Shallow-buried fluvial mudstones are of great significance as potential top seals for natural gas accumulations in the Zhanhua depression. Four samples were chosen to represent the range of fine-grained microfacies, from clay-rich to silt-rich to cemented, and mercury injection capillary pressure (MICP) porosimetry is combined with Scanning Electron Microscopy (SEM) to characterize microstructure and pore systems quantitatively. The nature of the pore systems that allow capillary breakthrough and thus leakage, were also estimated. Pore areas inferred from SEM data, obtained from representative elementary areas (REAs), follow a similar power law distribution to bulk sample MICP within a specific range, indicating that pores with areas larger than 10³ nm² are well connected. In samples without carbonate cement, pores within the clay matrix are larger in coarser-grained, siltier samples, and there are more pores at the edges of non-clay minerals; this results from force chains of large grains shouldering more effective stress. With increasing silt content, SEM-visible porosity increases and the contribution of pores between non-clay minerals grows significantly, while the contribution of pores within clay matrix reduces. In more clay-rich samples, capillary breakthrough is estimated to occur in pores associated with the clay matrix; in siltier samples, breakthrough will occur at lower entry pressures associated with larger interparticle pores. Carbonate cements play a key role in reducing pore space in some siltier samples by partially filling interparticle pores at (a) the interfaces between clay and non-clay minerals, and (b) pores between non-clay minerals areas larger than 10⁶ nm². By filling larger pores, capillary breakthrough in carbonate-cemented samples occurs at relative high entry pressures through pores in the clay matrix. However, carbonate cements, generally less than 20%, are not sufficient to enable silt-rich mudstones to become effective barriers. Clay content is the most critical control on mudstone seal capacity.

浅埋河流泥岩作为沾化坳陷天然气成藏的潜在顶盖具有重要意义。选择四个样品来代表细粒微相的范围，从富含粘土到富含淤泥再到胶结物，并且将压汞毛细管压力 (MICP) 孔隙度测定法与扫描电子显微镜 (SEM) 相结合，以定量表征微观结构和孔隙系统. 还估计了允许毛细管穿透并因此渗漏的孔隙系统的性质。从代表性基本区域 (REA) 获得的 SEM 数据推断出的孔隙面积在特定范围内遵循与散装样品 MICP 相似的幂律分布，表明孔隙面积大于 10 ³  nm ²连接良好。在没有碳酸盐胶结物的样品中，粗粒、粉质的样品粘土基质内的孔隙更大，非粘土矿物的边缘有更多的孔隙；这是由于大晶粒的力链承受了更有效的应力。随着粉砂含量的增加，SEM-可见孔隙度增加，非粘土矿物之间孔隙的贡献显着增加，而粘土基质内孔隙的贡献减少。在富含粘土的样品中，估计毛细管穿透发生在与粘土基质相关的孔隙中；在粉砂质样品中，在与较大颗粒间孔隙相关的较低进入压力下会发生突破。⁶ 纳米²。通过填充较大的孔隙，碳酸盐胶结样品中的毛细管突破发生在相对较高的进入压力下通过粘土基质中的孔隙。然而，一般低于 20% 的碳酸盐胶结物不足以使富含粉砂的泥岩成为有效的屏障。粘土含量是泥岩封闭能力最关键的控制。