Research on the Evolution Characteristics and Influencing Factors of Foamy Oil Bubbles in Porous Media

Some high-viscosity crude oils have the characteristics of high oil production, low gas production and slow pressure reduction speed during the pressure depletion production process, and the "foamy oil" phenomenon occurs. The coexistence time of the two phases of foamy oil is much longer than that of crude oil with ordinary dissolved gas. Its complex phase change process is an important reason for the high degree of primary oil recovery. In the past, most of the studies focused on the production performance of foamy oil, while there were relatively few studies on the regularity of the molecular phase behavior of microscopic foamy oil and its influencing factors. Taking the foamy oil in Venezuela as the research object, this paper uses an etched glass model with heterogeneous pore characteristics to simulate the pressure reduction process. It discovers an important phenomenon that the growth of bubbles mostly occurs during the migration process. It is speculated that the high content of heavy components in foamy oil leads to the stability of the interface between the oil phase and the gas phase, which is the main reason why foamy oil is not easy to degas and undergoes phase change slowly. And there is always a diffusion phenomenon between bubbles and the oil phase during the movement process. Combined with the experimental phenomena, molecular simulation was employed to calculate the diffusion process of components in the gas phase and oil phase. After taking the diffusion coefficient into account, the VOF (Volume of Fluid) method was adopted to simulate the growth process of bubbles in foamy oil by solving the individual momentum equations and handling the volume ratio of each fluid passing through the region. The influences of conditions such as the content of light components, oil phase viscosity and interfacial tension on the bubble growth process were analyzed. The simulation results show that the bubble growth process is affected by multiple conditions such as oil phase components, oil phase viscosity and interfacial tension. However, the degrees of influence of the above factors vary in different stages. In the initial stage of bubble formation, it is mainly influenced by the change in the content of light components. During the stage when the bubbles have relatively high stability, the oil phase viscosity is the main reason for slowing down the increase in the bubble growth rate. The slight influence of interfacial tension on the bubble growth rate is not a major influencing factor for foamy oil. Based on the above analysis, an empirical formula for bubble growth was obtained through data fitting means, and a reasonable explanation for the development characteristics of foamy oil was provided.