The utilization of synergistic mixtures of nanoparticles (NPs) and surfactants for enhanced oil recovery (EOR) has drawn increasing scientific attention. In this study, a series of coarse-grained (CG) molecular dynamics (MD) models were built to study the behaviors of NPs and surfactants in the vicinity of the oil/water interface. Hydrophilic, hydrophobic, and amphiphilic NPs were constructed to investigate the effect of hydrophobicity on the ability of NPs in term of interfacial tension (IFT) reduction. The synergistic effect of surfactants and NPs were also studied.
Surfactants and amphiphilic NPs can both accumulate at the interface of oil and water, while hydrophilic and hydrophobic NPs stay in water or oil phase. The NPs with various ratios of hydrophobic to hydrophilic domains were investigated to determine the types of NPs that result in the most IFT reduction. The comparison of IFTs indicates that amphiphilic NPs has a better ability to assist surfactants in further reducing the interfacial tension. Meanwhile, surface modification and the presence of surfactants can prevent the aggregation of NPs.
These MD simulation results allow us to figure out the physical behavior of NPs and surfactants at the oil/water interfaces. Analysis of the results can further assist the NPs synthesis for surfactant and/or surfactant-nanoparticle EOR applications in unconventional reservoirs.
Enhanced Oil Recovery (EOR) is well known for its potential to produce residual oil after the primary and secondary oil recovery. The residual oil is trapped in the narrow throat due to high capillary pressure, which is influenced by rock wettability and oil/water interfacial tension (IFT) (Wu et al., 2008). Surfactants have been widely investigated and employed in the EOR process to reduce the IFT and to alter the wettability (Sheng et al. 2015; Kamal et al., 2017; Negin et al., 2017). However, during the surfactant flooding, surfactants can adsorb onto the rock surfaces. This may result in the reduction of their concentrations, which significantly reduce the efficiency of surfactants in practical applications. The high cost of surfactants also makes this potential loss a critical issue. Many researchers have focused their studies on reducing the adsorption of surfactants by adding various materials in the chemical formulations.
Enhanced oil recovery (EOR) is the technique or process where the physicochemical (physical and chemical) properties of the rock are changed to enhance the recovery of hydrocarbon. The properties of the reservoir fluid system which are affected by EOR process are chemical, biochemical, density, miscibility, interfacial tension (IFT)/surface tension (ST), viscosity and thermal. EOR often is called tertiary recovery if it is performed after waterflooding. Conformance is the application of processes to reservoirs and boreholes to reduce water production, enhance recovery efficiency, or satisfy a broad range of reservoir management and environmental objectives. Although the use of conformance processes may not result in increased production, such processes can often improve an operator's profitability as a result of the following benefits: Ideally, conformance control should be performed before a condition can result in serious damage.
In this paper, interfacial tension (IFT) of two ternary water-rich hydrocarbon systems were investigated at a representative reservoir temperature of 150 °C and equilibrium pressures up to 140 MPa. Two-phase and three-phase IFT measurements of water-methane-hexadecane and water-methane-toluene mixtures were carried out in our previously validated Pendant Drop facility and the equilibrium phase densities, required to determine pertinent IFT values, were determined by measuring the volume and mass of samples separately. The results showed a high pressure dependency of IFT values below the hydrocarbon dew point (i.e., three-phase region) whereas a slight increase on the interfacial tension was observed in the two-phase region.
Aiming at developing a general model for describing this property in multiphase systems, the generated and literature IFT data were used to develop and validate our model based on the Linear Gradient Theory (LGT). The LGT has been proven capable of describing vapor-liquid and liquid-liquid interfaces in systems containing polar and non-polar compounds when coupled with an appropriate thermodynamic model. In this work the LGT was coupled with the Cubic-Plus-Association equation of state (CPA EoS) for a correct description of the equilibrium properties of the phases involved. The modelling results confirmed the superiority of the LGT over classical models in that one single model can be used for describing the IFT of multiphase systems with greater accuracy.
Vapor-liquid and liquid-liquid interfaces are present in numerous industrial applications and their properties play an important role in several processes such as extraction and Enhanced Oil Recovery (EOR). For instance, low interfacial tension in a hydrocarbon and water flooding process can improve the mobility of reservoir fluids resulting in higher displacement efficiencies. Hence, an accurate description of the interfacial tension (IFT) between vapor-liquid and liquid-liquid phases is crucial during the development and optimization of any extraction process or for efficient exploration of reservoirs. Despite the importance of this property, reliable experimental data are still scarce at high pressure/high temperature (HPHT) conditions and unsatisfactory system-dependent models are being used for describing the different interfaces of interest involved.