Maximization of capillary trapping ratio to injected CO2 by means of co-injection

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Abstract Co-injection of water with CO2 is an effective scheme to control the initial gas saturation in porous media. The fractional flow rate of water about 5 to 10% is enough to reduce the initial gas saturations, and after water injection, most of gas injected in porous media is trapped by capillarity with low fractional volume of migrating gas. In this paper, first we derive an analytical model to predict the gas saturations for the co-injection with water. Next, the effect of the initial gas saturation, which is controlled by the fractional flow ratio in co-injection process, on the residual gas saturation at capillary trapping is investigated experimentally for the water and nitrogen system at room condition. Depending on the relative permeabilities, the initial gas saturation is reduced by the co-injection of water. In case of the Berea sandstone core, if the initial saturation is controlled to be in the range between 20% and 40%, most of the gas is trapped by capillarity and less than 20% of gas with respect to the injected gas volume is migrate by water injection. In case of the packed bed of Toyoura standard sand, the initial gas saturation is about 20% for a wide range of gas fractional flow rate from 0.50 to 0.95. The residual gas saturation for these conditions is about 15%. Approximately less than 25% of gas migrates by water injection. Based on the analytical model and the experimental results, advantages and disadvantages of co-injection systems are discussed.