| Oil reservoir rock is typically a porous medium consisting of interconnected microscale pores and throats. During oil production process in a water-wet oil reservoir, water flooding, which is the most common and typical method used in secondary oil recovery process, is an imbibition process. In this imbibition process, some microscale phenomena, such as piston-like, pore body filling and snap-off can happen. These microscale phenomena, especially snap-off, have significant influence on oil recovery. According to many researches, residual oil saturation is the main factor to determine oil recovery. Higher residual oil saturation leads to lower oil recovery. It has been proved that residual oil saturation is mainly caused by snap-off formation. Therefore, the negative influence of snap-off caused great interest form researchers. When snap-off happens, unrecoverable oil droplets can form, and they could block throats of porous media. Trapping hysteresis and foam generation are also caused by snap-off formation. Recently, many researches have been done to further understand snap-off formation. Some factors could influence snap-off formation, such as wettability of oil reservoir, properties of reservoir fluid and pore topology. Therefore, in this dissertation, I focused on the influence of pore topology on snap-off formation in micro-scale.;Influence of pore topology mainly reflects on geometry of pores and throats. The pore-throat geometry of any individual reservoir can vary widely, based upon differing sizes and arrangements of sediment grains. Circle, rectangle and triangle are the most common idealized shapes for pore and throat geometries. Capillary tubes with circular cross-section work as suitable tools, and snap-off formation has been studied by using capillary tubes. For rectangular cross-section, microfluidic device with rectangular cross-sections, which are fabricated by using typical soft lithography micro-fabrication technology, has been used to study snap-off formation in this dissertation. It has been found that snap-off formation is more complicated in rectangular cross-section, because of the existence of angular corners. Even though both rectangle and triangle have angular corners, the different number of angular corner leads to changes in snap-off formation process. With help of laser cutting micromachining technology, triangular cross section could be fabricated on a glass surface. And snap-off formation has been studied in triangular cross-section devices, and comparison between rectangular and triangular cross section has also been made.;After understanding snap-off formation in basic simplified geometries, a model with a series of pore-throat arrangements, which is more complicated and close to real oil reservoir condition, was utilized to have a further study on snap-off formation. The result proved that 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.;Meanwhile, with the help of microfluidic device, we have also tried to utilize polymerization and inertial focusing technology to design some new kinds of surfactants with controlled structures. Even though we have not made it yet due to carrying fluid problem, we have already had the ability to encapsulate particles with controlled numbers. This kind of deterministic encapsulation technology made us to get a new idea of porous media fabrication, with which more researches on multiphase flow could be conducted in a more realistic condition. |
