Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1997-09-23
2001-03-20
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S430000, C175S431000
Reexamination Certificate
active
06202771
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to cutting elements for rotary drill bits for subterranean drilling, and more specifically to cutting elements providing a controlled superabrasive contact area during a predominant portion of the useful life of the cutting element, as well as bits so equipped and methods of drilling therewith.
2. State of the Art
Rotary bits are the predominant type of drill bits employed for subterranean drilling to oil, gas, geothermal and other formations. Of the types of rotary bits employed, so-called fixed cutter or “drag” bits have garnered an ever-increasing market share over the past few decades. This market share increase is attributable to a number of factors, but significant ones must be acknowledged as the wide availability and performance of superabrasive cutting elements.
Superabrasive cutting elements in their present state typically take the form of a polycrystalline diamond compact (PDC) layer or “table” formed onto a supporting substrate, typically of a cemented or sintered tungsten carbide (WC), in a press under ultra-high pressure and temperature conditions. Other superabrasive materials are known, including thermally stable PDCs, diamond films, and cubic boron nitride compacts. The present invention has utility with cutting elements employing any superabrasive material.
Several physical configurations of superabrasive tables for cutting elements are known, including square, “tombstone” shape, and triangular. However, the most common shape is circular, backed by a circular substrate of like size. These circular superabrasive tables are usually formed substantially to size in a press, but may be cut from larger, disc-shaped blanks. The other referenced shapes are generally required to be cut from a larger, disc-shaped blank, thus generating a large volume of scrap, reducing yield during fabrication and increasing fabrication costs.
As can be seen in
FIGS. 1 and 2
of the drawings, state-of-the-art, disk-shaped cutting element
10
includes a circular, PDC superabrasive table
12
of substantially constant depth mounted to a disk-shaped WC substrate
14
. Superabrasive table
12
includes a cutting face
16
, a cutting edge
18
at the periphery of cutting face
16
, and a side
20
to the rear of cutting edge
18
(taken in the direction of cutting element travel, cutting face-first). Cutting element
10
would typically be oriented on a drill bit with at least a nominal negative backrake so that cutting face
16
“leans” away from the formation being drilled. As the cutting edge
18
and side
20
of superabrasive table
12
of cutting element
10
first contact the formation under application of weight on bit (WOB) at location
22
of cutting edge
18
, it can be seen that the superabrasive contact area is extremely small in both longitudinal depth or thickness as well as width, in part due to the aforementioned backrake. Thus, for a given WOB, the responsive loading per unit surface area at the side
20
of superabrasive table
12
contacting the formation being drilled is extremely high.
Due to the circular shape of the superabrasive table
12
, however, as the cutting element
10
begins to wear and a so-called “wear flat” forms at one side of cutting face
16
, superabrasive table
12
and the WC substrate
14
therebehind, the contact area of the superabrasive material under WOB, or so-called Normal force applied along the axis of the drill string to which the bit is secured, increases markedly in width and therefore in total area. The increasing contact area consequently requires an increase in WOB to maintain cutting element loading in terms of load per superabrasive unit surface area in contact with the formation to continue an acceptable rate of penetration (ROP). However, as WOB increases, so does wear on the superabrasive table, as well as the likelihood of spalling and fracture damage thereto. In addition, the requirement to increase WOB may undesirably affect drilling performance in terms of reducing steerability of a bit, as well as precipitate stalling of a downhole motor when the torque required to rotate under excessive WOB is exceeded, with consequential loss of tool face orientation. As can readily be visualized by looking at the relative contact area widths at location
22
, location
24
(as the cutting element is about 20% in diameter worn) and location
26
(as cutting element
10
is about 40% in diameter worn and typically approaching, if not well past, the end of its useful life), the superabrasive contact area may increase by more than an order of magnitude from the time a cutting element first engages a formation until the end of its useful life, thus requiring an attendant increase in WOB to maintain ROP in a given formation.
This undesirable increase in superabrasive contact area is present in conventional PDC cutting elements bearing constant-thickness superabrasive tables of about 0.030 inch thickness. However, as cutting elements bearing tables of greater thicknesses are developed, for example 0.070 inch and 0.100 inch uniform-thickness tables, the contact area increase is exacerbated. The increase in wear flat area for such PDC cutting elements of 13 mm (0.529 inch) diameter is illustrated in
FIG. 9
, wherein superabrasive contact area versus percentage of cutting face diametric wear is shown respectively by lines A, B and C for cutting elements of 0.030, 0.070 and 0.100 inch superabrasive table thickness. For each of the 0.030 inch, 0.070 inch and 0.100 inch thickness tables, the contact area more than doubles between 5% and 30% diametric wear of the superabrasive table. More significantly, for the 0.070 inch and 0.100 inch thickness superabrasive tables, contact area quickly increases in absolute terms to in excess of 0.02 square inch (the maximum superabrasive contact area for a 13 mm, 0.030 inch thick table PDC cutting element), thus necessitating substantial and undesirable WOB increases extremely early in the life of the cutting element in order to maintain the load per unit surface area of superabrasive material contacting the formation. While use of a square or tombstone-shaped cutting face, would obviously provide a relatively constant superabrasive contact area, as noted above such configurations are undesirable for other reasons. Consequently, there is a need in the art for a cutting element exhibiting a circular cutting face and superabrasive table, the term “circular” as used herein including a segment of a circle a segment or which otherwise exhibits an arcuate or nonlinear cutting edge, which provides a relatively constant superabrasive contact area during a large portion of the useful life of the cutting element.
BRIEF SUMMARY OF THE INVENTION
In contrast to the circular or disk-shaped cutting elements comprising the state of the art, the cutting elements of the invention are configured with superabrasive tables having configurations such that the surface area of superabrasive material in contact with a formation being cut by the cutting element responsive to WOB quickly reaches a relatively stable value, which value remains relatively constant over a substantial portion of the useful life of the cutting element, for example, from about 5% to about 30% wear across the diameter of the cutting face. The present invention provides this relatively stable value of a relatively small magnitude, for example, from about 0.018 to about 0.021 square inch for a 13 mm (0.529 inch) diameter cutting element.
One embodiment of the cutting element of the present invention is configured with a planar cutting face and a non-planar interface between the superabrasive table and the supporting substrate, wherein at least one radially-oriented, substantially isosceles triangular projection of increased superabrasive table thickness lies adjacent the periphery of the superabrasive table with the triangle base oriented toward the formation. The superabrasive projection gradually decreases in thickness and width from a location adjacent the cutting ed
Chaves Arthur A.
Horton Ralph M.
Scott Danny E.
Smith Redd H.
Baker Hughes Incorporated
Dang Hoang
Trask & Britt
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