Q. Reasons of using compressed air as drilling fluid?

For rotary drilling in ground investigation works, drilling fluid is generally used to clear and clean the cuttings from the drilling bits and transport them to ground surface. Furthermore it also serves to create a cooling effect to the drilling bit. Additionally the stability of boreholes can be improved and the drilling fluid also creates lubricating effect to the bits. 

Compressed air when used as a drilling fluid possesses numerous advantages. Firstly, use of compressed air can decrease the loss offluid at the time of circulation that is commonly encountered for water being used as drilling fluid. Secondly, efficiency of air to clean drilling bits is higher than other kinds of drilling fluids. Thirdly, moisture condition of in-situ soils wouldn't be affected by air when compared with water as drilling fluid. Additionally, in cold countries occurrence of freezing of drilling mud/water can be avoided by using air. Though special attention must be taken to avoid breathing the generated dust when compressed air is used as drilling fluid and dust suppression measures have to be properly implemented.