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Graphical abstract Highlights • The designed setup is a useful tool for observing the oil-gas interfacial behavior. • The gas-oil interface of foamy oil was much more stable than that of nonfoamy oil. • The CO 2 -oil film exhibited the highest gas-oil interfacial stability. • Asphaltene properties had an important influence on foamy oil formation. • The asphaltenes from foamy oil contain a greater number of polar functional groups. Abstract Solution gas drive from some heavy oil reservoirs exhibits foamy oil behavior. However, the characteristics of oil that determine whether foamy oil behavior occurs have not been clarified. Therefore, we performed a comprehensive experimental study of gas-oil interfacial properties to provide more in-depth information about foamy oil formation. A new experimental setup for single film stability was designed to investigate the gas-oil interfacial stability and its influencing factors under reservoir conditions. Then, a series of micromodel experiments was conducted in high-pressure etched glass micromodels with foamy and nonfoamy oils to visually study the oil-gas interfacial stability in porous media. Finally, chemical characterization (acid and base number measurements, elemental analyses, nuclear magnetic resonance (NMR), and Fourier transformed infrared spectroscopy (FTIR)) was conducted to reveal the characteristic of foamy oil related to foamy oil formation. The results showed that the gas-oil interfacial stability increased at high oil component concentrations, small interfacial areas, and low temperatures. CO 2 -oil films exhibited higher gas-oil interfacial stability than N 2 and mixed gas (90 mol% CH 4 and 10 mol% CO 2) for both foamy and nonfoamy oils. A pressure at which the interfacial stability was minimized was observed. In addition, the gas-oil interface of foamy oil was much more stable than that of nonfoamy oil because the asphaltenes from foamy oil contain a greater number of polar functional groups (hydroxyl groups, carboxylic groups, amine, and heterocyclic rings), which adsorb at the oil-gas interface and increase stability. Therefore, a high asphaltene concentration with abundant polar functional groups could be the characteristic of oils responsible for foamy oil formation. [ABSTRACT FROM AUTHOR]

Foamy oil behavior contributes significantly to the anomalously high primary recovery of heavy oils observed in the Orinoco Belt, Venezuela. However, once below the pseudo-bubble pressure, disappearance of this phenomenon results in a rapid increase in the produced GOR and a fast decline in oil production. This paper presents the results of a laboratory investigation, including asphaltene precipitation studies, pressure–volume–temperature (PVT) studies of foamy oil–natural gas mixtures and coreflood tests, for evaluating the feasibility of the natural gas injection process for enhanced heavy oil recovery with foamy oil characteristics. Firstly, asphaltene precipitation tests were carried out to investigate the likelihood of asphaltene deposition problems in MPE3 reservoir during the gas injection process. The natural gas dissolution tests characterized the natural gas diffusion process in the foamy oil, and a new method for determining the natural gas diffusion coefficient in foamy oil was developed on the basis of experimental data. Thereafter, foamy oil swelling tests examined the effects on viscosity reduction and foamy oil swelling of the presence of natural gas. Finally, coreflood tests were carried out to investigate the effects on oil recovery of injection mode and their different process parameters. The results indicate that significant amounts of natural gas could dissolve in the oil, which would cause oil swelling, viscosity reduction and artificial foamy oil formation. Core-flooding tests show that the natural gas huff-n-puff process could increase oil recovery 7.8% compared to the primary pressure depletion process, indicating a greater potential for recovering heavy oil. However, the asphaltene instability could potentially nullify any expected benefits of improved oil recovery with natural gas. [ABSTRACT FROM AUTHOR]