TSR origin of sulfur in Permian and Triassic reservoir bitumen, East Sichuan Basin, China

Solid bitumen, H2S, pyrite and anhydrite samples from the Lower Triassic Feixianguan Formation and Upper Permian Changxing Formation, and source rock kerogen samples from the Cambrian, Ordovician, Silurian and Permian in the East Sichuan Basin were analyzed for their sulfur content and d 34 S values, to determine if the measurements were consistent with a thermochemical sulfate reduction (TSR) origin of the produced H2S and solid bitumen. The results show that the solid bitumen samples have sulfur contents from 2.6 to 12.5 wt.% and d 34 S values from +13.4‰ to +22.1‰. The d 34 S values are significantly heavier than those of potential Upper Permian source rock kerogens that average +1.3‰ (n = 3), suggesting that most of the sulfur in the solid bitumen is derived from isotopically heavy H2S of TSR origin (from +12.0‰ to +13.7‰). Interestingly, two gases produced from gas to water transition zones during drill stem testing (DST) show significantly lighter d