Paper: Automatic Jet Subs for Air Drilling

Liquid that accumulates in an air-drilled borehole after water-bearing zones are penetrated causes drilling problems that result in excessive compressor requirements and lost rig time. An automatic jet sub that aids removal of liquids that accumulate during downtime and helps lift slugs during drilling described. This device consists of a differential pressure valve mounted in a drilling sub. These subs are spaced in the drill string above the bit. A portion of the circulating gas is diverted to the annulus above the bit when required to lift liquid slugs. When the liquid is removed, the jet subs close and full circulation goes through the bit. Application principles of these subs are discussed.