Boring or penetrating the earth – Bit or bit element – Rolling cutter bit or rolling cutter bit element
Reexamination Certificate
1998-12-07
2001-06-05
Neuder, William (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Rolling cutter bit or rolling cutter bit element
C175S430000, C175S432000
Reexamination Certificate
active
06241035
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to earth-boring bits with superhard material enhanced inserts for drilling blast holes, oil and gas wells, and the like.
BACKGROUND OF THE INVENTION
Earth-boring bits, such as roller cone rock bits, are employed for drilling oil wells through rock formations, or for drilling blast holes for blasting in mines and construction projects. Earth-boring bits are also referred to as drill bits. During operation, a drill bit is connected to a drill string at one end and typically has a plurality of wear-resistant inserts imbedded in roller cones attached to a bit body at the other end. An insert usually has a substantially cylindrical body portion which is adapted to fit in an insert hole and a top portion which protrudes from the insert hole for contacting an earthen formation.
When a roller cone rock bit is used to drill a borehole, it is important that the diameter or gage of the borehole be maintained at a desired value. The first outermost row of inserts of each roller cone of a rock bit that cuts to a full gage borehole and the corner of borehole is referred to as the gage row. This row of inserts is generally subjected to the greatest wear as it reams the borehole wall and cuts the corner of the borehole. As the gage row inserts wear, the diameter of the borehole being drilled may decrease below the original gage diameter of the rock bit. When the bit is worn out and removed, a portion of the hole usually is under-gage. When the next bit is run in the hole, it is therefore necessary to ream that portion of the hole to bring it to the full gage. This not only takes substantial time but also commences wear on the gage row inserts of the newly inserted bit.
In addition to gage row inserts, a conventional bit typically includes a number of inner row inserts located on a roller cone and disposed radially inward from the gage row. These inner row inserts are sized and configured for cutting the bottom of the borehole. Sometimes, a conventional bit also may include a plurality of secondary inserts located between the gage row inserts. These inserts, referred to as “nestled gage inserts,” typically cut the full gage of the borehole and also assist the gage inserts in cutting the borehole corner. Because a borehole primarily is cut by the collective action of the gage row inserts, nestled gage inserts (if therein), and inner row inserts, they are considered as the main cutting inserts of a rock bit.
In contrast, a conventional rock bit may include a row of heel inserts located on the frustoconical surface of a roller cone. The heel row inserts generally scrape and ream the side wall of a borehole as the roller cone rotates about its rotational axis. As such, the heel row inserts are not considered as the main cutting inserts; rather, they are deemed as auxiliary cutting inserts.
Due to the different functions performed by the primary and auxiliary cutting inserts, the two types of inserts experience different loading conditions during use. Thus, their impact of the performance and lifetime of a rock bit is different. Generally, the main cutting inserts have far more significant influence than the auxiliary cutting inserts.
The performance of a rock bit is measured, in part, by total drilling footage and rate of penetration. As the main cutting inserts on a rock bit wear, the rate of penetration decreases. When the main cutting inserts have been substantially worn out, it is no longer economical to continue drilling with such a rock bit. At this time, the rock bit must be replaced by a new one. The amount of time required to make a round trip for replacing a bit is essentially lost from drilling operations. This time can become a significant portion of the total time for completing a well. Therefore, constant efforts have been made to manufacture main cutting inserts that would increase the rate of penetration and total drilling footage of a rock bit. In particular, there have been numerous attempts to reduce wear and breakage and increase the cutting efficiency of the main cutting inserts.
Cemented carbide, such as tungsten carbide dispersed in a cobalt matrix, has been used to manufacture inserts for rock bits. Such tungsten carbide inserts (TCIs) possess good wear resistance and toughness to cut a borehole by crushing and gouging a rock formation. To improve the cutting efficiency of a tungsten carbide insert, a piece of polycrystalline diamond (“PCD”) has been applied to a certain part of the top portion of the insert.
Although polycrystalline diamond is extremely hard and wear resistant, a polycrystalline diamond piece on a tungsten carbide insert may still fail during normal operation. The typical failure mode is cracking of the polycrystalline diamond due to high contact stress, lack of toughness, and insufficient fatigue strength. Once the polycrystalline diamond piece fails, the polycrystalline diamond cutting edge is essentially lost.
For the foregoing reasons, there exists a need for a superhard material enhanced main cutting insert that has the following attributes: (1) the insert has a cutting edge formed of superhard material; and (2) the superhard material is placed on the insert such that it does not fail prematurely.
SUMMARY OF THE INVENTION
The invention meets the aforementioned need by one or more of the following aspects. In one aspect, the invention relates to a main cutting insert for an earth-boring bit. The main cutting insert comprise (1) a body portion adaptable for being secured in the earth-boring bit; (2) a top portion that has a substrate and includes a leading transition and a trailing transition; and (3) a layer of superhard material provided over the substrate forming the leading transition. The substrate forming the trailing transition is substantially free of superhard material. Preferably, the top portion includes an outer lateral face, and the central region of the outer lateral face also is free of superhard material. In some embodiments, the layer of superhard material forms a cutting edge. The cutting edge may be sharp, chamfered, radiused, planar, or non-planar. The layer of superhard material may be recessed in, be flush with, or protrude from the substrate. The superhard material may includes diamond and cubic boron nitride. Such main cutting inserts may be used as a gage insert, off-gage insert, nestled gage insert, and inner row insert on a rock bit.
In another aspect, the invention relates to a main cutting insert for an earth-boring bit. The main cutting insert includes (1) a body portion adaptable for being secured in the earth-boring bit; (2) a top portion for extending from the earth-boring bit that includes an outer lateral face with a peripheral region and a central region; and (3) a layer of superhard material provided over a portion of the substrate in the peripheral region, but not over the substrate in the central region of the outer lateral face. Furthermore, the outer lateral face may include a centroid that is free of superhard material. The top portion may further include a leading edge in the peripheral region with the layer of superhard material.
In still another aspect, the invention relates to a rock bit for drilling a borehole. The rock bit includes (1) a bit body; (2) a roller cone rotatably mounted on the bit body; (3) a plurality of main cutting inserts located on the roller cone to cut at least a portion of a borehole corner or a borehole bottom. At least one insert includes (a) a body portion secured in the roller cone; (b) a top portion extending from the roller cone that has a substrate and includes a leading transition and a trailing transition; and (c) a layer of superhard material provided over the substrate forming the leading transition. The substrate forming the trailing transition is substantially free of superhard material.
In yet another aspect, the invention relates to a rock bit for drilling a borehole. The rock bit includes (1) a bit body; (2) a roller cone rotatably mounted on the bit body; (3) a plurality of main cutting inserts located on the roller cone t
Neuder William
Rosenthal & Osha L.L.P.
Smith International Inc.
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