Ultra-high temperature and salinity resistant microspheres featuring “Rigid hydrophobic core- soft hydrophilic Shell” structure for deep reservoir profile control

The development of ultra-deep oil reservoirs has posed greater demands on the performance of profile control agents, which composed by hydrophilic polyacrylamide main chain, heterocyclic ring structure and rigid side groups fail to perform decently in temperature beyond 120 °C. In this study, a sulfonated polystyrene microsphere (SPS-2–3) featuring a “rigid hydrophobic core and soft hydrophilic shell” architecture was synthesized through concentrated sulfuric acid sulfonation. At elevated temperatures, the hydrophilic sulfonated layer of SPS-2–3 exhibits increased thickness, alongside enhanced charge quantity and charge mobility. These changes facilitate a more uniform distribution of surface charges on SPS-2–3 and extend the spatial range of electrostatic interactions. Consequently, the fraction of bound water increases significantly from 4.37 % (room temperature) to 26.93 %, electrostatic repulsion between the SPS-2–3 is increased to 4.82 nN, endowing SPS-2–3 with superior dispersion stability under temperature surpassing 160°C and salinity up to 20 × 10⁴ mg·L^-1. The crude oil mobilization characteristics demonstrate that SPS-2–3 effectively enhances the mobilization efficiency of remaining oil in the matrix and achieves a 3.5-fold increase in injection pressure and 20.11 % increase in oil recovery. This study provides a new idea for designing high-performance profile control agents for applications in deep reservoir development.