Influence of fractured vuggy structure on oil recovery efficiency during immiscible gas flooding

Key words:  reservoir  fractured vuggy structure  numerical simulation  immiscible gas flooding  oil recovery efficiency  vug density  fracture density

Abstract:

In order to study the influence of complex fractured vuggy structure on gas flooding, 19 models with 4 types of different fractured vuggy structures were established for a numerical simulation of immiscible nitrogen flooding. The results show that, the higher the position of the vugs above the fracture, the higher the oil recovery, and the oil recovery of gas flooding increases with the increase of vug density and porosity, but decreases with the increase of fracture density along the gas flowing direction. The existence of vugs can have a positive effect on oil recovery during gas flooding, which can overshadow the influence of the fractured vuggy structure. In general, the gas flooding mechanisms can be mainly due to gravity stabilized displacement, increasing formation energy, gas expansion and reducing of oil viscosity. Therefore, the oil recovery factor of gas flooding is mainly influenced by gravity, the density and porosity of vugs and the density of fractures along the gas flooding direction.