陆相纹层型页岩油储集空间特征及其控制因素——以松辽盆地长岭凹陷青山口组页岩为例

Reservoir space and controlling factors of lacustrine laminated shale oil reservoir:A case study of Cretaceous Qingshankou Formation in the Changling Sag,southern Songliao Basin,NE China

松辽盆地陆相页岩油勘探前景广阔,但目前关于长岭凹陷白垩系青山口组纹层型页岩油储层微观孔隙结构特征的认识相对薄弱。基于薄片鉴定、TOC、岩石热解和XRD分析,结合场发射扫描电镜、低温氮气吸附及高压压汞等测试手段,对青山口组页岩进行岩相划分,系统分析页岩储集空间分布规律,明确优势岩相和孔隙结构的控制因素。依据“有机质丰度—矿物组成”标准,将页岩样品划分为低TOC混合质页岩(M—L)、中TOC硅质页岩(S—M)、中TOC混合质页岩(M—M)、中TOC黏土质页岩(C—M)、高TOC硅质页岩(S—H)、高TOC混合质页岩(M—H)及高TOC黏土质页岩(C—H) 7种岩相。其中,C—H岩相生烃潜力好,储集空间发育,以狭缝状黏土矿物晶间孔、粒间孔和微裂缝为主,孔隙结构参数优,是研究区储层的优势岩相。青山口组页岩储集空间分布受控于纹层特征、TOC含量和矿物组成等因素,长英质纹层能够有效缓解上覆岩石压实作用,有机酸扩溶作用和超压裂缝的形成改善了宏孔体积占比,而黏土矿物晶间孔和微裂缝提供了主要的比表面积和孔体积。

Based on thin section identification,the organic geochemistry,XRD,combined with scanning electron microscopy,N2 isothermal adsorption and high pressure mercury injection tests,the characteristics of laminated shale lithofacies were identified and the reservoir pore structure was comprehensively analyzed,and then the favorable shale lithofacies and main controlling factors of pore development were clarified.According to the classification standard of“abundance of organic matter and mineral composition”,the shale of Qingshankou Formation is divided into seven lithofacies:M-L,S-M,M-M,C-M,S-H,M-H and C-H.The kind of C-H shale lithofacies is regarded as the favorable type in the study area,because it has absolute hydrocarbon generation potential,and its reservoir space is well developed with superior pore structure parameters,which is dominated by slit clay mineral intercrystalline pores,intergranular pores and micro-fractures.The shale reservoir space of Qingshankou Formation is controlled by laminae development,TOC content and mineral composition.The felsic lamination effectively alleviates overlying rock compaction,organic acid diffusion and formation of overpressure fractures improve macropore volume ratio,and the clay mineral intercrystalline pores and fractures provide the main specific surface area and pore volume.