Effect of viscoelasticity and alkali on heavy oil EOR performance using HPAM, 'AA-NVP' co- and cross-linked polymers

Abstract

Polymer solutions are characterized based on their viscoelasticity to improve the displacement efficiency for enhanced oil recovery. Contribution of viscoelastic polymers solution’s elasticity on oil recovery needs to be analyzed thoroughly for better screening of polymers for field operations. In this work, the individual effect of the elasticity of polymers (hydrolyzed polyacrylamide) on oil recovery, and residual resistance factor (RRF) was determined for secondary polymer flood oil recovery experiments with varying degree of water saturation. HPAM solutions, having identical shear viscosity but different elasticity, were analyzed. A series of flooding experiments were performed using a cylindrical core (simulating linear flow) sand pack saturated with heavy oil for different blends of HPAM. Results show that although polymer solutions with higher elasticity yield higher oil recovery, but they have high RRF values. Also, if the water saturation is high before polymer flooding, this elasticity behavior is prominent. The injectivity and hydrolysis of HPAM in severe alkaline conditions is a major challenge for oil industry. It is of great importance that injected polymer or micro gels show higher injectivity and alkali resistance behavior without compromising with the amount of oil recovered. To overcome shortfall of conventional HPAM, new crosslinked (cP(AA-st-NVP)) and co (P(AA-co-NVP) polymer were synthesized using Acrylic Acid (AA) and N-vinyl-2-pyrrolidinone (NVP), and N,N’-methylenebisacrylamide as a crosslinking agent by free radical polymerization. These newly synthesized polymers were compared for rheology, heavy oil recovery, injectivity, RRF value with high molecular weight HPAM in alkaline and non-alkaline conditions. Crosslinked polymer and co-polymer showed stable viscoelastic properties in alkaline conditions than conventional HPAM due to intermolecular bonding, though the molecular weight for the later was high. The RF(resistance factor) and RRF for crosslinked polymer were much lower than HPAM, suggesting high injectivity and lower adsorption/retention of the crosslinked and co polymer. The overall recovery of heavy oil using cross linked polymer and copolymer was also ~7% higher than HPAM.