Using grand canonical Monte Carlo (GCMC) simulations, we study the adsorption behavior of CH 4 , CO , and their mixtures at 298.15 K and pressures up to 50 bar in Na-, Cs-, and Ca-montmorillonite clays in the presence of water. Montmorillonite clays in the presence of preadsorbed water, preferentially adsorb CO 2 over CH 4 during both pure component and mixture adsorption. The atomistic model we have used, gives good agreement with available single-component experimental adsorption isotherms, for CH 4 and CO 2 molecules adsorbed onto montmorillonite clays in the presence of water. We observe the general trend that the presence of increasing preadsorbed water content in the clay interlayers, reduced adsorption amounts of pure CH 4 and CO 2 molecules. With a relatively large basal spacing (d= 30Å), the favorability of adsorption of CO 2 by montmorillonite at relatively low pressures and intermediate water contents has been demonstrated using simulations. GCMC simulation is also used to assess the effect of water on the adsorption of N 2 /CH 4 , H 2 S/CH 4 , CO 2 /N 2 , and CO 2 /H 2 S binary mixtures in Na-montmorillonite clay. The ideal adsorbed solution theory is shown to agree well with the observed adsorption capacities and selectivities of mixtures in Na-montmorillonite clay.

We perform grand canonical Monte Carlo simulations to study the detailed molecular mechanism of intercalation behavior of CO2 in Na-, Ca-, and Mg-montmorillonite exposed to variably hydrated supercritical CO2 at 323.15 K and 90 bar. The simulations indicate that the intercalation of CO2 strongly depends on the relative humidity (RH). The intercalation of CO2 in the dehydrated interlayer is inhibited, followed by the swelling of the interlayer region due to uptake of water and CO2 as the RH increases. In all of the hydrated clay samples, the amount of the intercalated CO2 generally decreases as a function of increasing RH, which is attributed mainly to the weakening of the interaction between CO2 and clay. At low RH values, Ca- and Mg-montmorillonite are relatively more efficient in capturing CO2. The amount of CO2 trapped in all clay samples shows similar values above RH of ∼60%. Molecular dynamics simulations show that the diffusion coefficient of each species generally increases with increasing RH due to the associated expansion of the interlayer distance of the clay. For all the hydrated samples, the diffusion coefficients of CO2 and water in the interlayers are mostly comparable due to the fact that CO2 molecules are well solvated. The diffusion of CO2 in each hydration state is mostly independent of the type of cation in accordance with the fact that CO2 molecules hardly migrate into the first hydration shell of the interlayer cations.

Molecular dynamics simulations were carried out to study the structural and transport properties of carbon dioxide, methane, and their mixture at 298.15 K in Na-montmorillonite clay in the presence of water. The simulations show that, the self-diffusion coefficients of pure CO 2 and CH 4 molecules in the interlayers of Na-montmorillonite decrease as their loading increases, possibly because of steric hindrance. The diffusion of CO 2 in the interlayers of Na-montmorillonite, at constant loading of CO 2 , is not significantly affected by CH 4 for the investigated CO 2 /CH 4 mixture compositions. We attribute this to the preferential adsorption of CO 2 over CH 4 in Na-montmorillonite. While the presence of adsorbed CO 2 molecules, at constant loading of CH 4 , very significantly reduces the self-diffusion coefficients of CH 4 , and relatively larger decrease in those diffusion coefficients are obtained at higher loadings. The preferential adsorption of CO 2 molecules to the clay surface screens those possible attractive surface sites for CH 4 . The competition between screening and steric effects leads to a very slight decrease in the diffusion coefficients of CH 4 molecules at low CO 2 loadings. The steric hindrance effect, however, becomes much more significant at higher CO 2 loadings and the diffusion coefficients of methane molecules significantly decrease. Our simulations also indicate that, similar effects of water on both carbon dioxide and methane, increase with increasing water concentration, at constant loadings of CO 2 and CH 4 in the interlayers of Na-montmorillonite. Our results could be useful, because of the significance of shale gas exploitation and carbon dioxide storage.

Grand canonical Monte Carlo and molecular dynamics simulations were applied to understand the molecular mechanism of ion and water transport in montmorillonite clays as a function of relative humidity (RH). The variation of basal spacings of montmorillonite as a function of RH predicted based on the swelling free energy profiles was consistent with X-ray data. The hydration of the montmorillonite shows the following well-known order: Mg 2+ > Ca 2+ > Sr 2+ > Li + > Na + > K +. The relative contribution of water on external surfaces only becomes significant close to the saturation pressure. However, this behavior for K-montmorillonite starts to occur well below the saturation pressure due to the clay-swelling inhibition by potassium ions. The diffusion of water and ions generally increases with RH in all samples. However, for samples with weakly hydrated ions, the water mobility in thin films adsorbed on external basal surfaces of clay can be higher than that in the water-saturated mesopores. For a given RH, mobility of interlayer species is typically lower than that from the external surfaces. The results of the simulations were applied to interpret recent laboratory measurements of ion mobility with changing RH. We also assess the effect of layer charge distribution on such sorption and diffusion processes.

Isothermal compositional flow models require coupling transient compressible flows and advective transport systems of various chemical species in subsurface porous media. Building such numerical models is quite challenging and may be subject to many sources of uncertainties because of possible incomplete representation of some geological parameters that characterize the system's processes. Advanced data assimilation methods, such as the ensemble Kalman filter (EnKF), can be used to calibrate these models by incorporating available data. In this work, we consider the problem of estimating reservoir permeability using information about phase pressure as well as the chemical properties of fluid components. We carry out state-parameter estimation experiments using joint and dual updating schemes in the context of the EnKF with a two-dimensional single-phase compositional flow model (CFM). Quantitative and statistical analyses are performed to evaluate and compare the performance of the assimilation schemes.Our results indicate that including chemical composition data significantly enhances the accuracy of the permeability estimates. In addition, composition data provide more information to estimate system states and parameters than do standard pressure data. The dual state-parameter estimation scheme provides about 10% more accurate permeability estimates on average than the joint scheme when implemented with the same ensemble members, at the cost of twice more forward model integrations. At similar computational cost, the dual approach becomes only beneficial after using large enough ensembles.

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This study is aimed at investigating the effects of a poly 2-ethyl-2-oxazoline-type polymer on the prevention of methane hydrate formation. During the study, seven experiments with low concentrations of poly 2-ethyl-2-oxazoline (0 to 1 wt%) were run in a batch-type reactor. The analysis of the experimental study indicates that poly 2-ethyl-2-oxazoline can be considered as a potential kinetic inhibitor for hydrate formation.