Establishment and solution of a three-zone radial composite well test model for mixed gas drive production wells

In the process of gas flooding, the underground miscible law and oil displacement characteristics are complex, and there is no effective evaluation method. As an effective method to invert reservoir parameters and analyze seepage law, well test can be used to analyze the law of underground gas and oil action. This study focuses on the mechanism of gas-crude oil interaction, and establishes a three-zone radial composite well test model including interface skin effect and power-law change of physical properties of transition zone. The model innovatively introduces the interface coefficient to characterize the phase transition effect of the regional boundary, which is solved by dimensionless transformation, Laplace transformation and Stehfest numerical inversion method. Get the fluid phase distribution evaluation chart in the process of gas flooding. The results show that the radius of the crude oil zone (R₁) determines the duration of the radial flow, the radius of the gas-oil transition zone (R₂) regulates the seepage range, the power law index (θ) controls the derivative curve shape, and the energy storage index (I) has a weak influence on the curve shape. This study establishes a theoretical framework for dynamic monitoring of miscible gas drive wells and nonlinear reservoir parameter inversion.