The organic-rich shales in the Sichuan Basin in China include Pre-Cambrian Sinian to Middle Permian marine shales deposited in passive margin to foreland settings, Upper Permian transitional shales deposited in a coastal swamp setting, and Triassic and Jurassic lacustrine shales deposited in a foreland setting. Regional shale property mapping, analysis of geochemistry, mineralogy and petrophysics based on sample tests, reservoir characterization of potential shale intervals, and recent exploration and production (E&P) results reveal that: Pre-Cambrian to Middle Permian marine shales, especially the Lower Silurian Longmaxi shale, deposited during transgressive systems tract to early highstand systems tract period have significant reservoir storage, high TOC, high maturity, high brittle mineral content and high gas content, and are similar to the Barnett shale in USA to hold a huge amount of shale gas. The coal-associated Upper Permian transitional shales and Triassic to Jurassic lacustrine shales are relatively clay-rich compared to marine shales, but possess some shale gas potential in organic-rich shales. The shale gas resource potentials and emerging production have been confirmed by the reservoir characteristics and test results of recent drilled wells targeting marine, transitional and lacustrine shale gas in the Sichuan Basin.

Shale heterogeneity is important for micro- to macroscale-quality reservoir prediction. We evaluated the multiscale heterogeneity in shale based on thin-section observation, field emission scanning electron microscope observation, low-pressure N2 adsorption analysis, mercury intrusion porosimetry, organic carbon analysis, and bulk chemical analysis by X-ray powder diffraction. We evaluated the results in which the heterogeneity of minerals and organic matter in shale was shown by disorderly and unsystematically distributed mineral grains, lamina, and rapid lithology at multiple scales. The random arrangement of minerals, seasonal climate changes, large changes of sedimentary environment, and the provenance supply was considered to be the origin of the heterogeneity from the micro- to the macroscale in shale. In addition, a multiscale heterogeneity distribution model of marine shale in southeastern Sichuan basin was established, which can be used to predict shale gas distribution from the micro- to the macroscale.