Lithofacies characteristics and its effect on gas storage of the Silurian Longmaxi marine shale in the southeast Sichuan Basin, China

• Investigate the lithofacies characteristics and its effect on gas storage.
• A total of 9 types of lithofacies were recognized in the study area.
• Organic-rich siliceous shale is conducive to gas storage and hydraulic fracturing.
• Organic-rich argillaceous shale has the highest methane adsorption capacity.

Based on a detailed description and analysis of outcrops and drilling cores, onsite gas desorption, and laboratory testing data, shale lithofacies characteristics and its effect on gas storage of the Silurian Longmaxi Formation marine shale in the southeast Sichuan Basin have been studied. Twelve types of shale lithofacies are classified based on the organic matter content and mineral composition, of which 9 types were identified in the study area based on their dramatically differences in color, grain size, lamination, organic matter content, mineralogy, density, and other physical properties. The bottom of the Longmaxi shale Formation is primarily organic-rich siliceous shale with stable distribution of thickness and good continuity. The upper section has characteristics of rapid vertical and lateral change in lithofacies, exhibiting a strong spatial heterogeneity. Organic-rich siliceous shale in the lower section, showing the highest content of gas desorption in situ, has a high content of organic matter, a high brittleness index and good permeability, which is conducive to shale gas storage, hydraulic fracturing, and exploitation. Organic-rich argillaceous shale was also observed to have the highest methane adsorption capacity. The interval with lithofacies association of organic-rich siliceous shale with organic-rich argillaceous shale interlayer is the pay zone for shale gas generation and accumulation.