The core of core extraction with a core drill rig lies in “controlling parameters, protecting hole walls, stabilizing core cutting and preserving cores”. It is necessary to match drilling tools and operation processes according to formation characteristics, with a focus on preventing core blockage, core loss and core breakage.

Pre-preparation requires precise tool selection: use diamond drill bits plus single-acting double tubes for intact and hard formations; select double-tube drill tools plus alloy drill bits for loose and broken formations; and adopt short core barrels plus soil samplers for soft and expansive formations. Meanwhile, inspect components such as drill bits, core barrels and core springs to ensure good performance.

During drilling, start the hole with light pressure and low rotational speed, and adjust parameters based on formations: apply medium-high pressure and medium-low rotational speed for hard rocks, and low pressure and low speed for broken and soft rocks, matching corresponding flushing fluids and controlling displacement. The single-round footage shall not exceed 90% of the barrel length for hard rocks and 70% for broken and soft rocks. Stop drilling immediately for inspection if abnormal pump pressure or sudden changes in drilling speed occur.

Core cutting and tripping are key steps. After drilling, perform core grinding for 10–20 minutes at the original pressure, then reduce pressure to pull the core off smoothly at a steady speed. Trip the drill uniformly and slowly. Use special tools to take out cores gently. Wrap broken cores with plastic film in a timely manner for protection to avoid secondary damage.

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