Introduction
Sometimes measured gas contents are higher than those calculated from an isotherm and initial reservoir pressure, resulting in apparent oversaturation of the coal. It is physically impossible for a coal deposit to be oversaturated with gas but quite possible to have an erroneous conception of gas storage in the coal.
Moderate degrees of apparent oversaturation are not all that rare in practice and are usually due to routine errors in desorption tests and/or laboratory measurements.
In the figure below, adapted from Seidle (2011), it appears that the measured gas content is roughly 50% more than what we would expect from the isotherm - in this scenario, the isotherm represented pure methane and neglected carbon dioxide. The mixed isotherm of CO2 and H2 would be higher than a pure methane isotherm.
