Impact of solid surface energy on wettability of CO2/brine/mineral systems as a function of pressure, temperature and salinity

摘要

CO2 storage refers to the methods employed to inject CO2 in depleted oil and gas reservoirs and deep saline aquifers for long term storage of CO2 with the objective to reduce the anthropogenic CO2 emissions. Wettability and interfacial tension are two important multiphase parameters which are used to characterize the flow behavior of CO2 in reservoirs. Numerous studies have reported wettability data of CO2/brme systems on various rock forming minerals as a function of pressure, temperature and salinity. However, the associated trends have not been physically well-understood and require considerable attention which is objective of our present work. In this work, we apply Neumann's equation of state method to compute solid/CO2 and solid/water interfacial tension using our measured contact angle data for CO2/brine on mica and quartz. Our results indicate that solid/CO2 interfacial tension decrease with pressure and increase with temperature for both quartz and mica while the solid/water interfacial tension decrease with temperature for mica but increase with temperature for quartz. Moreover, the solid/water interfacial tension increased with water salinity. We further demonstrate that the interplay of these interfacial tensions lead to a typical behavior of contact angle as a function of pressure temperature and salinity. We thus conclude that hotter reservoirs with lower injection pressure and lower brine salinities exhibit relatively better water wetting state and hence better seal capacity leading to higher CO2 storage potential. We also conclude that solid surface energy approach adequately explains the dependency of wettability on pressure, temperature and salinity.