Changes

The Sichuan Basin, approximately covering 230000km2, is a large basin on the Yangtze Platform and contains up to 6-12 km of Pre-Cambrian Sinian to Cenozoic sediments. The Upper Ordovician to Lower Silurian Wufeng-Longmaxi Formation is widely distributed across the entire Yangtze region of South China, and the thickest organic-rich shales of Wufeng-Longmaxi Formation is located in the Sichuan Basin and adjacent areas (Fig. 1) (Zou et al., 2019). The shales display varying TOC content in the range of 0.2% to 6%, and are primarily composed of black siliceous mudstone, shelly limestone, gray silty-shaly interlaminated mudstone, gray argillaceous mudstone, and calcareous mudstone (Lu et al., 2020). The commercial gas production is typically from the lower part of Wufeng-Longmaxi Formation that is dominated by black siliceous mudstone (Fig. 2). The commercially producing shale interval has a thickness of 20-40m, an average TOC content of 2-4%, vitrinite reflectance (Ro) of 2-3.5%, porosity of 1.85-8.32%, and pressure coefficient of 1.3-2.1 (Zou et al., 2019; Guo et al., 2020).

The Sichuan Basin, approximately covering 230000km2, is a large basin on the Yangtze Platform and contains up to 6-12 km of Pre-Cambrian Sinian to Cenozoic sediments. The Upper Ordovician to Lower Silurian Wufeng-Longmaxi Formation is widely distributed across the entire Yangtze region of South China, and the thickest organic-rich shales of Wufeng-Longmaxi Formation is located in the Sichuan Basin and adjacent areas (Fig. 1) (Zou et al., 2019). The shales display varying TOC content in the range of 0.2% to 6%, and are primarily composed of black siliceous [[mudstone]], shelly limestone, gray silty-shaly interlaminated mudstone, gray argillaceous mudstone, and calcareous mudstone (Lu et al., 2020). The commercial gas production is typically from the lower part of Wufeng-Longmaxi Formation that is dominated by black siliceous mudstone (Fig. 2). The commercially producing shale interval has a thickness of 20-40m, an average TOC content of 2-4%, vitrinite reflectance (Ro) of 2-3.5%, porosity of 1.85-8.32%, and pressure coefficient of 1.3-2.1 (Zou et al., 2019; Guo et al., 2020).