Nano-SiO2/P(AM-AMPS-DMDAAC) composite microspheres with enhanced thermal stability for profile control in low permeability reservoirs

Polymer microspheres are widely used in petroleum, electronics, biomedicine, and other industrial fields. This article aims to overcome the problems of poor thermal stability and insufficient mechanical strength of conventional polymer microspheres in high-temperature and high-salinity reservoirs. A composite nanosphere with controllable size and excellent temperature and salt resistance was synthesized by introducing modified nano-SiO 2 to construct an organic-inorganic composite system. The composite nanosphere is crucial for the effectiveness of profile control, water plugging, and oil displacement under harsh reservoir conditions. In this study, amphoteric SiO 2 /P(AM-AMPS-DMDAAC) composite microsphere with small size and regular shape were successfully prepared by reverse phase microemulsion polymerization. A mixed solution of acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), diallyldimethylammonium chloride (DMDAAC), KH-570 modified nano-SiO 2 , and methylenebisacrylamide (MBA) was used as the aqueous phase, with Span-80 and Tween-80 as composite emulsifiers. The microsphere exhibits excellent comprehensive physicochemical properties, with a controllable median particle size of approximately 30 nm. Its thermal decomposition temperature increases from 201 °C to 241 °C, and has good viscoelasticity and pseudoplastic characteristics. These properties enable it to effectively cope with harsh reservoir conditions such as high temperature and low permeability. Through oil displacement experiments, the microspheres achieved an average plugging rate of 85.9 % in low-permeability cores and increased the oil recovery by 16.79 %. These indicate that the composite microspheres, as an efficient profile control and water plugging agent, have broad application prospects for enhanced oil recovery in low-permeability reservoirs.