Abstract: The evaluation criterion of tight sandstone reservoirs is not only the foundation to distinguish reservoir "sweet spot",but also the key and difficult point to explore tight oil. However,no unified understanding has been achieved so far. Taking the tight sandstone reservoirs of Quantou 4 Formation at the central depression in the southern Songliao basin as an example,we established the evaluation scheme of tight sandstone reservoirs on the basis of micro pore throat through integrating the subtle characterization of conventional mercury injection,constant-rate mercury injection, high-pressure mercury injection experiment,and other data. The results show that tight sandstone reservoirs in this area are characterized by small pore throats and poor physical property,whose reservoir space is dominated by the secondary solution pores. The reservoir permeability is mainly controlled by the large-radius pore throats whose volume are small. The larger the throat radius and the larger throat ratio is, the higher the permeability (K) of the tight reservoir and the better the quality. According to the differences of pore throat structures,tight sandstone reservoirs of Quantou 4 Formation at the central depression in the southern Songliao basin can be divided into four categories. Oil can be filled into the first,the second,and the third levels of tight reservoirs;and the first level of reservoirs (K=(0.1-1.0)×10^-3 μm²) are the best that can be taken as reservoir "sweet spots".

Key words: pore throat structure, evaluation scheme, tight sandstone reservoirs, Quantou 4 Formation, Central depression in southern Songliao basin