Abstract: In view of the instability in Wei2 member and the protection of reservoirs, studies on evaluation were done for the formation characteristics and drilling fluid performance in Weizhou oilfield. In order to realize the liquefaction of drilling and completion, the formic drilling fluid system was suggested as the drilling and completion fluid for the development well in Weizhou oilfield. The indoor evaluation shows that the system satisfies the requirements of the wellbore stability in the complicated layers of the development wells in Weizhou oilfield and the requirements on the protection of reservoirs, which is suitable for the drilling and completion of the development well in Weizhou oilfield.