Polyanionic cellulose(PAC) is white or light yellowish powder or granular.It is easily soluble in cold or hot water,.The PAC exhibits high performance in various salt resistance,including calcium,magnesium-resistance.It can reduce filtration loss. It can be used in all water based drilling fluids, e.g. salt water based,seawater based and saturated-brine drilling fluids.It can reduce filtration very well.