川东北地区烃源岩与沥青生物标志物特征及古油藏油源辨识

Biomarker characteristics of source rock and bitumen and oil-source correlation of paleo-reservoir in northeastern Sichuan

川东北地区是我国重要的天然气产区,古油藏原油裂解成气是该区天然气的主要来源。针对该区古油藏油源研究存在的争议,对古生界—中生界主要烃源岩层系和长兴组—嘉陵江组储层沥青的生物标志物特征进行了分析和对比。结果表明:烃源岩有机质母源下古生界以水生生物为主;上古生界具有水生生物与高等植物混源的特征,以水生生物为主;中生界以高等植物为主,兼有水生生物。烃源岩沉积水体古生界主要为咸水,中生界主要为淡水。烃源岩沉积环境古生界以弱还原—还原环境为主,中生界以弱氧化—弱还原环境为主。生物标志物特征表明,上二叠统龙潭组烃源岩为长兴组—嘉陵江组古油藏主力烃源岩,下二叠统梁山组烃源岩也有一定的贡献。

Northeastern Sichuan is an important gas producing area of China, and its primary origin of gas is the cracking of crude oil of paleo-reservoir. On account of the uncertainty of oil sources of paleo-reservoir, the biomarker of reservoir bitumen of Changxing-Jialingjiang Formation and source rocks of Paleozonic and Mesozoic in northeastern Sichuan was analyzed and contrasted. The result shows that the organic matter of Lower Paleozonic source rocks was derived from hydrobios and algae; the organic matter of Upper Paleozonic source rocks was derived from a mixing source in which hydrobios and algae prevail over higher plants; the organic matter of Upper Paleozonic source rocks was dominated by higher plants. Palcozonic source rocks deposited in reducing to weakly reducing transitional environment with saline water and Mesozoic source rocks deposited in weakly reducing to weakly oxic transitional environment with fresh water. The main oil source formation of paleo-reservoir in Changxing-Jialingjiang Formation is Upper Permian Longtan Formation,and lhe source rocks of Lower Permian Liangshan Formation also have partial eontribution to the paleo-reservoir.