"Sweet spot" identification and evaluation of tight sandstone reservoir

Located in the north of the Sichuan Basin, the 4th Member of Xujiahe Formation features braided-river, delta-front deposits, and extremely developed sand body. Due to the large burial depth, strong reservoir heterogeneity, and complex pore structure, the exploration and development of low permeability tight sandstone gas reservoir are greatly constrained by the identification and comprehensive evaluation of "sweet spots". Based on the extensive observation and identification of thin-section and in reference to logging data, this paper analyzes the key geological factors controlling the ultra-low permeability tight sandstone gas reservoir, puts forward a qualitative "sweet spots" identification model based on factor analysis for tight sandstone gas reservoir, and conducts comprehensive evaluation of the 4th Member of Xujiahe Formation in the target block in northern Sichuan Basin. The results show, ① "Sweet spots" region with good physical properties exists in some areas of tight sandstone gas reservoir; ② The three parameter factors extracted by the factor analysis can qualitatively explain the characteristics of tight sandstone gas reservoir and accurately identify the "sweet spots" section; ③ The quantitative evaluation results of the factor analysis are in good agreement with the actual exploration and development effect of the 4th Member of Xujiahe Formation in northern Sichuan Basin, and are much more accurate than those of the common evaluation methods; ④Reservoir of the 4th Member of Xujiahe Formation in North Sichuan can be divided into three types, and the target block has mostly developed type Ⅱ reservoir, and the key area of gas reservoir development rests in the NE trending gas-rich region in the southeastern part of the block.