Drill bit having increased resistance to fatigue cracking and method of producing same

Abstract

The present invention relates to a roller cone drill bit that includes a bit body adapted to be rotated about a longitudinal axis, where the bit body has at least one leg depending therefrom, wherein the leg comprises a treated portion that provides a residual compressive stress, and a roller cone rotatably mounted on a journal. The treated portion treatment may comprise one selected from shot peening, laser-shock peening, and hammer peening. Further, the present invention relates to a method of manufacturing a roller cone drill bit that includes inducing a compressive stress, through plastic deformation, in at least a portion of at least one leg depending from a bit body. The inducing a compressive stress may comprise one selected from shot peening, laser-shock peening, and hammer peening.

Description

BACKGROUND OF INVENTION [0001] 1. Field of the Invention [0002] The invention is related generally to the field of roller cone drill bits. More particularly, the invention is related to methods for increasing the durability of a roller cone bit. [0003] 2. Background Art [0004] Drill bits used to drill wellbores through earth formations generally fall within one of two broad categories of bit structures. Shear cutter bits are configured with a multitude of cutting elements directly fixed to the bottom, also called the face, of the drill bit. The shear bit has no moving parts, and its cutters scrape or shear rock formation through the rotation of the drill bit by an attached drill string. Shear cutter bits have the advantage that the cutter is continuously in contact with the formation and see a relatively uniform loading when cutting the gage formation. [0005] Furthermore, the shear cutter is generally loaded in only one direction. This significantly simplifies the design of the shea...

AI Technical Summary

Problems solved by technology

However, although shear bits have been found to drill effectively in softer formations, as the hardness of the formation increases, it has been found that the cutting elements on the shear cutter bits tend to wear and fail, affecting the rate of penetration (ROP) for the shear cutter bit.

A number of different forces can result in early failure of roller cone bits.

These stresses tend to be very high and are cyclical.

As a result, it is common for the cone to crack within some of the sockets.

Cracking in one or more of the sockets can result in loss of the inserts pressed into the sockets that undergo cracking, or can result in total cone failure.

However, while various improvements have been made in reducing the failure rate on the cones, as described in the above patents, less attention has been paid to the other surfaces of the bit.

In particular, the legs are subject to tensile stresses which lead to cracks in the surface, potentially resulting in breakage and failure of the bit.

In particular, a portion of backturn surface of the leg has a low section modulus, which leads to a high failure rate.

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