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Drilling trouble for impregnated diamond core bit

(1) Concave face wear (rounded in inside diameter)
Cause: Often caused by excessive penetration rate for the rpm used - rpi (r/cm) too low. Also can be caused by core grinding, over drilling.

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(2) Concave face wear (rounded in outside diameter)
Cause: Insufficient water flow - Check pump and rod string for leaks; increase pump output.

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(3) Gauge loss on inside diameter
Cause:
(A) Overfeeding — Increase rpi (r/cm);
(B) Broken formations — Cement or change to a lower bit;
(C) Drilling over lost core — Check core barrel/core lifter/core lifter case;
(D) Insufficient drilling fluid — Check inner tube length adjustment; check pump and rod string for leaks – increase pump output.

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(4) Gauge loss on outside diameter
Cause:
(A) Lack of circulation – increase coolant flow rate.
(B) Bit being reamed down under-size hole – Check reamer shell gauge and replace if under-sized.
(C) Vibration – alter rpm.

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(5) Excessive diamond exposure
Matrix abrades away before diamonds have worn sufficiently, resulting in high diamond exposure and low bit life. Caused by overfeeding/over drilling – Increase rpi (r/cm), change to a lower series bit or reduce bit weight rpm.

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(6) Face glazed (diamond polished and metal bound)
Bit does not feel sharp; diamonds flush w matrix; no significant “comet tails” behind each diamond. Sand blast face or use other recommended methods to re-expose diamond. Try again with rpi (r/cm) in the 200/250 (80/100) range. If the face glazes repeatedly, change to a higher bit.

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(7) Burnt
Cause:
(A) Lack of fluid.
(B) Too high a bit weight being used. – Check pump and rod string for leaks, check inner tube adjustment. Maintain coolant flow rates.

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