Probing the mechanism of in situ oil droplet swelling during low salinity water flooding

Low salinity water (LSW) flooding has been widely used to enhance oil recovery due to its low cost. The phenomenon of oil droplets swelling was discovered during the LSW flooding, which was deemed important for enhancing oil recovery. However, whether and how the swelling of oil droplets was driven by osmotic pressure have not been fully understood. In this paper, instrument built by our laboratory was used to record the volume of individual oil droplet in real time, analyze the influencing factors and swelling rule of oil droplet, explore the swelling mechanism. In addition, the contribution of oil droplet swelling to enhanced oil recovery was demonstrated by core displacement experiments. The results show that osmotic pressure, oil soluble surface-active agents and original water content of oil droplet are the necessary prerequisites for the swelling of oil droplet. The maximum swelling ratio of oil droplet reached 3.60 times and oil recovery improved by 5.16%. The diffusion of water molecules into inside of oil droplet was the basic reason of oil droplet swelling. Osmotic pressure was the driving force of water molecules diffusion, oil-soluble surfactant was the transport medium of water molecules through oil film, and water content in oil droplet dominated the final equilibrium state of water molecules diffusion. Our results would be helpful for subsequent researchers to further explored LSW flooding for enhancing oil recovery. [Display omitted]