Development of hydrodynamic model-based air drilling design procedures

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