中-低成熟湖相富有机质泥页岩含油性及赋存形式——以渤海湾盆地渤南洼陷罗63井和义21井沙河街组一段为例

摘要

This paper studied oil content and occurrence in low to medium mature organic-rich lacustrine shales by taking the cored section of the 1st Member of the Eocene-Oligocene Shahejie Formation in Well Luo63 and Yi21 in Bonan subsag,Zhanhua sag,Bohai Bay Basin,as an example.Oil content was evaluated qualitatively by using chloroform bitumen "A" and oil saturation indices (OSI) after light hydrocarbon correction,and oil occurrence was studied both qualitatively and quantitatively through thin section observation,SEM observation,and thermal desorption.The results show that organ ic-rich shales in the 1st Member of Shahejie Formation (Es1) contain over 1％ chloroform bitumen "A",whereas the oil saturation indices (OSI) indicate modest oil content to oil show,with a few samples display high potential for shale oil production,after light hydrocarbon correction.Oils retained in the organic-rich shales occur both in association with organic macerals (adsorption or dissolution in bitumenite and laminate alginate),and in bedding fractures,stress induced microfractures,intergranular and intercrystalline pores,grain boundary fractures and mineral dissolution pores.High molecular weight hydrocarbons occur mainly in association with insoluble organic matter,by adsorption or in dissolution,accounting for 68 ％ ～ 84 ％ of total oil content (with an average of 75 ％).The free low to medium molecular weight hydrocarbons occur mainly in various fractures and pores,accounting for 16 ％ ～32 ％ of total retained oil (with an average of 25 ％).The contents of practicable movable oil (sum contents of light hydrocarbon correction and thermal desorption at 200 ℃) are in the range from 0.62 mg/g to1.76mg/g (with an average of 1.12 mg/g) and the movable oil ratio (the percentage of practicable movable oil content in total oil content) from 5.39％ to 9.10％,with an average of 7.06％.The sum of light oil thermal desorption at 200 ℃ and light hydrocarbon correction can be used reasonably to evaluate shale oil resource potential in organic-rich shales.%为揭示中-低成熟湖相富有机质泥页岩含油性及其赋存形式,以渤海湾盆地沾化凹陷渤南洼陷罗63井和义21井沙一段取心段为例,采用轻烃校正后的氯仿沥青“A”含量、油饱和指数(OSI)开展了含油性定量评价,采用光薄片和扫描电镜观察以及多温阶热释分析技术,开展了滞留油赋存形式定性、定量研究.结果表明,沙一段富有机质泥页岩含油性较好,经轻烃校正后的氯仿沥青“A”平均含量和油饱和指数(OSI)分别达到1.0％以上和中等含油至油气显示级别,个别层段达到具有页岩油潜力级别;富有机质泥页岩内滞留油除以有机显微组分(沥青质体和层状藻类体等)吸附-互溶态形式赋存外,还赋存于层理缝、构造微裂缝、矿物粒间(晶间)孔隙、粒缘缝以及溶蚀孔隙内.以有机质吸附-互溶态和无机矿物吸附态赋存的重质油占总滞留油的68％ ～ 84％(平均达75％),而以游离态赋存的轻质和中质油则占总滞留油的16％ ～32％(平均25％).现实可动油量(轻烃校正量与200℃热释轻质油量之和)介于0.62～1.76 mg/g(平均1.12 mg/g),可动油率(现实可动油量与总滞留油量之比)5.39％ ～9.10％(平均7.06％).利用200℃时热释放的轻质油量和轻烃校正量之和,可以较合理地对富有机质泥页岩层系的页岩油资源潜力进行快速评价.