Investigation of alkali and salt resistant copolymer of acrylic acid and N-vinyl-2-pyrrolidinone for medium viscosity oil recovery

Heavy oil reservoirs, unsuited for thermal applications, are being exploited using chemical enhanced oil recovery (CEOR) techniques. The most widely used polymer in CEOR applications is hydrolyzed polyacrylamide (HPAM). However, it hydrolyzes very rapidly under alkaline conditions, making it susceptible for alkaline polymer flooding, the main variant of chemical EOR techniques. To overcome this shortfall of conventional HPAM, a copolymer P(AA-co-VP) of acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) was synthesized, that can offer stability and positive synergism against alkali. In the research presented herein, rheological properties of HPAM and P(AA-co-VP) were compared in terms of viscosity and elasticity for typical alkali-polymer (AP) flood operations. The core flooding experiments were conducted using the heavy oil samples collected from a reservoir in Alberta. The shear rheological and dynamic viscoelastic properties of P(AA-co-VP) copolymer improved in presence of strong alkali while the conventional HPAM showed much higher viscosity loss, becoming less effective for AP heavy oil recovery operations. In the presence of alkali, 45.9% and 47.3% incremental recovery factor are shown by HPAM and the newly synthesized P(AA-co-VP) copolymer. Although the incremental recovery factor shown by newly synthesized polymer is slightly higher, it resulted in a three times lower residual resistance factor than HPAM. Lower residual resistance factor is important for ensuring good transport properties during polymer flooding. AP flooding conducted using P(AA-co-VP) copolymer could effectively overcome the drawbacks of conventional HPAM polymer, thereby improving the heavy oil recovery and transport in porous media.