During the primary stage, the in-situ generated foamy oil has been found to be responsible for an unexpected high recovery factor, a remarkably low gas-oil ratio (GOR), and a higher-than-expected well production rate. Such a phenomenon can also be artificially induced by injecting alkane solvents (e.g., methane and propane) or CO2 to a heavy oil reservoir; however, the gas exsolution of foamy oil is not yet well understood due mainly to the complicated physical processes. On the other hand, the associated emulsifications resulted from the in-situ generated surfactant(s) during alkaline flooding in a heavy oil reservoir lead to an increase in oil recovery, though no theoretical models have been made available to quantify such physical phenomena at high pressures and elevated temperatures. Physically, both gas exsolution and emulsification are closely associated with the nonequilibrium phase behaviour. Therefore, it is of fundamental and pragmatic importance to accurately quantify the nonequilibrium phase behaviour of the alkane solvent(s)-CO2/alkaline water-heavy oil systems under reservoir conditions. A novel and pragmatic technique has been developed and validated to quantify gas exsolution of alkane solvent(s)-CO2-heavy oil systems under nonequilibrium conditions. Experimentally, constant composition expansion (CCE) tests of alkane solvent(s)-CO2- heavy oil systems are conducted with a visualized PVT cell. Theoretically, a mathematical model which integrates the Peng-Robinson equation of state (PR EOS), Fick’s second law, and nonequilibrium boundary conditions has been developed. It is found that the rising of experiment temperature and pressure has negative effects on diffusion coefficient during gas exsolution processes. At a higher temperature, a larger CO2 diffusion coefficient is observed, whereas, for alkane solvents (i.e., CH4 and C3H8), a lower diffusion coefficient is attained. Also, experimental and theoretical techniques have been developed to quantify the emulsion behaviour of alkaline water-heavy oil systems at high pressures and elevated temperatures. Experimentally, oil in water (O/W) emulsions with different settling times were prepared in order to track the continuous water content distribution along time. Theoretically, two groups of population balance equations (PBEs) were applied to quantify the phase behaviour during the emulsion destabilization. By applying the emulsion inversion point (EIP) as the boundary condition, the newly developed model is able to reproduce the dynamic water content distribution in the dual-emulsion systems. Due to the corresponding changes of oil viscosity and interfacial tension (IFT), either an increase in temperature or a decrease in pressure leads to a smaller EIP and higher coalescence efficiency. As a weak alkali, Na2CO3 facilitates the stabilization of the emulsion and inhibits the influence of higher temperatures, while NaOH solution-heavy oil systems achieve emulsion inversion more easily.