Boring or penetrating the earth – Bit or bit element – With fluid conduit lining or element
Reexamination Certificate
2000-01-24
2001-06-26
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
With fluid conduit lining or element
Reexamination Certificate
active
06250408
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to bits for drilling subterranean formations. More specifically, the invention relates to multiple nozzle rotary drag bits employing variations in nozzle size and orientation to apportion hydraulic flow volume on the bit face in relationship to formation cuttings volume generated by groups of cutters on the bit, as well as to bits employing junk slots with cross-sectional areas apportioned in relationship to cuttings generated by groups of cutters with which the junk slots are respectively associated, such features providing enhanced formation cuttings clearance from the bit face, through the junk slots, and into the well bore annulus above the bit.
2. State of the Art
Design of rotary drag bits employing superabrasive cutters, usually in the form of so-called “polycrystalline diamond compacts”, or “PDCs,” has reached a high degree of sophistication over the last several decades. Marked increases in rate of penetration (ROP) have been achieved. However, the inability of state-of-the-art rotary drill bits to clear formation cuttings at a rate commensurate with the bits' ability to generate such cuttings has proven to be a troublesome limitation to further increases in ROP.
Various designs and approaches have been employed in the art to facilitate cuttings removal from the bit, and thus facilitate increases in ROP. However, such designs and approaches have generally involved features which are not readily employable in bits of a variety of sizes and configurations, and many are limited to very specific configurations. Moreover, the prior art approaches have failed to consider and appreciate the tendency of poor cuttings clearance from a single blade of a multi-bladed bit to hinder ROP.
One prior art approach to cuttings removal from the bit involving a specialized bit design is disclosed in U.S. Pat. No. 5,417,296, wherein nozzles for supplying drilling fluid are placed both near the center of the bit and near the gage. An outer nozzle associated with one blade and fluid course on the bit face is oriented so as to provide a significant fluid flow component directed inwardly toward the centerline of the bit to augment the outward flow from an inner nozzle associated with another blade and fluid course through communication between the adjacent inner ends of the two fluid courses. Such an arrangement, in theory, enhances formation cuttings clearance, but it has been reported that this is not the case in practice. Specifically, cuttings from the blade with which the outer nozzle is associated are carried inwardly to a constriction between blades, causing clogging of the fluid course fronting that blade and consequent balling of the bit.
Accordingly, the art is, to date, devoid of enhancements to rotary drag bit design in terms of formation cuttings clearance readily applicable to improve the performance in terms of ROP of otherwise conventional bits.
SUMMARY OF THE INVENTION
The present invention provides enhancements to formation cuttings clearance from rotary drag bits through design enhancements readily implementable in a wide variety of blade-type rotary drag bits.
In one aspect, the present invention provides enhanced formation cuttings clearance through optimized distribution of hydraulic energy in the form of drilling fluid flow apportionment in relationship to the total volume of cuttings generated by different groups of cutters, typically those cutters grouped on each blade of a multi-bladed bit. Such apportionment may be achieved by employing nozzles of differing aperture sizes, and thus relative flow volumes, in association with blades generating differing formation cuttings volumes. For example, in a four-bladed bit with two primary blades and two secondary blades, the terms “primary” and “secondary” being indicative of their relative roles in volume of cuttings removed from the formation, the primary blades may each remove twice the cuttings volume as each of the secondary blades. Accordingly, in a one nozzle per blade bit, the nozzles associated with the primary blades are sized to provide substantially twice the fluid flow as those associated with the secondary blades.
In another aspect, the present invention provides optimized distribution of hydraulic energy through selective orientation, or “tilt”, of nozzles on the bit face in terms of angles relative to a line taken perpendicular to a tangent to the bit profile at the point the fluid jet from a nozzle impinges upon the formation being drilled. If the fluid jet is coincident with the line, substantially equal volumes of drilling fluid will flow outwardly toward the gage and inwardly toward the centerline or longitudinal axis, in the area defined between the bit face and the formation. A positive tilt, wherein a nozzle is oriented to direct a fluid jet from a point of origin radially inboard of the line, results in a greater fluid flow outwardly through a fluid course toward the gage rather than inwardly toward the centerline, enhancing clearance of formation cuttings from the blade fronted by that fluid course. Conversely, a negative tilt, wherein a nozzle is oriented to direct a fluid jet from a point of origin radially outboard from the line, results in a greater fluid flow inwardly along a fluid course toward the centerline than outwardly toward the gage, resulting in difficulty in clearing formation cuttings from the bit face. As noted with respect to the aforementioned '296 patent, such inward flow will tend to clog the fluid courses rather than clear them. The present invention employs positive tilt of the various nozzles on a bit face to ensure predominant outward flow of drilling fluid toward junk slots of the bit located proximate the bit gage, and to minimize cross-flow on the bit face between fluid courses with which different nozzles are associated.
In a further aspect of the invention, it may be desirable or required, due to the configuration or size of the bit, that fewer nozzles are employed than blades. In such an arrangement, a single nozzle may provide drilling fluid to two fluid courses, for example, one lying in front of a primary blade and the other in front of a secondary blade. Therefore nozzle orientation, or the orientation of the nozzle aperture, may be employed to allocate or apportion fluid flow from a single nozzle between the primary and secondary fluid courses, especially when the nozzle is placed at or near a convergence point of the two fluid courses. It should be noted that nozzle orientation may be altered in any direction, and not merely in terms of “tilt” along a radial line from the centerline of the bit to the gage, in order to bias nozzle flow toward a fluid course. In other words, to allocate or split flow between two fluid courses with which the nozzle is associated, normally by placement adjacent the radially inner ends of both, the “side to side” orientation of the nozzle or its aperture may be altered.
In yet another aspect, the present invention provides enhanced formation cuttings clearance through sizing the cross-sectional areas of junk slots associated with various blades of a bit in similar proportion to the total formation cuttings volume generated by each of the blades. Again taking a four-bladed bit having two primary and two secondary blades by way of example, if the primary blades each generate twice the formation cuttings volume of each secondary blade, the junk slots are sized in a similar ratio in terms of cross-sectional area transverse to the bit centerline.
In still another aspect of the invention, at least two of the above-described features are employed in the same bit to facilitate formation cuttings removal from the bit face and through the junk slots, to the well bore annulus above the bit.
The present invention also contemplates substantially balancing the cuttings volume removed by each of the primary blades of a multi-bladed bit with the volume removed by the other or others, and the cuttings volume removed by each of the secondary blades wi
Cooley Craig H.
Trujillo William R.
Baker Hughes Incorporated
Dang Hoang
TraskBritt
LandOfFree
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