Abstract: To investigate the characteristics of shale gas occurrence and evolution under stratigraphic conditions of the Longmaxi Formation in the Luzhou Area, volumetric methane isothermal adsorption experiments under different hydration states were conducted. A ternary Langmuir model was employed to fit the shale excess adsorption data, yielding a maximum corrected adsorption capacity of 2.5 cm³/g. Total organic carbon content and clay minerals were identified as favorable controlling factors for methane adsorption capacity, and increasing water saturation exerts an inhibitory effect on methane adsorption. With increasing burial depth, adsorbed gas content initially increases and then decreases, and free gas content continues to rise. Under hydrated conditions, an equivalent burial depth exists where adsorbed and free gas contents intersect. This critical depth migrates upward with increasing hydration, forming a mixed gas occurrence zone. The evolutionary process of deep shale gas in the Luzhou Area can be divided into four stages. From the early deposition period to the Late Silurian, rapid subsidence of the stratum facilitated the dominance of biogenically derived adsorbed gas. During the Early Devonian to Middle Triassic, continuous subsidence of the strata persisted alongside minor uplift events, yet adsorbed gas remained the predominant occurrence mode. From the Middle Triassic to Late Cretaceous, accelerated burial depth triggered a substantial increase in free gas content. Since the Late Cretaceous to the present, tectonic uplift has halted hydrocarbon generation, but favorable structural preservation conditions in the Luzhou Area have effectively retained free gas.

Key words: Luzhou Area, Longmaxi Formation, shale gas, methane isothermal adsorption, shale gas occurrence state