In this paper we study the ability of analytical solutions for four-component three-phase flow to predict displacement efficiency in water alternating gas (WAG) injection processes. We present equivalent analytical solutions for Riemann problems with injection compositions that are the average water and gas mixture for various WAG injection schemes. These solutions are compared to numerical calculations with variable slug sizes and used to explore the effect of slug size, injecting water versus gas first, and the average injection composition on displacement efficiency in compositional WAG schemes. We model immiscible WAG injection of water and CO2 into an oil reservoir containing C_(10) and CH4 with and without a mobile aqueous phase present initially. These are the first analytical solutions for three-phase initial conditions in quaternary systems. The magnitude of the oil bank and the breakthrough time of the injected fluids are accurately predicted by the analytical solutions, even for displacements where large water and gas slugs are injected. As slug size decreases, the displacements predicted by numerical calculations converge to the analytical solutions.
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