The rheological characteristics of copolymers of acrylamide (AM) with sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (PAMS), and of hydrolyzed polyacrylamide (HPAM) have been studied in both NaCl solutions and synthetic seawater. PAMS may possible have high salt tolerance and thereby find use in enhanced oil recovery processes for high salinity reservoirs. The viscosity and solubility effect of the PAMS copolymers have been systematically studied with variations in sulfonation degree and molecular weight. Emphasis has been studies as a function of shear rate, polymer concentration, NaCl and divalent ions concentration in aqueous phase. Shear rate dependence of PAMS varies with sulfonation degree, and PAMS with higher sulfonation degree is found to be less shear rate dependent. PAMS with high sulfonation degree are more salt tolerant also compared to HPAM. Also the effect of divalent ions on viscosity of PAMS is lower compared to HPAM. Two parameters will increase the solubility effect of the PAMS copolymers in mix brine, one is sulfonation degree and the other is in the presence of NaCl. Both parameters have a direct effect on the solubility of PAMS copolymer in mixed brine. In all cases the PAMS copolymers are more salt tolerant than HPAM.

ABSTRACT:The viscosity and retention of several copolymers of acrylamide (AM) with sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (PAMS), and also hydrolyzed polyacrylamide (HPAM) have been studied under aerobic condition with and without the sacrificial agent, isobutyl alcohol (IBA) added at a temperature of 80 C. Parallel experiments have been performed in synthetic seawater (SSW) and 5 wt % NaCl. The viscosity at high temperature has been studied as a function of aging time, shear rate, sulfonation degree, molecular weight, and concentration of IBA. The retention in porous medium for sulfonated polyacrylamide polymers was measured in core floods using outcrop Berea sandstone. For the studied polymer sacrificial agent may protect polymer structure at high temperature. Higher sacrificial agent concentration gives better thermal stability in both 5 wt % NaCl and SSW solvents. Sulfonation degree also has a direct effect on thermal stability, i.e., higher sulfonation degree lead to better thermal stability in terms of viscosity. By increasing temperature, less relative reduction in polymer solution viscosity was observed for the polymer with lower molecular weight. The presence of divalent ions at high temperature leads to strong reduction of HPAM polymer solution viscosity, but the viscosity is better maintained for PAMS copolymer solution at high temperature. The precipitation of HPAM first occurred after 3 months at 80 C and for PAMS copolymer with lowest sulfonation degree precipitation started after 7 months. For the studied polymers the retention was found to be relatively independent of temperature and compared to HPAM a much lower retention is observed for the sulfonated copolymers.

A key parameter for application of polymers for water flood mobility control is the loss of polymer due to adsorption to the rock and more general retention during flow in porous medium. The paper discusses the adsorption and retention properties of sulfonated co-polymers. These polymers have the same backbone structure as partly hydrolyzed polyacrylamide (HPAM), except for modified hydrophobic groups and