Adsorption of pure CO2 and a CO2/CH4 mixture on a black shale sample: Manometry and microcalorimetry measurements

The study of CO2/CH4 adsorption onto kerogen is relevant for shale gas production. Despite much expanded literature, reliable adsorption models still await for a complete description due to the complexity of kerogen. The objective of this study is to provide an original set of experimental data and to use the selectivity as an indicator to test the affinity of the sample for a component over another. The adsorption of pure CO2 and the equimolar mixture CH4/CO2 were explored on a Silurian black shale sample. This outcropping sample was collected in a formation, which is not considered as target for shale gas exploration. However its geochemical profile as well as its thermal maturity suggest this sample is an ideal candidate to study kerogen/carbon dioxide and methane interactions. Both isotherm and enthalpy of adsorption of carbon dioxide were measured up to 3.2 (MPa) by the use of a combined manometric-calorimetric device. The carbon dioxide isotherm was fitted with a modified Langmuir model allowing the determination of the adsorption uptake. The heat of adsorption is an indicator of the affinity of the carbon dioxide with kerogen. Additionally the equimolar mixture methane/carbon dioxide isotherm was performed up to 2 (MPa) by use of a device specially developed and built for gas mixture co-adsorption. The adsorption of each component within the mixture was provided. The estimated selectivity CO2/CH4 highlights a significant affinity of CO2 with the kerogen. •Carbon dioxide isotherm adsorption was performed on a black shale sample.•The adsorption capacity is higher for CO2 than for CH4.•Enthalpies of adsorptionCh4 and CO2 were measured to depict the interactions with kerogen.•The study of the equimolar mixture CH4/CO2 adsorption reveals a high selectivity of CO2 over CH4.