| 川北中、下侏罗统烃源岩重排藿烷组成变化与油源对比 |
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| 引用本文： | 朱扬明,郝芳,邹华耀,李平平,胡东风. 川北中、下侏罗统烃源岩重排藿烷组成变化与油源对比[J]. 沉积学报, 2022, 40(4): 1137-1150. DOI: 10.14027/j.issn.1000-0550.2020.118 |
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| 作者姓名： | 朱扬明 郝芳 邹华耀 李平平 胡东风 |
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| 作者单位： | 1.浙江大学地球科学学院, 杭州 310027 |
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| 基金项目： | 国家科技重大专项2017ZX05005-003-003 |
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| 摘 要： | 利用色谱—质谱定量分析技术，对40余个取自四川盆地北部石龙场和元坝地区不同成熟度的中、下侏罗统湖相烃源岩和原油样品进行分析，以此揭示其重排藿烷组成和分布的变化特征，并进行精细的油源对比。研究结果表明，不同成熟度的烃源岩中重排藿烷的丰度相差悬殊。石龙场地区Ro值为0.8%~1.0%的中侏罗统千佛崖组和下侏罗统自流井组大安寨段泥岩中，各类重排藿烷异常丰富，检出了17α（H）-重排藿烷、18α（H）-新藿烷和早洗脱重排藿烷3个完整碳数系列。它们的相对含量大都数倍于规则藿烷，是该层系烃源识别的分子标志。而在相邻的元坝地区相带、岩性相近的这两层段高成熟（Ro值主要在1.4%~1.9%）烃源岩中，藿烷类化合物出现异常变化，重排藿烷的相对含量很低，可能与干酪根在高热演化阶段生成的规则藿烷比例较高有关。烃源岩中高丰度重排藿烷并不取决于其绝对含量的高低，而在于它们相对于规则藿烷的富集。弱氧化的沉积环境是导致重排藿烷相对富集的一个重要原因，而有机质生源中的细菌组成可能更是一个关键因素。当烃源岩达到高成熟阶段时，藿烷类化合物的组成和分布不再受控于热化学动力学机制，各类重排藿烷均按一定比例分布，基本失去了其地球化学属性。区内中、下侏罗统原油中重排藿烷的组成和分布也随热演化程度而变化。它们在成熟原油中极丰富，而在高成熟原油中则很少，与烃源岩存在对应关系。经油—岩对比，认为这些原油来源于所在层位的烃源岩。
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| 关 键 词： | 重排藿烷 烃源岩 原油 油源对比 四川盆地 |
| 收稿时间： | 2020-06-28 |
Compositional Variations and Oil-source Implication of Rearranged Hopanes from the Middle-Lower Jurassic Source Rocks in the Northern Sichuan Basin |
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| Affiliation: | 1.School of Earth Sciences, Zhejiang University, Hangzhou 310027, China2.School of Geosciences, China University of Petroleum (East China), Qingdao, Shandong 266580, China3.College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China4.SINOPEC Exploration Company, Chengdu 610041, China |
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| Abstract: | Over 40 lacustrine source rock and oil samples with different maturities collected from the middle-lower Jurassic strata in the Shilongchang and Yuanba regions of the northern Sichuan Basin were analyzed using GC-MS （gas chromatography-mass spectrometry） to characterize the compositional variations of rearranged hopanes and carry out a genetic correlation between the oils and the source rocks. The results indicate the rearranged hopanes show a great difference in abundance for the different mature source rocks. The mudstones with Ro values ranging from 0.8% to 1.0% in the middle Jurassic Qianfoya Formation and the Da’anzhai member of the lower Jurassic Ziliujing Formation in the Shilongchang region are extremely enriched in three series of rearranged hopanes， i.e.， 17α（H）-diahopanes， 18α（H）-neohopanes， and early-eluting rearranged hopanes with a full carbon number member. These compounds are present several times in relative concentrations as regular hopanes and can serve as a molecular indicator for the identification of hydrocarbons from the middle-lower Jurassic source rocks. In contrast， the hopanoids from over-mature source rocks （Ro mostly in 1.4%-1.9%） with similar depositional facies and lithology in the Yuanba region are found to change abnormally. Their rearranged hopanes exhibit a low relative abundance， possibly as a result of more regular hopanes generated from kerogen at a high maturity level. Enhanced rearranged hopanes in the source rocks are attributed to the relative enrichment of these compounds with respect to regular hopanes， rather than their high absolute concentration. A sub-oxic depositional environment could favor the formation of these compounds， while the bacterial component in a biological source may be of critical importance. The constitution of hopanoids appears not to be controlled by thermodynamic processes at high thermal maturity， and rearranged hopanes show a highly similar molecular distribution with the deprivation of their geochemical proprieties. The composition and distribution of rearranged hopanes in oils from the middle-lower Jurassic reservoirs also change with increasing maturation. These compounds are unusually abundant in mature oils but are found at a much lower amount in over-mature oils， an analogy to the situation in the source rocks at different maturities. Based on the oil-source rock correlation， studied oils are believed to be self-sourced. |
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