To achieve rapid evaluation of adsorbed gas content in shale, typical marine shale (Longmaxi Formation in southern Sichuan) and the transitional shale (Shanxi Formation in the eastern margin of the Ordos Basin) in China were taken as examples. Through systematic TOC (total organic carbon content) measurements, XRD (X-ray diffraction), low-pressure and low-temperature gas adsorption and methane isothermal adsorption experiments, a three-layer methane isothermal adsorption petrophysical model for shale gas was established to elucidate the control mechanisms of different shale components on methane adsorption. The key findings are as follows. TOC is the primary control on methane adsorption in both marine and transitional shales. However, brittle minerals exhibit higher adsorption capacity than clay minerals in marine shale, whereas clay minerals dominate in transitional shale. Pore structure heterogeneity exists between marine and transitional shales. Organic matter in marine shale develops both micropores and mesopores, serving as storage space for both free and adsorbed gas. In contrast, organic matter in transitional shale primarily develops micropores, predominantly influencing adsorbed gas storage. Adsorption divergence is governed by mineral origin and specific surface area differences. Marine shale contains organic-derived quartz and low specific surface area illite, favoring brittle mineral adsorption. Transitional shale comprises detrital quartz with limited pore development capacity and clay minerals dominated by high specific surface area illite/smectite mixed-layer and kaolinite, leading to superior clay mineral adsorption. The established adsorbed gas content model enables rapid evaluation of shale gas sweet spots, providing a theoretical foundation for optimizing exploration and development of shale gas.