Predicting interfacial tension using advanced meso-scale modelling technique

Surfactant EOR is an attractive method to recover residual oil from light oil reservoirs. Selection of suitable surfactant for a particular reservoir conditions is a challenging and time consuming task. Surfactants have to be evaluated through a series of evaluation steps which include: compatibility, phase behavior, thermal stability, interfacial tension (IFT), adsorption and core flooding. IFT measurements are challenging and time consuming particularly at high-temperature. Due to dynamic nature of IFT it may take several hours to reach an equilibrium value. Moreover, commercially available techniques rely on the shape of the oil drop which is not necessarily to be exactly cylindrical. In this paper a meso-scale molecular modelling technique called Dissipative Particle Dynamics (DPD) will be used to predict IFT of water/oil/surfactant ternary system. In this technique different molecules of similar structures are lumped into single bead. Beads don't have fixed properties being composed of different elements. Bead properties need to be determined either using molecular simulation or by experimental values. In this work bead-bead repulsion parameters were calculated using molecular simulations. Hexane, nonane and pentadecane were used as model crude oil. Sodium dodecyl sulphate was used as surfactant. As different molecules are lumped into single beads, faster evaluation of surfactants can be performed. The interfacial properties like interface thickness and interfacial tension and their dependence on oil types, surfactant types, oil/water ratio, surfactant concentration and surfactant chain length at particular temperature and pressure were investigated. Good qualitative as well as quantitative agreement of the modelled properties was obtained with experimental data. Detailed methodology, theory and results will be discussed in the paper. DPD technique is a novel way for initial screening of surfactants and can reduce experimental tests and time.