Bearing blocks for drill bits, drill bit assemblies including bearing blocks and related methods

Abstract

Methods of drilling subterranean formations include coupling at least one bearing block having an initial thickness to a drill bit, engaging a formation with the drill bit within an initial depth of cut range, and reducing the initial thickness of the bearing block by contacting the formation to cause the initial depth of cut range to be at least partially increased. Methods of forming drill bits for drilling subterranean formations include forming at least one rubbing surface of at least one bearing block from at least one material exhibiting a reduced coefficient of friction and coupling the at least one bearing block to the drill bit. Drill bit assemblies include at least one bearing block having a distal portion configured to provide an initial depth of cut range and a base portion configured to provide an increased depth of cut range greater than the initial depth of cut range.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61 / 174,412, filed Apr. 30, 2009, the disclosure of which is hereby incorporated herein by this reference in its entirety.[0002]The application is also related to, but does not claim priority to, copending U.S. patent application Ser. No. 11 / 818,820, filed Jun. 14, 2007, the disclosure of which is hereby incorporated herein by this reference in its entirety.TECHNICAL FIELD[0003]The present invention, in several embodiments, relates generally to a rotary fixed cutter or “drag” drill bit employing superabrasive cutters for drilling subterranean formations and, more particularly, to use of bearing blocks in association with superabrasive cutters to provide improved accuracy for obtaining one or more target depths of cut for the cutters, a controlled bearing area on the face of the drill bit, or both. Methods of drilling are also encompassed by embodiments of t...

AI Technical Summary

Benefits of technology

[0013]In some embodiments, the present invention includes a method of drilling a subterranean formation comprising coupling at least one bearing block having at least one rubbing surface and an initial thickness to a drill bit, engaging a formation with at least one cutter of the drill bit within an initial depth of cut range, drilling the formation with the drill bit, and reducing the initial thickness of the bearing block by contacting the formation with the at least one rubbing surface to cause the initial depth of cut range to be at least partially increased.

[0014]In additional embodiments, the present invention includes a method of drilling a subterranean formation. The method includes coupling at least one bearing block having at least one rubbing surface and an initial thickness to a drill bit, engaging a formation with at least one cutter of the drill bit within an initial depth of cut range, drilling the formation with the drill bit, and increasing the initial depth of cut range by contacting the formation with the at least one rubbing surface to cause the initial thickness of the bearing block to be at least partially reduced. The method may, optionally, also include selecting one or more materials for the bearing block to wear at a predictable rate when engaged with a particular formation material or materials.

Problems solved by technology

Even in view of such improvements, however, PDC cutters still suffer from what might simply be termed “overloading” even at low weight-on-bit (WOB) applied to the drill string to which the bit carrying such cutters is mounted, especially if aggressive cutting structures are employed.

The problem of excessive bit aggressiveness is particularly significant in low compressive strength formations where an unduly great depth of cut (DOC) may be achieved at extremely low WOB.

The problem may also be aggravated by drill string bounce or torque and drag, wherein the elasticity of the drill string may cause erratic application of WOB to the drill bit or the drill pipe dragging on the wall of the borehole, with consequent overloading.

Moreover, operating PDC cutters at an excessively high DOC may generate more formation cuttings than can be consistently cleared from the bit face and back up the bore hole via the junk slots on the face of the bit by even the aforementioned improved, state-of-the-art bit hydraulics, leading to the aforementioned bit balling phenomenon.

Another, separate problem involves drilling from a zone or stratum of higher formation compressive strength to a “softer” zone of lower compressive strength.

The abruptly higher torque, in turn, may cause damage to the cutters and / or the bit body itself In directional drilling, such a change causes the tool face orientation of the directional (measuring-while-drilling, or MWD, or a steering tool) assembly to fluctuate, making it more difficult for the directional driller to follow the planned directional path for the bit.

In addition, a downhole motor, such as drilling fluid-driven Moineau-type motors commonly employed in directional drilling operations in combination with a steerable bottomhole assembly, may completely stall under a sudden torque increase.

Such interruptions in the drilling of a well can be time consuming and quite costly.

While some of the foregoing patents recognize the desirability to limit cutter penetration, or DOC, or otherwise limit forces applied to a borehole surface, the disclosed approaches are somewhat generalized in nature and fail to accommodate or implement an engineered approach to achieving a target ROP in combination with more stable, predictable bit performance.

Furthermore, the disclosed approaches do not provide a bit or method of drilling which is generally tolerant to being axially loaded with an amount of weight-on-bit over and in excess what would be optimum for the current rate-of-penetration for the particular formation being drilled and which would not generate high amounts of potentially bit-stopping (e.g., stick-slip) or bit-damaging torque-on-bit should the bit nonetheless be subjected to such excessive amounts of weight-on-bit.

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