Dimethyl ether-enhanced CO2 flooding for improved heavy oil recovery and geological CO2 sequestration

The viscosity fingering effect of CO2 during heavy oil extraction results in low recovery. The use of cosolvents enhances CO2 solubility in heavy oil, effectively reducing its viscosity and improving production efficiency. This study introduces dimethyl ether (DME) as an innovative cosolvent to enhance CO2 flooding, with the dual objectives of improving heavy oil recovery and facilitating the geological sequestration of CO2. A thermodynamic phase equilibrium model was developed to investigate the phase behavior of the heavy oil-CO2-DME system, focusing on the influence of DME on CO2 solubility in heavy oil. Numerical simulations were conducted to compare the performance of DME-enhanced CO2 flooding with conventional CO2 flooding in oil fields, while also assessing the impact of DME on the final CO2 sequestration rate within the reservoir. The results show that DME promotes the formation of a single-phase state in the heavy oil-CO2-DME system, enhancing the solubility of CO2 in heavy oil. DME lowers the interfacial tension between the oil and gas phases, inhibits excessive extraction of light hydrocarbon components by CO2, and avoids the deposition of heavy components that deteriorates crude oil fluidity, thereby enabling more efficient and sustainable heavy oil recovery. Additionally, under the same pressure conditions, DME-assisted CO2 flooding achieves a higher final CO2 sequestration rate compared to conventional CO2 flooding. DME enhances the solubility of CO2 in heavy oil, promoting more effective CO2 dissolution trapping. Additionally, DME reinforces the pore-scale trapping of CO2 within the reservoir, playing a crucial role in the sequestration of CO2 in heavy oil formations.