Differential Reservoir-Forming Processes and Genesis of High-Quality Tight Sandstone Reservoirs: A Case Study of the Jurassic Shaximiao Formation in the Sichuan Basin, China

The genetic mechanism of high-quality reservoirs in the tight sandstone of the Shaximiao Formation, Sichuan Basin, remains poorly understood, hindering effective exploration. This study integrates petrographic analysis and fluid inclusion homogenization temperature measurement to reconstruct the diagenetic sequence and restore porosity evolution. This approach reveals the controlling factors of reservoir densification and their interplay with hydrocarbon charging. We find that reservoir heterogeneity results from the competing effects of densifying processes (compaction and cementation) and porosity-enhancing dissolution. The critical control is identified as the timing of hydrocarbon charging relative to densification, leading to a new three-type reservoir classification. Based on the temporal relationship between hydrocarbon charging and densification, reservoirs are classified into three types: Type I (“hydrocarbon charging before densification”), Type II (“synchronous charging and densification”), and Type III (“densification before charging”). Type I (high-quality) reservoirs are primarily controlled by the synergistic effects of high-energy depositional facies and early chlorite coatings. The ‘deposition-diagenesis-hydrocarbon charging’ model elucidates high-quality reservoir mechanisms. These findings offer a genetic model and a predictive tool for pinpointing sweet spots, with significant implications for reducing exploration risk in this and similar tight gas basins worldwide.