Microstructure and pore systems of shallow-buried fluvial mudstone caprocks in Zhanhua depression, east China inferred from SEM and MICP

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