of the drill bit, subsequent cuttings are not allowed to simply slide along the surface of the cutters and through the junk slots. The subsequent cuttings must, in effect, slide over formation material already attached to the surface of the bit. Thus, a shearing force is created between the cuttings stuck to the bit and subsequent cuttings. As a result, much greater frictional forces between the drill bit and the formation are produced, which forces may result in a reduced rate of penetration and result in further accumulation of cuttings on the bit.
One approach in the art to remove this adhered formation material from the bit has been to provide nozzles in the bit body to direct drilling fluid from an interior plenum of the bit to the surface of the cutters. For example, in U.S. Pat. No. 4,883,132 to Tibbitts, to reduce bit balling, nozzles are provided that direct drilling fluid to impact the formation cuttings as they leave the cutting faces of the cutters. In some instances, however, the high velocity drilling fluid may not adequately remove the cuttings from the cutting elements. Moreover, the directed drilling fluid is not effective to remove cuttings from the bit face or junk slots of the bit.
The need to reduce frictional forces in the drilling process has been addressed in U.S. Pat. No. 4,665,996 to Foroulis et al. Foroulis discloses the application of a hard facing material to the surface of a drill pipe. The hard facing material is purported to reduce the friction between the drill string and the casing or rock. As a result, the torque needed for the rotary drilling operation, especially directional drilling, is decreased.
U.S. Pat. Nos. 5,447,208 and 5,653,300 to Lund et al. also disclose a way to reduce frictional forces associated with drilling, wherein the superabrasive cutting face of a cutting element is polished to a surface finish roughness of 10 &mgr; in. or less.
There have been many instances in which a portion or all of certain drill bit and drilling tool surfaces have been coated with a layer of another material to promote wear resistance. For example, U.S. Pat. No. 5,163,524 to Newton et al. discloses application of a smooth, hard facing layer of an abrasion-resistant material to gage pads, the materials being suggested as suitable including a matrix material (WC) or a layer of CVD-applied “polycrytalline” diamond. U.S. Pat. No. 4,054,426 to White suggests treating the surfaces of roller bit cones with a high particulate level ion plating process to form a dense, hard, smooth, thin film. U.S. Pat. No. 4,173,457 to Smith discloses hard facing of mining and drilling tools with sintered tungsten carbide-cobalt particles and with sintered or cemented chromium carbide particles. Of course, the use of tungsten carbide as a hard facing layer on drill bits has been known for decades, as disclosed in U.S. Pat. No. 2,660,405 to Scott et al., U.S. Pat. No. 2,883,638 to Owen and U.S. Pat. No. 3,301,339 to Pennebaker. Patterned hard facing on roller bit cones has been suggested in U.S. Pat. No. 5,291,807 to Vanderford et al., “carbide” being suggested as a suitable material. Finally, U.S. Pat. No. 5,279,374 to Sievers et al. teaches the continuous or uninterrupted coating of rollercones carrying inserts with refractory material such as tungsten carbide.
None of the foregoing approaches to bit and cutter design, however, have specifically addressed the need to reduce frictional forces created by cuttings adhering to the bit body or bit components other than cutting elements. More specifically, the prior art has not addressed the effects of friction due to buildup of formation material at or proximate gaps, voids or other discontinuities created at interfaces between the cutters and the cutting face, the nozzles and the bit face, the roller-cone surfaces and inserts, or other points where parts of the bit are joined together or exterior surfaces of the bit join at sharp angles. Accordingly, it would be advantageous to provide a drill bit that reduces or eliminates adhesion of formation cuttings to the drill bit. It would also be advantageous to provide a method of treatment of at least selected portions of exposed surfaces of a bit that might be implemented on any drill bit regardless of shape,
Kolterman Terry J.
Lin Chih
Overstreet James L.
Oxford James Andy
Radford Steven R.
Bagnell David
Baker Hughes Incorporated
Stephenson Daniel P
TraskBritt
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