Experimental Study on Injection and Plugging Effect of Core-Shell Polymer Microspheres: Take Bohai Oil Reservoir as an Example.

To meet the technical requirements of deep fluid diversion in Bohai oilfield, the swelling property, plugging effect, transport characteristics of polymer microspheres, and fluid diversion effect in heterogeneous cores are studied in this paper. There are two kinds of polymer microspheres including core-shell microspheres and traditional microspheres. The instruments used in this study include a biomicroscope, a metallurgical microscope, a scanning electron microscope, and core displacement experimental devices. The results of microscopes indicated that the core-shell microspheres were successfully synthesized, and the microspheres had good hydration expansion effect. The expanded microspheres could attract each other through the electrostatic force of anions and cations to achieve the purpose of coalescence. Compared with traditional microspheres (initial particle size is 3.8 μm), the initial particle size of the synthesized core-shell microspheres is close to 3.3 μm, but the particle size distribution is more concentrated, so the injection performance is close to that of traditional microspheres (initial particle size is 3.8 μm). After 8 days of hydration expansion, although the expansion multiple is small, it can coalesce and enhance the plugging effect, which can adapt to a wider range of permeability, ranging from 200 × 10 to 3000 × 10 μm (200 × 10-1500 × 10 μm for traditional microspheres). Under the same conditions (heterogeneous core), compared with the traditional microspheres, the core-shell microspheres have the characteristics of coalescence. Therefore, its fluid diversion effect is better, and the oil recovery is increased by 5.5%. Nevertheless, there is the "end effect" during the injection process, which weakens the steering effect of deep liquid flow. The results show that the "end effect" can be effectively reduced by alternate injection of microspheres and water. Meanwhile, the effect of deep fluid diversion is improved, and the increase of oil recovery is increased by 2.06%.