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

• Impact of Marangoni flow on oil recovery was studied during CO2 injection.
• Experimental results combined with analytical calculations were used.
• The level of recovery enhancement was proportional to the Marangoni number.
• The maximum recovery improvement was achieved at near-critical pressure.
• Marangoni flow vanished at critical pressure.

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.