Na-Montmorillonite Hydrates under Basin Conditions:  Hybrid Monte Carlo and Molecular Dynamics Simulations

Abstract

In this work the Na-montmorillonite hydrates are studied for different burial depths by means of hybrid Monte Carlo (HMC) and molecular dynamics (MD) simulations. The HMC simulations, performed using a NP zz T ensemble, allow us to study the interlaminar space distance, structural properties, and thermodynamical properties, such as the water chemical potential. The latter quantifies the system affinity for water, and hence, it is useful for determining the most probable hydration states for a given basin condition. For increasing burial depth, we found many agreements with experimental results such as a tendency to dehydration, an increasing disorder of the interlaminar space, and a constant coordination number for the first water shell around Na+. The MD simulations, on the other hand, were performed employing a microcanonical ensemble, from which the diffusion coefficients for water and Na+ were also investigated for high-temperature and high-pressure conditions.

In situ XRD study of Ca2+ saturated montmorillonite (STX-1) exposed to anhydrous and wet supercritical carbon dioxide

“…In addition to the existence of dry CO 2 predicted near the wellbore, there is the potential for a constant influx of dry CO 2 interacting with the caprock for extended periods of time (Gaus, 2010). Therefore, the implications of this study depend upon the depth of the caprock and CO 2 migration behavior (Monsalvo et al, 2006;Odriozola and Guevara-Rodriguez, 2004;de Siqueira et al, 1999;Gaus, 2010). If the caprock is quite deep, then the 1 W hydration state is favored and the introduction of dry CO 2 could help seal the formation.…”

Stability of Ca-montmorillonite hydrates: A computer simulation study

“…Here, the first double layer plateau ranges in 50-60 wm, and there seems to be a second in the range 70-80 wm. This plateau displacement is due to the large effective volume the water molecules occupy for burial depth, being just a consequence of the larger temperature 29 . The structures of the systems that correspond to the different plateaus are similar to those already shown in figure 2.…”

Brownian dynamics simulations of Laponite colloid suspensions

“…(14) we use the rotation matrix A͑t͒ instead of A͑t + ⌬t͒. This is because we split the complex evolution of the platelet in two parts.…”

“…In fact, lately there has been a lot of experimental work on Laponite dispersions by means of scattering and rheological techniques [5][6][7]9,10]. On the other hand, although the one-dimensional swelling of hydrated clays has been very well studied by computer simulations [11][12][13][14], a theoretical description of their suspensions is not very developed. This is at least partially due to the fact that the highly anisotropic shape of the particles makes the interparticle potential extremely complicated.…”