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Drilling in sensitive formations

A significant change occurs when the medium (air/water) leaves the hammer and changes function – from powering the DTH hammer to acting as a borehole cleaner and bringing the cuttings up to surface. As soon as water – which is not a compressible medium – leaves the drill bit, the pressure drops considerably and reaches the state of hydrostatic pressure.

Air, however, expands as soon as it leaves the drill bit and enters the surrounding formation. The air starts expanding, accelerating the cuttings up towards the surface at a speed of up to 80 meter per second (179 mph). This exposes the drill string and, even more importantly, the surrounding formation to high levels of stress. Unstable soft formations are at even greater risk, as compressed air will always find the "easiest" way out. This can be through the formation rather than up through the borehole. Accordingly, drilling in sensitive formation, such as close to a dam or in an inner city environment, can result in severe damage to the surrounding infrastructure.

Urban areas are usually "sensitive" in the sense that they have a limited capacity to absorb movements and/or changes in groundwater levels due to drilling operations. Furthermore, the injection of air or oil into the ground is typically prohibited. Due to the incompressible nature of the water flush, and its low "up-hole velocity", over-pressurization risks are minimized. This is not the case with compressed air.

Water-powered DTH's do not create dust and do not require any lubricants, the water used to power the hammer is the lubricant.

Water-powered drilling gives a safer working environment.

The water-powered drilling uses no additives, only plain water. As the water itself gives sufficient lubrication to the equipment, no oil is required. Air-powered drilling equipment often uses oil for lubrication. After passing the drill bit, the oil will get introduced to the environment.

All dust from the drill cuttings will be effectively bound and flushed to the surface when drilling with water-powered equipment. When drilling with air-powered equipment, the dust handling requires particular measures.

If a high-pressure water hose should fail, the pressure immediately disappears. Just like a garden hose, the supplying hose will lose the stiffness caused by the high-pressure water. A failing hose used for air-powered drilling will act like a powerful whip, bringing very high risk of harming both equipment and people.