Interfacial properties of reservoir fluids and rocks
Creators: name: Li, Xuesong
Publisher: name: Imperial College London
Year: 2012

description: Interfacial phenomena between CO2, brines or hydrocarbon, and carbonate rocks were investigated with the aim of understanding key aspects on CO2 storage and enhanced oil recovery (EOR) in carbonate reservoirs. The interfacial tensions between brines and CO2 were studied systematically with variation of the salt type and concentration under conditions applicable to the field. The results of the study indicate that, for strong electrolytes, the interfacial tension increases linearly with the positive charge concentration. Empirical models have been developed that represent the results as a function of temperature, pressure and molality with the small absolute average relative deviation of about 2 %. The interfacial tension measured between brine and crude oils indicated that interfacial tension has a strong dependence on both the viscosity of crude oil and the salinity of the brine. Molecular dynamics (MD) simulations of interfacial tension between water or brine and CO2 were carried out to investigate microscopic interfacial phenomena and to further understand the dependence of interfacial tension on temperature, pressure, and brine salinity. The simulation results were consistent with the experimental data obtained in this study. In particular, the simulations showed that the interfacial tension is linearly dependent on the positive charge concentration for strong electrolytes, most likely due to desorption of ions on the interface between brine and CO2. The contact angle of brine and crude oil on carbonate rocks was measured at both ambient and reservoir conditions. The results indicate that brine salinity has a strong effect on the wettability of the carbonate rock surface. This thesis provided the first attempt to explain the low salinity effect from the interactions between brine and rocks. Contact angle results and wettability index gathered from the NMR and Amott approaches measured on porous rocks were compared and found to be correlated in (crude oil + brine + calcite) systems at ambient condition. Molecular dynamics simulations of contact angle were carried out to give a deeper understanding of the underlying mechanism of the effect of brine salinity on wettabilty. Together with the experimental evidence, it can be concluded that increasing the salinity of brine results in an increase of the interfacial tension between calcite and brine. This is the first attempt to simulate contact angles by IFT simulations. Over all, interfacial phenomena between reservoir rocks and fluids were investigated by interfacial tension and contact angle measurement and by molecular simulation. Based on the wide range of experimental and simulation data obtained, this thesis provides a near complete understanding of the brine and CO2 interfacial behaviour under reservoir conditions. The empirical models obtained can predict reliably essentially any interfacial tension between brine and CO2 at reservoir conditions with given brine composition, temperature and pressure. MD simulations together with the experimental evidence, indicate that reducing the salinity of brine generally reduces the adhesion tension of crude oil in brine and calcite system. Thus proving that low salinity water flooding could potentially increase oil recovery from carbonate reservoir. More generally, low salinity aquifers are found to be more favourable for CO2 trapping.