25/04/2026
Air percussion drilling is one of the fastest and most common methods for drilling through hard rock formations. It is widely used in Namibia because much of the country consists of very hard underground terrain.
How it Works: The Mechanics
The core of the process is a combination of impact and rotation, powered by high-pressure compressed air.
The Hammer and Bit: A pneumatic hammer is attached to the bottom of the drill string. Air pressure forces an internal piston to move up and down at high speeds, repeatedly striking the drill bit against the rock.
Crushing: Unlike a wood drill that cuts, air percussion crushes the rock into small fragments (chippings and dust).
Debris Removal: The air that powers the hammer escapes through holes in the drill bit. This airflow blows the rock cuttings up the outside of the drill pipes to the surface. This is why you often see a large cloud of dust at the borehole.
Rotation: While the hammer is striking, the drill string rotates slowly to ensure the bit hits the entire surface of the hole evenly and keeps the hole straight.
Air Percussion Formations in Namibia
Air percussion is ideal for consolidated (hard) formations. If the rock is self-supporting and does not collapse, air is the best option.
In Namibia, you will find these formations primarily in the following regions:
The Central Highlands: Areas around Windhoek, Okahandja, and the Khomas Hochland consist of hard schist and quartzite. Air percussion is the standard here.
The North and Northwest (Kunene): In regions like Kamanjab and the Kaokoveld, you often encounter granite, gneiss, and hard limestone (dolomite). These hard rocks are perfect for air drilling.
The South: Hard sandstone and shale in the Hardap and Karas regions also lend themselves well to this method.
The Tsumis Area: South of Rehoboth, you often find hard sandstone and quartzite that can be drilled very effectively with air, provided there isn't too much loose overburden.
When does it NOT work?
Air percussion struggles in unconsolidated formations (loose ground), such as:
The Kalahari Sands: In parts of the Omaheke region, the sand is too deep. The air will "wash out" the hole, causing the walls to collapse.
Riverbeds: Where there is a lot of loose gravel and water near the surface.
In these cases, one often has to switch to "Mud Rotary" or systems like "Odex/Symmetrix," where casing is driven down simultaneously with the drilling to keep the hole open.
