Surfactant synergy on rheological properties, injectivity, and enhanced oil recovery of viscoelastic polymers

Surfactants synergized viscoelastic polymers can effectively balance the thickening and injectivity ability of the composite system and improve its enhanced oil recovery (EOR) effect. This work systematically studies the impact of concentration, compounding methods with surfactants, surfactant types, and salt concentrations on the rheological behavior of modified carboxymethyl cellulose (mCMC) based on the shear rheological properties. Then, injectivity experiments of the above solutions were carried out to compare the impact of differences in rheological properties on solution injection performance and optimize the injection parameters. Finally, oil displacement experiments were conducted to verify the mCMC viscoelasticity on the EOR effect. Experimental results show that surfactants can weaken the effect of shear on changing solution viscosity, and zwitterionic surfactants have the most obvious effect. The viscoelasticity of mCMC solution causes it to exhibit extensional viscosity, which gradually dominates as the shear rate increases, resulting in poor injection performance. Therefore, as the injection velocity increases, the injection factor has a maximum value (corresponding to the optimal injection velocity, about 10 ft/D). After that, increasing the injection velocity will greatly reduce mCMC injectivity under a higher extensional viscosity. When the shear rheology curves are similar and the injection velocity is 2 ft/D, mCMC can increase the oil recovery by 5.79% compared with Partially hydrolyzed polyacrylamide (HPAM), and the viscoelasticity contributes 16.95% to the EOR. As the injection velocity increases, the EOR of HPAM levels off, but the EOR of mCMC still increases significantly, which increases the viscoelastic EOR contribution to 25.98% at 10 ft/D.