Migration characteristics and deep profile control mechanism of polymer microspheres in porous media

The performance and migration characteristics of polymer microspheres in porous media and the mechanism of deep profile control for oil displacement were studied by theoretical analysis, instrument detection, and physical simulation to further improve oil recovery. Polymer microspheres were expansive in water and nonexpansive in oil. The polymer microspheres with short expansion times possessed excellent mechanical shear resistance. According to the matching factor (R-a), resistance factor, and residual resistance factor, the migration of polymer microspheres in porous media was divided into four periods: transportation (R-a > 2.41), bridging plugging (1 R-a < 2.41), elastic plugging (R-a < 1), and fatigue (microsphere breakage). The resistance factor and residual resistance factor of the polymer microspheres during the bridging and elastic plugging periods were larger than those during other periods. The deep oil displacement profile can be controlled by adjusting the occurrence positions (distance from the injection end) of these two periods. Increasing the injection rate during the transportation and bridging plugging periods and decreasing the injection rate during the elastic plugging period made elastic plugging occur farther from the injection end while maintaining the resistance factor and residual resistance factor at high levels. Aimed at the remaining oil accumulation area, the optimal profile control depth of oil displacement (distance from the injection end) of polymer microspheres in porous media can be regulated by changing the injection rate to enhance oil recovery. The simultaneous migration and expansion of polymer microspheres is the main mechanism of microsphere fluid diversion in porous media.