Study on the Profile Control and Oil Displacement Mechanism of a Polymer Nano-microsphere for Oilfield

In this study, the mechanism of migration/plugging and the main performance of polymer nano-microspheres (HQ) were investigated using environmental scanning electron microscopy (ESEM), swelling hydration experiments, sand-filling pipe flooding experiments, and microscopic displacement experiments. Results show that the swelling ratio of HQ in salt solution first increases and then reaches equilibrium with the increase in swelling time. The expansion ratio of HQ increases rapidly at the initial stage of swelling and reaches its maximum value after swelling for 7 days. The maximum value of the expansion ratio was 15. In addition, the higher the salinity, the smaller the particle size of the studied microspheres. The particle size of the microspheres increases with increasing temperature. According to the visualized microscopic experiments, the migration and blocking mechanism of microspheres in the pore throat were discovered. When the particle size is 1/3-1/7 times the pore throat diameter, the microsphere particles can enter the interior of the pores. The microspheres aggregate together, and bridge plugging occurs due to the mechanical trapping of pore throats. In this case, the pore throats are blocked by the produced inner filter cake. The pressure at each point fluctuates up and down in a zigzag pattern during the displacement experiment, revealing the "migrated-plugged-breakthrough-replugged" mechanism for HQ. It can be seen from the oil displacement experiment that the final cumulative recovery and the enhanced oil recovery were 65.71 and 17.31%, respectively. Thus, the studied nano-microspheres have excellent oil displacement performance.