Impact of Inorganically Bound Sulfur on Late Shale Gas Generation

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• 作者：Qingtao Wang ; Hong Lu ; Chenchen Shen ; Jinzhong Liu ; Ping’an Peng ; Chang Samuel Hsu
• 刊名：Energy & Fuels
• 出版年：2014
• 出版时间：February 20, 2014
• 年：2014
• 卷：28
• 期：2
• 页码：785-793
• 全文大小：447K
• ISSN：1520-5029

文摘

Nonisothermal, confined pyrolysis was applied to a mature shale sample from the Ordovician Salgan Formation in Tarim Basin, northwest China. Experiments were conducted using gold-tubes with added water at a very slow heating rate (2 掳C/h) and end temperatures between 336 and 600 掳C. To investigate the influence of inorganically bound sulfur on the generation of gases and to consider the geological occurrence of sulfur-containing minerals, such as prevalent pyrite in shales, the experiments were carried out with and without admixtures of MgSO₄, CaSO₄, and pyrite. High amounts of methane along with lower amounts of wet gases were formed from highly mature shale without minerals added, demonstrating a huge late gas generation potential at post peak-oil window maturities. In the experiments with added sulfates and pyrite, all organic gases were consumed in varying proportions, resulting in different chemical and stable carbon isotopic compositions. Pyrite treatment affects wet gas (C₂鈥揅₅) evolution directly, but it affects methane (C₁) evolution indirectly. In contrast, sulfate treatments affect C₁鈥揅₅ evolution directly. The cumulative yield ratio of CO₂/H₂S indicates that pyrite impacts on the hydrocarbon gas generation through low valence sulfur such as S⁰ or others, which are associated with H₂S generation. In the pyrite series, the smooth increase in ethane yield at temperatures exceeding 504 掳C, together with a concomitant stable carbon isotope reversal, demonstrates a new origin for ethane at high temperatures. The isotopic reversal may come from reactions between water and solid kerogen/coke/pyrobitumen. Isotopic reversal of ethane occurs only in the control and pyrite series but not in the sulfate treatments. This provides evidence that anoxic conditions are required. Thus, one can expect to encounter isotopic reversals in high maturity, unconventional gas shale environments in the presence of pyrite.