Boring or penetrating the earth – Bit or bit element – With fluid conduit lining or element
Reexamination Certificate
1999-10-06
2001-10-16
Dang, Hoang (Department: 3672)
Boring or penetrating the earth
Bit or bit element
With fluid conduit lining or element
C175S394000, C175S408000
Reexamination Certificate
active
06302223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to rotary drilling of subterranean formations and, more specifically, to a rotary drill bit exhibiting particularly beneficial characteristics for drilling slow drilling shales as well as for high rate of penetration drilling.
2. State of the Art
Equipment used in subterranean drilling operations is well known in the art and generally comprises a rotary drill bit attached to a drill string, including drill pipe and drill collars. A rotary table or other device such as a top drive is used to rotate the drill string from a drilling rig, resulting in a corresponding rotation of the drill bit at the free end of the string. Fluid-driven downhole motors are also commonly employed, generally in combination with a rotatable drill string, but in some instances as the sole source of rotation for the bit. The drill string typically has an internal bore extending from and in fluid communication between the drilling rig at the surface and the exterior of the drill bit. The string has an outer diameter smaller than the diameter of the well bore being drilled, defining an annulus between the drill string and the wall of the well bore for return of drilling fluid and entrained formation cuttings to the surface.
An exemplary rotary drill bit includes a bit body secured to a steel shank having a threaded pin connection for attaching the bit body to the drill string, and a body or crown comprising that part of the bit fitted on its exterior with cutting structures for cutting into an earth formation. Generally, if the bit is a fixed-cutter or so-called “drag” bit, the cutting structure includes a plurality of cutting elements including cutting surfaces formed of a superabrasive material such as polycrystalline diamond and oriented on the bit face generally in the direction of bit rotation. A drag bit body is generally formed of machined steel or a matrix casting of hard particulate material such as tungsten carbide in a (usually) copper-based alloy binder.
In the case of steel body bits, the bit body is usually machined, typically using a computer-controlled five-axis machine tool, from round stock to the desired shape, including internal watercourses and passages for delivery of drilling fluid to the bit face, as well as cutting element pockets or sockets and ridges, lands, nozzle displacements, junk slots and other external topographic features. Hardfacing is applied to the bit face and to other critical areas of the bit exterior, and cutting elements are secured to the bit face, generally by inserting the proximal ends of studs on which the cutting elements are mounted into apertures (sockets) bored into the bit face or, if cylindrical cutting elements are employed, by inserting the substrates into pockets bored into the bit face. The end of the bit body opposite the face is then threaded, made up and welded to the bit shank.
The body of a matrix-type drag bit is cast in a mold interiorly configured to define many of the topographic features on the bit exterior, with additional preforms placed in the mold defining the remainder of such features as well as internal features such as watercourses and passages. Tungsten carbide powder and sometimes other metals to enhance toughness and impact resistance are placed in the mold under a liquefiable binder in pellet form. The mold assembly, including a steel bit blank having one end inserted into the tungsten carbide powder, is placed in a furnace to liquify the binder and form the body matrix with the steel bit blank integrally secured to the body. The blank is subsequently affixed to the bit shank by welding. Superabrasive cutting elements, also termed “cutters” herein, may be secured to the bit face during the furnacing operation if the elements are of the so-called “thermally stable” type, or may be brazed by their supporting (usually cemented WC) substrates to the bit face, or to WC preforms furnaced into the bit face during infiltration. Such superabrasive cutting elements include polycrystalline diamond compacts (PDCs), thermally stable polycrystalline diamond compacts (generally termed “TSPs” for thermally stable products), natural diamonds and, to a lesser extent, cubic boron nitride compacts.
During a typical drilling operation using such a rotary bit, drilling fluid is pumped from the surface through the internal bore of the drill string to the bit (except in a reverse flow drilling configuration such as is described in U.S. Pat. No. 4,368,787, wherein drilling fluid passes down the annulus and up the interior of the drill string). In conventional bits, the drilling fluid flows out of the drill bit through a crow's foot or one or more nozzles placed at or near the bit face for the purpose of removing formation cuttings (i.e., chips of material removed from the formation by the cutting elements of the drill bit) and to cool the cutting elements, which are frictionally heated during cutting. Both of these functions are extremely important for the drill bit to efficiently cut the formation over a commercially viable drilling interval. That is, because of the weight on bit (WOB) applied by the drill string necessary to achieve a desired rate of penetration (ROP) and the frictional heat generated on the cutters due to WOB and rotation of the bit, without drilling fluid or some other means of cooling the bit, materials comprising the drill bit and particularly the cutting elements attached to the bit face would structurally degrade and prematurely fail. Moreover, even if it were possible to cool the bit without drilling fluid but no means of removing the cuttings from the bit face was employed, the cutting elements (and the bit) would simply become balled up with material cut from the formation and would not be able to effectively engage and further penetrate into the formation to advance the well bore.
The need to efficiently remove cuttings from the bit during drilling has long been recognized in the art. Junk slots formed on the exterior of the bit body adjacent the gage of the bit provide channels for drilling fluid to flow from the face of the drill bit past the gage and to the annulus above, between the drill string and the side wall of the well bore, generally termed the well bore annulus. The pressure of the drilling fluid as delivered to the cutting elements through the nozzles or other ports or openings must be sufficient to overcome the hydrostatic head at the drill bit, and the flow velocity sufficient to carry the drilling fluid with entrained cuttings through the well bore annulus to the surface.
In a conventional bladed rotary drill bit, there may be a plurality of nozzles, each associated with one or more blades, the nozzles directing drilling fluid to cool and clean cutting elements of the blades. There may also be a plurality of junk slots, positioned between the blades and extending along the gage of the bit, to promote the flow of drilling fluid along each blade through its respective, associated junk slot. However, because the position and angular orientation of each nozzle is usually different relative to the centerline of the bit, and nozzle flow volumes may vary due to the hydraulics of the internal bit passages delivering the drilling fluid to the nozzles, the magnitude and orientation of flow energy of the drilling fluid will vary from one junk slot to the next. Consequently, because a relatively higher flow energy generates an adjacent zone or area of relatively lower hydraulic pressure in the manner of a venturi, drilling fluid emanating from a particular nozzle that would ideally flow past the desired cutting elements of a particular blade and up through the associated junk slot may actually be pulled or drawn downward and even laterally (circumferentially) across the exterior of the blade into a low pressure zone created by a fluid jet of another junk slot. In effect, some junk slots of conventional bits will have a positive or upward flow of drilling mud, while others will have a negative or downward flow resulting from thi
Baker Hughes Incorporated
Dang Hoang
TraskBritt
LandOfFree
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