Experimental study of combined thermal flooding in improving heavy oil flowability

China boasts abundant heavy oil resources, which is vital for its energy security. However, its heavy oil typically exhibits high viscosity, which severely hinders its flow and extraction. Enhancing heavy oil flowability is vital for its effective exploitation. This study independently developed a visualization experimental system and explored the mechanisms through which combined thermal flooding (a combination of heat, chemical agents and gas) enhances heavy oil flowability. Results indicate that combined thermal flooding, that is, synergistically integrating heat, chemical agents, and gas, can effectively enhance the recovery of heavy oil by improving its flowability. Its working mechanisms were explored from the aspects of thermal effects, emulsification, precursor film, profile control capacity, and CO₂ solution and extraction effects. The emulsification was observed using a confocal laser scanning fluorescence microscope (CLSFM). Findings reveal that steam flooding can boost crude oil flowability by augmenting temperature, while a chemical system tends to produce low-viscosity oil-in-water emulsions, thus further aiding the flow of crude oil. During CO₂ flooding, the solvent initially reduced crude oil viscosity and formed foamy oil, followed by the pronounced component separation of the produced fluids in the later stage. This demonstrates the effectiveness of CO₂ in viscosity reduction and component extraction. Additionally, the results of interfacial tension experiments indicate that surfactants can reduce the heavy oil's interfacial tension, fostering the formation of nano-scale precursor films. They can also thicken these films and diminish their spreading resistance, thus accelerating residual oil removal and promoting heavy oil production. This study further elaborated the mechanisms behind the combined thermal flooding's efficiency in enhancing heavy oil recovery, offering a theoretical foundation for its broader application.