Marangoni flow: An unknown mechanism for oil recovery during near-miscible CO₂ injection

Previously, we investigated the effect of interfacial tension gradient induced convective fluxes - Marangoni flow - on the recovery of bypassed oil during near-miscible and immiscible CO₂ injection in a 1D-matrix/fracture model. In the current study, the impact of Marangoni flow on oil recovery is studied during CO₂ injection into a matrix (flooding) using experimental results combined with analytical calculations. CO₂ injection is conducted at different pressures below the critical point where the oil/gas interface exists. The ternary system of CO₂/C10/C3 was compared with a binary system of CO₂/C10 as the zero level of the Marangoni flow. In this manner, the influence of other conventional recovery mechanisms can be simultaneously eliminated. The results show that there is good agreement between the recovery differences of these two systems and the Marangoni number derived from analytical estimations. Therefore, in the multi-component systems of hydrocarbons, where IFT increases with CO₂ concentration, Marangoni flow improves oil recovery by about 35%. During CO₂ flooding, it postpones the breakthrough time by conducting the oil towards the gas channel and guaranteeing the continuity of recovery. The level of recovery enhancement in the ternary system is proportional to the Marangoni number, and is maximized at a near-critical state, but vanishes towards the critical point. In far from critical region, the Marangoni effect is relatively weak.