We present sulfur isotopic data for H2S from three different unconventional resource plays, the Haynesville, Eagle Ford, and Permian Basin, which produce dry gas, gas condensate and light oil respectively. Each play produces low levels of H2S, with sulfur derived from clearly defined but different sources. H2S in each of these cases was generated by different mechanisms, including both Bacterial (BSR) and Thermochemical Sulfate Reduction (TSR). A consistent theme observed in all three resource plays is that H2S generated by both BSR and TSR processes coexist at present day reservoir conditions. These conditions in some cases are too hot for BSR and/or too low for TSR. In one example, we show that TSR-generated H2S was likely formed on a production time scale due to elevated sulfate levels in water used for hydraulic fracturing. In the other two examples H2S was generated over geologic time and appears to persist as a mixture of H2S derived from two different reservoirs of sulfur, generated at different times relative to their burial and uplift histories.


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