Prediction of Viscosity for Xanthan Solutions in Brines

Abstract

ABSTRACT Loss of solution viscosity in brines of increasing ionic strength (salinity/hardness) is a major problem in the use of partially hydrolyzed Polyacrylamides for enhanced oil recovery mobility control. The solution viscosity of xanthan gum polysaccharide, however, is generally accepted to be unaffected by salt content in the water. In fact, recent work by Philips, et al1, has shown that solutions of high-pyruvate xanthan actually increase substantially in viscosity with increasing salt concentration. Earlier papers by Ward and Martin2 and French, Stacy, and Collins3 reported results of US DOE-sponsored programs to establish relationships between total ionic strength, concentration of calcium or magnesium ion, polymer concentration, and the resulting solution viscosity for partially hydrolyzed Polyacrylamides with varying degree of hydrolysis and molecular weight. This paper presents similar work with xanthan biopolymers of varying pyruvate content. Formulae are given to enable prediction of solution viscosity for a given brine salinity and polymer concentration, and to calculate the polymer concentration needed to give a desired solution viscosity. For both medium- and high-pyruvate xanthans, solution viscosity increased with increasing brine salinity; the presence of multivalent cations (hardness) had no additional effect on viscosity beyond their contribution to total salinity. For a given polymer concentration, xanthan solution viscosity exceeded that of hydrolyzed polycrylamides above about 0.3% total dissolved salt.