Abstract: Air drilling, as a member of under balance pressure drilling family, is different from conventional drilling methods.The drilling fluid along double wall drilling tool annular gap reach the hole bottom.There is a positioning device which is also called correcting block between the inner tube and the outer tube of the double wall, and because of the correcting block, the flow field is more complex.The pressure parameter of correcting block between the inner tube and the outer tube of the double wall is researched.Based on the fluid dynamics, pressure model is built through mathematical derivation.Combined with practical engineering examples, programming calculations, the model is solved.The total pressure loss value as a result of correcting blocks is obtained.It provides a strong basis to further explore the entire circulatory system pressure model.

Key words: Reverse circulation, Double wall drilling tool, Correcting block, Pressure model