“…3 The major CO 2 immiscible processes mainly include CO 2 cyclic injection, CO 2 huff-n-puff, continuous CO 2 injection, and water-alternating-CO 2 injection, among which CO 2 huff-n-puff appears to be more efficient to increase heavy oil recovery, although the recovery factor is still low. 4,5 The addition of solvents to the CO 2 stream generally accelerates the processes of swelling heavy oil, reducing its viscosity, decreasing the IFT between heavy oil and CO 2 , and thus leading to a higher oil recovery in the vapor extraction (VAPEX) process. 6 Although some laboratory efforts have been conducted to study the mechanisms for enhancing heavy oil recovery by CO 2 injection, 5,7−12 few attempts have been made to evaluate the IFT performance of the solvent(s)−CO 2 −heavy oil systems under sub-and supercritical conditions.…”