Carbonate reservoirs introduce great challenges due to their complex fabric nature (low matrix permeability, poor effective porosity, fractures) and unfavorable wettability. These challenges are further displayed when combined with increased depth and low grade oil (high density and viscosity). A huge amount of oil is contained in such reservoirs without any technological breakthrough for improving the recovery efficiently. Until recently, heavy oil reserves did not attract much interest. The lowest oil profitability, the low price of the oil barrel in the international market, the difficulties involved in its extraction and its refining, and the large amount of light and medium oils to be explored could not justify the investments. Maturity of light and medium oil fields and the significant increase in oil price placed that source of energy under a new perspective.