A sound understanding of the pore-fracture system across all scales provides an in-depth look at the intricate gas transport mechanisms in shale reservoirs. We performed a comprehensive multiscale characterization analysis on the Longmaxi shale samples using five complementary techniques: low-temperature gas (N₂) adsorption (LTGA), mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE-SEM), and X-ray computed tomography (CT) scanning. For pore size distribution (PSD) determination, LTGA (N₂) analysis can detect small pores (2 to 300 nm sized), while MIP analysis is suitable for large pores or fractures (> 300 nm). NMR can reveal full-scale PSD characteristics of shale. Combining NMR with LTGA or MIP is recommended, since NMR alone would over- or under-estimate the pore size. The Longmaxi shale pores observed by FE-SEM imaging are of good connectivity and, by and large, are tens of nanometers sized. The scale-dependent analysis shows that the representative elementary volume (REV) for porosity of the Longmaxi shale based on FE-SEM imaging is almost 600 μm. As evident from the CT scanning, the connectivity of the entire shale pore-fracture system increased significantly after saturating the sample with water. The gas slippage (Klinkenberg) effect is significant at relatively low pressures. A second-order model would better estimate the intrinsic permeability compared with the traditional Klinkenberg equation. Microfractures manifest preferred orientation or alignment parallel to the shale bedding plane and are the dominant pathways for gas transport in shale. Finally, we proposed a new pore size classification of shale considering gas transport mechanisms: adsorption pores (pore size ˂ 10 nm), slippage pores (10 nm ˂ pore size ˂ 1000 nm), and seepage pores or fracture-pores (pore size > 1000 nm). Although slippage pores dominate in terms of the total volumetric contribution of the Longmaxi shale, with a clear presence of adsorption pores, overall gas transport in shale is predominantly controlled by the seepage pores (fracture-pores), which constitute a very small portion of the total volume.

对所有规模的孔隙裂缝系统的透彻了解，可以深入了解页岩储层中复杂的气体传输机制。我们使用五种互补技术对Longmaxi页岩样品进行了全面的多尺度表征分析：低温气体（N ₂）吸附（LTGA），压汞法（MIP），核磁共振（NMR），场发射扫描电子显微镜（ FE-SEM）和X射线计算机断层扫描（CT）扫描。对于孔径分布（PSD）的测定，LTGA（N ₂）分析可以检测到小孔（2至300 nm大小），而MIP分析则适合于大孔或裂缝（> 300 nm）。NMR可以揭示页岩的完整PSD特征。建议将NMR与LTGA或MIP结合使用，因为仅NMR会高估或低估孔径。通过FE-SEM成像观察到的Longmaxi页岩孔隙具有良好的连通性，并且总体上为数十纳米大小。基于比例的分析表明，基于FE-SEM成像的Longmaxi页岩孔隙度的代表性基本体积（REV）几乎为600μm。从CT扫描可以明显看出，用水浸润样品后，整个页岩孔隙破裂系统的连通性显着提高。在相对较低的压力下，瓦斯滑移（Klinkenberg）效应显着。与传统的Klinkenberg方程相比，二阶模型将更好地估计固有渗透率。微裂缝表现出优选的方向或平行于页岩层理平面的排列，并且是页岩中气体传输的主要途径。最后，我们提出了一种考虑气体输送机理的页岩新孔径分类：吸附孔（孔径pore 10 nm），滑动孔（10 nm nm孔径˂1000 nm）和渗漏孔或裂隙孔（孔径> 1000 nm）。虽然就Longmaxi页岩的总体积贡献而言，滑移孔占主导地位，但明显存在吸附孔，但页岩中的总气体输送主要受渗流孔（裂隙孔）控制，而渗漏孔仅占很小一部分。总容积。