Nitrogen- and chemical-assisted steam huff-and-puff of heavy oil in heterogeneous microfluidic pore network

Steam huff-and-puff has been widely applied for heavy-oil thermal recovery. However, the opacity of reservoir rocks limits direct pore-scale observation of oil mobilization, hindering the evaluation and optimization of co-injected fluids. To address this issue, a microfluidic experimental system is developed to simulate authentic reservoir huff-and-puff conditions, enabling the pore-scale investigation of steam-based oil recovery assisted by nitrogen and an oil displacement agent. The pore network used in our experiments features both low-permeability and high-permeability zones. In single-fluid injection experiments, stable flow channels form predominantly in the high-permeability zone, thereby limiting overall heavy oil mobilization. When multiple fluids are injected, however, the injection sequence proves to be highly influential. In a dual-fluid injection of oil displacement agent followed by nitrogen, emulsion and oil-in-microbubble cluster are formed, significantly improving oil mobility. In a ternary injection of nitrogen followed by oil displacement agent and steam, although steam reduces oil viscosity by raising the temperature, the accompanying condensate dilutes the oil displacement agent and thus affects its interactions with heavy oil and gas. These results clarify the role of injection fluids and their sequence in the nitrogen- and chemical-assisted steam huff-and-puff of heavy oil, providing important insights for the optimization of heavy oil recovery strategies. Document Type: Original article Cited as: Wei, T., Yu, J., Cao, Q., Han, W., Liang, J., Wu, R. Nitrogen- and chemical-assisted steam huff-and-puff of heavy oil in heterogeneous microfluidic pore network. Capillarity, 2026, 19(1): 1-14. https://doi.org/10.46690/capi.2026.04.01