四川盆地上三叠统油气源对比

Hydrocarbon source correlation of the upper Triassic reservoirs in the Sichuan Basin

对储集层油气来源的对比追踪,是储集层烃源条件研究及资源潜力评价的重要内容。为此,基于前人对四川盆地上三叠统须家河组气源研究的成果,对比分析了该区天然气的组成特征、天然气碳同位素值分布特征、原油及储层沥青组成特征和生物标志化合物的特征。结果发现:①须家河组所产天然气与上覆侏罗系及下伏嘉陵江组、二叠系地层所产天然气的组成特征、碳同位素值、浓缩烃等方面差异明显,例如在同一构造上,上三叠统天然气的δ13 C1比上覆侏罗系的偏重而比下伏层的偏轻,δ13 C2则较上、下邻层均偏重;②须家河组原油的物理性质、原油轻烃和饱和烃色谱特征与侏罗系原油也存在明显的差异;③上三叠统储层沥青的族组与烃源岩接近,而与上、下邻层有明显的差异,储层的生物标志化合物特征与烃源岩接近,而与侏罗系烃源岩差异明显。综合分析的结果认为:须家河组的油气主要来自本层烃源岩,局部地区须家河组气藏有下伏气源层对其成藏的贡献。

The oil and gas source correlation is one of the most important contents in the investigation of source rock conditions and the evaluation of hydrocarbon resource potential.Based on the previous studies on gas sources of the upper Triassic Xujiahe Formation in the Sichuan Basin,the gas composition,gas carbon isotope distribution,the composition of crude oil and reservoir bitumen,and biomarkers are analyzed.The following conclusions are drawn.（1） Gas generated in the Xujiahe Formation reservoirs is significantly different from that in the overlying Jurassic and the underlying Jialingjiang Formation and Permian reservoirs in respect of gas composition,carbon isotope,and condensed hydrocarbons.For example,δ 13 C 1 of the upper Triassic gas is heavier than that of the overlying Jurassic gas but lighter than that of gas in the underlying reservoirs within the same structure.In contrast,itsδ 13 C 2 is heavier than that of gas in both the overlying and underlying reservoirs within the same structure.（2） The crude oil of the Xujiahe Formation is also significantly different from that of the Jurassic in respect of physical property,chromatographic characteristics of light and saturated hydrocarbons.（3） Group composition of the reservoir bitumen in the upper Triassic is similar to that of source rocks,but significantly different from that of the overlying and underlying reservoirs.In addition,its biomarkers are similar to that of source rocks in the upper Triassic,but significantly different from that of the source rocks in the Jurassic.A comprehensive analysis shows that the oil / gas in the upper Triassic Xujiahe Formation mainly originated from the source rocks in the same layer,and the underlying source rocks only locally contributed to the gas accumulation in the Xujiahe Formation.