In order to reduce the anthropogenic greenhouse-gas emissions, CO2 geological storage has been proposed. Many applications for CO2 geological storage exist, such as injecting CO2 into depleted hydrocarbon reservoirs, enhanced coalbed methane recovery, and enhanced oil recovery (EOR) operations. CO2 injection has been extensively studied by many researchers and has resulted in large oil recoveries. Injecting CO2 alone experienced an early breakthrough problem, which is unfavorable in CO2 sequestration projects. CO2 must be kept inside the oil reservoir. This pushes researchers to combine water with CO2 flooding to improve the sweep efficiency. In this study, we investigated the effect of water salinity on CO2 flooding and on the water–rock interactions during WAG. The results of this study show that combining LS water with CO2 flooding prevents early breakthrough by improving CO2 sweep efficiency. The oil recovery was also high due to merging LS water with CO2 flooding. Controlling the injected water chemistry has a large influence on both oil recovery and CO2 solubility in crude oil. The highest effect of added chemicals can be ranked in an order of NaCl> CaCl2> Mixed NaCl, CaCl2, and MgCl2>MgCl2.

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