Liu Min, Kong Qingfen, Wang Huaichang, Zhang Hui, Guo Huijuan, Wang Yunpeng, Shi Shuyong, Wang Qiang, Liu Jinzhong, Peng Ping'an
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, China.
ACS Omega. 2024 Sep 5;9(37):39088-39099. doi: 10.1021/acsomega.4c05874. eCollection 2024 Sep 17.
Industrial quantities of tight gas from the Carboniferous Benxi Formation have been found in the southern Ordos Basin. The source and contributions from mudstone and coal in the Benxi Formation to the tight gas are still unclear, and the hydrocarbon generation potential and kinetics of the Benxi Formation mudstone have rarely been reported, which has halted resource evaluation of tight gas. Confined pyrolysis experiments were performed to determine the yields and kinetic parameters for gaseous hydrocarbon formation for a representative sample of a Benxi Formation mudstone from the Ordos Basin, with a hydrogen index (HI) of 137 mg/g TOC and of 434 °C. The maximum yield of C-C hydrocarbons is 143 mg/g TOC. For samples with similar HI, Upper Paleozoic mudstone samples might have a higher total gas generation potential than Upper Paleozoic coal samples because of the more reducing environment during mudstone deposition, which is beneficial for the preservation of sedimentary lipids. Even though the HI of Upper Paleozoic coals is apparently higher than that of Upper Paleozoic mudstones, they have a similar late gas generation potential. Basin modeling shows that the amount of natural gas generated from Benxi Formation mudstone increases southward. Coaly source rocks from the Ordos Basin with a lower oil generation potential have more negative δC values when the vitrinite reflectance is lower than 1.4-1.7%. This phenomenon might be related to the more negative δC of wet gas or the small hydrocarbon molecules incorporated into the kerogen compared with the components generating primary cracking gases. This study deepens the understanding of gaseous hydrocarbons generated from mudstone and coal in transitional depositional environments and provides the key parameters for tight gas resources in this area.
鄂尔多斯盆地南部已发现石炭系本溪组致密气的工业产量。本溪组泥岩和煤对致密气的气源及贡献尚不明确，本溪组泥岩的生烃潜力及动力学研究鲜见报道，这阻碍了致密气资源评价。针对鄂尔多斯盆地本溪组泥岩的代表性样品开展了封闭热解实验，该样品氢指数（HI）为137mg/g TOC，热解温度为434℃，以确定气态烃生成的产率和动力学参数。C-C烃的最大产率为143mg/g TOC。对于氢指数相近的样品，上古生界泥岩样品的总生气潜力可能高于上古生界煤样品，因为泥岩沉积时的还原环境更强，有利于沉积脂质的保存。尽管上古生界煤的氢指数明显高于上古生界泥岩，但它们的晚期生气潜力相近。盆地模拟表明，本溪组泥岩生成的天然气量向南增加。鄂尔多斯盆地生油潜力较低的煤系烃源岩，当镜质体反射率低于1.4-1.7%时，δC值更负。这种现象可能与湿气的δC更负或与生成初次裂解气的组分相比，干酪根中掺入的烃类小分子有关。本研究深化了对过渡沉积环境中泥岩和煤生成气态烃的认识，并为本区致密气资源评价提供了关键参数。
