Effect of water saturation on heavy oil relative permeability in three-phase flow during gravity drainage-based recovery processes

摘要

Gas gravity drainage is one of the major displacement mechanisms in enhanced heavy oil recovery processes such as SAGD and VAPEX. The estimation and modelling of the relative permeability of heavy oil in the above three-phase flow processes have not been well established. In this study, gravity assisted gas injection experiments were performed in water-wet porous media to study the effect of water saturation on heavy oil relative permeability. Experiments include two stages of gas gravity drainage. The first drainage was conducted in the presence of connate water saturation followed by the second drainage after increasing water saturation. Results showed that increasing water saturation after the first gas gravity drainage could change the equilibrium between gravity and capillary forces and result in redistribution and mobilization of the residual oil. A significant incremental oil recovery was obtained with an increased production rate in the period of the second gas gravity drainage. The oil relative permeabilities for three-phase flow were calculated from the experimental data. It is found that the increase of water saturation can improve oil recovery and increase production rate through the oil relative permeability effect. It is concluded that heavy oil relative permeability depends on not only oil saturation but also the liquid phase saturation (sum of oil and water) in the gas gravity drainage process. Gas drainage experiments in micromodel were also conducted and the results showed that after the first gas drainage process increasing water saturation could affect drainage process. The results from this study can help better understand the fundamentals of relative permeability in threephase ftow and improve the design and simulation of heavy oil recovery processes which involve gravity-assisted gas injections.