Insights into Rheological Behavior of Starch Grafted Polyacrylamide Under Higher Salinity Reservoir Conditions

In this work, a suitable biomaterial polymer was successfully prepared by microwave graft copolymerization of starch-acrylamide system. Under optimal conditions, highest percent grafting was attained with microwave initiated grafting procedure. The synthesized grafted starches were characterized by various physicochemical techniques which confirmed the successful grafting of polyacrylamide chains onto the starch backbone and the effective thermal stability of the grafted samples. Subsequently, rheological analysis was performed as a main objective to study the steady and dynamic shear flow of the grafted copolymers under a range of reservoir conditions. Tests of shear stress and viscosity vs. shear rate of copolymer solutions showed that the starch-g-polyacrylamide samples are pseudoplastic fluids with yield stress. By increasing temperature, a thermothickening effect is observed and the flow gradually becomes shear-thickening, especially for the flow in deionized water. At the nominal injection rates, the viscosity loss of copolymers is lower and more consistent with respect of temperature and high saline solutions. In oscillatory deformation tests behavior of viscoelastic fluid (with a predominantly weak gel character) was observed for all samples across the entire temperature range and for both concentrations of the copolymer solutions. Accordingly, the starch-g-polyacrylamide injection is more effective under higher salinity reservoir conditions