Mist drilling is used to achieve what effect in air rotary drilling?

• A. Cool the bit and lift cuttings
• B. Increase mud viscosity
• C. Prevent wear by chemical means
• D. Remove cuttings by gravitational settling

Answer: (A)

Mist drilling introduces a fine water mist into the air stream used in air rotary drilling to manage heat and carry cuttings upward. The water droplets absorb heat from the bit, cooling it and reducing wear, while the rising air mist helps lift the cuttings out of the hole so they reach the surface rather than simply accumulating at the bottom.

Increasing mud viscosity doesn’t apply here since this method uses a mist rather than a heavy drilling mud system. Wearing protection by chemical means isn’t what mist provides—there’s no chemical coating involved, just cooling. Relying on gravitational settling to remove cuttings would be slow and ineffective in the active air-driven environment, where the cuttings are carried upward by the air-mist flow.