沧东凹陷深湖亚相纹层状页岩成因及页岩油可动性影响因素

Genesis of deep lacustrine subfacies laminated shale and influence factors on shale oil mobility in Cangdong sag,Bohai Bay Basin

纹层是深湖亚相页岩的重要沉积结构,对页岩油的可动性具有重要影响。以渤海湾盆地沧东凹陷孔店组二段(孔二段)为例,综合X射线衍射、岩石热解、X射线荧光光谱、全自动矿物分析、场发射扫描电镜和氮气吸附等测试技术,从微米—纳米尺度探讨了纹层状页岩中页岩油的特征和成因,并深入分析了页岩油可动性的控制因素。研究结果表明:孔二段页岩主要有5类纹层,即长英质纹层、灰云质纹层、黏土质纹层、方沸石质纹层和混合质纹层,其中,前3类纹层的平均厚度分别约为250μm、125μm和65μm。这些纹层主要构成了3类纹层状页岩:纹层状长英质页岩、纹层状灰云质页岩和纹层状混合质页岩。根据细粒沉积的有机相分类,纹层状长英质页岩形成于强外源输入的淡水沉积环境,而纹层状灰云质页岩形成于高含硫的碳酸盐/蒸发岩等相对咸水沉积环境,这反映二者在高效生烃机理上存在差异。进一步研究表明,有机-无机地质因素共同影响纹层状页岩中页岩油的可动性。有利于页岩油流动的因素包括:页岩具有适中的总有机碳含量(1%~4%)和最高热解峰温(435~450℃),发育产气型干酪根而非产油型干酪根,具有更高的碳酸盐含量而非长英质含量、大孔径和更低的孔隙比表面积。研究成果有望为深化陆相页岩油“甜点”评价、指导页岩油勘探开发提供理论指导。

The laminae,the fundamental sedimentary structure of deep-lacustrine subfacies shales,have an important influence on the mobility of shale oil.This paper is a case study of the Member 2 of Kongdian Formation in Cangdong sag of Bohai Bay Basin.Comprehensively using the testing techniques such as X-ray diffraction,Rock-eval,X-ray fluorescence spectra,advanced mineral identification and characterization system,high resolution field emission scanning electron microscopy,and N2 adsorption,the paper explores the features and genesis of laminated shale oil at the micro-and nano-scale,and deeply analyzes the controlling factors of shale oil mobility.The results show that there are mainly five types of laminae in the study area,i.e.,felsic laminae,calcareous-dolomitic laminae,clayey laminae,analcime laminae,and mixed laminae.The average thickness of felsic,lime-dolomitic and clayey laminae is approximately 250μm,125μm,and 65μm,respectively.These laminae mainly develop three types of laminated shales,i.e.,laminated felsic shale,laminated calcareous-dolomitic shale,and laminated mixed shales.The classification of organic facies based on fine-grained sedimentation indicates that laminated felsic shale originate from freshwater depositional environment with strong external input,whereas laminated calcareous-dolomitic shale are formed in saline water depositional environment of sulfur-rich carbonate and evaporite.This reveals the differences in efficient hydrocarbon generation mechanisms between laminated felsic and calcareous-dolomitic shales.The further research suggests that the mobility of shale oil is jointly affected by both organic and inorganic geological factors.The conditions favorable for the mobility of shale oil is as below.(1)Shale has the moderate total organic carbon contents in the range from 1%to 4%,with the maximum pyrolysis temperatures in the range from 435℃to 450℃.(2)Gas-producing kerogen is developed in shale,rather than oil-producing kerogen.(3)Shale possesses higher carbonate content compared to felsic content,large pore diameter,and low pore specific surface area.This study is expected to improve the evaluation of"sweet spots"in continental shale oil and guide shale oil exploration and development.