Thermal Transformation of Sulfur Species and Hydrogen Sulfide Formation in High-Pyrite-Containing Lacustrine Type-II Shale during Semiopen Pyrolysis

The shale of the seventh member of the Triassic Yanchang Formation in the Ordos Basin (abbreviated as Chang 7 shale) is the most prospective shale for in situ conversion process. In our previous study, a series of artificial maturation experiments were conducted to simulate the hydrocarbon generation–retention–expulsion process. However, during the experiments, a large amount of hydrogen sulfide (H2S) was generated along with hydrocarbon products. Therefore, in this study, a combination of X-ray photoelectron spectroscopy, X-ray diffraction, and elemental analysis was used to reveal the thermal transformation of sulfur species and the formation process of H2S. The results showed that kerogen decomposition and the corresponding products exert a strong influence on the transformation of organic sulfur and pyritic sulfur and, thus, on H2S formation. Before the peak hydrocarbon-generating stage (