鄂尔多斯盆地延长组烃源岩中单甲基烷烃来源及意义  

Origin and significance of monomethylalkanes from Yanchang Formation source rocks in Ordos Basin

作　　者：钱宇[1,2] 王作栋[1] 妥进才[1] 张婷[1,2] 贺永红 

机构地区：[1]甘肃省油气资源研究重点实验室/中国科学院油气资源研究重点实验室,兰州730000 [2]中国科学院大学,北京100049 [3]陕西延长石油(集团)有限责任公司研究院,西安710000

出　　处：《石油实验地质》2017年第1期86-93,共8页Petroleum Geology & Experiment

基　　金：国家自然科学基金(41602151,41672127);兰州油气资源研究中心“十三五”创新基金(135CCJJ20160523)资助

摘　　要：单甲基烷烃是湖相烃源岩饱和烃中常见的支链烷烃,其母质来源的研究一直存在争议。对鄂尔多斯盆地上三叠统延长组烃源岩样品进行了TOC测定、岩石热解、饱和烃GC-MS和单体碳同位素等分析,并在饱和烃中检出了丰富的单甲基烷烃化合物。地化分析表明,该区长7-长10烃源岩的有机质类型为Ⅱ-Ⅲ型,C_(29)≥C_(27)规则甾烷,高等植物的贡献略微大于低等水生藻类或细菌;单甲基烷烃碳数分布为C_(12)-C_(32),甲基取代位置以C_2和C_3为主。饱和烃单体碳同位素组成数据显示,姥鲛烷和植烷的δ^(13)C比同碳数正构烷烃重1‰~2‰;同碳数2-和3-甲基烷烃具有相近的碳同位素组成,表明两类化合物具有相同物源;单甲基烷烃比正构烷烃更富集^(13)C,表现出更大的δ^(13)C值。结合古环境等信息表明,鄂尔多斯盆地检出的单甲基烷烃可能来自于浮游植物或者异养细菌,单甲基烷烃可以作为一种指示生油母质的生物标志化合物。Monomethylalkanes are common branched alkanes in the saturated hydrocarbon fraction of lacustrine source rocks. However,there is no agreement about their original source. The abundance of monomethylalkanes,from the Triassic Yanchang Formation source rocks in the Ordos Basin is relatively high. Determination of TOC,Rock-Eval,compound specific carbon isotopic composition,and GC-MS analysis of saturated hydrocarbons show that the organic matter of source rocks from Chang7-Chang10 have a mixed source,and that the type of organic matter isⅡ-Ⅲ. The steroid hydrocarbon distributions of source rocks showed nearly equal abundances of C27 and C29 steranes,suggesting mixed organic matter. The monomethylalkanes have 12 to 32 carbons,having a similar distribution to the n-alkanes,and the 2-MMAs and 3-MMAs are predominant. The δ^13 values of Pr and Ph are 1‰ to2‰ heavier than corresponding n-alkanes. 2-MMAs and 3-MMAs with the same carbon number have almost the same δ^13 value,indicating they have the same source. The δ^13 values of monomethylalkanes range from-29.3‰to-32.8‰,which are higher than n-alkanes. Moreover,combining with the sedimentary environment information of the Ordos Basin,it appears that the monomethylalkanes might come from phytoplankton and heterotrophic bacteria,and they can be used as a biomarker to judge the predecessor of sediment and petroleum.

关 键 词：偶数离子碎片峰 单甲基烷烃 单体碳同位素 生物标志化合物 延长组 鄂尔多斯盆地 

分 类 号：TE122.113[石油与天然气工程—油气勘探]