Diamond Drilling Information
Essential knowledge about diamond drilling technology and parameters
Diamond Drilling Basics
Diamond drilling is a precision drilling technique that uses diamond-impregnated drill bits to cut through hard materials. The process is widely used in mining exploration, geotechnical investigations, and construction projects where precise core samples are required.
The diamond bits contain industrial-grade diamonds embedded in a metal matrix. As the bit rotates, the diamonds cut through the material, while water or drilling fluid is pumped through the drill string to cool the bit and flush away cuttings.
The effectiveness of diamond drilling depends on selecting the right bit type and size for the material being drilled, and optimizing drilling parameters such as rotation speed, weight on bit, and flushing rate.
Standard Bit Sizes
Diamond drilling uses standardized bit sizes, each designated by a letter code. The most common standards are:
| Designation | Hole Diameter (mm) | Core Diameter (mm) | Hole Diameter (inch) | Core Diameter (inch) |
|---|---|---|---|---|
| AQ | 48.0 | 27.0 | 1.890" | 1.062" |
| BQ | 60.0 | 36.5 | 2.360" | 1.432" |
| NQ | 75.7 | 47.6 | 2.980" | 1.875" |
| HQ | 96.0 | 63.5 | 3.782" | 2.500" |
| PQ | 122.6 | 85.0 | 4.827" | 3.345" |
| Geobor S | 146.0 | 102.0 | 5.750" | 4.010" |
The choice of bit size depends on the required core sample size, drilling depth, and ground conditions. Larger bits provide bigger core samples but require more power and may have slower penetration rates.
Mohs Scale and Rock Hardness
The Mohs scale is a measure of mineral hardness, ranging from 1 (softest) to 10 (hardest). It's an important factor in diamond drilling as it helps determine the appropriate bit type for different rock formations.
| Mohs Hardness | Example Minerals/Rocks | Recommended Bit Type |
|---|---|---|
| 1-3 | Talc, Gypsum, Calcite, Limestone, Sandstone | Soft matrix bits |
| 4-6 | Fluorite, Apatite, Marble, Dolomite | Medium matrix bits |
| 7-8 | Quartz, Granite, Basalt | Hard matrix bits |
| 9-10 | Corundum, Diamond | Extra-hard matrix bits |
Matching the bit hardness to the rock hardness is crucial for optimal drilling performance. Using too soft a bit in hard rock will cause rapid wear, while using too hard a bit in soft rock can reduce penetration rates and cause bit glazing.
Drilling Parameters
Optimizing drilling parameters is essential for efficient diamond drilling operations. The three main parameters to consider are:
Rotation Speed (RPM)
Rotation speed affects how quickly the bit cuts through material. Generally:
- Harder formations require lower RPM
- Softer formations allow higher RPM
- Larger bits require lower RPM
- Smaller bits can use higher RPM
Typical range: 300-1500 RPM, depending on bit size and rock type.
Weight on Bit (WOB)
Weight on bit (or bit pressure) determines how hard the bit presses against the rock:
- Too little pressure results in slow penetration and bit glazing
- Too much pressure can damage the bit and reduce core recovery
- Larger bits can handle more pressure
- Harder formations generally require more pressure
Typical range: 500-5000 kg, depending on bit size and rock type.
Flushing Rate
Flushing rate controls how much water or drilling fluid is pumped through the system:
- Adequate flushing cools the bit and removes cuttings
- Insufficient flushing leads to bit overheating and reduced performance
- Excessive flushing can erode the hole wall and reduce core recovery
- Larger bits require higher flushing rates
Typical range: 0.5-10 GPM, depending on bit size and rock type.
Quick Links
- → Launch Simulator
- → Diamond Drilling Basics
- → Standard Bit Sizes
- → Mohs Scale and Rock Hardness
- → Drilling Parameters
Did You Know?
The Rate of Penetration (ROP) is a critical performance metric in diamond drilling, measuring how quickly the bit advances through the material in meters per hour.
Pro Tip
When drilling in variable formations, it's better to select a bit that matches the hardest material you expect to encounter to avoid frequent bit changes.