PDC inserts are commonly used to increase the wear resistance of surfaces in certain types of downhole tools. For example, inserts on a reamer, in association with a drill bit, are used on outer blade surfaces to resist wear from the bore hole wall. The reamer enlarges the bore hole to a diameter larger than that created by the drill bit.
The function of the reamer is to maintain the diameter of the hole as the drill bit proceeds downwardly through the rock formation. As the bore hole is being drilled, the rock drill bit gradually wears to undersize and thus the hole which is cut gradually becomes of undersize diameter. The function of the reamer, which typically has PDC inserts along the outer blade edge, is to grind the circumference of the hole, shortly after it has been cut by the rock drill bit, and thus keep the hole diameter to size.
Inserts are also commonly used in fixed cutter drill bits along a cutting blade which is stationary in respect of the drill string, in contrast to roller cone bits. Such a fixed cutter drill bit typically has a leading face from which a plurality of blades extend, each blade carrying a plurality of cutting elements comprising PDC inserts. Inserts may also be placed along a gauge pad at the extreme outer diameter of each blade.
PDC inserts have a polycrystalline diamond surface formed on wear surfaces, which may be formed in a variety of ways, principally in a conventional process under heat and pressure, or by sintering. The inserts are formed of a tungsten carbide material, and the wear surface is then applied. In the past, such inserts commonly have had a flat or slightly ovoid outer contact region, where the insert contacts the rock formation being cut. Regardless of the configurations of the inserts, they have all had a characteristic in common, and that is the inserts define one point, line, or area contact with the rock formation. As the rock formation increases in hardness, the resistance or “work load” necessary to disintegrate the formation at that area also increases. The increased resistance causes two common problems. The increased resistance on individual inserts can cause premature chipping or breakage failure of the inserts. Also, the combined increase of resistance on all the PDC inserts increases the amount of torque required to drive the bit and causes the bit to stop momentarily while drilling, a condition known as “stick slip” drilling. There is a present need in this art for PDC inserts that can drill harder formations with less risk of failure and with less risk of “stick slip”. The present invention is directed to this need in the art.