Dual porosity modelling of coal core flooding experiments with carbon dioxide

Abstract

This paper presents the validation of a recently developed dual porosity numerical model and provides insights into coal core flooding experiments with N2 and CO2. Experimental data for anthracite coal from the South Wales Coalfield, UK, allows the coal-gas constitutive behaviour to be defined, leading to the validation of the model using gas flooding data for a mm long and mm diameter core. N2 and CO2 injection scenarios are considered with the coal initially saturated with CH4. It is demonstrated that the model can simulate the physical and chemical phenomena involved in multicomponent gas flow and storage in coal. Further analysis shows that N2 breakthrough in the effluent gas is controlled by dual porosity flow without significant influence of adsorption-desorption, whereas for CO2 this influence is greater. Coal swelling caused by CO2 is identified as the predominant factor, with the preferential displacement of adsorbed CH4 being limited by the time scale of flow across the core relative to the CH4 desorption kinetics. These insights are useful for future experiments concerning the influence of core size. The importance of using sorption data from intact coal rather than powdered coal is highlighted by comparing the numerical predictions and experimental measurements.