The unclear understanding of the micro pore structure in the offshore low permeability reservoir affects the determination of the key parameter limits of water injection quality. Therefore

water injection quality evaluation experiment is carried out based on the characterization of reservoir micro pore structure in Liushagang Formation of WZ11-4 N Oilfield studied by indoor constant velocity mercury injection experiment

then to evaluate the influence of the key parameters of water quality on the seepage capability. The results show that the throat size and distribution are the main factors that determine the seepage capability of reservoir. There is a good power function relation between permeability and mainstream throat radius. The throat radius of the first section in the Liushagang Formation is about 4 μm

while 1 μm for the third section

and the former has strong flow capacity. The increase of the particle size

particle concentration and bacterial content of the suspended solids in the injected water will greatly increase the injection pressure but decrease the core permeability. Taking the damage degree of water absorption index to reservoir

20 %

as the lower limit

the key parameter limits of injected water quality of reservoirs with different permeability levels are established. For the first section of the Liushagang Formation

the water quality of the recommended injected seawater are of the concentration that the suspended solids particles is less than or equal to 2.0 mg/L

the median diameter of suspended solid particles is less than or equal to 3.0 μm

and the number of bacteria per milliliter is less than or equal to 100. According to the guidance of these above data

the effective development of the main formation in Weizhou 11-4 N Oilfield is realized by the combination of water injection and seawater softening treatment technology.