页岩油储层多尺度孔隙结构三维表征及应用

Three-dimensional characterization and application of multi-scale pore structure in shale oil reservoir

中国陆相页岩油发育的地质时代跨度较大,沉积相变化快,热演化程度整体偏低,岩性复杂多样。为明确复杂岩性的渗流规律,以鄂尔多斯盆地延长组长73、渤海湾盆地沙河街组页岩样品为研究对象,利用微米CT和聚焦离子束扫描电镜(FIB-SEM)成像技术,结合Avizo软件建立页岩油储层多尺度三维重构模型,定性定量分析了页岩油储层多尺度孔隙结构特征,并通过数值模拟计算了岩心渗透率。研究结果表明:微米尺度下,样品C(纹层状页岩)孔隙最为发育,样品G(层状页岩)次之,样品F(块状页岩)最差;纳米尺度下,3块样品孔隙发育相当,其中样品G连通性更好,得出微纳尺度下具有不同的孔隙发育特征。渗透率数值模拟计算得到样品C、F、G的渗透率分别为0.437 mD、0.031 mD、0.224 mD,和气测渗透率结果具有一致性,表明渗透率数值模拟方法可快速准确计算岩心渗透率。结合微纳尺度孔隙发育情况和渗透率数值模拟结果,可知样品C品质最好,油气勘探开发应重点关注纹层状页岩储层。因此,结合微米CT和FIB-SEM可准确表征页岩储层多尺度孔隙结构特征,识别优质储层,对页岩油气高效开发具有指导意义。

Continental shale oil in China has a long geological period, and its sedimentary phases change rapidly, with low thermal evolution degree and complex and diverse lithology. To figure out the permeability rule of complex lithology, shale samples selected from Chang 73member of Yanchang Formation in Ordos Basin and Shahejie Formation of Bohai Bay Basin were scanned by means of Nano-CT and FIB-SEM, constructing three-dimension model of multi-scale pore structure of shale sample combined with Avizo software. On this basis, the pore structure characteristics of shale are analyzed qualitatively and quantitatively, and the core permeability is calculated by numerical simulation. The results show that the pore structure characteristics of the samples are significantly different at micro and nano scales. At the micrometer scale, the pore-throat distribution of sample C(laminated) was stratified, the pore-throat distribution of sample G(layered) was slit-like, and the pore-throat distribution of sample F(massive) was not developed. At the nano scale, there is no significant difference in the pore structure characteristics of samples with different shale structures, and the pore-throat morphology is mostly sheet and strip. By numerical calculation, the permeability of samples C, F and G are 0.437 mD,0.031 mD and 0.224 mD, respectively, which are consistent with the gas permeability measurement results, indicating that the method can be used to calculate core permeability quickly and accurately. Combined with the micro-nano pore throat development and numerical simulation results of permeability, it can be concluded that sample C has the best quality, and the oil and gas exploration focus on the laminated shale reservoir. Combined with micron-CT and FIB-SEM permeability numerical simulation, multi-scale pore structure characteristics of shale samples can be characterized qualitatively and quantitatively, which has guiding significance for efficient oilfield development.