Research on effect of CO2 microbubbles on oil film in pores

The oil displacement technology of the water and gas dispersion system is a new enhanced oil recovery technology developed for low-permeability oilfields with low recoveries， which has obviously increased oil production in Changqing Oilfield. However， the effects among microbubbles in the dispersion system and pores are complex， and the research on its microscopic oil displacement mechanism is gradually deepening. According to the characteristics of heterogeneous low permeability core， a glass etching model with a side length of 1.5 cm was made， and the flow experiment of the CO2-water dispersion system was carried out under the conditions of reservoir temperature and pressure. The data such as bubble adsorption capacity， oil film pushing capacity， and bubble elastic energy were obtained by observing the interaction processes among microbubbles and oil， water， and rocks， and then the oil displacement effects were quantitatively characterized and analyzed. The experimental results show that the microbubble combines with the oil interface， to form a special oil adsorption film， which is significantly different from the mechanisms of water flooding and gas flooding. The merging of adjacent bubbles in the displacement process also promotes the convergence of oil films， and the merging of microbubbles helps the flow of bubbles so that the oil film adsorbed on the surface of the bubbles moves with the bubbles. The bubble volume expands due to the decrease in pressure， and the elastic energy released can promote the migration of the oil film adsorbed on the wall when the microbubble is transported. In addition， the oil film migration process of the microbubbles in the water and gas dispersion system was simulated and analyzed with the Volume of Fluid multiphase flow model， and the main factors that displace the oil film were obtained， which are the elastic energy generated by the deformation of the microbubbles and the energy of the microbubbles themselves. The energy of the bubble acts on the leading edge of the bubble and the bubble is pushed by contact with the surface of the oil film.