The lack of systematic analysis of the hydraulics involved in air drilling has inhibited the development and utilization of air-drilling technology because the optimal design of any drilling program requires thorough knowledge of the wellbore hydraulics. A comprehensive study of air-drilling hydraulics yielded the system model used as the basis for a viable systematic set of design procedures. The system model was developed by coupling the models for air flow in the drillstring, air flow through the bit nozzles, and pneumatic transport of cuttings in the annulus. The resulting system model was used to design an air-drilling program. A set of design was used to design an air-drilling program. A set of design procedures is outlined to predict the standpipe pressure, to estimate maximum well depth, and to determine the optimal air flow rate required in air drilling. Practical examples are presented to test these design procedures.
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