渤海湾盆地东营凹陷古近系沙河街组页岩油储集层微米-纳米级孔隙体系表征

Characterization of micro-nano pore networks in shale oil reservoirs of Paleogene Shahejie Formation in Dongying Sag of Bohai Bay Basin,East China

针对渤海湾盆地济阳坳陷东营凹陷古近系沙河街组典型(块状、纹层状、层状)灰质泥页岩样品的微米—纳米级孔隙体系结构特征进行了系统研究。利用高压压汞法(MICP)检测多个连通孔隙体系,同时表征其孔隙度、渗透率和孔道迂曲度;采用不同样品(粒径500~841μm GRI(美国应用天然气研究所)标准的颗粒,边长1 cm的立方体,直径2.54 cm、高度2~3 cm的岩心柱),通过低压气体物理吸附、基质渗透率测定、高压压汞分析、氦气孔隙度测定、非稳态脉冲渗透率测定等分析方法测定泥页岩的孔渗参数。高压压汞法测得泥页岩样品平均孔隙度为(6.31±1.64)%,基质渗透率在(27.4±31.1)×10^(-9)μm^2,基于体积法的中值孔喉直径为(8.20±3.01)nm,孔隙主要分布在孔喉直径5 nm区域,孔喉比随着孔隙直径的减小而降低。具有层理的泥页岩样品的渗透率是泥页岩基质渗透率的近20倍。泥页岩纳米级(孔喉直径为2.8~10.0 nm)孔隙体系的几何迂曲度高达8.44,说明具有较差的孔隙连通性和输导流体的能力,会影响泥页岩油气的保存和开采。

For typical blocky, laminated and bedded mudrock samples from the Paleogene Shahejie Formation in the Dongying Sag of Bohai Bay Basin, this work systematically focuses on their structure characterization of multiple micro-nano pore networks. A use of mercury injection capillary pressure （MICP） documented the presence of multiple μm-nm pore networks, and obtained their respective porosity, permeability and tortuosity. Different sample sizes （500-841μm GRI fractions, 1 cm-sized cubes, and 2.54 cm in diameter and 2-3 cm in height core plugs） and approaches （low-pressure N2 gas physisorption, GRI matrix permeability, MICP, heliumpy cnometry, and pulse decay permeameter） were used to measure pore size distribution, porosity and permeability. The average porosity and matrix permeability determined from MICP are （6.31±1.64）% and （27.4±31.1）×10^9μm^2, the pore throat diameter of pores is mainly around 5 nm, and the median pore throat diameter based on 50% of final cumulative volume is （8.20±3.01） nm in shale. The pore-throat ratios decrease with a decrease of pore size diameter. Moreover, the permeability of shale samples with lamination is nearly 20 times larger than matrix permeability. The geometrical tortuosity of the nano-scale 2.8-10.0 nm pore networks is 8.44 in these shales, which indicates a poor connectivity of matrix pore network and low flow capability. Overall, the variable and limited pore connectivity of shale samples will affect hydrocarbon preservation and recovery.