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This article presents an extensive relative permeability study for low salinity water flooding (LSWF) in minerally different carbonate rocks. The experiments were performed with unsteady state method using artificial cores, crude oil and synthetic brines. The effect of water salinity and rock composition on relative permeability was obtained. The results show that the oil (water) relative permeability increases (decreases) first and then decreases (increases) with the decrease of the salinity of brines. Actually, there exists an optimal salinity (2384.6 mg/L) which maximizes the oil relative permeability and minimizes water relative permeability. When low salinity water is kept the same, the higher calcite content in the carbonate rock, the bigger oil relative permeability and the smaller water relative permeability will be. [ABSTRACT FROM AUTHOR]

There is not a consistent view about the mechanism of wettability alteration during low salinity water flooding. This paper highlights extensive wettability studies to investigate the wettability alteration on mineralogically different carbonates. Contact angle measurements were conducted to characterize wettability changes quantitatively. The results clearly revealed that wettability of carbonate rock surfaces can be altered to a more water-wet condition by lowering water salinity. The trend of the maximum change of contact angle (MCCA) variation with dolomite/calcite content in the rock is fairly linear under the same salinity, which demonstrates that carbonate minerals can affect rock wettability in a way. Also, the higher calcite content in the rock, the greater MCCA, i.e. the stronger effect of LSWF. Besides, the sensitivity of rock wettability to minerals is different under different salinity conditions. When the salinity is in the range of 2384.6 ∼ 4769.2 mg/L, rock wettability is most sensitive to minerals. The analysis of the effect of ion composition showed that the effect of Ca2+ on wettability alteration is greater than that of Mg2+ at room temperature, and with the increase of the content of calcite in the rock, the effect of Ca2+ is more pronounced than that of Mg2+. [ABSTRACT FROM AUTHOR]