In recent decades, shale gas, which has been regarded
as a source
of clean energy, is gradually replacing conventional energy. Shale
gas adsorption in carbon dioxide (CO2)–moisture
systems has been discussed in many previous studies; however, the
intrinsic mechanism has not been clarified yet. In this work, the
molecular dynamic (MD) method is adopted to study the adsorption behaviors
of shale gas adsorption in the realistic kerogen nanoslit. The spatial
density distributions of shale gas and different components have strong
inhomogeneity. To reveal the heterogeneous adsorption mechanism, the
potential of mean force (PMF) distributions of shale gas components
are calculated on different target positions for the first time. The
water (H2O) component prefers to adsorb on the oxygen-enriched
position, as a result of the strong molecular polarity and hydrogen
bond interactions. The CO2 component tends to adsorb on
the carbon-rich site, which is the result of combining the van der
Waals interaction and molecular polarity with kerogen walls. The potential
energy contours are computed to verify the affinities between different
components and the kerogen surface, and the potential energy difference
can be observed between the bulk phase and adsorbed phase, which corresponds
to the density and PMF analyses. The sensitivity analysis is also
carried out to verify the above mechanism explanation. Higher temperature
facilitates the desorption of shale gas, and higher pressure leads
to more adsorption quantity. In the larger pore space, because of
more content of H2O and CO2 molecules, the adsorption
amount of methane (CH4) decreases. More content of CO2 is conducive to the desorption of shale gas, verified by
cases in various component proportions.