Dilute iota- and kappa-Carrageenan solutions with high viscosities in high salinity brines

We evaluated the rheological characteristics of iota- and kappa-Carrageenan in aqueous solutions. Viscosities strongly increased with increasing polymer concentration or salinity. Monovalent Na+ cations were more effective in increasing viscosity than divalent Ca2+ cations. A more complex brine containing Na+, Mg2+ and Ca2+ cations also showed high viscosities at a high salinity. We observed shear thinning behavior for these polysaccharide solutions. We explain these rheological phenomena with molecular processes, specifically the conformation change of the iota-Carrageenan from random coil to double helix. In the context of enhanced oil recovery, iota-Carrageenan solutions can reach much higher viscosities at high salinities than standard polyacrylamide solutions. Moreover. Carrageenans are renewable, nontoxic, green substances. (C) 2010 Elsevier B.V. All rights reserved.