Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
1999-12-07
2001-03-20
Tsay, Frank S. (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S431000, C175S434000
Reexamination Certificate
active
06202770
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to devices used in drilling and boring through subterranean formations. More particularly, this invention, relates to a polycrystalline diamond or other superabrasive cutter intended to be installed on a drill bit or other tool used for earth or rock boring, such as may occur in the drilling or enlarging of an oil, gas, geothermal or other subterranean borehole, and to bits and tools so equipped.
2. State of the Art
There are three types of bits which are generally used to drill through subterranean formations. These bit types are: (a) percussion bits (also called impact bits); (b) rolling cone bits, including tri-cone bits; and (c) drag bits or fixed cutter rotary bits (including core bits so configured), the majority of which currently employ diamond or other superabrasive cutters, polycrystalline diamond compact (PDC) cutters being most prevalent.
In addition, there are other structures employed downhole, generically termed “tools” herein, which are employed to cut or enlarge a borehole or which may employ superabrasive cutters, inserts or plugs on the surface thereof as cutters or wear-prevention elements. Such tools might include, merely by way of example, reamers, stabilizers, tool joints, wear knots and steering tools. There are also formation cutting tools employed in subterranean mining, such as drills and boring tools.
Percussion bits are used with boring apparatus known in the art that moves through a geologic formation by a series of successive impacts against the formation, causing a breaking and loosening of the material of the formation. It is expected that the cutter of the invention will have use in the field of percussion bits.
Bits referred to in the art as rock bits, tri-cone bits or rolling cone bits (hereinafter “rolling cone bits”) are used to bore through a variety of geologic formations, and demonstrate high efficiency in firmer rock types. Prior art rolling cone bits tend to be somewhat less expensive than PDC drag bits, with limited performance in comparison. However, they have good durability in many hard-to-drill formations. An exemplary prior art rolling cone bit is shown in
FIG. 2. A
typical rolling cone bit operates by the use of three rotatable cones oriented substantially transversely to the bit axis in a triangular arrangement, with the narrow cone ends facing a point in the center of the triangle which they form. The cones have cutters formed or placed on their surfaces. Rolling of the cones in use due to rotation of the bit about its axis causes the cutters to embed into hard rock formations and remove formation material by a crushing action. Prior art rolling cone bits may achieve a rate of penetration (ROP) through a hard rock formation ranging from less than one foot per hour up to about thirty feet per hour. It is expected that the cutter of the invention will have use in the field of rolling cone bits as a cone insert for a rolling cone, as a gage cutter or trimmer, and on wear pads on the gage.
A third type of bit used in the prior art is a drag bit or fixed-cutter bit. An exemplary drag bit is shown in FIG.
1
. The drag bit of
FIG. 1
is designed to be turned in a clockwise direction (looking downward at a bit being used in a hole, or counterclockwise if looking at the bit from its cutting end as shown in
FIG. 1
) about its longitudinal axis. The majority of current drag bit designs employ diamond cutters comprising polycrystalline diamond compacts (PDCs) mounted to a substrate, typically of cemented tungsten carbide (WC). State-of-the-art drag bits may achieve an ROP ranging from about one to in excess of one thousand feet per hour. A disadvantage of state-of-the-art PDC drag bits is that they may prematurely wear due to impact failure of the PDC cutters, as such cutters may be damaged very quickly if used in highly stressed or tougher formations composed of limestones, dolomites, anhydrites, cemented sandstones, interbedded formations such as shale with sequences of sandstone, limestone and dolomites, or formations containing hard “stringers.” It is expected that the cutter of the invention will have use in the field of drag bits as a cutter, as a gage cutter or trimmer, and on wear pads on the gage.
As noted above, there are additional categories of structures or “tools” employed in boreholes, which tools employ superabrasive elements for cutting or wear prevention purposes, including reamers, stabilizers, tool joints, wear knots and steering tools. It is expected that the cutter of the present invention will have use in the field of such downhole tools for such purposes, as well as in drilling and boring tools employed in subterranean mining.
It has been known in the art for many years that PDC cutters perform well on drag bits. A PDC cutter typically has a diamond layer or table formed under high temperature and pressure conditions to a cemented carbide substrate (such as cemented tungsten carbide) containing a metal binder or catalyst such as cobalt. The substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing element to enhance its affixation to the bit face. The cutting element may be mounted to a drill bit either by press-fitting or otherwise locking the stud into a receptacle on a steel-body drag bit, or by brazing the cutter substrate (with or without cylindrical backing) directly into a preformed pocket, socket or other receptacle on the face of a bit body, as on a matrix-type bit formed of WC particles cast in a solidified, usually copper-based, binder as known in the art.
A PDC is normally fabricated by placing a disk-shaped, cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains loaded into the cartridge adjacent one face of the substrate. A number of such cartridges are typically loaded into an ultra-high pressure press. The substrates and adjacent diamond crystal layers are then compressed under ultra-high temperature and pressure conditions. The ultra-high pressure and temperature conditions cause the metal binder from the substrate body to become liquid and sweep from the region behind the substrate face next to the diamond layer through the diamond grains and act as a reactive liquid phase to promote a sintering of the diamond grains to form the polycrystalline diamond structure. As a result, the diamond grains become mutually bonded to form a diamond table over the substrate face, which diamond table is also bonded to the substrate face. The metal binder may remain in the diamond layer within the pores existing between the diamond grains or may be removed and optionally replaced by another material, as known in the art, to form a so-called thermally stable diamond (“TSD”). The binder is removed by leaching or the diamond table is formed with silicon, a material having a coefficient of thermal expansion (CTE) similar to that of diamond. Variations of this general process exist in the art, but this detail is provided so that the reader will understand the concept of sintering a diamond layer onto a substrate in order to form a PDC cutter. For more background information concerning processes used to form polycrystalline diamond cutters, the reader is directed to U.S. Pat. No. 3,745,623, issued on Jul. 17, 1973, in the name of Wentorf, Jr. et al.
Prior art PDCs experience durability problems in high load applications. They have an undesirable tendency to crack, spall and break when exposed to hard, tough or highly stressed geologic structures so that the cutters sustain high loads and impact forces. They are similarly weak when placed under high loads from a variety of angles. The durability problems of prior art PDCs are worsened by the dynamic nature of both normal and torsional loading during the drilling process, wherein the bit face moves into and out of contact with the uncut formation material forming the bottom of the wellbore, the loading being further aggravated in some bit designs and in some formations by so-called bit “whirl.
Jensen Kenneth M.
Jurewicz Stephen R.
Tibbitts Gordon A.
Baker Hughes Incorporated
Trask & Britt
Tsay Frank S.
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