Because of poor understanding of the wellbore hydraulics involved in air drilling, the operating conditions are not optimal and consequently costs are higher in terms of rig time, personnel time, and equipment. Moreover, various post-drilling wellbore repair operations must often be performed to repair the damage done to the formation in the pay zone region in an improperly designed air drilling operation.

The importance of having a thorough understanding of wellbore hydraulics in air drilling can not be over-emphasized. Predictive capability of the hydraulics involved arises mainly from the intricate interactions between the wellbore, the drill string, the formation, and the particulate transport in the wellbore-drill string annulus. Lack of this understanding and the resulting lack of predictive capability leads to unexpected occurrences downhole, which at times lead to catastrophic fatality. An adequate understanding of the wellbore hydraulics will evolve into appropriate predictive capability, which can aid in the reduction of operational costs and risks involved and can help to provide optimal operation. The results of the work summarized in this paper will significantly enhance the scientific base for this highly desirable and economically attractive technology.

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