Late Permian Reef Buildups and the Puguang Gas Field in the Northeastern Sichuan Basin, SW China

The Yangtze region is one of the regions with the best stratigraphic record and the most abundant fossils of the Permian–Triassic in the East Tethys and even in the world. It records the evolution of the Paleotethys, the Permian–Triassic Boundary (PTB) mass extinction, the Emei tafrogenesis and other important geological events. The proposed investigation route in Upper Yangtze region, i.e., the marginal reef of Jiantianba platform in Lichuan and the marginal reef and shoal of Panlongdong platform in Xuanhan—Puguang gas field, demonstrates the Late Permian platform margin sedimentary system, and development of typical Late Permian reefs—Early Triassic grain shoals in the world. It shows the successful application that the sedimentological study serves oil and gas exploration. The Jiantianba outcrop in Lichuan (hereinafter referred to as the Jiantianba outcrop) reveals a complete sedimentary system which contains basin, slope, carbonate platform margin, and open platform, where the platform margin reef core is observed with very clear assemblages of architecture units and a variety of identifiable microfacies. Calcisponge is the main reef-building organism with abundant species and various form. It is one of the most typical reefs of Late Permian in Yangtze region. The Panlongdong outcrop is located in Xuanhan County (hereinafter referred to as the Panlongdong outcrop), and platform margin reefs and shoals are developed here. The platform margin zone developed across the Permian–Triassic biological mass extinction event, formed the platform margin sedimentary characteristics that the reefs of Changxing stage on the lower part while the shoals of Feixianguan stage on the upper part. Platform margin reef and shoal are superimposed and inherited spatially. The sedimentary evolution sequence of reef base–reef core–reef cap is clear and complete. The platform margin shoal is mainly oolitic, and gravel clasts the second, with tabular and wedged cross-bedding developed. Puguang gas field is represented by the reef and shoal reservoirs with high porosity and high permeability of the Permian Changxing Formation and the Lower Triassic Feixianguan Formation. This discovery benefited from the breakthrough in sedimentological study on sedimentary facies and favorable reservoir. The Science and Technology Exhibition Hall of Puguang gas field exhibits the process and achievements of the discovery, development and construction of Puguagn gas field in various forms, provides a good reference for the exploration and development of ultra-deep marine carbonates in the world.