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Enhanced oil recovery (EOR) techniques play an essential role in the maintenance of petroleum production worldwide. These techniques are receiving special attention due to the continuous decline in availability of oil resources. The study of surfactants and correlated systems have been considered due to their capacity to alter the wettability and interfacial proprieties, consequently reducing residual oil saturation and increasing oil production. In this context, heterogeneity becomes one of the main challenges to overcome, for it makes the fluid flow preferably thought the highest permeability regions, affecting sweep efficiency. It is also known that acids react with carbonate formations promoting matrix dissolution. However, few works in the literature report the use of reactive fluids in EOR. Therefore, this work analyzes the effects of reactive acid flow on porous carbonate media and its impact on advanced oil recovery operations. It presents an experimental study of the effects of acid microemulsion flooding in the enhancement of oil recovery in carbonate reservoirs. Acid microemulsions studied were characterized by surface tension, droplet diameter, viscosity, and corrosiveness. Flooding experiments demonstrated that the reactive flow of acid microemulsions in porous media increases oil recovery, achieving up to 30% additional recovery of the total oil in place. However, by increasing the reactivity of the systems, severe dissolution of the porous matrix can occur. The results presented open a new path on the use of low reactive fluids in enhanced oil recovery.

Well stimulation and enhanced oil recovery (EOR) plays an important role in oil production. Microemulsions and nanoemulsions fluids have been studied as a fluid to enhance the efficiency of these processes. In EOR, the chemical methods act on the alteration of physicochemical rock/fluid properties reducing the residual oil saturation and increasing the displacement of oil in the porous medium. Several authors have investigated the use of acid micro and nanoemulsions as systems of production enhancement. The study, under different conditions, indicated that acid nanoemulsion systems present a potential to be used as a retarded acid system, stimulating carbonate formation using a low concentration of surfactant and oil phase, offering an alternative fluid system to stimulate production in carbonate formations, especially in environmentally sensitive areas. Overall, this paper presents a review of laboratory studies of production improvements and enhanced oil recovery using microemulsion and nanoemulsion systems.

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