Drill bits and tools for subterranean drilling

Abstract

A drill bit includes at least one extension pad extending rotationally forward or backward of an associated blade in a gage region of the bit body. The extension pad includes a circumferential bearing surface that extends the circumferential bearing surface of the associated blade and reduces the chordal drop between any blade having an extension pad associated therewith and a circumferentially adjacent blade toward which the extension pad protrudes. A drill bit that reduces a chordal drop segment extending across a junk slot is also disclosed.

Description

FIELD OF INVENTION[0001]The invention, in various embodiments, relates to drill bits and tools for subterranean drilling and, more particularly, to a drill bit or tool incorporating structure for enhancing stabilization and reducing lateral motion.BACKGROUND[0002]Fixed cutter rotary drill bits for subterranean earth boring have been employed for decades. It is well known that increasing the rotational speed of such drill bit, for a given weight on bit and subject to the ability of the bit's hydraulic structure to adequately clear formation cuttings from the bit, increases the rate of penetration of the drill string. However, increased rotational speed also tends to decrease the life of a drill bit due to premature damage to and destruction of cutting elements, commonly polycrystalline diamond compacts (PDC's).[0003]It has been recognized that cutting element destruction, particularly at higher rotational speeds, is at least in part attributable to a phenomenon known as “whirl” or “b...

AI Technical Summary

Benefits of technology

[0008]In one embodiment, a drill bit includes at least one extension pad for increasing stability and reducing lateral motion acting on the drill bit while drilling a subterranean formation. The drill bit includes a bit body having a face extending to a gage region, at least one blade extending longitudinally and radially outward over the face of the bit body from a longitudinal axis thereof, the at least one blade including an extension pad substantially contiguous with the blade in the gage region of the bit body. The extension pad includes a circumferential bearing surface that rotationally precedes or trails the blade, with respect to the direction of intended bit rotation about the longitudinal axis. The blade may also include a circumferential bearing surface as extended by the extension pad.

[0009]In other embodiments, a drill bit comprises at least one extension pad extending into an open fluid course circumferentially between two blades, the fluid course communicating with a junk slot of the drill bit. The extension pad is configured and positioned to reduce a chordal drop segment and to improve stability of the drill bit by reducing the extent to which lateral motion may occur while drilling a subterranean formation.

Problems solved by technology

However, increased rotational speed also tends to decrease the life of a drill bit due to premature damage to and destruction of cutting elements, commonly polycrystalline diamond compacts (PDC's).

In the latter instance, aggressive cutter placement and orientation creates a high tangential cutting force relative to the normal force applied to the bit and aggravates the imbalance.

In any event, these imbalance forces tend to cause the drill bit to rotate or roll about the bore hole in a direction counter to the normal direction of rotation imparted to the bit during drilling.

Furthermore, while the prior art provides for focusing or directing the imbalance forces as a resultant side force vector toward a particular side of the bit, it does so by compromising aggressiveness of the bit, particularly affecting the placement and aggressiveness of cutting elements.

Moreover, while the above-referenced patents reduce hole wall tangential forces which are generally noted to induce whirl, they do not protect the cutting elements from chipping as a result of the impact loads caused by vibrational instabilities commensurate with bit whirl, particularly when drilling in harder subterranean formations.

Damage to the cutting elements may also be mitigated by increasing the circumferential width of the of the bearing surface, which undesirably reduces the hydraulic cross-section available for the junks slot, thus reducing hydraulic flow of drilling fluid and potentially decreasing the volume of cuttings which may be carried therethrough by the drilling fluid.

While these so called “steering wheel” bits may increase stability by militating against vibrational instabilities and enhance the ability of such bits to hold bore hole gage diameter, such bits undesirably increase the outer perimeter surface of the bit bearing on the bore hole side wall, making directional drilling more difficult.

Furthermore, the configuration of such so called “steering wheel” bits also undesirably reduces the available hydraulic cross-section of the junk slots and may restrict formation cuttings removal from the bit face by substantially circumscribing the flow channels provided by the junk slots.

In additional the configuration of the steering wheel bits impedes tripping the bit in and out of the bore hole, and may cause swabbing (removal of formation material from the bore hole side wall) during tripping.

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