Sulfate Sources Required for Thermochemical Sulfate Reduction in Dolostone Reservoirs in the Upper Permian Changxing Formation, Yuanba Gas Field, Sichuan Basin, China: Insights from the Origin of Celestite

Thermochemical sulfate reduction (TSR) commonly occurred in the dolostone reservoirs of Upper Permian Changxing Formation (P3c) Yuanba (YB) gas field, Sichuan Basin, yet controversy remains regarding source required for TSR. To trace sulfate, sulfur and strontium isotopic compositions were measured three diagenetic celestite (SrSO4) samples found P3c YB field. In addition, Carbonate-associated sulfates (CAS) from carbonates spheroidal pyrites dolomicrites P/T boundary (PTB) field comparative studies. The results show that celestites are significantly heavier than those contemporaneous seawater, these have values consistent with host dolostones seawater. −33.68‰ fractionation average δ34S between indicated their formation was likely to be related bacterial (BSR). During extinction event accompanied end-Permian regression, reflux brine directly precipitated 34S-rich fractures vugs due BSR evaporation These celesites associated pore fluids provide a new explanation late