Patent Application
20120193149
Not applicable.
Not applicable.
1. Field of Technology
The disclosure relates generally to earth-boring bits used to drill a borehole for the recovery of oil, gas or minerals. More particularly, this disclosure relates to rolling cone drill bits having enhanced hydraulics and erosion-resistant cutting teeth.
2. Background Information
A conventional earth-boring drill bit is mounted on the lower end of a drill string. The bit is turned by rotating the drill string at the surface, by actuation of downhole motors or turbines, or by both methods. With weight applied to the drill string, the rotating drill bit engages the earthen formation and drills a borehole toward a target zone. The borehole created will have a diameter generally equal to the diameter or “gage” of the drill bit.
One type of conventional bit includes one or more rolling cone cutters. As the bit is rotated, the cutters roll and slide upon the bottom of the borehole, breaking up the formation material. Typically, the cutting action of the cone cutters is enhanced by providing cutting elements (e.g., teeth) on the rolling cones. The borehole is formed as the action of the rolling cones and their cutting elements gouge, crush and shear formation material in the bit's path.
Rolling cone bits are typically characterized by the type of cutting elements employed on the rolling cones. A first type employs inserts formed of a very hard material, such as tungsten carbide, that are press fit into undersized holes formed in the cone surface. Such bits are typically referred to as “TCI” bits or “insert” bits. A second general bit type includes teeth that are milled, cast, or otherwise integrally formed from the material of the rolling cone, such bits being generally known as “steel tooth bits.”
While drilling, it is conventional practice to pump drilling fluid (also referred to as “drilling mud”) down the length of the tubular drill string where it is jetted from the face of the drill bit through nozzles. The hydraulic energy thus supplied flushes the drilled cuttings away from the cutters and the borehole bottom, and carries them to the surface through the annulus that exists between the tubular drill string and the borehole wall.
The cost of drilling a borehole is very high, and is proportional to the time it takes to drill to the targeted depth and location. In turn, the time required to drill the well is greatly affected by the number of times the drill bit must be changed before reaching the targeted formation, as is necessary, for example, when the bit becomes worn or encounters formations for which it is not well suited to drill. The length of time before a drill bit must be changed depends upon its rate of penetration (“ROP”) as well as its durability. Whenever a bit must be changed, the entire drill string, which may be miles long and is made up of discrete sections of drill pipe that have been threaded together, must be retrieved from the borehole, section by section. Once the drill string has been retrieved and the new bit installed, the bit must be lowered back to the bottom of the borehole. This is accomplished by reconstructing the drill string, section by section. This process, known as a “trip” of the drill string, requires considerable time, effort and expense. Accordingly, it is desirable to employ drill bits that drill faster and longer, and that drill with an acceptable ROP over a wide range of formation types.
A drill bit's ROP and durability may be substantially affected by the design, placement and orientation of the nozzles in the bit face. For example, when drilling softer formations and plastic formations, cuttings tend to adhere to the cone cutters and between the cones' cutting elements, a phenomenon commonly referred to as “bit balling.” When bit balling occurs, the penetration of the individual cutting elements into the formation is restricted. With less penetration, the amount of formation material gouged or otherwise removed by the cutting elements is reduced, leading to a reduction in the bit's ROP. Also, formation packed against the cone cutters may close or greatly restrict the flow channels needed for the drilling fluid to carry away cuttings. This may promote premature bit wear. In either instance, having sufficient fluid flow can help to clean the cutting teeth, allowing them to penetrate to a greater depth, and to maintain the desired ROP.
A conventional nozzle arrangement includes the placement of a nozzle between each of the cone cutters and near to the cones' outermost row of cutter elements. Typically, the bit's hydraulics are designed such that each of these nozzles has the same orientation as the others that are similarly positioned. In other conventional designs, additional nozzles are positioned elsewhere in the bit body to direct a high velocity stream at other predetermined locations. However, conventional arrangements may not direct the hydraulic flow to the locations where cleaning is most needed and, for example, may not provide sufficient cleaning along the inner rows of the cones' cutting elements.
Further, drilling fluid, as it picks up and mixes with the drilled cuttings, becomes highly abrasive. The impact of the cutting-laden fluid directly on cutting teeth may severely erode the teeth. As with poor bit hydraulics, tooth erosion and/or loss of teeth may lead to a reduction in ROP and bit life, and necessitate a costly and premature trip of the drill string.
Accordingly, there is a need for bits having improved bit hydraulics that provide cleaning of cutting elements along the outer and inner rows of the cones in order to minimize bit balling and maintain acceptable ROP, without causing detrimental erosion of the cutting teeth.
In one embodiment, a drill bit is disclosed having a circumferential outer gage row of cutting teeth on a cone cutter, and a circumferential inner row of cutting teeth spaced apart from the gage row. The cutting teeth of the inner row include an erosion shield on at least a portion of the upstream-facing end of the cutting tooth and on at least a portion of the crest of the cutting tooth, and include shield-free portions on the flanking surfaces of the tooth at locations disposed between the root and its crest. In certain embodiments, the outer row of gage cutting teeth provides a channel and conveys drilling fluid along a predetermined fluid path toward an inner row cutting tooth. In some embodiments, the cutting teeth in the outer gage row are skewed such that their crests are not aligned with the cone axis of rotation. The crests may be angled between approximately 5° and approximately 30° relative to the cone axis.
In other embodiments described herein, a rolling cone drill bit includes cutting teeth having a root portion adjacent to the generally conical surface of the cone cutter, a pair of flanking surfaces extending from the root portion and intersecting in an elongate crest, and a erosion-shielding cap disposed along at least a portion of the crest and along at least a portion of the upstream end of the tooth, with the flanking surfaces including shield-free portions adjacent to the root. In certain embodiments, the shielding cap on the flanking surface extends from the crest towards said root portion for a distance greater than or equal to one-half the height of the tooth. In some embodiments, the shield-free portion on the flanking surfaces extends from the root towards the crest for a distance that is less than one-half the height of the tooth.
In some embodiments disclosed herein, the tooth is formed of an inner core portion that is partially covered by a shield provided to resist erosion. In some of the embodiments, the shield is made of a material having at least 40% by volume of a hard metal powder, such as that selected from the group consisting of tungsten carbide, diamond, cubic boron nitride, and ceramics. The inner core portion is intended to be more impact resistant and, in certain embodiments, is made of powdered metal having not more than 30% by volume of the hard metal material. In some embodiments, the inner core portion forms at least two-thirds of the perimeter of the tooth.
The embodiments disclosed herein further include an inner row cutting tooth having a fluid baffle or fin extending from the upstream end of the tooth provided to divert drilling fluid quickly around the tooth and to lessen the erosion as may be caused by the impact with cuttings-laden drilling fluid.
Other embodiments disclosed herein include a rolling cone bit with first and second nozzles having non-uniform orientations so as to provide a flow of drilling fluid to predetermined locations or zones on the bit face where a substantial volume of drill cuttings are being generated.
Thus, embodiments described herein comprise a combination of features intended to address various shortcomings associated with certain prior devices. The various features and characteristics described above, as well as others described below, will be readily understood by those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings.
For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:
The following description is exemplary of embodiments of the invention. These embodiments are not to be interpreted or otherwise used as limiting the scope of the disclosure, including the claims. One skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and is not intended to suggest in any way that the scope of the disclosure, including the claims, is limited to that embodiment.
The drawing figures are not necessarily to scale. Certain features and components disclosed herein may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in interest of clarity and conciseness.
The terms “including” and “comprising” are used herein, including in the claims, in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first component couples to a second component, that connection may be through a direct engagement between the two components, or through an indirect connection via other intermediate components, devices and/or connections.
Referring first to
Referring now to both
Referring to
Referring to
Each cone cutter 30a-30c includes a plurality of cutting teeth disposed about the cone and arranged in circumferential rows. For example, as best shown in
In the embodiment described above, gage and inner row teeth 51, 53 are formed simultaneously with cones 30a-30c via known metallurgical processes. Suitable such processes, referred to variously as densification powder metallurgy, powder forging, and powder forge cutter processes, are disclosed in U.S. Pat. Nos. 4,368,788; 4,372,404; 4,398,952; 4,554,130; 4,562,892; 4,592,252; 4,597,456; 4,630,692; 4,853,178; 4,933,140; 4,949,598; 5,032,352; 5,653,299; 5,967,248; 6,045,750; 6,060,016; 6,135,218; 6,338,621; 6,347,676; all of which are incorporated herein by reference. These metallurgical processes enable cutting teeth to be formed into shapes and configurations that may be difficult to manufacture via other methods, and allow for the teeth to be integral with the cones.
As shown in
It is to be further understood that nozzles of various sizes and types may be provided and may be positioned in various other locations on the bit body. For example, although not shown, a nozzle may also be provided in a generally central location on the underside 26 of the bit body 22 with an orifice directed toward the center of the borehole bottom 6. Likewise, nozzles can also be provided at radial positions generally inboard from the position of nozzles 28 and oriented so as to inject fluid on the cutting teeth when they have rotated to the position furthest from the borehole bottom. Whether such nozzles in addition to nozzles 28 are included in bit 10 will depend, in part, on the bit diameter.
Referring to
The position and orientation of nozzle 28 and fluid stream 60 may be further described with reference to
A first reference plane 80 contains bit axis 20 and passes through orifice center point 72, extending radially away from bit axis along radial reference line 82. A second reference plane 84 passing through orifice center point 72 is perpendicular to first reference plane 80 and is also perpendicular to radial reference line 82. As best shown in
Presently, it is conventional practice to orient the radially-outermost nozzles in a uniform manner so as to direct the flow of hydraulic fluid generally at the same portion of each cone. For example, and in the context of the angles described above, a conventional three-cone bit would include nozzles 28 between each pair of cone cutters and oriented so that all have the same A angles and all have the same B angles. However, due the different placement of inner row cutter elements, cone and journal offset, and certain other factors, it is understood that some areas of the bit generate more cuttings than others. Accordingly, nozzles 28a-c in bit 10 may be provided with unique orientations such that, after the drilling fluid is first directed to clean gage row cutting teeth 51, the high velocity drilling fluid is next directed to locations on inner rows 54 where maximum cutting generation is ongoing. Accordingly, as best understood with reference to
Given the position and orientation shown above in Table I, it is believed that, for the bit 10 shown in
These nozzle positions and orientations are provided in an effort to prevent or minimize bit balling by cleaning drilled cuttings first from the gage row cutting teeth 51, and substantially from inner row cutting teeth 53. The position and orientation noted in Table 1 above is exemplary for the bit 10 previously described. It is to be understood that, for other bits, including bits of different size and different cutting structures, the position and orientation defined by R, H and by angles A and B may be different than those disclosed in Table I. In a general sense, angle A will typically be in the range of 12°-25° and angle B will typically be in the range of 0-15 for the radially-outermost nozzles. Further, although, as described above, the position and orientation of the nozzles 28a-c may be different, other features of bit 10 described herein may be employed with bits having nozzles 28a-c are identically positioned and oriented.
With the desire to convey the drilling fluid inwards toward the zones Z1-Z3 where the greatest volume of chip and cutting formation is taking place, the gage row teeth 51 may be oriented in order to provide the least obstruction to the fluid flow and, further, to guide and channel the fluid directly to the locations where cleaning is most needed. Accordingly, referring to
For other bit sizes and cutter arrangements, the crests 64 of gage teeth 51 may be oriented at other angles, depending upon the location where the fluid flow is most desired. For example, in other embodiments, the crest 64 and crest line 67 may be aligned with and lie within the same plane as cone axis 31 such that the angle C would be 0°, as shown in the example of
As described above, it is desirable to direct fluid flow inwards to the inner row cutter elements in a manner such that the drilling fluid maintains a high velocity for optimum cleaning. As best described with reference to
As best shown in
As best shown in
Core 110 is formed of a first material that is tougher and more fracture resistant than the material of the shield 112, while the shield 112 is formed from a material that is harder and more wear and abrasion-resistant than the material of the core 110. Typically, a composition with higher hardness indicates a higher resistance to erosion and wear, but also lower resistance to fracture (i.e., a lower toughness). Similarly, a material with a higher fracture toughness normally has a lower relative hardness and a lower resistance to wear and erosion. As such, the material of the shield 112 is more resistant to damage from erosion as may be caused by the high velocity drilling fluid impacting the tooth. At the same time, by leaving portions 115 of the flanks 93 shield-free and forming those unshielded portions 115 from the more fracture and impact resistance material from which core 110 is made, the tooth 53 is less susceptible to breakage of other damage caused by impact loading.
As previously mentioned, cones 30a-30c and inner row teeth 51, 53 may be formed by powder forging. Various hard materials are used in the powder forging processes, including materials where tungsten carbide, diamond, cubic boron nitride or ceramic materials are dispersed in a relatively softer metal matrix material, typically along with a binder metal such as cobalt. In manufacturing inner row cutting teeth 53, shield 112 is made of materials such that it will be harder than the material forming core 110. Exemplary compositions for shield 112 include a mixture of powdered tungsten carbide in amounts greater than 50% by volume of the powdered mixture. Optionally, the mixture may have greater than 60% volume of tungsten carbide and, further may have greater than 70% by volume of tungsten carbide. By way of contrast, it is preferred that the hardness of core 110 differ from that of shield 112. As an example, compositions for core 110 include mixtures where powdered tungsten carbide makes up less than 50% by volume of the composition, where the shield material is made of a composition of powdered tungsten carbide in amounts greater than 50% by volume. The percentage by volume of tungsten carbide in the powder composition of core 110 and shield 112 can be varied to achieve a desired wear-resistance and toughness.
By selecting different percentages of powdered hard metals (e.g., tungsten carbide, diamond, cubic boron nitride or ceramics) for use in forming shield 112 and core 110, after undergoing the powder forging process, the hardness of shield 112 will differ from the hardness of core 110. To describe physical characteristics (such as wear resistance or hardness) of different materials, the term “differs” as used herein means that the value or magnitude of the characteristic being compared varies by an amount that is greater than that resulting from accepted variances or tolerances normally associated with the processes used to formulate the raw materials and to form cutter elements from those materials. Thus, materials selected so that the forging process yields materials having the same nominal hardness or the same nominal wear resistance will not “differ,” as that term has thus been defined, even though various samples of the material, if measured, would vary about the nominal value by a small amount.
Shielding of inner row cutting teeth may take other forms. For example, referring to
Another embodiment for an inner row cutting tooth is shown in
A further embodiment for an inner row cutting tooth is shown in
In addition to providing shield 112, further erosion-resistance for inner row teeth can be provided by aligning the teeth such that their crests 94 are generally aligned with channel 69 and with the direction of fluid flow impacting the upstream end of the tooth. Accordingly, and referring again to
Providing a shield for inner row cutting teeth as described herein, and particularly on the upstream ends, offers the potential to improve bit durability and maintain ROP by resisting erosion to the cutting teeth. Forming the inner row teeth on the cone cutters so as to be generally aligned with the direction of drilling fluid flow may further aid in erosion resistance. Further, the positioning and orientation of nozzles 28 and orifices 70 offers the potential to enhance cleaning and to provide improved ROP by directing the high velocity drilling fluid first on the gage row teeth and then to regions on the bit face where cleaning is most needed. Likewise, orienting gage row, teeth so that flanking surfaces channel the flow from gage portions of the bit to the regions where the inner rows are most active in generating cuttings offers further potential for ROP improvement.
While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only, and are not limiting. Many variations and modifications of the disclosed apparatus are possible and are within the scope of the invention. Although embodiments of the bits described herein are steel tooth bits, embodiments of the hydraulic layouts and designs for erosion-resistant teeth may also be employed with insert bits. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.
