Seismic stimulation is a promising technology aimed to mobilize the entrapped non-wetting fluids in the subsurface. The applications include enhanced oil recovery or, alternatively, facilitation of movement of immiscible/partly-miscible gases far into porous media, for example, for CO2 sequestration. This work is devoted to detailed quantitative studies of the two basic pore-scale mechanisms standing behind seismic stimulation: the mobilization of bubbles or drops entrapped in pore constrictions by capillary forces and the break-up of continuous long bubbles or drops.

In typical oil-production operations, oil is produced by the natural reservoir-pressure drive during the primary stage and by artificial water flooding at the secondary stage. Capillary forces act to retain a substantial residual fraction of reservoir oil even after water flooding. The seismic stimulation is an unconventional technology that serves to overcome capillary barriers in individual pores and liberate the entrapped oil by adding an oscillatory inertial forcing to the external pressure gradient. According to our study, the effect of seismic stimulation on oil mobilization is highly dependent on the frequencies and amplitudes of the seismic waves. Generally, the lower the frequency and the larger the amplitude, more effective is the mobilization. To describe the mobilization process, we developed two theoretical hydrodynamics-based models and justified both using computational fluid dynamics (CFD). Our theoretical models have a significant advantage over CFD in that they reduce the computational time significantly, while providing correct practical guidance regarding the required field parameters of vibroseismic stimulation, such as the amplitude and frequency of the seismic field. The models also provide important insights into the basic mechanisms governing the vibration-driven two-phase flow in constricted capillaries.

In a waterflooded reservoir, oil can be recovered most efficiently by forming continuous streams from isolated droplets. The longer the continuous oil phase under a certain pressure gradient, the more easily it overcomes its capillary barrier. However, surface tension between water and oil causes the typically non-wetting oil, constituting the core phase in the channels, to break up at the pore constriction into isolated beads, which inhibits further motion. The break-up thus counteracts the mobilization. We developed a theoretical model that provides an exact quantitative description of the dynamics of the oil-snap-off process. It also formulates a purely geometric criterion that controls, based on pore geometry only, whether the oil core phase stays continuous or disintegrates into droplets. Both the theoretical model and the break-criterion have been validated against CFD simulations.

The work completed elucidates the basic physical mechanisms behind the enhanced oil recovery by seismic waves and vibrations. This creates a theoretical foundation for the further development of corresponding field technologies.