Tight sandstone accumulation characteristics of Huagang Formation in Y Structure of Xihu Sag

The controlling factors and accumulation characteristics of relatively high-quality tight sandstone reservoir have become the most important factors limiting the deep exploration in the Xihu Sag on shelf of the East China Sea. Thin section analysis, scanning electron microscopy, and mercury injection test were conducted based on gas bearing property, from which the characteristics and gas accumulation process of tight sandstone reservoir were clarified. Results show that the tight sandstone reservoirs could be divided into four types, among which the type Ⅰ reservoir is relatively high quality reservoir with a high quality channel for gas charging. Coarse-grained deposition in high-energy sedimentary environment is the prerequisite for the formation of the relatively high-quality reservoirs. Authigenic chlorite pore liner is the key to the improvement of physical properties, which is beneficial to the preservation of primary intergranular pores and the promotion to late dissolution. The gas bearing property of the reservoir is co-controlled by the relatively high quality reservoir and the structural amplitude. The gas layer is also developed in the relatively poor reservoir (type Ⅱ and Ⅲ) along with the increase of structural amplitude. This study has important significance for the exploration of tight sandstone gas in the Xihu Sag.