Nano-silica hybrid polyacrylamide/polyethylenimine gel for enhanced oil recovery at harsh conditions

Abstract

Nanomaterial composite gel has been successfully applied for enhanced oil recovery (EOR). However, the fatal flaw of using bare SiO2 nanoparticles in polymer gel systems is their agglomeration and poor dispersion stability. In this paper, hexadecyl trimethyl ammonium bromide (CTAB) modified SiO2 nanoparticles for the reinforcement of PAM/PEI polymer gels was proposed. Basic performances of surface modified SiO2 (C-SiO2) including chemical structure, thermal stability and micro morphology were characterized by thermogravimetry, scanning electron microscope (SEM) and infrared spectroscopy (IR). In addition, the gelation performance with respect to C-SiO2 dosage, pH, temperature and salinity were also examined in comparison with pure PAM/PEI gels. The results indicated that no gel was formed when pH < 7. Gel strength was improved with the increase of C-SiO2 concentration, pH (> 7) and temperature, both the gelation time and gel strength decreased with the increase of salinity. C-SiO2/PAM/PEI gel revealed long-term stability and the gel strength maintained Grade I within 360 days under the harsh reservoir conditions (salinity = 70,000 mg/L, temperature = 120 °C, pH = 9) in comparison with PAM/PEI (gel strength reduced to Grade D with syneresis). The mechanism of C-SiO2/PAM/PEI gel for reservoirs with high temperature and high salinity due to the rigid hybrid network resulting from the combination of ionic bonds and hydrogen bonds between PAM and C-SiO2.