Stable Rotary Drill Bit

Abstract

A drill bit comprises a bit body having a plurality of upstanding main blades formed thereon. The main blades have a plurality cutting elements mounted thereon, and they are shaped such that a cutting profile of the bit includes a nose portion, an inner cone region located radially inwards of the nose portion and an outer region located radially outwards of the nose portion. The bit further has at least one additional blade. The additional blade carrying cutting elements located radially inwards of the outer region of the cutting profile, but being substantially free of cutting elements located in the outer region of the cutting profile.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to a rotary drill bit that is vibrationally stable, and in particular to a rotary drill bit suitable for use in the formation of subterranean well bores. [0002] The cost of drilling a borehole in the subsurface formations of the Earth is dependent on the length of time taken to drill the borehole to the desired depth. The time spent drilling is in turn determined by the rate of penetration and the number of times the drill bit has to be changed in order to achieve the target depth. [0003] A known form of drill bit for use in the formation of subterranean well bores comprises a bit body having formed thereon a series of upstanding blades. Each blade is provided with a series of cutting elements. The cutting elements each typically comprise a substrate of, for example, tungsten carbide to which is bonded a table of a superhard material, for example in the form of polycrystalline diamond. Between the blades are formed flow chann...

AI Technical Summary

Benefits of technology

[0008] Such an arrangement is advantageous in that the number of cutters located in the cone region, relative to the number of cutters on the outer region, can be increased, and these additional cutters create a restoring force to prevent the drill bit moving off its center of rotation while drilling. This can be used to achieve an improvement in bit stability, reducing lateral vibration thereof.

[0009] The outer regions of the additional blades are conveniently of increased blade height as compared to the outer regions of the main blades. As a result, during drilling, the outer regions of the additional blades can bear against the surface of the formation being drilled, thereby limiting the depth of cut achievable by the cutting elements, and this can be used to limit lateral and torsional vibration.

[0012] The outer surface of the outer regions of the additional blades may be rendered of improved resistance to wear. This could be achieved for example by mounting suitably shaped and positioned, non-cutting, polycrystalline diamond compact elements thereon. Alternatively, or additionally, a hard facing material coating may be applied thereto.

Problems solved by technology

As a result, during drilling, the outer regions of the additional blades can bear against the surface of the formation being drilled, thereby limiting the depth of cut achievable by the cutting elements, and this can be used to limit lateral and torsional vibration.

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