Characteristics of Tight Gas Accumulation and Main Controlling Factors of Differential Enrichment in the Shaximiao Formation, Yanjinggou Area, Southwest of the Western Sichuan Depression

ABSTRACT The Jurassic Shaximiao Formation in the southwest of the Western Sichuan Depression is an important tight gas reservoir. However, due to the strong heterogeneity of its reservoir properties and gas saturation, the factors influencing the differential enrichment of tight gas remain unclear. Based on logging, seismic, experimental, and drilling data, we have systematically studied the gas‐bearing property characteristics, source rock characteristics, reservoir physical properties, fault characteristics, accumulation Period, and the factors controlling differential enrichment using the tight gas reservoir in the Yanjinggou area as a case. The study shows that the Shaximiao Formation is underlain by high‐quality source rocks of the Xujiahe Formation (Upper Triassic) and capped by a regional seal of the Suining Formation (Jurassic). In the Yanjinggou area, anticline structures are well‐developed, with sandbodies widely distributed and vertically stacked, and the overall reservoir is tight. The thickness and petrophysical properties of the reservoir display significant heterogeneity, which is controlled by the coupling of depositional and diagenetic processes. Gas layers are mainly found in channel sands trending NE‐SW that exhibit superior reservoir properties. The fault–sand transport system is a crucial pathway for gas charging, migration, and accumulation, with structural highs and “V” shaped fault–sand configurations controlling the preferential enrichment zones. A tight gas accumulation model of “reservoir controlled enrichment, fault–sand controlled migration, and structural adjustment” was established. This model emphasizes that under the control of the fault–sand transport system, hydrocarbons initially migrate upward along faults into reservoirs that are separated from the source rocks, then laterally through the sandbodies. Favorable enrichment occurs in reservoir characterized by structural highs, good petrophysical properties, and greater thickness. The differential enrichment of tight gas in the Shaximiao Formation is controlled by a combination of factors, including the petrophysical properties and distribution of sandbodies and reservoirs, fault distribution, tectonic movement, and tectonically high positions. Comprehensive analysis indicates that the tight gas accumulation conditions in the Shaximiao Formation of the Yanjinggou area are favorable, providing a theoretical basis for predicting tight gas sweet spots in similar regions of the southwest of the Western Sichuan Depression.