Hybrid drill bit

Abstract

A drill bit for coupling in use downhole drilling apparatus, the drill bit comprising: an annular coring drill bit that is rotatable to cut a formation bore face to create a core plug, a concentric drill bit that can be repeatedly axially moved (such as by oscillation (such as a vibration) and / or impact) to break the core plug.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a drill bit for use in drilling apparatus. For example, it can be used in a reverse circulation drilling apparatus, and a reverse circulation drilling apparatus utilising such a drill bit. The drill bit can also be for use in a borehole drilling apparatus, and such a borehole drilling apparatus can utilise such a drill bit. Such a drill bit could be used in dry formations and also flooded environments.BACKGROUND[0002]Reverse circulating (RC) drilling is used within the mineral exploration sector. The objective is to drill rapidly through formations (often very hard) to sample for various valuable minerals. There are two main types of RC drilling.[0003]One is, air (pneumatic) reverse circulation drilling. This is the most common method, whereby large air compressors pump large volumes of compressed air down the outer cavity of dual walled drill rods. The compressed air: a) energises an air hammer for rapid penetration of ha...

AI Technical Summary

Benefits of technology

The present invention is a drill bit that can be used with lower energy drilling fluid driven hammer / oscillation tools. It combines the benefits of aggressively shaped angled inserts and conservatively shaped inserts by using a concentric coring bit with inner and outer rows of bit inserts that run in the axial direction of the bore hole. The bit inserts are tapered to increase point loading and promote core plug breaking, and are at right angles to the concentric drill bit face. The repeatable force generating apparatus provides a vibration to the annular coring bit sufficient to enhance the performance of the coring bit. The drill bit works in conjunction with fluid driven hammer / oscillation tools with modest energy output and can work in flooded environments with strong drilling performance and good bit life.

Problems solved by technology

While effective in dry competent formations, pneumatic hammers struggle as they encounter groundwater (a common occurrence) to the point that they cease to operate.

In addition even in dry formations the volume of compressed air that needs to be pumped down deep holes becomes impractical.

In addition the very large compressors required are extremely expensive to operate, as well as being potentially dangerous.

This increase becomes impractical, more expensive and dangerous at large depths due to the larger compressors posing significant safety concerns to operators such that the increased expense and safety concerns outweighs the benefits.

However to date, commercially available fluid hammers only work with very clean water, and are not able to survive with recycled drilling fluids.

This makes them commercially impractical, except for niche applications where a ready supply of clean water is available, i.e., modifying water with drilling mud for bore control is not required.

This means that when they are used with conventional impact “hammer bits” the performance is less than desirable.

However, such apparatus have less impact energy than pneumatic hammers.

The use of aggressively shaped inserts in hard formations is desirable to assist drilling—however the angled outer rows of the conventional hammer bit fail prematurely in these applications.

Tougher rounded inserts on the angled gauge rows could be used, however this results in unsatisfactory drilling performance when used with lower energy tools.

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