鄂尔多斯盆地长7_(3)亚段泥页岩型页岩油赋存状态与有机地球化学特征

Occurrence states and organic geochemical characteristics of shale-type shale oil from Chang 7_(3) sub-member in the Ordos Basin

页岩油的赋存状态与有机地球化学特征对页岩油的甜点区评价与资源潜力评估具有重要意义。为明确鄂尔多斯盆地延长组长73亚段泥页岩中页岩油的赋存位置、含油量、族组分和饱和烃分布特征,选取长73亚段的泥页岩岩心样品进行多溶剂连续分级抽提、低温氮气吸附—解吸、荧光薄片鉴定、场发射扫描电镜和饱和烃气相色谱—质谱等分析。结果表明:长73亚段泥页岩型页岩油主要赋存于页理缝和有机质孔中;页岩油的含油总量大于10 mg/g,其中游离油约占50%,吸附油约占20%;游离油、吸附油含量与有机质丰度之间呈较好的正相关关系,表明有机质丰度是控制页岩油分布的主要因素;游离油含有较多的饱和烃和轻质组分,而吸附油则含有较多的非烃与沥青质等重质组分。此外,与暗色泥岩相比,黑色页岩具有广泛发育的页理缝和有机质孔,游离油含量较高,黑色页岩可能是更有利于页岩油勘探开发的岩相类型。

The occurrence state and organic geochemical characteristics of shale oil are of great significance to the evaluation of sweet spot and resource potential of shale oil.In order to clarify the storage location,oil content,group component and saturated hydrocarbon distribution characteristics of shale oil from Chang 7submember of the Yanchang Group in the Ordos Basin,the shale core samples of the Chang 7sub-member were analyzed by multi-solvent continuous fractional extraction,low-temperature nitrogen adsorption,fluorescent thin-section petrological observation,field emission scanning electron microscopy and saturated hydrocarbon gas chromatography-mass spectrometry.The results show that shale oil mainly occurs in shale fractures and organic pores in Chang 7sub-member.The total oil content of shale oil is more than 10 mg/g,of which free oil accounts for 50%and adsorbed oil accounts for 20%.The content of free oil and adsorbed oil is positively correlated with the abundance of organic matter,which indicates that the abundance of organic matter is the main factor controlling the distribution of shale oil.Free oil contains more saturated hydrocarbons and light components,while adsorbed oil contains more heavy components such as non-hydrocarbon and asphaltene.In addition,compared with dark mudstone,black shale has widely developed cleavage fractures and organic pores,and has higher free oil content,which may be a more favorable lithofacies for shale oil exploration and development.