四川盆地低熟沥青生气模拟研究

Study on gas generation from low maturity asphalt in Sichuan Basin,China

通过四川盆地低成熟沥青热解实验,分析了气体产物组分、产率和碳同位素组成及变化特征。结果表明,四川盆地古生界低成熟沥青产出烃类气体的能力较高,是一种重要的生气有机质母质;生成的非烃气体总体上具有高氮气、低二氧化碳含量的特点;不同碳数烃类气体之间具有δ13C1<δ13C2<δ13C3的特征。探讨了模拟结果对页岩气成因和聚集成藏研究的意义。模拟页岩气具有低干燥系数和较轻碳同位素分布特征,可能指示地质条件下页岩气有效聚集的良好封闭条件;高含量N2可能是指示页岩气成因和成藏研究的潜在指标;利用甲烷碳同位素进行油气(包括页岩气)成因判识需要注意气体地质保存条件对同位素分馏作用的影响。

Pyrolysis experiments on low maturity asphalt from Sichuan Basin were carried out in a confined system,and the composition,yield and carbon isotopic composition of gas products were analyzed.Results show that there are large amounts of hydrocarbons gases generation from low maturity asphalt indicating that it is an important potential secondary organic material as Paleozoic shale gas source in Sichuan Basin.Yields of nitrogen（N2） in non-hydrocarbon gases generation from low maturity asphalt are generally high,but carbon dioxide（CO2） low.There is a carbon isotopic distribution with δ13C1δ13C2δ13C3 among different carbon number hydrocarbon gases.Simulation results were also applied for understanding genesis and accumulation of shale gases in geological environment.For example,low dry coefficient and light carbon isotopic composition likely indicate the well-closed geological conditions favorable for the accumulation of shale gases.High content of N2 is a potential indicator for its genesis and accumulation of shale gas.Effects of preservation conditions of gas generation on carbon isotope fractionation should be noted when the methane carbon isotope composition is used to identify the genesis of oil and gas including shale gas.