Boring or penetrating the earth – Natural vibration characteristic of an element of boring...
Reexamination Certificate
1999-01-12
2002-01-15
Neuder, William (Department: 3672)
Boring or penetrating the earth
Natural vibration characteristic of an element of boring...
C175S381000
Reexamination Certificate
active
06338390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to methods of drilling subterranean formations using rotary-type drag bits, and more particularly to such methods employing an oscillating drill bit for more effective removal of formation chips from around the drill bit using drilling fluid.
2. Description of Related Art
Fixed-cutter rotary drag bits have been employed in subterranean drilling for many decades with various sizes, shapes and patterns of natural and synthetic diamonds used on drag bit crowns as cutting elements. Rotary drag-type drill bits typically comprise a bit body having a shank for connection to a drill string and an inner channel for supplying drilling fluid to the face of the bit through nozzles or other apertures. Drag bits may be cast and/or machined from metal, typically steel, or may be formed of a powder metal (typically tungsten carbide (WC)) infiltrated at high temperatures with a liquified binder material (typically copper-based) to form a matrix. Such bits may also be formed with layered-manufacturing technology, as disclosed in U.S. Pat. No. 5,433,280, which is assigned to the assignee of the present invention and incorporated herein by reference.
The bit body typically carries a plurality of cutting elements which is mounted directly on the face of the bit body or on carrier elements. The cutting elements are positioned adjacent fluid courses which allow cuttings (i.e., formation chips) generated during drilling to flow from the cutting elements to and through junk slots on the gage of the bit. The cuttings then move to the borehole annulus above the bit. Cutting elements may be secured to the bit by preliminary bonding to a carrier element, such as a stud, post, or cylinder, which is, in turn, inserted into a pocket, socket, recess or other aperture in the face of the bit and mechanically or metallurgically secured thereto.
One type of drag bit includes polycrystalline diamond compact (PDC) cutters typically comprised of a diamond table (usually of circular, semi-circular or tombstone shape) which presents a generally planar cutting face. A cutting edge (sometimes chamfered or beveled) is formed on one side of the cutting face which, during boring, is at least partially embedded into the formation so that the formation impacts at least a portion of the cutting face. As the bit rotates, the cutting face contacts the formation and a chip of formation material shears off and rides up the surface of the cutting face. When the bit is functioning properly, the chip breaks off from the formation and is transported out of the borehole via circulating drilling fluid. Another chip then begins to form in the vicinity of the cutting edge, slides up the cutting face of the cutting element, and breaks off in a similar fashion. Such action occurring at each cutting element on the bit removes formation material over the entire gage of the bit, and thereby causes the borehole to become progressively deeper.
In some subterranean formations, PDC cutting elements are very effective in cutting the formation as the drag bit rotates and the cutting edge of the cutting element engages the formation. However, in certain formations exhibiting plastic behavior, such as highly pressurized deep shales, mudstones, siltstones, some limestones and other ductile formations, the formation chips have a marked tendency to adhere to the leading surface of the bit body and the cutting face of the cutting element.
When formation chips adhere to the cutting elements, fluid courses or junk slots of the drill bit, the accumulated mass of chips impedes the flow of drilling fluid to the cutters and impedes the flow through the fluid courses and junk slots resulting in the reduction of cooling efficiency of the drilling fluid. Additionally, adherence of formation chips at or near the cutting faces of the cutting elements can actually prevent chips from sliding over the cutting face resulting in reduced cutting efficiency.
When these formation chips adhere to the cutting face of a cutting element, they tend to collect and build up as a mass of cuttings ahead of and adjacent to the point or line of engagement between the cutting face of the PDC cutting element and the formation, potentially increasing the net effective stress of the formation being cut. The buildup of formation chips moves the cutting action away from and ahead of the edge of the PDC cutting element and alters the failure mechanism and location of the cutting phenomenon so that cutting of the formation is actually effected by the built-up mass, which obviously is quite dull. Thus, the efficiency of the cutting elements, and hence of the drag bit itself, is drastically reduced.
Undesired adhesion of formation cuttings to the PDC cutting elements has long been recognized as a problem in the subterranean drilling art. A number of different approaches have been attempted to facilitate removal of formation cuttings from the cutting face of PDC cutting elements. For example, U.S. Pat. No. 5,582,258 to Tibbitts et al., assigned to the assignee of the present invention and herein incorporated by this reference, includes a chip breaker formed adjacent the cutting edge of the cutting elements to impart strain to a formation chip by bending and/or twisting the chip and thereby increasing the likelihood that the chip will break away from the face of the bit. Other approaches to solving the problem of formation chip removal include U.S. Pat. No. 4,606,418 to Thompson which discloses cutting elements having an aperture in the center thereof which feeds drilling fluid from the interior of the drill bit onto the cutting face to cool the diamond table and to remove formation cuttings.
U.S. Pat. No. 4,852,671 to Southland discloses a diamond cutting element which hag a passage extending from the support structure of the cutting element to the extreme outermost portion of the cutting element, which is notched in the area in which it engages the formation being cut so that drilling fluid from a plenum on the interior of the bit can be fed through the support structure and to the edge of the cutting element immediately adjacent the formation. U.S. Pat. No. 4,984,642 to Renard et al. discloses a cutting element having a ridged or grooved cutting face on the diamond table to promote the break-up of formation chips, or in the case of a machine tool, the break-up of chips of material being machined, and enhance their removal from the cutting face. The irregular topography of the cutting face assists in preventing balling or clogging of the drag bit by reducing the effective surface or contact area of the cutting face, which also reduces the pressure differential of the formation chips being cut. U.S. Pat. No. 5,172,778 to Tibbitts et al., assigned to the assignee of the present application, employs ridged, grooved, stair-step, scalloped, waved and other alternative non-planar cutting surface topographies to permit and promote the access of fluid in the borehole to the area on the cutting element cutting face immediately adjacent to and above the point of engagement with the formation. Such a non-planar cutting surface helps to equalize differential pressure across the formation chip being cut and thus reduce the shear force which opposes chip movement across the cutting surface.
U.S. Pat. No. 4,883,132 to Tibbitts, assigned to the assignee of the present application, discloses a novel drill bit design providing large cavities between the face of the bit and the cutting elements engaging the formation. Formation cuttings entering the cavity area are thus unsupported and more likely to break off for transport up the borehole. In addition, clearing of the cut chips is facilitated by nozzles aimed from behind the cutting elements (taken in the direction of bit rotation) so that the chips are impacted in a forward direction to break off immediately after being cut from the formation. U.S. Pat. No. 4,913,244 to Trujillo, assigned to the assignee of the present invention, discloses bits which employ large cut
Baker Hughes Incorporated
Neuder William
TraskBritt
LandOfFree
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