(173d) A Microfluidic Model for Visualizing Snap-Off during Imbibition

Oil reservoir rock is typically a porous medium consisting of interconnected microscale pores and throats. The pore-throat geometry of any individual reservoir can vary widely, based upon differing sizes and arrangements of sediment grains. Circular, rectangular and triangular cross-sections are regarded as the most common simplified geometries of pores and throats. Both capillaries with circular cross-sections and microfluidic devices have been utilized as experimental models to study multiphase flow process. However, studies on multiphase flow phenomena in triangular cross-sections are unusual, due to the limitation of triangular cross-section fabrication. To overcome this limitation, we have introduced ultrafast pulsed laser direct writing to quickly produce channels with arbitrary cross section. Femtosecond pulsed laser systems were used to directly write channels in glass with triangular cross-sections. This approach surpasses planar lithography in speed and flexibility, while providing the ability to vary depth within individual channels. We have employed triangular channels of arbitrary cross section to examine the influence of geometry on oil-water snap-off, which is a determining phenomenon in enhanced oil recovery (EOR) processes. In addition, a model with a series of pore-throat arrangements was utilized to show a Rayleigh-Plateau instability induced oil-water or air-water snap-off could be generated solely through the control of the throat geometry, whose cross-section was triangle. This work validates Rayleigh-Plateau theory on snap-off formation in triangular channels and establishes a new class of micromodels for hypothesis-driven EOR studies.