Carbonated water injection (CWI) refers to a method of injecting brine saturated with CO2 into the formation to displace oil. CWI is a promising enhanced oil recovery (EOR) method because it combines the advantages of CO2 flooding and water flooding. This has a better oil displacement efficiency than water flooding and better sweep efficiency than CO2 flooding. Since the 1950s, many scholars conducted studies of CWI, including lab experiments and pilot tests in oil fields. This paper reviews the current research into the CWI method. This covers the CWI EOR mechanisms, experimental studies, numerical simulation, field application, sensitivity analysis of displacement parameters and current problems. The main CWI EOR mechanisms include oil swelling, reducing the water shield effect, oil viscosity reduction, wettability alteration, and interfacial tension reduction. The results of laboratory experiments show that CWI has better oil recovery than either water flooding or CO2 flooding. Compared with water imbibition, carbonated water imbibition has a better imbibition recovery and imbibition
rate. Field application indicates that CWI can significantly increase oil production and improve injection capacity of injection wells. In theoretical studies of CWI, some scholars proposed various models to describe the mass transfer process of CO2 from the aqueous phase to the oil phase, which involves the partition coefficient and diffusion coefficient of CO2. The most relevant parameters for CWI performance include carbonated water concentration, the timing for injection, injection rate, and salinity. Meanwhile, the presence of surfactant can further improve CWI performance, leading to better oil recovery. At present, there are two main problems for CWI application. One is that carbonated water can corrode metal material such as tubing, and the other is the possible occurrence of asphaltene precipitation during CWI.
