CO2 based enhanced oil recovery methods, such as continuous CO2 injection, intermittent CO2 injection, water-alternating CO2 injection, and CO2 huff 'n' puff, are successfully implemented in heavy oil reservoirs. Among them, the CO2 huff 'n' puff method has been proved as an applicable recovery method. Although many previous researches were conducted on the CO2 huff 'n' puff process applied in heavy oil reservoirs, some technical issues are still not investigated, such as non-equilibrium phase behaviors of foamy oil flow, CO2 diffusion into heavy oil, and the production performance in CO2 huff 'n' puff process coupled with non-equilibrium phase behaviors and CO2 diffusion. Therefore, this study aims at addressing the following major topics. Non-equilibrium phase behaviors of foamy oil flow. In order to investigate the foamy oil flow behavior in the primary production process, experimental studies on nonequilibrium phase behaviors of heavy oil-methane system are implemented in a pressure/volume/temperature cell with different pressure decline methods. The experimental results indicate that, with pressure decline rate increases, the pseudo-bubblepoint pressure decreases, leading to longer pressure duration of foamy oil, so that the foamy oil stability becomes stronger under higher pressure depletion rate. To study foamy oil stability in the production stage of the CO2 huff 'n' puff process, the non-equilibrium phase behaviors are investigated using the heavy oil-CO2 system. The same experimental methods are applied with that in the heavy oil-methane system, but the gas transfers rates (solution gas transfers to dispersed gas, dispersed gas transfers to free gas) in heavy oil- CO2 system are much higher than that observed in the heavy oil-methane system. A dynamic reaction rate model is developed to match the foamy oil stability using heavy oil- CO2 system, and high agreements are achieved. The reaction rate constants (k1 and k2) among different gas phases are determined through the history match. The performance of foamy oil flow, in the production stage of the CO2 huff 'n' puff process, highly relates to the amount of CO2 dissolves into heavy oil during the soaking stage. To understand the CO2 diffusion process in the heavy oil, CO2 diffusion coefficient is measured in both bulk phase (high pressure cell) and porous media (real reservoir core). The CO2 diffusion coefficient determination process mainly includes: (1) experimental study is conducted to measure the pressures in the diffusion process using the pressure decay method; (2) mathematical modeling study is carried out to calculate the CO2 diffusion coefficients using the history match method. Based on the understandings of the non-equilibrium phase behaviors and CO2 diffusion, the heavy oil production performance in CO2 huff 'n' puff process coupled with non-equilibrium phase behavior and CO2 diffusion is investigated. Six CO2 huff 'n' puff experiments are carried out using long cores (60 cm). The main affect parameters are studied, including pressure depletion rates (0.5, 1, 4, and 16 kPa/min), soaking time (5, 10, and 20 hours) and cycle numbers. Via experimental study, an equation which indicates the relationship of the cumulative oil and gas production in each cycle and each test is gained with high agreement. The experimental results indicate that the CO2 huff 'n' puff process can be an efficient approach to enhance heavy oil production with a recovery factor of 38.02%. The optimized pressure depletion rates, soaking time and cycle numbers are 1 kPa/min, 5 hours and 3 cycles, respectively, and the optimization parameters are upscaled for field application using scaling criteria.