Numerical Simulation of Pore-Scale Water–Gas Displacement Based on the Conservative Level-Set Method

To study the pore-scale two-phase flow, a method for extracting and reconstructing the pore structure by scanning electron microscopy and combining the conservative level-set method and Navier–Stokes equations for the solution was introduced. The results show that the water–gas interface exhibits a gentle U-shape upon the consideration of interfacial tension. The pore diameter, connectivity, and pore throat size have a direct effect on the displacement velocity. The larger the pore diameter is, the faster the displacement is. A smaller pore throat will hinder the displacement. In addition, better pore connectivity also plays a decisive role in displacement. A water-lock effect will develop at the end of the pore, causing the gas to be trapped by the water. The fluid is displaced faster in pores that extend in the same direction as the flow than in pores that are perpendicular to the flow direction. The simulation was performed again by neglecting the effect of interfacial tension while keeping other conditions constant. The results show that the water–gas interface is a sharper V-shape and the area of gas in the pore space is smaller at the end of the simulation. In summary, reducing the interfacial tension of the liquid phase in the replacement process can effectively improve the replacement efficiency.