(90c) Mobility Improvement Using Water Soluble Polymers: Role of Chemical Structure and Anionicity

Acrylamide-based polymers such as partially hydrolyzed polyacrylamide (HPAM) and copolymer of acrylamide and 2-acrylamido-2-methylpropane sulfonic acid (AMPS-AM) are being used a mobility control in chemical EOR. The rheology of their solutions has been studied extensively in several conditions such as increasing molecular weight, salinity, and temperature. Most of the previous study mainly deals with the evaluation of polymers at reservoir conditions without having fundamental insight. In this work, we investigated how the rheology of a polymer changes by changing the polymer structure, anionicity, and degree of hydrolysis.

Steady and dynamic shear rheology of eight polymers from HPAM and AM-AMPS group were investigated at 25°C and 80°C using high-pressure high-temperature Discovery hybrid rheometer. These polymers contain different molecular weight, different functional group, and varying degree of hydrolysis. In steady shear rheology, the viscosity was measured at a shear rate ranging from 0.1/s to 1000/s. The viscoelastic properties such as elastic storage and loss modulus were determined by dynamic shear rheology by varying frequency from 0.1 rad/s to 100 rad/s.

The anionicity and degree of hydrolysis found to have a major impact on the rheological properties of the polymers. This result was consistent for both HPAM and AM-AMPS copolymers both at high and low temperature. The viscosity increased by increasing the anionicity. The elastic storage modulus also increases by increasing the molecular weight and anionicity. Molecular weight and anionicity also influence the steepness of viscosity reduction with temperature and the change in energy dissipation capacity with time at high temperatures. The possible influences of charge distribution and the nature of the anions present in the polymer need to be considered when considering the type of polymer (HPAM of AM-AMPS copolymer) for a specific EOR application.

This study brings the novel insight of polymer structure-property relationship that can help in quickly screening the polymers for EOR application in carbonate reservoirs.