Abstract: Water production from oil wells would result in sand production,bottom-hole flowing pressure increase,flowing stop of the natural flowing well,underground equipments corrosion, and even more serious accidents of oil wells.The application of selective water shutoff agent developed worldwide is limited due to their undesirable selectivity and high cost.Organic silicon active functional groups were introduced into anionic,cationic and non-ionic monomer terpolymer through water solution polymerization reaction,a new organic silicon water-absorbing expansion selective water shutoff agent was developed.In the synthetic formula,it contains water 40 mL,acrylamide 6.2 g,methanesiliconic acid 5.0 g,2-acrylamide-2-methyl propane sulfonic acid 4.2 g,tetramethylammonium chloride 1.0 g,organosilicon coupler GL-1 0.03 g,organosilicon coupler GL-2 0.10 g,K2S2O8 0.025 g,and NaHSO3 0.05 g.The synthetic condition was to reacte for 8 h under 60 ℃.Test results of the performance evaluation showed that:new selective water shutoff agent has good selective plugging ability for oil and water,water shutoff rate is more than 95% while oil shutoff rate is lower than 10%.It can selectively seal high penetration throats and water layers while have little damages to low permeability reservoirs.It also has high sealing strength,and its water breakthrough pressure gradient is more than 10 MPa/m,which meets the engineering requirements of water shutoff for oil well on-site.