Experimental Study of Phase Transformation Effects on Relative Permeabilities in Fractures

Phase transformation affects multiphase flow in geothermal and gas-condensate reservoirs due to the same substance occurring in different phases. These effects change the phase behavior and the flow characteristics. The goals of this research were to compare the flow behavior and relative permeabilities difference between two-phase flow with and without phase transformation effects in smooth-walled and rough-walled fractures. During this research, an experimental apparatus was built to capture the unstable nature of the two-phase flow fractures and display the flow structures in real time. Two-phase flow experiments with phase transformation effects (steam-water flow) and without phase transformation effects (nitrogen-water flow) were conducted. The porous medium approach was used to calculate two-phase relative permeabilities. From the results in this study, steam-water relative permeabilities are different from nitrogen-water relative permeabilities. The enhanced steam-phase relative permeability is due to the effects of phase transformation. This shows consistency with some earlier studies in porous media. The nitrogen-water relative permeability is described most appropriately by using the viscous coupling model. However, steam-water flow in the rough-walled fracture, which is coupled with strong phase transformation effects, seems to be represented better by Brooks-Corey relative permeability functions for fractured media (λ →∞). The results from this study suggest that relative permeabilities accounting for phase transformation effects have to be used in simulations of geothermal and solution gas reservoirs to represent two-phase interactions adequately.