The Effect of Monovalent and Divalent Ions on Biodegradable Polymers in Enhanced Oil Recovery

Abstract

The stability of polymers used in enhanced oil recovery especially in polymer flooding is largely based on their ability to withstand challenging reservoir conditions such as the effect of high salinity and high temperature. Polymers like Hydrolysed Polyacrylamide (HPAM) and its derivatives lose their viscosity when subjected to high salinity conditions due to the screening of the ions of the polymer backbone chain. HPAM is not only sensitive to salinity and temperature but also very susceptible to shear degradation. Research show that Xanthan gum; a commercial biopolymer used mostly in polymer flooding show more tolerance to shear degradation and even better stability to salinity and temperature than HPAM but not frequently used due to its high cost. The work is centered on the study of stability of some selected low cost biopolymers like Guar gum, Locust bean gum, Gum Arabic as well as the commercial Xanthan gum. This study captures the effect of monovalent and divalent ions on the polymers in order to establish their degree of stability and the impact of these ions with respect to varying salinity conditions. The rheological performance of these polymers were analysed using both NaCl and CaCl under both medium and high saline conditions which are similar to reservoir conditions. The results show that all polymers show appreciable resistance and stability when compared to Xanthan gum especially Locust bean gum in the presence of monovalent ions, Gum Arabic displayed the least tolerance to the ions. Although, the presence of divalent ions had more impact than the monovalent ions on all polymers' stability, however, higher concentrations of the polymers resulted in more resistance to the presence of these ions.