Mechanical Degradation of Biopolymers for Enhanced Oil Recovery Applications

Abstract

Summary Polymer degradation is detrimental to enhanced oil recovery (EOR) because it ultimately leads to solution viscosity loss. Molecular breakage during flow owing to high stresses, known as mechanical degradation, can occur in numerous stages during field polymer injection. One of the reasons biopolymers are promising for EOR is their enhanced mechanical stability compared to their polyacrylamide counterparts. This study presents a comparative investigation of the mechanical degradation of biopolymers with potential applications in EOR. The mechanical degradation was evaluated by flowing the solutions through a short-length capillary (internal diameter of 0.127 mm and length of 10 mm) and then testing their viscosity loss through a rheometer. Nine flow velocities were tested between 0.13 and 66 m/s (shear rates between 8.29 × 103 and 1.66 × 107 s−1) in addition to the undegraded baseline. Four biopolymers were evaluated [xanthan gum (XG), scleroglucan (SCLG), schizophyllan (SCP), and guar gum (GG)] and compared to two polyacrylamides [hydrolyzed polyacrylamide (HPAM) and HPAM-AMPS (2-acrylamido-2-methylpropane sulfonic acid)] that serve as benchmarks for EOR processes. All the polymers were evaluated in three different concentrations (100, 500, and 2,000 ppm) in synthetic seawater (3.01% total dissolved solids). The degradation was evaluated through the Ostwald-de Waele indices. The consistency index (K) indicates loss of overall viscosity, and the behavior index (n) accounts for the loss of pseudoplasticity. Overall, the mechanical degradation correlated positively with shear rate and negatively with polymer concentration. When increasing the polymer concentration, the dominant mechanisms at play were macromolecule extension inhibition, caused by interactions with surrounding molecules, and hydrodynamic volume reduction. The biopolymers displayed superior resistance to mechanical degradation than the synthetic ones, with XG being the most resistant polymer. In this work, the main factors for the mechanical degradation resistance of different polymers were rigidity of the polymer structure in solution and the molar mass of the polymer chains.