Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
2000-09-26
2003-03-04
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
Reexamination Certificate
active
06527069
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to rotary bits for drilling subterranean formations and, more specifically, to superabrasive cutting elements or cutters suitable for use on such bits, particularly of the so-called fixed-cutter or “drag” bit variety.
2. Background of Related Art
Fixed-cutter or drag bits have been employed in subterranean drilling for many decades, and various sizes, shapes and patterns of natural and synthetic diamonds have been used on drag bit crowns as cutting elements. Polycrystalline diamond compact (PDC) cutters comprised of a diamond table formed under ultra-hightemperature, ultrahigh-pressure conditions onto a substrate, typically of cemented tungsten carbide (WC), were introduced about twenty-five years ago. PDC cutters, with their diamond tables providing a relatively large, two-dimensional cutting face (usually of circular, semicircular or tombstone shape, although other configurations are known), have provided drag bit designers with a wide variety of potential cutter deployments and orientations, crown configurations, nozzle placements and other design alternatives not previously possible with the smaller natural diamond and polyhedral, unbacked synthetic diamonds previously employed in drag bits. The PDC cutters have, with various bit designs, achieved outstanding advances in drilling efficiency and rate of penetration (ROP) when employed in soft to medium hardness formations, and the larger cutting face dimensions and attendant greater extension or “exposure” above the bit crown have afforded the opportunity for greatly improved bit hydraulics for cutter lubrication and cooling and formation debris removal. The same type and magnitude of advances in drag bit design in terms of cutter robustness and longevity, particularly for drilling rock of medium to high compressive strength, has, unfortunately, not been realized to a desired degree.
State of the art substrate-supported PDC cutters have demonstrated a notable susceptibility to spalling and fracture of the PDC diamond layer or table when subjected to the severe downhole environment attendant to drilling rock formations of moderate to high compressive strength, on the order of nine to twelve kpsi and above, unconfined. Engagement of such formations by the PDC cutters occurs under high weight on bit (WOB) required to drill such formations and high impact loads from torque oscillations. These conditions are aggravated by the periodic high loading and unloading of the cutting elements as the bit impacts against the unforgiving surface of the formation due to drill string flex, bounce and oscillation, bit whirl and wobble, and varying WOB. Thus, high compressive strength rock, or softer formations containing stringers of a different, higher compressive strength, may produce severe damage to, if not catastrophic failure of, the PDC diamond tables. Furthermore, bits are subjected to severe vibration and shock loads induced by movement during drilling between rock of different compressive strengths, for example, when the bit abruptly encounters a moderately hard strata after drilling through soft rock.
Severe damage to even a single cutter on a PDC cutter-laden bit crown can drastically reduce efficiency of the bit. If there is more than one cutter at the radial location of a failed cutter, failure of one may soon cause the others to be overstressed and to fail in a “domino” effect. As even relatively minor damage may quickly accelerate the degradation of the PDC cutters, many drilling operators lack confidence in PDC cutter drag bits for hard and stringer-laden formations.
It has been recognized in the art that the sharp, typically 90° edge of an unworn, conventional PDC cutter element is especially susceptible to damage during its initial engagement with a hard formation, particularly if that engagement includes even a relatively minor impact. It has also been recognized that pre-beveling or pre-chamfering of the PDC diamond table cutting edge provides some degree of protection against cutter damage during initial engagement with the formation, the PDC cutters being demonstrably less susceptible to damage after a wear flat has begun to form on the diamond table and substrate.
U.S. Pat. Nos. Re 32,036, 4,109,737, 4,987,800, and 5,016,718 disclose and illustrate beveled or chamfered PDC cutting elements, as well as alternative modifications such as rounded (radiused) edges and perforated edges which fracture into a chamfer-like configuration. U.S. Pat. No. 5,437,343, assigned to the assignee of the present application and incorporated herein by this reference, discloses and illustrates a multiple-chamfer PDC diamond table edge configuration which, under some conditions, exhibits even greater resistance to impact-induced cutter damage. U.S. Pat. No. 5,706,906, assigned to the assignee of the present application and incorporated herein by this reference, discloses and illustrates PDC cutters employing a relatively thick diamond table and a very large chamfer, or so-called “rake land”, at the diamond table periphery.
However, even with the PDC cutting element edge configuration modifications employed in the art, cutter damage remains an all too frequent occurrence when drilling formations of moderate to high compressive strengths and stringer-laden formations.
Another approach to enhancing the robustness of PDC cutters has been the use of variously configured boundaries or “interfaces” between the diamond table and the supporting substrate. Some of these interface configurations are intended to enhance the bond between the diamond table and the substrate, while others are intended to modify the types, concentrations and locations of stresses (compressive, tensile) resident in the diamond tables and substrates as a result of the cutter being formed in an ultra high-pressure, ultra high-temperature process. Such residual stresses, as known in the art, are prone to arise because the diamond table typically has a lower coefficient of thermal expansion than that of the substrate to which it is cojoined. Additionally, the diamond table and substrate will typically have differing values of bulk modulus, thereby compounding the likelihood of residual stress being present in the cutter. As a newly formed cutter cools from the elevated temperature required to form the cutter, the residual stresses in the cutter tend to be especially concentrated at and near the interface where the diamond or superabrasive table is disposed upon the supportive substrate. Thus, depending on cutter construction, the direction and magnitude of such residual stresses may, and often do, cause the diamond table or superabrasive layer to prematurely fracture, delaminate, and/or spall as compared to cutters in which residual stresses are fortuitously of lesser magnitude or in which the residual stresses by chance happen to be oriented favorably.
Many attempts have been made to provide PDC cutters which are resistant to premature failure. The use of an interfacial transition layer with material properties intermediate of those of the diamond and substrate is known within the art. The formation of cutters with noncontinuous grooves or recesses in the substrate filled with diamond is also practiced, as are cutter formations having concentric circular grooves or a spiral groove.
The patent literature reveals a variety of cutter designs in which the diamond/substrate interface is three-dimensional, i.e., the diamond layer and/or substrate have portions which protrude into the other member to “anchor” it therein. The shape of these protrusions may be planar or arcuate, or combinations thereof
U.S. Pat. No. 5,351,772 to Smith shows various patterns of radially directed interfacial formations on the substrate surface, the formations projecting into the diamond surface.
As shown in U.S. Pat. No. 5,486,137 to Flood et al., the interfacial diamond surface has a pattern of unconnected radial members which project into the substrate, the thickness of the diamond layer decreasing toward the
Chaves Arthur A.
Doster Michael L.
Meiners Matthew J.
Skeem Marcus R.
Baker Hughes Incorporated
Dang Hoang
TraskBritt
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