With the advancement of oil and gas exploration and development, tight sandstone gas has become a major current exploration field. However, the effective development of tight sandstone gas faces significant challenges due to the strong heterogeneity of tight sandstone reservoirs, diverse reservoir types, complex pore structures, and unclear understanding of reservoir formation mechanisms, which brings great difficulties. Clarifying the types and formation mechanisms of tight sandstone reservoirs is vital for guiding oil and gas exploration and development. This study investigates the characteristics, types, and formation mechanisms of tight sandstone gas reservoirs in the Xujiahe Formation (T₃X₂) of the Anyue area using core observation, cast thin-section identification, scanning electron microscopy, high pressure mercury intrusion, nuclear magnetic resonance, and other experimental methods. It defines the physical property lower limit of T₃X₂ reservoirs in Anyue, classifies reservoir types, elaborates on the basic characteristics of each type, and analyzes their genetic mechanisms. The results show that T₃X₂ reservoirs in the Anyue area can be divided into four types. Sedimentary, diagenetic, and tectonic processes are identified as the primary factors controlling reservoir quality, governing the formation mechanisms of different reservoir types. Based on these findings, a reservoir formation mechanism model for T₃X₂ reservoirs in the Anyue area is established, providing an important basis for subsequent oil and gas exploration and development in the region.

Member 2 of the Xujiahe Formation in the Anyue area of the Sichuan Basin exhibits significant resource potential for tight sandstone gas. However, its characteristic of “extensive gas presence with localized enrichment” leads to substantial variations in single-well productivity, challenges in target zone optimization, and unclear enrichment mechanisms, which hinder efficient exploration and development. This study proposes a hierarchical classification scheme of “two-level, six-type” source–reservoir structures based on the developmental characteristics of fault–fracture systems and vertical source–reservoir configurations. The gas-bearing heterogeneity is quantitatively characterized using parameters such as effective gas layer thickness, charge intensity, and effective gas layer probability, thereby revealing the differential enrichment mechanisms of tight sandstone gas controlled by source–reservoir structures. Our key findings include the following: (1) Member 2 of the Xujiahe Formation develops six subtypes of source–reservoir structures grouped into two levels, with gas-bearing capacities ranked as follows: source–reservoir separation type > source–reservoir adjacent type I > source–reservoir adjacent type II. Among these, the source–reservoir separation type (Level I) and fault–fracture conduit type (Level II) represent the most favorable structures for gas enrichment. (2) Tight sandstone gas enrichment is governed by a tripartite synergistic mechanism: hydrocarbon supply from source rocks, vertical cross-layer migration dominated by fault–fracture systems, and reservoir storage capacity determined by fracture density and reservoir thickness. (3) Three enrichment models are established: (i) a strong enrichment model characterized by “multi-layer source rocks beneath the reservoir, cross-layer migration, and thick fractured reservoirs”; (ii) a moderate enrichment model defined by “single-layer source rocks, localized migration, and medium-thick fractured reservoirs”; and (iii) a weak enrichment model featuring “single-layer hydrocarbon supply, pore-throat migration, and thin tight reservoirs.” This research provides a theoretical basis for optimizing exploration targets in Member 2 of the Xujiahe Formation in the Anyue area and offers insights applicable to analogous continental tight gas reservoirs.