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

Gas flooding, as a key enhanced oil recovery (EOR) technology, has seen extensive research on its miscible mechanisms and displacement characteristics. However, dynamic monitoring and analysis of realistic phase-state distribution in subsurface fluids during gas flooding remain insufficient. This study focuses on gas-crude oil interaction mechanisms by developing a three-zone radial composite well-testing model that incorporates interfacial skin effects and power-law variations in physical properties within the transition zone, aiming to reveal the spatial distribution patterns of fluid phases during gas injection. Interfacial coefficients are introduced to characterize pressure jump effects at zone boundaries. The model is solved using dimensionless transformation, Laplace transform, and the Stehfest numerical inversion method, identifying seven characteristic flow regimes in pressure transient curves: oil zone radial flow, transition zone power-law concave-slope flow, and pure gas zone horizontal stabilization. Sensitivity analysis demonstrates that oil zone radius governs radial flow duration, transition zone radius regulates percolation scope, and power-law index controls derivative curve morphology. This research breaks through the homogenization assumptions of traditional composite reservoir models, establishing a theoretical framework for dynamic monitoring of miscible gas flooding wells and inversion of nonlinear reservoir parameters.