Temperature-dependent differences in CO2 foaming behavior between crude oil and its water-in-oil emulsion

Emulsification and foaming frequently occur during crude oil production, transportation and separation. However, the mechanisms underlying the temperature-dependent differences in foaming behavior between crude oil and its emulsion remain insufficiently understood. This study examines these differences through measurements of viscosity-temperature behavior, wax precipitation, net CO 2 release, interfacial tension, interfacial dilational modulus, and foam drainage. Temperature markedly affects the foaming behavior of both fluids. At temperatures of 30 °C and below, the emulsion exhibits greater foamability than crude oil, whereas the difference is small at 35 °C and above. This behavior is associated with the coupled effects of bulk rheology and interfacial properties. Below the wax appearance temperature, dispersed droplets and networks of precipitated wax crystals increase the apparent viscosity of the emulsion. The oil-gas interface in the emulsion exhibits lower viscoelasticity than that in crude oil, which may be associated with the adsorption of surface-active components at oil-water interfaces. Higher viscosity favors foam persistence, whereas the lower interfacial dilational modulus may counteract this effect. The lower CO 2 -liquid interfacial tension of the emulsion also favors bubble formation. In contrast, its lower net CO 2 release does not explain its greater foamability. The observed differences are therefore interpreted in terms of the combined effects of viscosity, interfacial tension, and net CO 2 release. These findings provide insight into the combined contributions of bulk rheology, interfacial properties, and CO₂ release dynamics, with implications for foam control, oil-gas separation, and flow assurance.