Pressure-driven capillary snap-off of gas bubbles at low wetting-liquid content

Snap-off is an important mechanism for generating discontinuous gas bubbles in porous media. Here, we use a hydrodynamic, corner-flow theory to re-examine the breakup of gas threads in constricted pores. Our primary focus is on the initial liquid volume within the corners of a pore and on the possibility of a minimum liquid content below which snap-off is inhibited. It is found that smoothly constricted pores with relatively small throats connected to large bodies exhibit excellent ability to snap-off regardless of their initial liquid content. Where such pores are present in porous media, it is predicted that strong foam is generated. Additional factors contributing to snap-off include elevated pressure gradients in the liquid phase and lamella or lens movement that establishes gradients in the axial profile of interfacial curvature. Our new results re-support successive snap-off as a viable mechanism of steady foam generation in homogeneous porous media at low overall aqueous-phase liquid content and at high liquid-phase pressure gradient.