Impact of Polymer Ripening Degree on Fluidity Control and Enhanced Oil Recovery in Heterogeneous Reservoirs

The performance and evaluation methods of polymers with different ripening degrees in enhanced oil recovery were investigated in this paper, which can provide guidance for reducing the viscosity loss during polymer injection in the oilfield. The results show that the indoor complete ripening time of the polymer was set as 50 min. The storage modulus and loss modulus of polymer systems with 60% and 80% ripening degrees are higher than those with a 100% ripening degree, indicating that incompletely ripened polymer systems exhibit superior viscoelasticity. For the fully ripened systems, polymer molecular chains unfold completely, while incompletely ripened systems restrict solvent penetration and retain unhydrated micellar particles, which directly affect the seepage resistance and oil flooding recoveries. Capillary shear can further promote the ripening of the polymer unripened micelles and increase the apparent viscosity of the polymer solution. Compared with the polymer with a 100% ripening degree, higher resistance coefficients and residual resistance coefficients can be established by the polymer systems with 60% and 80% ripening degrees. In heterogeneous porous media, incompletely ripened polymer systems exhibit an excellent plugging and flooding performance owing to the residual undissolved micellar particles, which enhance the fluid uptake in low-permeability layers to improve oil recoveries. As validated by quantitative particle-size and image analyses, whether it is a macrodisplacement or microdisplacement experiment, when the incompletely ripened polymer is used, the effective viscosity of the flooding fluid can be improved and the areal sweep efficiency can be increased to enhance the oil recovery. Thus, incompletely ripened polymers show promising potential for oil flooding.