In this article a mass transfer model for multiphase flow in naturally fractured reservoirs was derived. The scaling analysis is presented in order to identify the characteristic scales where the fractured porous media can be studied. The system under consideration consists of two regions and an inter-region. One region is porous medium saturated with multiphase flow (η-region) and the other region is multiphase flow in the fracture (ω-region). The multiphase flow analyzed in both regions is water-oil-gas. The oneequation model for the fractured system was obtained considering thermodynamic equilibrium, which can be applied in η-region, ω-region, and ηω-inter-region due to the non-local averaging approximation.