Pore-scale investigation of immiscible gas-assisted gravity drainage

Gas-assisted gravity drainage (GAGD) is an effective method of oil recovery that is influenced by the properties of the fluids and formations involved. In this paper, a direct numerical simulation method is employed to investigate immiscible GAGD in an oil-wet porous medium. The interface between oil and gas is tracked via the phase-field method. A series of numerical simulations are performed over a large range of values of various factors (gravity force, capillary force, viscous force, viscosity ratio, and porous medium properties) to investigate the gas flooding process in a porous medium. The results show the oil–gas interface as a transition zone that migrates during the GAGD process. Gravity improves oil–gas interfacial stability because the continuous oil film gravity-assisted hydraulic connection effect can overcome the capillary force in a small pore. The oil displacement process is dominated by gravity instead of the capillary and viscous forces when the gravitational number exceeds 500. Finally, the pore-scale dimensionless number (Npore) enables a quantitative analysis of the effects of various factors on GAGD. Npore helps predict GAGD oil recovery.