Drill bit with staged durability, stability and ROP characteristics

Abstract

Drill bit with multiple stages of durability and ROP characteristics is disclosed. The drill bit has multiple layers of cutters established by deploying the cutters on blades of different heights or maintaining the blades at the same height and deploying the cutters to have different heights on one or more blades. Each layer provides independent bottom hole coverage and has independent stabilization, ROP, and durability characteristics so as to effectively drill through different subsurface formations. Cutters deployed on the different layers have their respective centers at substantially different radial positions. Due to the different radial positions, cutters in different layers cut different swaths in the subsurface formation. Cutters in different layers may also have different initial peripheral portions or shear lengths, resulting in different impact resistance characteristics for the different layers. This changes the wear and / or cutter deterioration processes for the different layers, resulting in different and / or improved toughness characteristics.

Description

CROSS REFERENCE TO RELATED APPLICATION [0001] This application for patent claims priority to, and hereby incorporates by reference, U.S. Provisional Application Ser. No. 60 / 746767, entitled “Drill Bit with Staged Durability and ROP Characteristics,” filed May 8, 2006 with the United States Patent and Trademark Office.FIELD OF THE INVENTION [0002] The present invention relates to rotary drill bits for rotary drilling of subterranean formations and, more specifically, to a rotary drill bit having multiple stages of durability and ROP (rate of penetration) characteristics. BACKGROUND OF THE INVENTION [0003] Subsurface formation drilling to recover hydrocarbons is well known in the art. The equipment for such subsurface formation drilling typically comprises a drill string having a rotary drill bit attached thereto that is lowered into a borehole. A rotary table or similar device rotates the drill string, resulting in a corresponding rotation of the drill bit. The rotation advances the ...

AI Technical Summary

Benefits of technology

[0017] Embodiments of the invention are directed to a drill bit, and method of assembling same, that can drill at economical ROPs for longer durations and in a wider range of formation materials. The drill bit has multiple layers of cutting elements established by deploying the cutting elements on blades of different heights or maintaining the blades at the same height and deploying the cutting elements to have different heights on one or more blades. Each layer provides independent bottom hole coverage and has independent stabilization, ROP, and durability characteristics so as to effectively drill through different subsurface formations. Cutting elements deployed in different layers have their respective centers at substantially different radial positions. Due to the different radial positions, cutting elements in different layers cut different respective swaths in the subsurface formation, and are thus loaded and deteriorate differently and independently of the other layers. Cutting elements in different layers may also have different initial peripheral portions or shear lengths, resulting in different impact resistance characteristics for the different layers. This drastically changes the wear and / or cutting element deterioration processes for the different layers, which results in different and improved toughness characteristics. In some embodiments, cutting elements deployed on different layers have different sizes, shapes, and / or back rake angles, respectively. In other embodiments, cutting elements deployed on different layers have different thermal stability, impact resistance, and / or abrasion resistance, respectively.

[0022] In general, in still another aspect, the invention is directed to a drill bit capable of effectively drilling in formations infested with chert, pyrite or nodules, where these specific materials are located at the top, middle or bottom sections of the formation interval, and where conventional drilling practices typically require the use of multiple drill bits, which may have drastic effects on drilling and operational costs.

Problems solved by technology

As the primary cutting elements progressively wear away, however, the secondary cutting elements compensate increasingly more for the decreased effectiveness of the primary cutting elements in terms of bit durability and ROP.

Because they cut the same swath the primary layer and secondary layer do not establish independent coverage of the bottom hole.

This arrangement has a negative effect on overall bit performance, especially durability or longevity.

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