Boring or penetrating the earth – Bit or bit element – Specific or diverse material
Reexamination Certificate
2000-05-30
2004-06-01
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
Specific or diverse material
C175S434000
Reexamination Certificate
active
06742611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to cutting elements for use on earth-boring drill bits and bits so equipped. In particular, the present invention relates to cutting elements having abrasive particles impregnated in a matrix. More specifically, the cutting elements of the present invention may include a tough and ductile support structure which may be internal or external to the impregnated segment. Yet more specifically, cutting elements, and segments, embodying the present invention may be arranged in preselected arrays, or patterns, and orientations to enhance drilling efficiency.
2. Background of Related Art
Conventionally, earth-boring drill bits with impregnated cutting structures, commonly termed “segments,” have been employed to bore through hard and abrasive formations, such as basalt, dolomite and hard sandstone. As depicted by
FIG. 1
, the impregnated segments
16
of such drill bits are typically secured to the boring end
14
, which is typically termed the “face,” of the bit body
12
of the drill bit
10
in a generally radial fashion. Impregnated segments may also be disposed concentrically over the face of the drill bit. As the drill bit gradually grinds through a very hard and abrasive formation, the outermost layer of the impregnated segments containing abrasive particles (such as small diamonds, diamond grit, or other superabrasive particles such as cubic boron nitride) wear and may fracture. Many conventional impregnated segments are designed to release, or “shed,” such diamonds or grit in a controlled manner during use of the drill bit. As a layer of diamonds or grit is shed from the face, underlying diamonds are exposed as abrasive cuttings and the diamonds that have been shed from the drill bit wear away the exposed continuous phase of the segment in which the interior diamonds are dispersed, thereby “resharpening” the bit until the entire diamond-impregnated portion of the bit has been consumed. Thus, drill bits with diamond-impregnated segments typically maintain a substantially constant boring rate as long as diamonds remain exposed on such segments.
Conventional impregnated segments typically carry the superabrasive particles in a continuous phase of a hard material, such as tungsten carbide, a tungsten alloy, a metal carbide, a refractory metal alloy, a ceramic, copper, a copper-based alloy, nickel, a nickel-based alloy, cobalt, a cobalt-based alloy, iron, an iron-based alloy, silver, or a silver-based alloy. Such materials are, however, typically relatively brittle and may fracture when subjected to the stresses of drilling. Accordingly, when subjected to the high stresses of drilling, and particularly impact stresses, the continuous phase of such impregnated segments may break, resulting in the premature failure thereof and potentially the premature failure of the bit upon which such segments are carried. Thus, drilling times and costs are increased by premature failure of conventional impregnated segments, as it is necessary to remove the drill string from the bore hole, replace the entire drill bit, and reintroduce the drill string into the bore hole.
U.S. Pat. No. 4,234,048 (the “'048 patent”), which issued to David S. Rowley on Nov. 18, 1980, discloses an exemplary drill bit that bears diamond-impregnated segments on the crown thereof. Typically, the impregnated segments of such drill bits are C-shaped or hemispherically shaped, somewhat flat, and arranged somewhat radially around the crown of the drill bit. Each impregnated segment typically extends from the inner cone of the drill bit, over the nose and up the bit face to the gage. The impregnated segments may be attached directly to the drill bit during fabrication or partially disposed within a slot or channel formed into the crown and secured to the drill bit by brazing. When attached to the crown of a drill bit, conventional impregnated segments have a relatively low profile (i.e., shallow recesses between adjacent segments) relative to the bit face and a footprint that covers the majority of the drill bit surface from the nose to the gage. The low profile is typically required due to the relatively brittle materials from which the continuous phases of conventional impregnated segments are formed. Similarly, the generally semicircular shape of conventional impregnated segments and their somewhat radial arrangement around the crown of a bit body are required to prevent the breakage and premature wear of such impregnated segments due to the hard but relatively brittle continuous-phase materials thereof. The large “footprint” of conventional impregnated segment-bearing drill bits is typically necessary to provide a sufficient amount of cutting material on the face of the bit. To some extent, the conventionally required semicircular shape of impregnated segments has also prohibited the use of alternative impregnated segment shapes, drill bit designs, and arrangements of impregnated segments on drill bits, which could otherwise optimize drilling rates and reduce the rate of bit wear and failure.
Because of the low profile or exposure and large surface area footprint of conventional impregnated segments, very little clearance exists between the face of the drill bit and the drilled formation during use of the drill bit upon which such segments are carried. Consequently, the build-up of formation fines, frequently referred to as rock flour, on the impregnated segments may prevent contact of the impregnated segments with the interior surface of the borehole and may reduce the depth of cut of the drill bit.
Moreover, due to the large surface area footprint and the low profile of impregnated segments on conventional drill bits, the hydraulics of such drill bits cannot be fully employed to remove formation fines therefrom or to cool the segments. Therefore, the penetration rate of drilling and the amount of weight on bit that may be employed on the drill bit may both decrease, while the rate of wear will be undesirably high, and failure of the drill bit may occur.
An additional characteristic with conventional impregnated segments having large surface area footprints is that much of the exposed cutting surface of the segments is located a significant lateral distance from the nearest waterway, or area in which drilling-fluid is circulated. Such relatively large lateral distances from the flow of water or drilling fluid thereby impedes the flushing away of cuttings, or fines, from the segment and can aggravate the previously mentioned problems such as the face and crown of the drill bit being built up with sands and fines.
Another problem encountered in the art is that when drilling differing formations or when drilling a formation having soft layers, medium hard layers, and hard layers, it is usually necessary to employ drill bits particularly designed and especially suited for drilling in the layer being encountered in order to ensure steady progress on the well being drilled. Thus, a drilling crew is frequently selecting a drill bit having an appropriate diamond cutter density to balance the rate of penetration (ROP) with wear resistance for extending the useful life of the bit. For example, upon encountering a relatively soft layer, a relatively economical drill bit having a light diamond cutter density particularly suited to drilling soft layers would be used to maximize the rate of bit penetration in the formation. Upon encountering a medium hard layer, a relatively more expensive drill bit having a medium cutter density particularly suited to drilling medium hard layers would be required to maximize the rate of bit penetration in that particular medium hard strata of the formation being drilled. Lastly, upon encountering a hard layer, a yet more expensive drill bit having a high diamond cutter density particularly suited to drilling hard layers would be required to prevent excessive wear of the cutters while allowing a sufficient weight-on-bit that would provide an acceptable ROP through such hard portion of the formation bei
Illerhaus Roland
Tibbitts Gordon A.
Baker Hughes Incorporated
Dang Hoang
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