基于轻烃组成的气–油–源三元直接对比——以松辽盆地南部梨树断陷为例

Direct Oil-Gas-Source Correlation Based on Light Hydrocarbons—A Case Study of Lishu Depression in the Southern Songliao Basin

摘要: 气源对比相对油源对比而言，一直是油气勘探开发研究中的难点。利用热脱附–冷阱富集技术直接获得烃源岩吸附轻烃，从而实现了基于轻烃组成的气–油–源三元直接对比。松辽盆地南部梨树断陷原油轻烃族组成相对贫芳香烃，表征其为腐泥型母质来源，其(2-MC₆ + 3-MC₆)/nC₆、MCC₆/CC₆和(Bz + CC₆)/nC₆均较高，具有较高的甲基环己烷指数，尤以秦家屯原油最高；富含甲苯，表征了腐殖型母质的贡献，从而表明原油母质来源为水生生物和陆源植物双重生源，秦家屯原油则具有较高的腐殖型母源贡献。研究区内天然气轻烃族组成富含链烷烃，(2-MC₆ + 3-MC₆)/nC₆、MCC₆/CC₆和(Bz + CC₆)/nC₆均较低，相对贫甲基环己烷和甲苯，表征主力烃源岩原油沉积有机质主体为腐泥型。总体上，沙河子组(K₁s)烃源岩热脱附烃轻烃组成与原油更相似，而营城组(K₁y)烃源岩热脱附烃则与天然气轻烃更相似，进一步表明了研究区原油与天然气的非同源性，其中原油主力烃源岩为K₁s，而天然气主力烃源岩则为K₁y。

Abstract: Compared with the oil-source correlation, the gas-source correlation has been the difficulty in oil and gas exploration and development. In this paper, thermo-desorption-cold trap technique was used to collect light hydrocarbons absorbed by source rock; thus, direct oil-gas-source correlation based on light hydrocarbon was implemented. Crude oil in the Lishu Depression in the southern Songliao Basin was relatively poor in aromatics, and rich in methylcyclohexane and toluene; espe-cially for Qinjiatun oil samples, they were characterized by higher ratios of (2-MC₆ + 3-MC₆)/nC₆, MCC₆/CC₆, and (Bz + CC₆)/nC6, indicated dual inputs of aquatic organism and higher plant. While the dominant organic matter input of Qinjiatun oil was humic type. Gas samples were rich in alkans, poor in methylcyclohexane and toluene, and they were characterized by relatively lower ratios of (2-MC₆ + 3-MC₆)/nC₆, MCC6/CC₆, and (Bz + CC₆)/nC₆, indicated sapropel organic matter input. In general, the composition of light hydrocarbons thermo-desorbed from Shahezi Formation samples is more similar to the light hydrocarbons of crude oil, while the composition of light hydrocarbons by thermo-desorbed from Yingcheng Formation samples is more similar to the gas. It further indicates different origins of oil and gas; the dominant source rock of oil is from Shahezi Formation and the dominant source rock of gas is from Yingcheng Formation.