Geochemical Constraints on the Origin and Source of Tight Sandstone Gas in the Zitong Gas Field, Western Sichuan...

Recent exploration breakthroughs in terrestrial tight sandstone gas within the Western Sichuan Depression led to the discovery of the Zitong gas field, where the Middle Jurassic tight sandstone serves as the primary reservoir. However, critical knowledge gaps persist regarding the origin of gas owing to limited geochemical evidence. To address this, we conducted comprehensive geochemical analyses, including stable carbon and hydrogen isotopes and light hydrocarbon compositions. Key findings revealed that the Jurassic tight gas exhibits typical coal-derived gas characteristics. The R₀ values and the light hydrocarbon parameters demonstrate a clear genetic affinity between the J₂s¹ gas and the T₃x³ source unit, confirming the latter as the primary gas source. Comparative analysis shows that Zitong gas has lower δ¹³C₁ and δD₁ values than the Xindu and Luodai fields but resembles those of the Xinchang field. Its higher C₁/(C₁-C₅) and C₁/(C₂₊₃) ratios indicate a distinct geochemical behavior. The geochemical disparities among Jurassic gases in the Western Sichuan Depression are attributed to source rock horizons, thermal maturity, and migration distances.