Effects of the Methane Content on the Water–Oil Interface: Insights from the Molecular Level

Abstract

The interfacial tension (IFT) is an important factor for the hydrocarbon flow in a porous reservoir. Methane, one main accompanied gas of hydrocarbon, has a crucial influence on the IFT. However, the methane effect is still unclear. In this work, the effects of the methane content, temperature, and pressure on the water−oil interface were investigated, employing molecular dynamics simulations. The interfacial density profiles were given and indicated that the methane molecules accumulate at the interface, leading to a decreasing IFT. As the methane mole fraction increases, the interfacial roughness and interfacial thickness increase and the induced deeper molecular penetrations and stronger miscibility initiate a decrease of the IFT. Further, an enhancing fluid diffusivity at the interface is observed, which accounts for the strengthening interfacial mobility. On the other hand, our calculations indicate that the IFT decreases with the rising temperature while increases with the strengthening pressure.Our study provides an in-depth understanding of the interfacial behavior in the ternary phase system and has some promise for the exploitation of shale oil.

Interfacial behavior of the decane + brine + surfactant system in the presence of carbon dioxide, methane, and their mixture

“…The system sizes used here ensure that the finite-size effects are negligible. 38,[40][41][42][43][72][73][74] Each system was equilibrated for 5 ns in the NPT ensemble (only L z varied) and we ran a 5 ns production under NVE conditions. The temperature was controlled using the Nose ´-Hoover thermostat and pressure using the Parrinello-Rahman barostat.…”

“…Experiments, [25][26][27][28][29][30][31][32][33][34][35][36][37] theory, [32][33][34][36][37][38][39] and simulations [38][39][40][41][42][43][44][45] have been successfully employed to understand the bulk and interfacial properties of alkane + water + CH 4 /CO 2 systems. These studies have reported the occurrence of, for example, a two-phase region at high pressures.…”

“…The IFT of the alkane + water + CH 4 /CO 2 two-phase systems was more similar to that of the corresponding alkane + water system alone. 25,35,36,[38][39][40][41][42][43]45 The IFTs of the alkane + water + CH 4 /CO 2 and alkane + brine + CH 4 /CO 2 systems increased with decreasing x CH 4 /x CO 2 (x CH 4 and x CO 2 are the mole fractions of CH 4 and CO 2 in the alkane-rich phase, respectively). This can be attributed to the fact that the interface was enriched with CH 4 and CO 2 molecules.…”

“…This can be attributed to the fact that the interface was enriched with CH 4 and CO 2 molecules. [38][39][40][41][42][43] The IFTs of the alkane + brine and alkane + brine + CH 4 /CO 2 systems were reported to increase with increasing salt concentration. 26,27,29,39,44,45 It is also known that the addition of surfactants such as sodium dodecyl sulfate (SDS) generally decreases the IFT.…”

Molecular dynamics simulation to estimate minimum miscibility pressure for oil with pure and impure CO2

“…de Lara et al explored the structural and dynamic properties of crude oil at the molecular level, and their calculations suggest an increase in fluid diffusivity of the oil phase with the IFT reduction [24]. More recently, the effects of methane on the water/octane interface were studied by molecular modeling, which showed that enlarging the ratio of methane could increase the interfacial roughness and interfacial thickness of the water/oil interface [25]. However, although researchers have studied the microstructure of the interface and the change of the IFT with MD simulation providing molecular information and insights, little work reported how to estimate the MMP of CO 2 injected into crude oil by MD simulation and understand the underlying mechanism.…”