Abstract: The reservoirs of the Shanxi Formation in the main gas-bearing layers of the Yan′an Gas Field exhibit strong heterogeneity and poor physical properties, typical of tight sandstone gas reservoirs. It is difficult to predict favorable exploration areas and exploit gas reservoirs. To clarify the causes of low porosity and permeability in the reservoir and identify the main controlling factors, various experimental analyses such as core thin sections, scanning electron microscopy, and whole-rock X-ray diffraction were conducted. Based on differences in plastic particle content, five lithofacies were identified within the tight sandstone of the Shanxi Formation. Phase control was used to guide modeling, and three-dimensional geological modeling software was employed for stochastic lithofacies modeling. The results indicate that sedimentary facies, hydrodynamic conditions, and diagenesis collectively influence sandstone pore development and reservoir performance. Mechanical compaction of plastic materials is identified as the fundamental cause of poor reservoir properties. Pure quartz sandstone and quartz-rich, low-plasticity lithic sandstone exhibit well-developed pores and better physical properties, representing effective reservoirs. These lithofacies are mainly distributed in the middle to lower parts of underwater distributary channels and deltaic barrier microfacies with strong hydrodynamic conditions. Lithofacies modeling provides a better understanding of the three-dimensional spatial distribution patterns, enhancing the accuracy of predicting effective reservoir distribution. This approach has significant implications for the fine development of the Yan′an Gas Field.

Key words: tight sandstone, lithofacies, microscopic characteristics, main controlling factors, reservoir prediction, Shanxi Formation, Yan′an Gas Field