Abstract

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Wettability is defined as rock tendency to spread or stick a fluid at rock's surface in presence of an immiscible liquid. In a water - oil rock system, wettability is defined base on amount of priority that stone surface cover with water or oil. Nearly, 50 percent of the world's oil reserves proven are located in carbonate reservoirs. The recovery factor in this reservoir is relatively low (less than 30%). With regard to fractured Carbonate Reservoirs and also low permeability of matrix rock in reservoirs in contrast with sandstone reservoirs. Therefore, the potential of oil recovery methods is so high in these reservoirs. The common method to enhance oil recovery in conventional reservoirs (sandstone and carbonate reservoirs with water wet rock reservoir) is water injection in these reservoirs that could be increased reservoir oil production by holding up the reservoir pressure above the bubble point pressure as well as increasing sweep efficiency. In carbonate reservoir or oil - wet reservoirs rock this method has no effect because in contrast with sandstone reservoirs at around 80 to 90% of carbonate reservoirs have a low capillary force, or in other words tends to oil wet more. In this case, due to low capillary force, injected water has no ability to penetrate into matrix rock and this process is flowed without a significant amount of oil move in high permeable fractures and breakthrough occurs in a shorter time thus the recovery factor decreases consequently.