in order to evaluate the feasibility of water flooding for the 3rd member of Shahejie formation in block-Qu 9-21,a series of concerned experiments were carried out,such as reservoir petrophysical properties analysis,static compatibility evaluation between source water and formation water,formation sensitivity analysis and dynamic compatibility evaluation between source water and formation.In addition,the damage mechanism of water flooding process was analyzed and the quality index of the injected water was established by means of laboratory water flooding tests.It was shown that permeability retention rate was low to 29.4% when core had been more seriously damaged from water flooding of long duration by untreated field source water.It was concluded that the higher salinity of the injected water than formation water and the mechanical impurities of the injected water were key factors influencing water flooding development.Hence,in order to remove formation damage,the reduction of the content of mechanical impurities of the injected water was a major measure taken.According to test results,the recommended mechanical impurities index of the injected water for the third member of Shahejie formation in block-Qu 9-21 is grade B2.