Adsorption isotherms of methane and carbon dioxide adsorption isotherms on shale samples are measured and the simplified local density (SLD) model is used to match the experimental data. The SLD equation also has the generic modeling capabilities to draw the deviation from bulk properties as a function of fluid-solid interaction energies. Still, compared to other available techniques such as molecular simulation, SLD has an advantage of mathematical simplicity and being run at shorter time interval. The model also has satisfactory potential to paint the underlying mechanisms for adsorption preference of one fluid component over the other.

The higher adsorption preference of carbon dioxide is reflected in the measurement data and the adsorption model is successfully used to fit the data. In addition to different critical properties of carbon dioxide compared to methane, the main important factor that may describe the high adsorption affinity of carbon dioxide is the fluid-solid potential energy. As shown in this work, the potential energy function shows deeper well depth, the deeper the well depth, the stronger the interaction between the fluid particles and solid surface.

By storing gas in high density, liquid like adsorbed phase, the adsorption mechanism can enhance the overall storage capacity of CO2 in deep reservoir rock relative to if there were a free phase alone.

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