Abstract: The classification assessment of tight sandstone reservoirs is one of the most important research focus of tight oil resource evaluation.Criteria of classification assessment for tight reservoirs can be effectively and accurately established by calculating the limits of various physical properties of tight oil reservoir,providing a theoretical basis for the classification of tight reservoirs.The tight sandstone reservoir in the 1st member of Funing Formation in the Gaoyou Sag,is taken as an example in the study.Its lower limit of oil-bearing property is calculated by methods of oil-bearing occurrence and nuclear magnetic resonance (NMR);its lower limits of physical properties for oil flowing are worked out by methods of NMR,minimum flowing pore throat radius and formation testing;and its upper limits of physical properties are figured out by balancing the buoyance and capillary resistance of oil in pores.Then following the characterization of tight reservoir permeability and verification of pore structure classification,we established the criteria for classification assessment of tight sandstone reservoirs.The tight reservoirs in the 1st member of Funing Formation,Gaoyou Sag,were accordingly classified into four classes,namely ineffective tight reservoir,oil-bearing tight reservoir,oil-movable tight reservoir and highly oil-movable tight reservoir,with the permeability boundaries of 0.07×10^-3 μm²,0.12×10^-3 μm²,0.50×10^-3 μm²,1.13×10^-3 μm² respectively.The consistency of the classification results and production tests serves to prove the accuracy and applicability of the method proposed in the study.

Key words: lower limit of physical property, upper limit of physical property, classification assessment, tight sandstone reservoir, Gaoyou Sag