Abstract: The use of air as a circulating medium for drilling is the best way for the development of low pressure and low permeable formation. As air drilling will reduce the pressure of annulus liquid column to the smallest degree, it can acquire a greater penetration rate without any damage to the pay zones. However, because of the limitation of the drilling logging, and cementing technologies as well as the formation conditions, the well drilled
by air has to be replaced by work fluid (drilling fluids). During the replacenent process,the liquid and solids in the work may invade the formation, and cause the formation damage. Furthermore, once the low pressure and low permeable formation is damaged, it is difficult to restore the primary formation permeability. on the basis of the experiments,and by using the shielding temporary plugging technique, the technical measures of pre-
venting formation from damage during the replacement process in air drilling are put forward in this paper. the experimental results show that the temporary plugging effect is relative to the annulus fluid column pressure and plugging agent concentration in work fluid. The annulus pressure controlling method in the process of replacement discussed in thes paper is able to plug the formation in a short period, and to prevent the fluid and solids from invading the formation. The temporary plugged particles can be easily removed since they do not enter the formation deeply, and the primary formation permeability can be restored.

Key words: Air drilling, Formation damage, Shielding, Temporary plugging