Most rocks of carbonate reservoirs is preferably lipophilic, this feature of rock-fluid interaction, also known as wettability and is closely linked at low oil recovery rates. The application of surface modifying agents is a way to changing the wettability of carbonates, making them preferentially hydrophilic and thereby favoring the reduction of residual oil saturation (Ros).

Actually reservoirs with heterogeneous permeability, which have regions of low permeability and presence of fractures and high permeability channels, there is a tendency that the injection water to flow preferentially through these channels with high permeability. This type of reservoir, the oil recovery process is improved by capillary forces, spontaneous process known as imbibition, where water tends to soak the smaller pores, expelling the oil to the larger pores. This phenomenon retard " breakthrough" and reducing the residual oil saturation (Ros). However, spontaneous imbibition only occurs appreciably in water wet reservoir. In the oil wet formations, the water has less affinity for the wall of the pores and the capillary forces are small and in many cases could be negative.

The paper presents results of Enhanced Oil Recovery (EOR) Group from Cenpes/ Petrobras, evaluating two anionics and one cationic surfactants, with different interfacial tension (IFT) and their ability to increase hydrophilicity of carbonates. The results showed that the anionic surfactant with higher IFT values was responsible for increased to make the carbonate preferably hydrophilic, keeping in high values the capillary pressure.

The results were demonstrated by the core flow tests, which showed higher oil relative permeability and Ros reduction; spontaneous imbibition test, presents higher oil recovery and contact angle evaluated, which showed lower adhesion of the oil phase on the surface of carbonate.

The agent wettability modifying can be applied as a chemical method of EOR, as well as around the producing well. In this last one, could be created convergence zones for oil and be increased the effective oil permeability near the oil production well.

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