Fluid mobility has been important topic for unconventional reservoir evaluation. The tight sandstones in Chang 7 Member of the Ordos Basin has been selected to investigate the fluid mobility based on the application of core flooding-NMR combined method and core centrifugation-NMR combined method, and the porous structure is studied using optical microscope, field emission scanning electron microscope (FE-SEM), CT and mercury injection. Our results include: (i) Feldsparrock fragments dissolution pores, calcite dissolution pores, clay mineral dissolution pores, intergranular dissolution expansion pores, inter-granular pores, intra-kaolinite pores, and intra-illite/smectite mixed layer pores are developed in Chang 7 tight sandstones; 3D CT pore structure shows that the pore connectivity is positively related to physical properties, and the overall storage space is connected by the throat with diameter between 0.2 and 0.3 µm. The percentage of storage space connected by throats with diameter less than 100 nm can reach more than 35%. (ii) Movable fluid saturation of Chang 7 tight sandstones is between 10% and 70%, and movable oil saturation is between 10% and 50%. Movable fluid saturation may cause misunderstanding when used to evaluate fluid mobility, so it is recommended to use movable fluid porosity in the evaluation of fluid mobility. The porosity ranging from 5% to 8% is the inflection point of the fluidity and pore structure. For samples with porosity less than 8%, the movable fluid porosity is generally less than 5%. Moreover, the movable fluid is mainly concentrated in the storage space with a throat diameter of 0.1 to 1 µm. For samples with porosity greater than 8%, the porosity of the movable fluid is more than 5%, and the movable fluid is mainly concentrated in the storage space with a throat diameter of 0.2 to 2 µm. (iii) The movable fluid saturation measured by core flooding-NMR combined method is generally higher than that measured by core centrifugation-NMR combined method. The former can evaluate the mobility of the oil-water two-phase fluid in samples, while the latter can better reflect the pore structure and directly evaluate the movable fluid in the pore system controlled by different throat diameters. All these results will provide valuable reference for fluid mobility evaluation in tight reservoirs.

流体流动性一直是非常规储层评价的重要课题。选取鄂尔多斯盆地长7段致密砂岩，应用岩心驱替-核磁共振联合法和岩心离心-核磁共振联合法研究流体流动性，利用光学显微镜、场发射法研究其孔隙结构扫描电子显微镜 (FE-SEM)、CT 和压汞。研究成果包括：(i)长7段发育长石碎屑溶蚀孔、方解石溶蚀孔、黏土矿物溶蚀孔、粒间溶蚀膨胀孔、粒间孔、高岭石内孔、伊利石/蒙脱石混合层内孔致密砂岩；3D CT 孔隙结构显示孔隙连通性与物理性质呈正相关，整个存储空间由直径在0.2至0.3微米之间的喉部连接。直径小于100nm的喉道连接的存储空间百分比可达35%以上。(ii) 长 7 致密砂岩可动流体饱和度在 10%～70% 之间，可动油饱和度在 10%～50% 之间。可动流体饱和度在用于评价流体流动性时可能会引起误解，因此建议在评价流体流动性时使用可动流体孔隙度。5%~8%的孔隙度是流动性和孔隙结构的拐点。对于孔隙率小于8%的样品，可动流体孔隙率一般小于5%。而且，可动流体主要集中在喉管直径为0.1～1μm的储存空间内。对于孔隙率大于 8% 的样品，可动流体孔隙率大于5%，可动流体主要集中在喉道直径为0.2～2μm的储存空间。(iii)岩心驱替-核磁共振联合法测得的可动流体饱和度普遍高于岩心离心-核磁共振联合法测得的可动流体饱和度。前者可以评价样品中油水两相流体的流动性，后者可以更好地反映孔隙结构，直接评价不同喉道直径控制的孔隙系统中的可动流体。这些结果将为致密储层流体流动性评价提供有价值的参考。(iii)岩心驱替-核磁共振联合法测得的可动流体饱和度普遍高于岩心离心-核磁共振联合法测得的可动流体饱和度。前者可以评价样品中油水两相流体的流动性，后者可以更好地反映孔隙结构，直接评价不同喉道直径控制的孔隙系统中的可动流体。这些结果将为致密储层流体流动性评价提供有价值的参考。(iii)岩心驱替-核磁共振联合法测得的可动流体饱和度普遍高于岩心离心-核磁共振联合法测得的可动流体饱和度。前者可以评价样品中油水两相流体的流动性，后者可以更好地反映孔隙结构，直接评价不同喉道直径控制的孔隙系统中的可动流体。这些结果将为致密储层流体流动性评价提供有价值的参考。