Core Barrel/Accessories

In diamond wireline drilling, NQ, HQ, and PQ are standard size classifications that define the diameter of the rock core retrieved. As you move from NQ to PQ, the core size increases, requiring more powerful rigs but providing larger geological samples.
Core Size Comparison
Size Hole Diameter (Approx.) Core Diameter (Approx.) Best Use Case
NQ 75.7 mm (2.98 in) 47.6 mm (1.87 in) Deep mineral exploration; lightweight & fast.
HQ 96.0 mm (3.78 in) 63.5 mm (2.50 in) Industry standard for geotechnical & mining.
PQ 122.6 mm (4.83 in) 85.0 mm (3.35 in) Highly fractured rock or bulk sampling.
The Wireline System Anatomy
Regardless of size, these barrels consist of a dual-tube system designed for wireline retrieval:
Outer Tube Assembly: Rotates with the drill string and holds the Diamond Core Bit and Reaming Shell. It provides the structural strength to advance the hole.
Inner Tube Assembly: Remains stationary while the outer tube rotates around it. This protects the rock core from “washing” or mechanical damage.
Head Assembly (Latching Mechanism): The “brains” of the tool. It locks the inner tube into the outer tube for drilling and features a spearhead for the Overshot to grab during retrieval.
Core Lifter & Case: A tapered, spring-steel ring that grips the core at the base, snapping it off from the bedrock when the inner tube is hoisted.
Key Advantages
Efficiency: The inner tube is pulled to the surface via a steel cable (wireline), meaning you don’t have to pull hundreds of feet of drill rods to get your sample.
Sample Quality: Because the inner tube doesn’t rotate, it can recover “soft” or fractured zones that would be destroyed by a conventional rotating barrel.
Triple Tube Option (NQ3/HQ3/PQ3): For extremely sensitive or crumbly ground, a third “split” liner is added inside the inner tube to keep the core perfectly intact for logging.