| 庙西凹陷严重生物降解原油序列中三环萜烷的异常分布成因初探 |
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| 引用本文： | 程熊,侯读杰,徐长贵,王飞龙.庙西凹陷严重生物降解原油序列中三环萜烷的异常分布成因初探[J].沉积学报,2017,35(1):193-202. |
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| 作者姓名： | 程熊 侯读杰 徐长贵 王飞龙 |
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| 作者单位： | 1.中国地质大学(北京)能源学院/海相储层演化与油气富集机理教育部重点实验室, 北京 100083; |
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| 基金项目： | 中海石油(中国)有限公司天津分公司科技项目(CCL2015TJXZSST0436) |
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| 摘 要： | 对渤海湾盆地一系列生物降解原油的色谱-质谱分析结果表明，庙西凹陷PL15-8D与PL9-4井四个严重生物降解原油三环萜烷系列分布较为异常，主要表现为以C23为主峰的后峰型、C20与C23为主峰的微弱双峰型以及以C20与C24为主峰的双峰型分布模式。强烈的生物降解作用导致C19~C23三环萜烷优先于C24+三环萜烷被不同程度地侵蚀，是形成这一异常分布的根本原因。三环萜烷系列相对丰度与绝对浓度的变化规律表明，不同碳数三环萜烷的生物降解作用同时发生，但其降解速率有明显差别，即抗生物降解能力不同。三环萜烷系列化合物（除C20三环萜烷以外）的抗生物降解能力具有随碳数增加而增强的趋势，而C20三环萜烷抗降解能力似乎强于C21~C23三环萜烷。原油中未检测到脱甲基三环萜烷，表明三环萜烷的降解并非通过微生物的脱甲基化作用，推测其降解途径是微生物氧化三环萜烷C环支链末端的甲基，形成对应的羧酸化合物。四个原油样品甾烷、藿烷与三环萜烷被微生物严重侵蚀，不能用于油源对比研究，而三芳甾烷未受生物降解影响，可作为研究区严重生物降解原油油源对比的有效指标。
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| 关 键 词： | 生物降解 三环萜烷 原油 庙西凹陷 渤海湾盆地 |
| 收稿时间： | 2016-03-25 |
Abnormal Distributions of Tricyclic Terpanes and Its Genesis in Severely Biodegraded Oils from the Miaoxi Depression,Bohai Bay Basin |
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| CHENG Xiong,HOU DuJie,XU ChangGui,WANG FeiLong.Abnormal Distributions of Tricyclic Terpanes and Its Genesis in Severely Biodegraded Oils from the Miaoxi Depression,Bohai Bay Basin[J].Acta Sedimentologica Sinica,2017,35(1):193-202. |
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| Authors: | CHENG Xiong HOU DuJie XU ChangGui WANG FeiLong |
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| Institution: | 1.Key Laboratory of Marine Reservoir Evolution and Hydrocarbon Accumulation Mechanism, Ministry of Education, School of Energy Resources, China University of Geosciences, Beijing 100083, China;2.Key Laboratory of Shale Gas Exploration and Evaluation, Ministry of Land and Resources, School of Energy Resources, China University of Geosciences, Beijing 100083, China;3.Tianjin Branch of CNOOC, Tianjin 300452, China |
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| Abstract: | A series of biodegraded crude oils collected from Bohai Bay Basin, China, has been characterized by gas chromatography and gas chromatography-mass spectrometry. The results show that the distributions of tricyclic terpanes are abnormal in four severely biodegraded crude oil samples collected from Well PL15-8D and PL9-4. The four crude oils subjected to severe biodegradation which removed all regular steranes and most of the pentacyclic triterpanes, leaving the 25-norhopane as a dominant component in the m/z191 mass chromatograms of the saturated hydrocarbon fraction. However, the pregnanes, diasteranes and triaromatic steroid hydrocarbons appear to be relatively unaffected. The tricyclic terpanes show three abnormal distribution patterns, namely, predominant by C23, C20 and C23, C20 and C24 components, respectively, which are totally different from the source rocks and other crude oils from the Bohai Bay Basin. These abnormal distribution patterns of tricyclic terpanes are due to the preferential removal of C19~C23 over C24+ tricyclic terpanes. The ratios of the C19~C26 tricyclic terpanes to pregnane and the C19~C26 tricyclic terpanes to C27 diasteranes decrease with increasing biodegradation, but with different rates, indicating that alteration of tricyclic terpanes with different carbon numbers occurs concurrently and the C24+ tricyclic terpanes are much more resistant to microbial degradation than the C19~C23 compounds. The changes of the ratios of C19~C25 tricyclic terpanes to C26 tricyclic terpane also suggest that the C19~C23 tricyclic terpanes are more susceptible to biodegradation than C24~C26 tricyclic terpanes and C24~C25 tricyclic terpanes are more susceptible to biodegradation than C26 tricyclic terpanes. The absolute concentration of C19 to C26 tricyclic terpanes and the relative depletion of C19~C23 tricyclic terpanes show that the susceptibility of C19 to C26 tricyclic terpanes to biodegradation decreases with increasing carbon number of the components. In general, the resistance to biodegradation of tricyclic terpane series is found to increase with increasing of the carbon number, except for the C20 tricyclic terpane. No demethylated tricyclic terpanes were detected in these severely biodegraded oils, suggesting that the degradation pathway of tricyclic terpanes occurred in reservoirs might be similar to hopanes, namely, they could be degraded without forming demethylated counterparts. A putative biodegradation pathway is that the methyl on the side chain of the C cycle was oxidized to carboxyl. The prerequisite of taking tricyclic terpanes as indicators for correlating degraded oil is that they are unaffected by microbe. The regular steranes, hopanes and tricyclics which have been degraded can not be used for oil-source correlation research, while, the triaromatic steranes are non-degraded and can be used for such purpose. |
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| Keywords: | biodegradation tricyclic terpanes curde oil Miaoxi Depression Bohai Bay Basin |
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