Changes in micromechanical properties of Na-montmorillonite caused by CO2/H2O sorption

CO2/H2O intercalation causes changes in the elastic mechanical properties of clay. This phenomenon is critical to geologic carbon sequestration (GCS) and enhancing oil rate (EOR) via CO2 adsorption. In this work, the elastic stiffness and hydrostatic mechanical behavior of Na-montmorillonite (MMT) exposure to variable component of CO2/H2O mixture are investigated using combinations of Monte Carlo and Molecular Dynamic methods. In the hydrostatic test simulation of 1 W and 2 W hydrated state, volume and basal spacing d(001) linearly decrease with the increasing hydrostatic pressure. Moreover, gradients of 1 W hydrated state are smaller than that of the gradients of 2 W hydrated state. The linear gradient is related to the elastic modulus. Therefore higher hydrated state results in softer structure. Additionally, the yielding bulk modulus linearly decreases with the pressure. The decreasing gradient almost keeps at a constant of 1.0 GPa/GPa with variable component of CO2/H2O. At the super critical condition of CO2 (P= 0.01 GPa, T= 304.5 K), the elastic stiffness fluctuates with the variable component of H2O/CO2. CO2 intercalation strongly affects the out-of-plane elastic stiffness while has little influence on the in plane stiffness. (C) 2016 Elsevier B.V. All rights reserved.