An Overview of the Oil+Brine Two-Phase System in the Presence of Carbon Dioxide, Methane, and Their Mixture

Abstract

An overview of the molecular simulation studies of the oil+brine two-phase system in the presence of CO2, CH4, and their mixture at geological conditions is presented. The simulation results agreed well with the experimental results and the density gradient theory predictions on the basis of the cubic–plus–association equation of state (CPA EoS) (withDebye–Hückel electrostatic term) and the perturbed chain statistical associating fluid theory (PC-SAFT) EoS. The interfacial tension (IFT) of the alkane+H2O system showed almost a linear increase with an increasing number of carbon atoms in the alkane molecule. These IFTs are approximately equal for linear, branched, and cyclic alkanes. Here, the negative surface excess of the alkanes might explain the increase in the IFTs with an increase in the pressure. The surface excesses of the alkanes increased with decreasing temperature. This may explain the decrease of the slopes in the IFT versus pressure plot with a decrease in the temperature. The IFT behavior of the alkane+water+CH4/CO2 system was found to be similar to that observed for the alkane+water system. The addition of CO2 had a more significant influence on the IFT than the addition of CH4. Here, CH4 and CO2 exhibited a positive surface excess. The negative surface excess of the salt ions probably explains the increase in the IFTs of the alkane+brine system with increasing salt content. The solubilities of CH4 and/or CO2 in the H2O-rich phase of the alkane+brine+CH4/CO2 system increased with decreasing salt content (salting-out effect). The IFT of the aromatic hydrocarbon+H2O system is much lower than that of the alkane+H2O system. The surface excess followed the order o-xylene > ethylbenzene > toluene > benzene for the aromatic hydrocarbon+H2O system. This trend has a direct correlation with the aromatic–aromatic interaction.

Interfacial Properties of the Hexane + Carbon Dioxide + Brine System in the Presence of Hydrophilic Silica

“…Our simulation and theoretical results [36][37][38]40,41,43 of the IFT of the H 2 O + alkane and brine + alkane systems were in reasonable agreement with the experimental data. [14][15][16]22 The DGT based on the CPA EoS is able to predict the IFT of the H 2 O + alkane system with an AAD of less than 4%.…”

“…24,33 However, the simulated solubility of H 2 O in the CO 2 -rich phase 32,35,39 underestimates the experimental data 30 by a factor of up to about 2. Also, the simulated solubility of H 2 O in the alkane-rich phase 36,40 underestimates the experimental data 17 by a factor of up to about 10. The Exp-6 model can provide accurate solubility data of the H 2 O + CO 2 system.…”

“…We evaluated the surface excess based on the density profiles. 39,40,88 Figure S10 displays the surface excess of CO 2 , hexane, and salt relative to H 2 O for the brine + CO 2 , brine + hexane and brine + CO 2 + hexane systems. Typically, a positive surface excess is observed for CO 2 in the H 2 O + CO 2 and brine + CO 2 systems.…”

“…The bulk and interfacial properties of brine in the presence of CO 2 and/or alkane at elevated temperatures and pressures have attracted a lot of interest. − There have been extensive experimental, − ,,− , theoretical, ,,,,− ,− and molecular simulation ,,,,− studies on these systems. The brine + CO 2 + alkane system was found to be largely in two- or three-phase, with the two-phase occurring at high pressures and low temperatures.…”

“…Computer simulations provided significant insights into the bulk and interfacial properties of complex systems. − ,,− ,− In this work, molecular dynamics (MD) simulations are carried out to explore the interfacial properties of brine and brine + silica systems in the presence of CO 2 , hexane, and their equimolar mixture under reservoir conditions. The simulation studies of brine + CO 2 , brine + hexane, and brine + CO 2 + hexane systems are complemented by theoretical calculations.…”