With the advancement of exploitation technologies of tight oil

the porosity and permeability cutoffs of tight oil exploitation have been greatly reduced

and are approaching to that of tight oil accumulation.In combination with experimental analysis and theatrical computation

this paper introduced the water film theory to determine the porosity and permeability cutoffs of the Damintun Sag.The results show that tight reservoirs mainly consist of oil shale in the 4

th

Member of the Shahejie Formation in the Damintun Sag.Under the same geological conditions

there are water films (composed of strong bound water and weak bond water) adsorbed on the surface of tight sand particles.The minimum throat radius is equal to the thickness of water film which is so small that they can only be measured with nanometers.When the throat radius is smaller than water film thickness

the pore is filled with bound water.Only throats whose radius are larger than the film thickness can be valid oil charging pathways.Based on equilibrium of forces

relationship between water film thickness and throat radius is established

and the minimum throat radius valid for oil charging is calculated.The relationship of water film thickness with porosity

specific area and bound water saturation can be used to turn the critical value of throat radius into the critical porosity.This method not only has strong theoretical basis

but also the support of experimental data.