GEOCHEMICAL CHARACTERISTICS AND SOURCE OF PALEO- RESERVOIR SOLID BITUMEN IN SHIWANDASHAN BASIN
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摘要: 根据沥青产状、族组成、饱和烃色谱、生物标志化合物、碳同位素以及沥青热演化程度等,对广西十万大山盆地北缘的老虎山古油藏、上屯古油藏二叠系灰岩中固体沥青的地球化学特征进行了系统分析,并结合有关烃源岩地球化学特征及油气成藏研究成果对其来源和成因进行了探讨.结果表明,古油藏沥青抽提物含量低,族组成中芳烃和非烃含量高,饱和烃含量低,芳烃含量最高可达58.60%.饱和烃气相色谱分析表明,沥青具还原环境、以低等水生生源为主的母质来源及较高的热演化程度.沥青稳定碳同位素为-27.8‰~-28.7‰,反映其生烃母质以低等生源为主.沥青中的甾、萜烷含量很低,且以低分子量化合物占绝对优势,其中甾烷系列中具很高的孕甾烷含量,萜烷则以三环萜烷为主,反映其高热演化特征.沥青几乎不含芳香甾烷,与本区上二叠统泥质烃源岩特征相似;沥青反射率为1.9%~2.5%,结合本区生烃成藏演化史分析结果,反映其经历过230℃高温.最后结合相关烃源岩地球化学特征及有关油气成藏信息,综合认为古油藏沥青与上二叠统泥质烃源岩有较好的亲缘关系,是古油藏早期原油高温裂解的产物之一,即焦沥青.Abstract: Systematic geochemical analysis such as bitumen occurrence,group composition of dissolved organic matter,saturated hydrocarbon chromatography,biomarker compounds,carbon isotope and bitumen thermal maturation is applied to the solid bitumen of Laohushan and Shangtun paleo-reservoirs from Permian limestones in Shiwandashan Basin of Guangxi Province,China.And combined with geochemical characters of hydrocarbon source rocks and reservoir-forming mechanism,the source and genesis of above two solid bitumen has been discussed.The results show that the content of dissolved organic matter and saturated hydrocarbon is very poor and the content of aromatic hydrocarbon(the highest being 58.60%)and nonhydrocarbon is rich.The gas chromatogram analysis of saturated hydrocarbon show that bitumen is from reduction environment originating from lower grade aquatic geology with higher thermal evolution degree.The stable carbon isotope of bitumen is -27.8‰~-28.7‰,reflecting that the main source of input of source rock is lower aquatic biology.The lower content of sterane and terpane(dominated by low molecular compounds),higher content of pregnane in sterane series and tricyclic terpane predominated in terpane indicate that the bitumen was characterised by high evolution.Like the argillaceous source rock of Permian,there is nearly no aromatic sterane in bitumen.The reflectance of bitumen is 1.9%～2.5%,and the equivalent vitrinite reflectance is 1.6%~2.0%,associated with the results of reservoiring and evolution history,it shows that the bitumen experienced 230℃ temperature.Finally combined with relative geochemical characters of hydrocarbon and certain information of reservoir-forming,it is considered that the paleo-reservoir bitumen has closer genetic relationship with Upper Permian argillaceous source rock,and it is one of the final pyrolysis products of crude oil in paleo-reservoir,(that is pyrobitumen).
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Key words:
- paleo-reservoir /
- reservoir bitumen /
- geochemical characteristics /
- bitumen source /
- bitumen genesis /
- aromatic sterane
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