(623h) CO2 Solubility in Water Confined By Kerogen Nanopore in Relation to CO2 Sequestration in Depleted Shale Reservoirs: A Molecular Dynamics Simulation Study

Depleted shale reservoirs are feasible geological media for CO₂ sequestration. CO₂ solubility trapping plays an important role because massive water presents in the depleted shale reservoirs due to connate water, hydraulic fracturing, and water invasion. Besides, kerogen is a major component of shale, generating an extensive number of porous media at nanometer scale. The properties of kerogen (e.g., wettability) are significantly changed with different thermal maturities. In this work, we use graphene oxide (GO) to model kerogen. Various oxidized degrees (ODs) from 0.04 to 0.16 are used to represent different maturities of kerogen. Three pore sizes (1, 2, and 4 nm) and two hydroxyl patterns (regular and random) are designed to describe different kerogen nanopores. The results indicate that, as OD increases (kerogen maturity degree decreases), CO₂ adsorption amount dramatically decreases, and CO₂ solubility also decreases. CO₂ solubility is generally enhanced compared to bulk solubility in the kerogen nanopores except under the super low maturity kerogen and super small nanopore (≤1 nm). As pore size increases, CO₂ solubility increases when the kerogen is at low maturity, while it decreases when the kerogen is at high maturity. The random hydroxyls pattern cases always have higher CO₂ solubility than those regular pattern cases and the difference of water alignment in these two pattern cases can be attributed to the hydrogen bonds structure between water and hydroxyls. From CO₂ sequestration perspectives, the high maturity kerogen nanopore is more capable to store CO₂. Besides, in the high maturity kerogen nanopores, small nanopores can sequestrate more CO₂ than large nanopores under the equivalent pore volume, and it reverses in the low maturity kerogen nanopores.