Studies on the rheological properties of amphiphilic nanosilica and a partially hydrolyzed polyacrylamide hybrid for enhanced oil recovery

Because amide groups can be easily hydrolyzed to carboxyl groups at high temperature, polyacrylamide (PAM) and its derivatives cannot be applied to high temperature and salinity reservoirs. To solve this problem, a new kind of surface modified nanosilica with different functional groups, including amine and octyl groups, was prepared in this article. Benefiting from its structure, the viscosity of the nanosilica/polymer solution increased by 26.08% when the degree of hydrolysis was high (degree of hydrolysis 47.5%, to simulate the HPAM solution after experiencing long-term flooding), whereas the viscosity of the nanosilica/polymer solution only increased by 0.26% when the degree of hydrolysis was low (degree of hydrolysis 17.8%, to simulate the HPAM solution at the beginning of polymer flooding). In core flooding experiments, the polymer/nanosilica hybrid solution exhibited a higher oil recovery factor (17.30%) than the polymer solution (5.00%). Enhanced oil recovery (EOR) mechanisms were systematically investigated by carrying out rheological measurements, visualization tests of polymer flooding, and interfacial activity and long-term stability analyses. The excellent performance of the nanosilica/polymer solution could be attributed to the high interfacial activity of nanosilica and the strong electrostatic and hydrophobic interactions between nanosilica and polymer chains. These results indicate that the nanosilica/polymer hybrid solution could be an effective oil-displacing agent. (C) 2019 Elsevier Ltd. All rights reserved.