Standard Definition of Shallow Holes
In Down-the-Hole (DTH) drilling operations, holes up to 20 meters deep are generally classified as shallow holes. This classification is primarily based on:
Drill string weight: Significant sagging occurs beyond 20 meters.
Cuttings removal efficiency: Rock cuttings can be naturally discharged from shallow holes.
Positioning accuracy: Deviation accumulates as depth increases.
Key Variables for Depth Determination
Three dynamic factors must be considered in actual operations:
Rock hardness: The limit can be extended to 25 meters for granite formations.
Bit type: Button bits allow for 3–5 meters more drilling depth than cross bits.
Flushing method: Direct circulation allows for approximately 2 meters more depth than reverse circulation.
Golden Rules for Equipment Selection
Practical recommendations for selecting DTH drilling equipment based on depth:
Up to 15 meters: Lightweight handheld units (high mobility).
15–25 meters: Medium-sized rig-mounted units (stability prioritized).
Over 25 meters: Specialized deep-hole equipment required (consideration of guidance systems).
