Diffusion and Dissolution Behaviors of CO2, CH4, and N2 in Heavy Oil under High-Temperature and -Pressure Conditions: Insights into Heavy Oil Production via Multithermal Fluid Stimulation

To comprehend heavy oil production well via the multithermal fluid stimulation technology, the diffusion and dissolution processes of CO2, CH4, and N2 in heavy oil were conducted under a temperature range of 308.15–423.15 K and bulk pressures up to 20 MPa. Accordingly, the diffusion coefficients and solubilities of CO2, CH4, and N2 were measured. Results indicated that the diffusion coefficients of CO2, CH4, and N2 in heavy oil increase with rising temperature and decrease with rising pressure. The diffusion capability of these fluids in heavy oil conforms to the order CH4 > CO2 > N2. Moreover, the solubility of CO2, CH4, and N2 in heavy oil is negatively related to temperature and positively related to pressure. The solubility of various fluids in heavy oil decreases in the sequence of CO2 > CH4 > N2. The diffusion and dissolution of CO2, CH4, and N2 could induce volume expansion, colloidal structure damage, intermolecular force alteration, gap filling, and light component extraction toward heavy oil, thereby promoting its quality and recovery. Overall, heavy oil production via the multithermal fluid stimulation technology is recommended to be implemented under high-temperature and -pressure conditions.