Anti-temperature anti-salinity nanospheres: Preparation, characterization, thermal stability, plugging ability and oil displacement

Based on the difficult problem that conventional polymer and gel can't be used for enhancing oil recovery in extra-high temperature (200 °C) and extra-high salinity (2 × 105 mg/L) reservoirs，an anti-temperature anti-salinity nanospheres was prepared with APB, ODPA and PA as the monomers. The results of FTIR showed the final products were target nanospheres. TG showed that thermal decomposition of the polyimide (PI-1) nanospheres occurred at 440 °C; these values greatly exceeded those of commercial HPAM, weak gel particles and pre-crosslinked gel particles. After the polyimide nanospheres were aged for 120 d, the enhanced oil recovery of the PI-1 nanospheres does not decrease significantly, so the long-term stability of two polyimide nanospheres are very good at 200 °C and TDS = 2 × 105 mg/L. The PI-1 nanospheres had better properties than the conventional polymer and gel as profile control agent and water plugging agent. The nanospheres have the characteristics of “able to inject, able to block, able to move”, and the oil displacement efficiency is very excellent. The results of core displacement experiments revealed that PI-1 microspheres had high oil displacement efficiency and strong ability to improve water injection profile. Therefore, the PI-1 microspheres can be used as oil displacement agent in extra-high temperature and extra-high salt reservoirs.