Experimental study of supercritical methane adsorption in Longmaxi shale: Insights into the density of adsorbed methane

•Excess adsorption capacity increases to its maximum value and then decreases with further increasing pressures.•The DR-based excess adsorption model is more reliable to determine the density of adsorbed methane.•The actual adsorption capacity will be underestimated if we only conducted the low-pressure experiments.•Adsorbed methane is not only filled in the micropores and also monolayer-adsorbed in the meso-macropores.