Water Alternated Gas (WAG) flooding is largely used as an Enhanced Oil Recovery (EOR) method in oil fields. It is based on the high sweep efficiency of the water phase and the high displacement efficiency of the gas phase. Additionally, other components may be dissolved in both displacing phases, increasing the oil recovery factor and leading to modern WAG schemes such as PWAG (Polymer WAG), MWAG (Miscible WAG), and others. In this paper, we present approximate analytical solutions for the linear immiscible Water Alternated Gas problem. The mathematical model is composed by a 2×2 system of nonlinear hyperbolic Partial Differential Equations (PDE), solved by the Method of Characteristics (MOC) for a set of reservoir properties. The analytical solution is compared with numerical simulation showing the accuracy and robustness of the method under different WAG configurations. The presented solutions can be used to select the best recovery technique for a particular field in a fast and efficient way.

水交替气（WAG）驱在油田中广泛用作提高石油采收率（EOR）方法。它是基于水相的高波及效率和气相的高驱替效率。此外，其他组分可能会在两个驱替阶段溶解，从而提高采收率并导致现代 WAG 方案，例如 PWAG（聚合物 WAG）、MWAG（混相 WAG）等。在本文中，我们提出了线性不混溶水替代气体问题的近似解析解。该数学模型由 2×2 非线性双曲偏微分方程 (PDE) 系统组成，通过特征方法 (MOC) 求解一组储层特性。将解析解与数值模拟进行比较，显示了该方法在不同 WAG 配置下的准确性和鲁棒性。所提出的解决方案可用于快速有效地为特定油田选择最佳回收技术。