A formulation based on a cationic surface-active ionic liquid and an anionic surfactant for enhanced oil recovery at a carbonate reservoir

With the still huge dependence on crude oil, it is crucial to develop enhanced oil recovery techniques to improve reservoir production and lifespan. Carbonate reservoirs constitute over half the world's oil reserves, but they are challenging in terms of recovery due to their complex pore network, oil-wet or mixed-wet rocks, and harsh conditions of temperature and salinity. This work offers a significant contribution to the exploitation of these reservoirs. A new formulation, able to provide very low interfacial tension at high temperatures with reduced adsorption on carbonate rocks, was designed. A low-cost traditional alkyl benzene sulfonate (RECOLAS158) was mixed with the cationic surface active ionic liquid N,N-diethoxylated-N-tallow-N-ethylammonium ethylsulfate. A formulation containing 56.4 wt% RECOLAS158 was selected for its good performance in terms of phase behavior, injectability and interfacial tension at a wide range of temperatures and salinities. A very significant tertiary oil recovery (19.53% of the original oil in place) and low blend adsorption (0.086 mgblend/grock), demonstrated the promising performance of the formulation. The key mechanism associated to the improvement of oil recovery is interfacial tension reduction.