准噶尔盆地玛湖凹陷二叠系风城组页岩油赋存定量表征及其主控因素

Quantitative characterization and main controlling factors of shale oil occurrence in Permian Fengcheng Formation,Mahu Sag,Junggar Basin

准噶尔盆地玛湖凹陷二叠系风城组页岩油赋存特征及控制因素复杂,赋存状态与定量表征难度大,厘清页岩油赋存特征和主控因素对优选甜点体具有重要意义。为表征玛湖凹陷不同赋存状态页岩油含量,对凹陷中心区和斜坡区的风城组页岩样品进行分步抽提,建立了不同赋存状态页岩油定量表征实验方法,分别得到游离轻烃、游离重烃和吸附烃的含量。在有机地球化学和储层微观特征研究的基础上,得到以下认识:由于研究区有机碳和黏土含量较低,风城组页岩油以游离赋存状态为主,吸附烃含量最少;页岩油多以油膜状赋存于矿物表面和干酪根中,重烃通常赋存于微孔比表面积大的页岩中,宏孔是游离油的主要赋存场所;有机质丰度和孔径增大,不同赋存状态页岩油含量均呈增加趋势,较高有机质丰度和孔径较大的储层有利于页岩油富集;成熟度可以很大程度上影响页岩中流体的吸附能力,有机质成熟度越高的页岩样品游离烃占比越多、吸附烃占比越少;比表面积的增大促进吸附油与游离重烃的富集,制约游离轻烃的富集,中孔比表面积对于页岩油的吸附量具有控制作用,比表面积越大页岩的吸附能力越强。相关研究和认识可为研究区优选甜点段和评价页岩油开采效益提供依据。

The characteristics and controlling factors of shale oil occurrence in Permian Fengcheng Formation of the Mahu Sag,Junggar Basin are complex,making occurrence state identification and quantitative characteriza⁃tion difficult.It is of great significance to clarify the occurrence characteristics and controlling factors of shale oil for selecting sweet spots.In order to characterize the content of shale oil in different occurrence states,some shale samples in the central and slope areas of the sag were extracted step by step,and a quantitative characte⁃rization experiment method of shale oil in different occurrence states was established,obtaining the contents of free light hydrocarbon,free heavy hydrocarbon and adsorbed hydrocarbon,respectively.Based on the study of organic geochemistry and reservoir micro⁃characteristics,the following conclusions are obtained.Due to the low TOC and clay contents in the study area,the shale oil in the Fengcheng Formation mainly occurs in dissociative state and has the least adsorbed hydrocarbon content.Shale oil occurs mostly on mineral surface and in kerogen in oil film state,heavy hydrocarbons usually occur in shale with large micropore specific surface area,and macropores are the main occurrence space of free oil.With the increase of organic matter abundance and pore size,the shale oil content in different occurrence states shows an increasing trend,indicating that the higher organic matter abundance and larger pore size are conducive to shale oil enrichment.Maturity can greatly affect the adsorption capacity of fluid in shale,and the higher the maturity of organic matter,the higher the proportion of free hydrocarbons and the lower the proportion of adsorbed hydrocarbons.The increase of specific surface area promotes the enrichment of adsorbed oil and free heavy hydrocarbons,and restricts the enrichment of free light hydrocarbons,indicating that the specific surface area of mesoporous pores has a controlling effect on the adsorp⁃tion capacity of shale oil,i.e.,the larger the specific surface area,the stronger the adsorption capacity of shale oil.The relevant research and recognition can provide a basis for selecting sweet spots and evaluating the benefits of shale oil exploitation in the study area.