Drill bit

Abstract

The present invention provides a drill bit (1), and a method for its manufacture, that is suitable for use within a casing drilling process. The drill bit (1) comprises a monolithic body (5, 6, 8) made from bronze, e.g. aluminium bronze or nickel aluminium bronze, and a relatively hard material mounted thereon. The hard material may comprise polycrystalline diamond (PDC), tungsten carbide or cubic boron nitride. In one embodiment the monolithic body comprises a crown (6) and a plurality of cutting members (5). The hard material may be mounted directly on the crown or, alternatively, on the cutting members (5). The described drill bit (1) facilitates the drilling of hard rock formations while still being capable of being drilled through by a standard oilfield drill bit.

Description

[0001]The present invention relates to the field of hydrocarbon exploration. More specifically, the present invention concerns a drill bit suitable for use within a casing drilling process.[0002]When drilling subterranean formations for the purpose of hydrocarbon exploration it is known in the art to initially drill a first section of a well bore having a first diameter and thereafter to remove the drill bit from the well bore. A first tubular member of lesser diameter, known as casing string, is then placed in the well bore and subsequently the annulus between the well bore and the outside of the casing string is filled with a cement. The purpose of the cement is to isolate certain of the subterranean strata from each other. The next stage of the operation involves passing a second drill bit, having a smaller diameter than the first, through the casing string so as to permit the drilling of a second section of the well bore beyond the previously attained depth of the first section....

AI Technical Summary

Benefits of technology

[0033]mounting a relatively hard material on the monolithic body so as to provide a means for cutting earth or rock.

Problems solved by technology

The cost of oil exploration particularly in offshore regions is extremely high.

At great depths, the round trip time to pull out a drill bit and replace it with another one can be many hours.

A limiting factor in many of the traditional techniques known in the art is the form of the drill bit.

However, modern drill bits optimised for rock removal are generally unable to drill through the materials from which they themselves are constructed without sustaining a level of damage which would render the task of drilling the next section of rock formation impossible.

It is possible to drill through these traditional drill bits with a special tool known as a mill, but these tools are unable to effectively penetrate the subsequent rock formations and so the mill would have to be removed from the well bore and replaced with an appropriate drill bit.

In these circumstances, the trip saving advantage gained by drilling with the casing string would be lost.

The casing drilling shoe described in PCT application number PCT / GB99 / 01816 is extremely expensive to produce due to the requirement to incorporate a displaceable outer drilling section.

In practice, these tools are also found to be sensitive to vibration and so they are not particularly robust which can cause mechanical failure during the drilling process.

A further drawback of the described tool is the use of aluminium for the inner section.

These strands then wrap themselves around the secondary drill bit so reducing the efficiency of any subsequent drilling process.

Furthermore, aluminium is easily eroded by the action of the drilling fluids which are necessarily used to clean the well bore.

In practice, and as recognised within the application itself, direct application of the relatively hard coatings to the crown and cutting member materials is difficult and in some combinations are just not practical.

For example, extremely hard tungsten carbide particles cannot easily be applied to crown sections when these are made from aluminium.

It is also recognised within the application that the described drill bit is not readily suitable for drilling through hard formations.

When deployed with hard formations the fragments of the relatively hard material tend to be sheared away from the crown section, thus quickly reducing the efficiency of the drilling process.

However, as is recognised in the art, lower blade heights generally result in lower drilling rates.

Such modifications to the casing bit however can be detrimental to the rate at which it can drill the subterranean formations and also the distance that the drill bit may drill before wearing out.

The requirement of a bespoke secondary drill bit to drill through the casing systems of PCT application number PCT / US2005 / 004106 has obvious disadvantages since in the absence of such a bit the drilling operation is required to be suspended.

This often results in the mechanical failure of the standard drill bit leading to increased down time as the damaged drill bit and associated debris have to be removed from the well bore.

Furthermore, the design of the bespoke secondary drill bit may not be ideally suited to the particular formations that need to be drilled in the section below the casing drill bit.

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