This paper develops a novel WFS model for transient pressure analysis in multi-stage fractured horizontal wells. In the WFS model, two concepts called WFS pressure and WFS index are introduced and an additional skin factor in the interface of inner and outer regions is applied based on a radial composite reservoir. Then, a novel multi-stage fractured horizontal well model is developed by considering the WFS, stress-sensitivity effects, and finite-conductivity fractures. The reservoir model is solved by the perturbation transformation, Laplace transform, and numerical inversion. While the fracture model is solved by fracture discretization and superposition principle. Finally, the bottom hole pressure is obtained. Following that, model verification and sensitivity study are performed. It is found that the flow regimes of the WFS model includes bilinear flow, linear flow, first radial flow, bi-radial flow, pseudo radial flow, and WFS flow. An interesting feature of "hump" caused by WFS flow exhibits in the pressure derivative curve. The results of sensitivity study show that the height of that "hump" increases as the WFS pressure increases, but is independent of WFS index. What’s more, WFS flow exhibits a closed boundary flow when the WFS index is equal to zero, while it appears as a constant pressure boundary flow when WFS pressure is very tiny. Through the WFS model, the fluid supply characteristics of tight gas reservoirs are fully understood.

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