| Abstract: | The Upper Ordovician Wufeng-Lower Silurian Longmaxi shale is widely distributed in the Sichuan Basin and its periphery, which is the key stratum for marine shale gas exploration and development (E&D) in China. Based on sedimentary environment, material basis, storage space, fracability and reservoir evolution data, the reservoir characteristics of the Wufeng-Longmaxi shale and their significance for shale gas E&D are systematically compared and analyzed in this paper. The results show that (1) the depocenter of the Wufeng (WF)-Longmaxi (LM) shale gradually migrates from east to west. The high-quality shale reservoirs in the eastern Sichuan Basin are mainly siliceous shales, which are primarily distributed in the graptolite shale interval of WF2-LM5. The high-quality reservoirs in the southern Sichuan Basin are mainly calcareous-siliceous and organic-rich argillaceous shales, which are distributed in the graptolite shale interval of WF2-LM7. (2) Deep shale gas (the burial depth >3500 m) in the Sichuan Basin has high-ultrahigh pressure and superior physical properties. The organic-rich siliceous, calcareous-siliceous and organic-rich argillaceous shales have suitable reservoir properties. The marginal area of the Sichuan Basin has a higher degree of pressure relief, which leads to the argillaceous and silty shales evolving into direct cap rocks with poor reservoir/good sealing capacity. (3) Combining shale gas exploration practices and impacts of lithofacies, depth, pressure coefficient and brittle-ductile transition on the reservoir properties, it is concluded that the favorable depth interval of the Wufeng-Longmaxi shale gas is 2200~4000 m under current technical conditions. (4) Aiming at the differential reservoir properties of the Wufeng-Longmaxi shale in the Sichuan Basin and its periphery, several suggestions for future research directions and E&D of shale gas are formulated. |
