Determination of optimal air flow rate in air drilling

Optimal design of any drilling program requires good knowledge of wellbore hydraulics. Established techniques are available for formulating some understanding of the associated wellbore hydraulics for conventional mud drilling, but this is not the case for air drilling. The wellbore hydraulics of air drilling present distinctly different problems from those associated with mud drilling. A systematic study of these problems, especially utilizing fundamental approaches, is lacking. This study addresses this problem using a fundamental, hydrodynamic multiphase flow model for air drilling. Extensive parametric analysis of the system is performed to validate the viability of the model as a predictive tool. The model is demonstrably capable of predicting the pressure-drop profile in the annulus and the optimal lifting velocity, an essential ingredient in the optimal design of air drilling. The results demonstrate the ability of the model to predict a number of phenomena that are associated with lifting cuttings from the hole during air drilling. The model possesses scale-up capability.