Abstract: Based on a series of experiments,a composite water block removal technology of SLT,a kind of low interfacial tension agent,and modified organic phosphonic acid compound was developed to solve the water block damage problems in the low permeability reservoir in Well B of Weizhou Oilfield.The experimental results showed that when the gas-liquid surface tension of SLT was reduced to 18.2 mN/m and wetting angle was 0,the backflow resistance caused by water block can be effectively reduced;The dissolution rate of organic phosphonic acid reached 5% and no secondary pollution;the recovery value of core permeability was 98.2% after the removal of water block damage.The application in Well B also demonstrated that the effect in increasing oil production,at the rate of average 250 m³/d,was obvious,which has a good reference and popularization significance to dig the potential of low permeability reservoir in the other area of this block.