松辽盆地白垩系青山口组一段页岩生、排烃组分特征及页岩油相态演化

Composition of generated and expelled hydrocarbons and phase evolution of shale oil in the 1st member of Qingshankou Formation,Songliao Basin

松辽盆地白垩系青山口组一段(青一段)页岩有机质热演化程度跨度大、烃类流动性差异强。页岩油相态分析预测是页岩油勘探开发的重要难题。用低成熟页岩样品开展封闭体系及半封闭体系有机质热解实验,根据生、排烃组分特征对滞留烃的轻烃散失进行补偿校正,研究了页岩油组分演化特征。结合中央坳陷区主要生油凹陷典型井埋藏史、热演化史,研究了页岩油相态演化规律,提出了轻质页岩油勘探有利区和开发压力保护条件。研究结果表明:地质条件下随着有机质成熟度的升高,页岩油组分中轻质组分比例不断增加、气体逐渐增多,相包络线从高露点温度、低泡点压力依次向低露点温度、高泡点压力演化。齐家-古龙凹陷青一段页岩油在嫩江组中期油藏向挥发油油藏转化,长岭凹陷青一段页岩油从嫩江组末期开始油藏向挥发油油藏转化,三肇凹陷青一段页岩油则始终为黑油油藏。无论是黑油油藏还是挥发油油藏,均为单一液相。松辽盆地中央坳陷区青一段页岩油挥发油油藏主要分布在齐家-古龙凹陷中心和长岭凹陷北部有机质成熟度(镜质体反射率Ro)为1.3%~1.6%、地层压力为12.2~22.4 MPa的区域。

Shales in the first member of the Qingshankou Formation(the Qing 1 Member)in the Songliao Basin exhibit a large variation of organic matter maturity and strong heterogeneity of hydrocarbon mobility.How to analyze the shale oil phase and physical properties has posed a major challenge for efficient shale oil exploitation and production.We investigate the characteristics of shale oil composition evolution by carrying out closed and semi-closed organic matter pyrolysis experiments on low-maturity shale samples,in which compensation correction for light hydrocarbon loss of retained hydrocarbons is performed based on the composition of generated and expelled hydrocarbons.By integrating the burial and thermal evolution histories of typical wells in main source kitchens in the Central Depression,we explore the phase evolution pattern of shale oil.Furthermore,we identify play fairways for light shale oil exploration and outline protection conditions for maintaining production pressure.The results reveal that under geological conditions,light components’proportions and gaseous hydrocarbon content in shale oil increase progressively with the maturity of organic matter.Concurrently,the phase envelopes evolve from high dew point temperature(DPT)and low bubble point pressure(BPP)toward low DPT and then to high BPP with an increase in the organic matter maturity.In the Qijia-Gulong Sag,the shale oil reservoirs of the Qing 1 Member evolved into light oil reservoirs in the middle stage of the Nenjiang Formation deposition.In the Changling Sag,these reservoirs began to evolve into light oil reservoirs at the end of the Nenjiang Formation deposition.In contrast,these reservoirs in the Sanzhao Sag have been consistently present as black oil reservoirs.Shale oil within both black and volatile oil reservoirs remains in a single liquid phase.In the Central Depression of the Songliao Basin,the light shale oil reservoirs of the Qing 1 Member are primarily distributed at the center of the Qijia-Gulong Sag and in the northern Changling Sag,with maturity of organic matter(Ro)varying from 1.3%to 1.6%and formation pressure from 12.2 to 22.4 MPa.