Pore-scale modeling of water-gas flow in heterogeneous porous media

Water-gas flow in heterogeneous porous media is a ubiquitous natural phenomenon. A pore-scale investigation can help to understand the mechanisms of water-gas flow. This study employs a direct simulation method to model the immiscible water-gas flow while tracking the phase interface via the phase-field method. We first verified the mathematical model by layered two-phase flow and capillary intrusion tests. Then, the quartet structure generation set was used to generate a heterogeneous porous media, based on which water-gas displacement was simulated. The characteristics of drainage and imbibition displacements were systematically investigated. Results show that the forced imbibition process shows stable displacement due to cooperative filling, yet with local capillary fingering. Capillary valve effects always exist during the process, making the capillary force act as both driving and resistance forces in heterogeneous porous media. Nevertheless, these pore scale events inhabit the rapid breakthrough in the small pore-throat zone, ensuring the uniform advancement of the interface. During drainage, viscous fingering in the wide pore-throat zone and capillary fingering in the narrow pore-throat zone are simultaneously observed. Compared with the imbibition process, the water-gas front advances faster due to the smaller viscous force of invading fluid. The phase distribution after drainage displacement at different capillary numbers is quite different due to inconsistent flow patterns. Nevertheless, the final phase saturation of the imbibition process under different capillary numbers is similar, but the area of each type is different. For both the imbibition and drainage processes, the larger the capillary number, the higher the final displacement efficiency.Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0157655

Automated summary

Water-gas flow in heterogeneous porous media was simulated using a direct simulation method and the phase-field method. The study found that forced imbibition showed stable displacement with local capillary fingering. Capillary valve effects acted as both driving and resistance forces during the process. Drainage showed viscous fingering and capillary fingering simultaneously. The water-gas front advanced faster during drainage due to smaller viscous forces. The final phase saturation of imbibition was similar under different capillary numbers, but the area of each type differed. The larger the capillary number, the higher the final displacement efficiency.