| 极端生物降解沥青中8,14- 开环藿烷系列及其地球化学意义 |
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| 引用本文： | 包建平,朱翠山,杨茜.极端生物降解沥青中8,14- 开环藿烷系列及其地球化学意义[J].地质学报,2023,97(8):2659-2675. |
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| 作者姓名： | 包建平 朱翠山 杨茜 |
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| 作者单位： | 长江大学油气地球化学与环境湖北省重点实验室，地球化学系，湖北武汉，430100 |
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| 基金项目： | 本文为国家自然科学基金项目（编号 41772119）资助的成果 |
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| 摘 要： | 借助色谱- 质谱（GC- MS）和色谱- 质谱- 质谱（GC- MS- MS）分析，对黔南坳陷凯里残余油藏凯棠和洛棉剖面上储层沥青中的烃类组成进行了系统分析，以判断其所遭受生物降解作用的程度，探寻在极端降解原油中是否还存在原生生物标志物，为这类原油的油源研究开拓新的途径和方法。结果表明：凯棠剖面上的储层沥青中尽管仍可检测到较为完整的C19- 30三环萜烷和C27- 35藿烷系列，但C19- 29脱甲基三环萜烷系列和C26- 34 25- 降藿烷系列丰富而完整，甾烷系列中C21- 22低分子量甾烷和重排甾烷优势明显，这一系列特征表明这些沥青遭受了剧烈生物降解作用的改造。但三芳甾类仍保存完好，依据原油生物降解程度的评判标准，判断其生物降解级别介于8~9级之间。洛棉剖面上的储层沥青中藿烷系列基本消失殆尽，三环萜烷系列及其脱甲基产物和25- 降藿烷系列的分布因极端生物降解作用而发生显著变异，某些化合物如C23T、C24T、C23NTE和C28- 29NH成为优势成员；甾烷系列中C21- 22低分子量甾烷占绝对优势，三芳甾类完全消失，据此判断该剖面上沥青的生物降解级别已达到10级或更严重。由于这两个剖面上的沥青遭受了极端生物降解作用的改造，常用的甾、萜类生物标志物完全失去了实用价值。但是，在所分析的这些沥青中都检测到三个系列的C27- 35 8,14- 开环藿烷系列，它们与塔里木盆地塔中地区海相端元油中存在的同类标志物的分布特征相似。正常海相端元油和极端生物降解沥青中同时检测到这三个系列的8,14- 开环藿烷，这一事实表明这类生物标志物在成因上具有原生性，而与生物降解作用无关。此外，在极端生物降解作用沥青中的完好保存，表明它们具有极强的抗生物降解能力，因而它们在此类原油的油源研究中可能具有潜在的实用价值。
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| 关 键 词： | 生物标志物 25- 降藿烷系列 脱甲基三环萜烷系列 三芳甾类 8 14- 开环藿烷系列 极端生物降解沥青 凯里残余油藏 黔南坳陷 |
| 收稿时间： | 2023/5/8 0:00:00 |
| 修稿时间： | 2023/6/25 0:00:00 |
8,14- secohopanes and their geochemical significance in extremely biodegraded bitumen: A case study from the Kaili residual reservoir in southern Guizhou depression |
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| BAO Jianping,ZHU Cuishan,YANG Xi.8,14- secohopanes and their geochemical significance in extremely biodegraded bitumen: A case study from the Kaili residual reservoir in southern Guizhou depression[J].Acta Geologica Sinica,2023,97(8):2659-2675. |
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| Authors: | BAO Jianping ZHU Cuishan YANG Xi |
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| Institution: | Hubei Key Laboratory of Petroleum Geochemistry and Environment, Geochemistry Department, Yangtze University, Wuhan, Hubei 430100, China |
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| Abstract: | The bitumen from the Kaitang and the Luomian outcrop sections in the Kaili residual reservoir in southern Guizhou depression have been severely biodegraded. Their hydrocarbon compositions were analyzed in detail by aid of gas chromatography- mass spectrometry (GC- MS) and gas chromatography- mass spectrometry- mass spectrometry (GC- MS- MS) to determine their exact biodegradation extent and discern whether there remain some primary biomarkers suitable for the severely biodegraded oil- source correlation. Analytical results show that in the reservoir bitumen from the Kaitang outcrop sections, relatively whole C19- 30 tricyclic terpanes and C27- 35 hopanes could be detected, but secondary biomarkers derived from biodegradation of crude oils such as C19- 29 demethylated tricyclic terpanes and C26- 34 25- norhopanes are abundant and complete, C21- 22 steranes and diasteranes are dominant in steroids, suggesting that the bitumen has been severely biodegraded. Because triaromatic steroid biomarkers are preserved in the bitumen, their biodegradation may have been up to 8- 9 level based on the known criteria to determine the biodegradation extent of crude oils. However, in the reservoir bitumen from the Luomian outcrop section, hopanes have been almost destroyed, the distributions of C19- 30 tricyclic terpanes and their demethylated counterparts and 25- norhopanes are completely different from those in the bitumen from the Kaitang outcrop section, some biomarkers such as C23T, C24T, C22NT, C23NTE and C26- 29 NH are dominant components, triaromatic steroids biomarkers have completely disappeared, demonstrating that the biodegradation extent of the bitumen in this section may be up to 10 level or more. Because the severe biodegradation has changed the distributions and compositions of common steranes and terpanes in the bitumen from two sections, their practical values have been completely lost. However, in the severely biodegraded bitumen from two sections, three series of C27- 35 8,14- secohopanes are detected. It is noted that this kind of biomarkers are present also in the marine end- member oils from the Tazhong uplift in the Tarim Basin, with a very similar distribution, suggesting that they are primary biomarkers and not related to biodegradation of crude oils. Moreover, their existence in the severely biodegraded bitumen show that they have unusual resistance to biodegradation may have potential practical value in the oil- source correlation of severely biodegraded oils. |
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| Keywords: | biomarkers 25- norhopanes demethylated tricyclic terpanes triaromatic steroids 8 14- secohopanes extremely biodegraded bitumen Kaili residual reservoir southern Guizhou depression |
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