致密砂岩气藏油气轻烃特征及其地质意义——以四川盆地西北部须家河组气藏为例

四川盆地西北部上三叠统须家河组天然气、凝析油样品的C₇及C₅-C₇轻烃分布显示出油气主要来源于富含腐殖型干酪根的煤系泥岩与煤岩，该区油气样品的K₁值平均为1.04，整体相关性较好；K₂值差异较大，相关系数也较低，母体-子体比值梓潼凹陷须家河组呈现出较强的离散型。利用庚烷值、异庚烷值及MANGO稳态催化动力学等方法计算表明，天然气处于成熟-高成熟演化阶段，明显低于该区烃源岩实测成熟度及天然气δ13C₁值计算的成熟度。梓潼凹陷须家河组凝析油及天然气轻烃星状指纹图分析显示，同一构造不同层位、同一层位不同构造油气可对比性较差，表明该区油气藏内部砂体之间的连通性较差，油气成藏以近源短距离运聚为主。由于该区储层早期已达致密演化阶段，从而导致在封闭-半封闭的地质环境中，天然气受不同热演化阶段天然气的累积效应影响，而凝析油受到同源不同期的天然气多次气侵而产生“蒸发分馏”效应影响，导致部分轻烃参数在应用过程中出现偏差。 

Light hydrocarbon characteristics of petroleum in a tight sandstone gas reservoir and its geological significance: a case study of the Upper Triassic Xujiahe Formation gas reservoir in the northwestern Sichuan Basin

Light hydrocarbons (C₇ and C₅-C₇) of the natural gas and condensate from the Upper Triassic Xujiahe Formation in the northwestern Sichuan Basin indicated that the petroleum was sourced primarily from coaly mudstones and coal rocks that were rich in humic kerogen. K₁ values from the study area average 1.04 and are relatively well correlated, while the K₂ values vary greatly and are relatively poorly correlated. The parent-daughter ratio of the Xujiahe Formation is of the discrete type in the Zitong Sag. The heptane value, isoheptane value and MANGO steady-state catalytic kinetic method indicates that the natural gas is currently in the mature to highly mature stage, with a maturity clearly lower than the measured maturity of the source rocks in the study area and the δ13C₁-calculated maturity. The star-plot diagram of light hydrocarbons of natural gas and condensate from the Xujiahe Formation in the Zitong Sag revealed the poor correlation with oil trapped in the same structure but different layers or in the same layer but different structures. This suggested that sand bodies in the reservoirs within the study area were poorly connected and the reservoirs were formed mainly as the result of near-source and short-distance migration and accumulation. Since the early reservoirs in this area have entered the tight evolution stage, natural gas is at different thermal evolution stages, and condensate oil is influenced by the effect of "evaporation and fractionation" of natural gas at different stages of the homologous period, resulting in the discrepancy of the interpretation of some light hydrocarbon parameters.