Borehole Drilling Methods

Air rotary drilling is a method for wellbore excavation. It involves the circulation of air through the drill pipe to cool the spinning drill bit. Air rotary drilling is used to drill deep boreholes in rock formations and may be effective where other drilling methods fail. It’s one of the excavation techniques available to trenchless construction operators. Air rotary drilling may also be referred to as rotary air blast drilling.

A method of drilling whereby an impact tool or bit, suspended in the well from a steel cable, is dropped repeatedly on the bottom of the hole to crush the rock. The tool is usually fitted with some sort of cuttings basket to trap the cuttings along the side of the tool.

Drilling mud, also called drilling fluid, aids in the process of drilling a borehole into the earth. Such holes are drilled for oil and gas extraction, core sampling, and other purposes.

The reverse circulation drilling system is quite unlike any of the other systems profiled in that it is a very large rig requiring a big footprint for both the rig itself, as well as the machine-dug settling pit.

Hand sludging (also known as Asian, or Indian sludging) is a traditional technique used in parts of Nepal, India, and Bangladesh. It involves reciprocating a steel pipe (of 25 to 40mm diameter) vertically in a shallow pit, which is kept full of water. The reciprocating action is achieved by a lever, which is attached to a bamboo frame. One operator operates the lever while the other uses his hand over the top like a flap valve. On the upstroke, the hand covers the pipe, while on the downstroke it lifts off. This action enables the cuttings to be carried up through the drill pipe and exit at the top.

Jetting is considered to be a manual drilling technology, even though it utilizes a small pump. The technique involves pumping water (with a hand, or motorized pump), down the drill pipe, which is held vertically in the hole.