Abstract: Pretect reservoir is very important during drilling.According to the size of average pore radius, appropriate grain size of temporarily plugging agent blend into drilling fluid which upon reservoir. The drilling fluid, with colloid filler particle, was changed completion fluids.In practice, the completion fluids only had good effect shielding temporarily plugging in some wall of a well by the wide range of. pore radius.Aim at this abuse, 17 formulations via test of pollution were prepared.Test, as a result, indicated original slurry mixs cation emulsified asphalt was a best way pretect reservoir.