Effects of Salinity and N-, S-, and O-Bearing Polar Components on Light Oil–Brine Interfacial Properties from Molecular Perspectives

Abstract

Oil–brine interfaces play an important role in oil recovery and oil–brine separation, in which the effects of salinity on interfacial tension (IFT) have been much of debate in the past in experiments and modeling studies owing to complex oil compositions. In this work, we use molecular dynamics (MD) simulations to study the oil–brine interfacial properties by designing seven systems containing different oil compositions (decane with/without polar compounds) and the salinity in brine of up to ∼14 wt %. We carefully investigate the salinity and polar component effects by analyzing IFTs, density profiles, orientation parameters, hydrogen bond densities, and charge density profiles. The results indicate that O-bearing compounds (phenol and decanoic acid) can significantly reduce the oil–brine IFT and exhibit the highest Gibbs surface excess relative to water, while the others, including N-bearing compounds (pyridine and quinoline) and S-bearing compounds (thiophene and benzothiophene), only slightly decrease the oil–brine IFTs and show a relatively small Gibbs surface excess. Increasing salinity can slightly increase the oil–brine IFT except in the system containing phenol, which shows a decrease. Phenol and decanoic acid incline to be perpendicular to the interface and generate numerous hydrogen bonds with water in the interfacial region, while others prefer to be parallel to the interface with much fewer hydrogen bonds with water. On the other hand, salinity has an insignificant effect on the orientation of polar molecules and hydrogen bond density in the interfacial region. The charges at the interfaces on the brine and oil sides are negative and positive, respectively, and the polar compounds disturb the arrangement of water molecules in the interfacial regions, while the addition of salt ions result in the higher peak values of charges in terms of water and system. Our study should provide new insights into the oil–brine interfacial issues and clarify some unsettled disputes.

Molecular Dynamics Study on CO2 Storage in Water-Filled Kerogen Nanopores in Shale Reservoirs: Effects of Kerogen Maturity and Pore Size

“…The H-Bond is determined when the donor−acceptor distance is less than 0.35 nm and the angle between the vectors of donor-H and H-acceptor is less than 30°. 73 As depicted in Figure 5a, type II-A kerogen has the highest heteroatom surface density, followed by type II-D, type II-C, and type II-B. Interestingly, the heteroatom surface density does not monotonically decrease as kerogen maturity increases even though it is believed that the heteroatoms are gradually lost as kerogen evolves from low to high maturity.…”

“…In Figure , we present the density profiles of CO 2 and water altogether in various 4 nm kerogen pores. In addition, we also present the orientation parameters of water and CO 2 in Figure , which are given as − where S z represents the orientation parameter of water or CO 2 , θ z is the angle between the z -axis and molecular axis (the lines connecting two Hw for water and two Oc for CO 2 , respectively, as shown in the schematic diagrams in Figure b), and ⟨···⟩ implies the ensemble average. Positive orientation parameters represent that the molecules are perpendicular to the kerogen surface (fully perpendicular to the surface at S z = 1); negative values mean that the molecules are parallel to the kerogen surface (fully parallel to the surface at S z = −0.5); and S z = 0 indicates a random orientation.…”

“…0.4 nm is chosen as it is close to the diameters of the heteroatoms) in the analysis region (see Figure a) divided by the projected area of both the bottom and upper surfaces in the x – y plane. The H-Bond is determined when the donor–acceptor distance is less than 0.35 nm and the angle between the vectors of donor-H and H-acceptor is less than 30° . As depicted in Figure a, type II-A kerogen has the highest heteroatom surface density, followed by type II-D, type II-C, and type II-B.…”

Role of Alcohol as a Cosurfactant at the Brine–Oil Interface under a Typical Reservoir Condition

“…The simulation box sizes are 5, 5, and about 20 nm in the x -, y -, and z -directions, respectively. This size has been proven to be large enough to overcome the finite size effect . A series of calculations with varying concentrations/numbers of cosurfactants (propanol) are studied to investigate their roles.…”

Adaptive intermolecular interaction parameters for accurate Mixture Density Functional Theory calculations

“…Presently, the behavior of fluid mixtures at the molecular scale is mainly studied using Molecular Dynamics (MD) [5,6,42,43], Statistical Associating Fluid Theory (SAFT) [23,[44][45][46][47], Grand Canonical Monte Carlo simulations (GCMC) [7,[48][49][50], and Gibbs Ensemble Monte Carlo simulations (GEMC) [13,51]. However, only a few studies use DFT [16,37,52] caused by the number of limitations of the DFT approach.…”