Experimental Investigation and Mathematical Modeling of Gas Diffusivity by Carbon Dioxide and Methane Kinetic Adsorption

Gas transportation is of significance, especially in carbon dioxide sequestration and successful performances of enhanced methane recovery from shale layers. Among the three primary transportation mechanisms for the gas phase in shale layers, diffusion is considered as the most important phenomenon. The main objective of this comprehensive study is to propose a mathematical model of unipore diffusion and modified unipore diffusion to consider the kinetic adsorption of methane and carbon dioxide for two different shale samples at different pressure ranges. To validate the accuracy of this model, experimental investigations such as methane kinetic adsorption at pressure ranges of 3.2-9.3 MPa and carbon dioxide kinetic adsorption at pressure ranges of 2.5-6.5 were performed to compare with the results of the proposed model. The kinetics adsorption analysis for methane indicated that the required time for the completion of fractional uptake process is about 4-13 min, whereas for the adsorption of carbon dioxide it takes approximately 5-17 min to reach 70% fractional uptake for both shale samples. Subsequently, the modified unipore diffusion model provides a good agreement for both carbon dioxide and methane kinetic adsorption from gas shale layers.