ODEX and Air Rotary Drilling
What are ODEX and Air Rotary Drilling?
ODEX and Air Rotary drilling are both rotary drilling methods that use compressed air instead of drilling fluid (“mud”) to advance the borehole. These methods are especially useful in unconsolidated formations (loose gravel, sand, boulders) where traditional rotary or mud drilling can be inefficient or unstable.
What is ODEX Drilling?
ODEX stands for Overburden Drilling EXcentric system. It’s a specialized drilling technique used for advancing casings through overburden (loose, unconsolidated material) to reach bedrock.
How It Works
- A pilot bit with an eccentric wing drills ahead of the casing.
- As the bit rotates, the wing swings out to drill a hole larger than the casing diameter.
- The casing is simultaneously driven down behind the bit using a down-the-hole (DTH) hammer powered by compressed air.
- Once bedrock is reached, the wing retracts, allowing the bit to be pulled back through the casing.
Ideal For
- Difficult overburden with gravel, cobbles, or boulders
- Setting casing through loose formations
- Water well pre-drilling, anchoring, or foundation drilling
Key Benefits
- Fast advancement through overburden
- Casing installed as you drill = no cave-ins
- Reaches bedrock quickly and efficiently
What is Air Rotary Drilling?
Air rotary drilling uses compressed air to power a rotating bit and to remove cuttings from the borehole. It is widely used in hard rock formations and can be combined with DTH hammer tools.
How It Works
- A tricone or drag bit is rotated via a drill string.
- Compressed air is pumped down through the drill rods.
- The air exits through ports near the bit, lifting cuttings up the borehole annulus to the surface.
Variants
- Straight air rotary – used in consolidated (hard) formations
- Air rotary with DTH hammer – ideal for hard rock where percussion is needed
Ideal For
- Hard or consolidated rock
- Deep water wells, geotechnical drilling
Fast, clean borehole production
| Feature | ODEX | Air Rotary |
| Borehole Type | Through overburden to bedrock |
Primarily in rock or consolidated soil |
| Casing Installed | During drilling |
After drilling (if needed) |
| Ideal Ground | Gravel, cobbles, boulders | Competent rock |
| Tooling | Excentric wing + casing shoe |
Tricone bit or DTH hammer |
| Air Use | Drives hammer + clears cuttings | Clears cuttings + powers hammer |