Abstract: The core analysis data and mercury injection analysis data are used to study the micro-feature of Xujiahe tight reservoir of the Upper Triassic in Sichuan basin, and its position of "continuous spectrum" of worldwide reservoirs is determined. By means of statistical approach, this paper classifies the grade of the tight reservoir according to its permeability and pore-throat radius and analyzes the value-distributive range of each grade reservoir parameters. From the intrinsic relations among the pore-throat radius, porosity and permeability, the fitting formula among them is given, by which the conventional physical data are conversed into the pore-throat radius, hence deducing the grade that reservoir belongs and obtaining other parameters of the reservoir for the purpose of providing a new idea for research of the tight sandstone reservoir of Xujiahe formation in Sichuan basin.

Key words: Sichuan basin, Upper Triassic, Xujiahe formation, reservoir rock, grade, evaluation