Effect of CO2 on Heavy Oil Recovery and Physical Properties in Huff-n-Puff Processes Under Reservoir Conditions

In this paper, experimental and numerical techniques have been utilized to quantify heavy oil properties in CO2 huff-n-puff processes under reservoir conditions. Experimentally, fluid properties together with viscosity reduction of heavy oil and interfacial properties between CO2 and heavy oil have been quantified, while five cycles of CO2 huff-n-puff processes have been conducted to determine oil recovery together with component variation of produced and residual oils. Theoretically, numerical simulation has been conducted to analyze the underlying recovery mechanisms associated with the CO2 huff-n-puff processes. CO2 huff-n-puff processes are only effective in the first two cycles under the existing experimental conditions, while the effective sweep range is limited near the wellbore region, resulting in poor oil recovery in the subsequent cycles. As for produced oil, its viscosity, density, resin and asphaltene contents, and molecular weight of asphaltene are reduced, whereas, for the residual oil, they are increased. The asphaltene component in the residual oil shows weak stability compared to that of the produced oil, while the ultimate oil recovery after the fifth CO2 cycle of huff-n-huff processes is measured to be 31.56%.