四川盆地震旦系下古生界天然气成藏过程和特征

四川盆地震旦系-下古生界具有三套泥质油系烃源岩,具有很好的生油潜力和生烃强度。受加里东隆升作用的影响,烃源岩有二次生、排烃的特征,三叠纪是主要圈闭形成期和二次生油的主峰期,大量的石油运聚至乐山-龙女寺古隆起范围内形成震旦系-下古生界古油藏。随着古油藏埋深的增加,温度和压力的增高,石油裂解成天然气,古油藏自身形成气源,在原地系统形成古气藏。这一过程持续到喜马拉雅期,之后受喜马拉雅运动的影响,强烈隆升和剥蚀,圈闭重新调整,气藏重新分配,最终形成现今气藏。因此,四川盆地震旦系-下古生界天然气的成藏过程是一个古油藏→古气藏→现今气藏的过程,具有生排差异、多期运聚、早聚晚藏的特征。

Characteristic and accumulation process of the natural gas from Sinian to Lower Paleozoic in Sichuan Basin,China

There are three sets of oil-type hydrocarbon source rocks from Sinian to Lower Paleozoic in Sichuan basin. These source rocks are good in the oil-generating potential and hydrocarbon-generating intensity and have secondly generating hydrocarbon capacity by the influence of the Caledonian uplifting movement. The Triassic is the period of forming the main traps and the peak of the secondary oil generation, and the huge amount of oil migrated and accumulated in the area of the Leshan-Longnüsi paleo-uplift and formed Sinian to Lower Paleozoic paleo-oil pools. With the increase of buried depth and the rise of temperature and pressure, the oil cracked to gas, and the paleo-oil pools became the source of gas and formed paleo-gas pools. The traps were modified and the gas pools were rearranged by strong uplifts and erosion during Himalayan movement. Finally the present gas pools formed. Hence, the accumulation process of natural gas from Sinian to Lower Paleozoic in Sichuan basin is a transforming process from paleo-oil pools to paleo-gas pools to present gas pools with the characteristics of difference in generation and expulsion, multi-stage migration and accumulation, early accumulation and late pool formation.