The
adsorption behavior and underlying mechanism of CO2 and
CH4 binary mixture in shale kerogen significantly
affect the CO2 sequestration with enhanced gas recovery
project (CS-EGR). In this study, we investigated the competitive adsorption
behaviors of CO2 and CH4 in shale kerogen nanopores
using grand canonical Monte Carlo (GCMC) method. Kerogen model takes
into effect of matrix and slit nanopores and moisture content based
on Ungerer’s molecular model and scanning electron microscope
(SEM) analysis, and is successfully validated against experimental
data. The effects of temperature, CO2 and CH4 distribution, moisture content, adsorption selectivity, and optimal
formation for injection were discussed. The results show that adsorption
amount of CH4 on the kerogen increases with increasing
pressure and decreases with increasing temperature. The adsorption
selectivity of CO2 over CH4 is 2.53–7.25,
which indicates that CO2 is preferentially adsorbed over
CH4 under different temperatures. H2O prefers
to adsorb inside the kerogen matrix and decrease the volumes of matrix
pores with increasing moisture content and even divide some of them
into ineffective pores. Compared with the kerogen matrix, H2O molecules have a slight effect on CO2 and CH4 adsorption capacity on the slit surface. Moist content has a negative
effect on the desorption amount of CH4. The optimal injection
formation for the CS-EGR project is in the shallow stratum. The study
will reveal the micromechanism of competitive adsorption of CO2 and CH4 on kerogen and provide some theoretical
support for the CS-EGR project.
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