塔斯马尼亚油页岩生烃模拟排出油与滞留油地球化学对比Ⅱ：分子地球化学特征

A comparative study on the geochemical characteristics of expelled and retained oil from hydrocarbon generation simulation of Australian Tasmanian oil shale Ⅱ: molecular geochemical characteristics

吴芬婷 谢小敏 徐耀辉 林静文 张雷 许锦 马中良

WU Fenting XIE Xiaomin XU Yaohui LIN Jingwen ZHANG Lei XU Jin MA Zhongliang

油气地球化学与环境湖北省重点实验室, 武汉 430100 油气资源与勘探技术教育部重点实验室, 武汉 430100 长江大学 资源与环境学院, 武汉 430100 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126

Hubei Key Laboratory of Petroleum Geochemistry and Environment, Wuhan, Hubei 430100, China Key Laboratory of Exploration Technologies for Oil and Gas Resources, Ministry of Education, Wuhan, Hubei 430100, China School of Resources and Environment, Yangtze University, Wuhan, Hubei 430100, China Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China

澳大利亚塔斯马尼亚油页岩为一套特殊的富含单种浮游藻类(塔斯马尼亚藻)的烃源岩，原始油页岩样品等效镜质体反射率为0.5%，是进行热模拟的理想样品。为对比分析不同模拟温度下排出油和滞留油的分子地球化学特征，对该油页岩样品开展生排烃模拟实验。研究结果显示：(1)原始样品抽提物与滞留油分子标志物指示还原环境，排出油则显示出还原与氧化的混合来源特征。(2)生物标志物成熟度参数，C29甾烷20S/(20S+20R)、C29藿烷ββ/(αα+ββ)和Ts/(Ts+Tm)显示滞留油和排出油在350 ℃时为成熟阶段；在生烃高峰前(≤350 ℃)滞留油成熟度指标随温度的升高而升高，而在排出油中相关性较差；在350 ℃以后滞留油与排出油成熟度指标与模拟温度均无相关性。(3)油源对比参数，滞留油与排出油饱和烃甾烷分布特征C27、C28、C29规则甾烷分布随温度的升高均表现出从反“L”型逐渐过渡为不对称近“V”型，再过渡到正“L”型的分布模式；同一温度下，滞留油与排出油之间具有较好的可对比性。因此，同一成熟度阶段，甾烷分布特征能有效地进行油源对比；而不同成熟度下，排出油与滞留油的可对比性差异明显。该研究揭示了生物标志化合物在排出油与滞留油之间的差异性，以及模拟温度对生物标志化合物指标的影响；在用分子化合物进行沉积环境、成熟度及油源对比研究时，需要重视成熟度对分子化合物参数的影响，尤其是在生油高峰以后，分子化合物参数指标可能难以有效适用。

The Australian Tasmanian oil shale is a special set of source rocks in which a single species of planktonic algae (Tasmanite) is significantly enriched and has relatively lower degree of maturity with equivalent vitrinite reflectance of 0.5%. It can be considered as a good material for artificial maturation experiment. In order to compare the molecular geochemical characteristics of expelled oil and retained oil at different simulation temperatures, a hydrocarbon generation and expulsion simulation experiment was carried out. Results show that: (1) The extracts of original rock sample and the retained oil indicate a reducing environment, while a mixed source region of both reduction and oxidation is indicated by the expelled oil. (2) The maturity-related biomarker parameters (e.g C29 steranes 20S/(20S+20R), C29 hopanes ββ/(αα+ββ) and Ts/(Ts+Tm)) indicate that the retained and expelled oil are mature at 350 ℃ of the experiment. These biomarker parameters in retained oil increase with temperature before the simulation temperature lower than 350 ℃; however, the correlation is poor for expelled oil. When temperature is higher than 350 ℃, the parameters of retained or expelled oil have irrelevant correlation with the simulated temperature. (3) The distribution of C27, C28 and C29 steranes in retained and expelled oil shows variations with maturation degree, and changes fromreverse "L" type, to slightly asymmetric "V" type, and finally to "L" type at 400 ℃. At the same temperature, retained oil and expelled oil are comparable. Therefore, at the same maturity stage, the sterane distribution characteristics is effective for oil source correlation; while at different maturity stages, the comparability of expelled oil and retained oil may vary greatly. It is revealed by this study the differences of molecules between expelled oil and retained oil, as well as the influence of simulated temperature on the parameters. The influence of maturity to the biomarker parameters has to be considered when studies of depositional environment, maturity and oil-source correlation are carried out, especially after the peak of oil generation.

中国自然科学基金面上项目 41972163;中国自然科学基金面上项目 42173055

https://doi.org/10.11781/sysydz202202314