The consumption of hydrocarbons worldwide is increasing gradually due to growth of economy,while the conventional reservoirs are declining rapidly and there is need of new resources to balance the shortage of conventional resources.Therefore,the production from unconventional resources were increased in the last decades due to advance in technologies that are horizontal well drilling and multiple stage fracturing are provides highly conductivity paths for the injected gas to diffuse and penetrate into the micro to nano permeable matrixes.However,the primary productions of the tight oil reservoirs were declined about 75%within the first two years and primary recovery remains low to only 5-10%of the OOIP or less,even though longer horizontal wells have been drilled and vastly fractured,resulting in tremendous oil resource remaining in place.In the other hand,globally environment is changing due to carbon dioxide（CO₂）emission,which is mainly from the combustion of fossil fuels.If tight reservoirs have storage capacity will be a major step towards advances in CO₂ sequestration in order to reduce CO₂ emissions existing in the atmosphere and enhance oil recovery from unconventional tight reservoirs.CO₂ huff-n-puff process or cyclic CO₂ injection process in a single horizontal well is not affected by early gas breakthrough as compared to CO₂ flooding.The study of CO₂ huff-n-puff and hydrocarbon recovery in tight reservoirs is mainly function of several structural and operational parameters Beside the effects of the above uncertain parameters on the process,water saturation,asphaltene deposition and solubility of CO₂ in the aqueous phase have not been clearly understood.In addition,the nanopores confinement in tight reservoirs causes a high capillary pressure which substantially influences fluid phase equilibrium,causing reduction in minimum miscibility pressure（MMP）and effecting fluid flow in tight reservoirs.Hence,it is absolutely important to study the most significant parameters dominant in this process.The results of the phase behavior simulator were compared with the experimental data showing that the saturation pressure of the recombined fluid and CO₂ system were strongly affected by the concentration of CO₂.In the swelling tests,three phase observed at 0.3 CO₂mass concentration in the CO₂/live oil system.Furthermore,its noticed from optimization process of CO₂ huff-n-puff that the longer production period will lead to more oil production while the soaking period has an influence on the oil recovery and further extending the soaking period doesn’t improve any incremental oil recovery.However,the presence of water has a negative impact on the oil recovery,thus it is demonstrated that the reversion of fracturing fluids will improve the oil recovery.In addition,the vanishing interfacial tension（VIT）technique is required short time and less expensive in determining MMP as compared to slim-tube procedure.Finally,the simulation results show that combination effect of CO₂diffusion and capillary pressure have a positive influence on the CO₂ huff-n-puff performance.