It is traditionally considered that sutures in the carbonates were formed under the pressure solution caused by rock load or tectonic stress, which is a result of chemical compaction. The authors demonstrate that sutures are characterized by integrality, hydrophilicity, anti-hole, and burst and concourse. On the basis of the studies of formation mechanism of sutures, the authors investigated the difference of hydrocarbon expulsion between carbonates and mudstones, and compared their sealing capabilities.