Molecular Simulation Of The CO₂ Adsorption Behavior In Geological Storage

Geological storage of carbon dioxide(CO2)is an important component for the strategy of the greenhouse gas emission reduction.CO2 will exist in a supercritical state under these circumstances and their adsorption and diffusion ability will also be affected.However,there are few studies on geological storage of CO2 and the interactive mechanism between CO2 and the rock is still not clear.As a result,we perform molecular simulation methods to investigate the adsorption behavior and transport properties of CO2 under different temperature,pressure,water saturation and wettability.The results summarize the mechanism for the effect of different formation conditions on CO2 storage.The results show that: CO2 appear a hierarchical adsorption state in the silica slit pore,there exist significant potential,density diversity for CO2.And the density of CO2 in a free state is corresponding to the bulk phase.The maximum adsorption capacity of CO2 decrease with temperature increasing and enhance with pressure increasing.However,at a fixed temperature condition,the excess adsorbed density of CO2 show an inflection point.The lower increasing trend of absolute adsorption and the faster increasing trend of free state leading to the maximum value occurs at a specific pressure,which has a significant guide for the geological storage of CO2.In the CO2/H2O/SiO2 slit systems with different numbers of H2 O,we find the presence of H2 O has some impacts on the adsorption quantity and the adsorption heat of CO2.At low pressure,H2 O doesn't completely occupy the adsorption sites on the surface and the impact on the adsorption quantity of CO2 is not obvious.As the pressure increases,the H2 O occupy adsorption sites and the volume of space phenomena become more evidently,resulting in the adsorption capacity reduction of CO2.However,the effect of H2 O on adsorption heat is not obvious.With the increasing of H2 O,the surface adsorption density of CO2 increase and the diffusion properties in the X-Y plane reduce.The adsorbed density of CO2 for different wettability system will show layer strucutres,and the adsorption density decrease with the decreasing of the wettability.CO2 have different orientation distributions for different wettability system.When the system is strongly hydrophilic silica surface,CO2 preferentially stay aligned vertically near the surface;and when the system is a hydrophobic surface,CO2 preferentially stay lying on the surface.This is due to the non-bonded interactions and hydrogen bonding between CO2 and the quartz.With the wettability changed,the migration property of CO2 is not monotonic,which show a maximum at k = 0.6.