It is well established that polymers are successful drag reducers due to their viscoelastic properties that can suppress the turbulence eddies and fluctuations and hence, reduce friction pressure losses. Various factors can affect the polymers’ drag reduction characteristics such as polymer type, concentration, shear degradation, and flow geometry. However, few studies have shown the effects of salt type and concentration on drag reduction characteristics with almost no studies discussing their effects in the light of the ionic strength. The ionic strength is considered a more widespread scale to quantify the effects of salt contents on a specific characteristic. This study is undertaken to better understand the relation between ionic strength and drag reduction performance of polymers in straight tubing.
For this purpose, two widely used anionic AMPS copolymers; Nalco ASP-700 and ASP-820, are investigated. The salt matrix includes 2% KCl, 4% KCl, and synthetic seawater. For synthetic seawater, different recipes exist. The recipe adopted includes 1.0 lb/bbl Na2SO4, 10.5 lb/bbl NaCl, and 0.4 lb/bbl CaCl2. A ½-in. OD flow loop with a 15-ft. straight tubing section is used.
The results show that drag reduction behavior is better correlated with the solution ionic strength, and not the salt concentration. Higher ionic strength yields lower drag reduction despite the lower salt concentration. However, the adverse effects of salt and its ionic strength diminishes as higher Reynolds numbers. Both ASP-700 and ASP-820 exhibit a very effective drag reduction behavior and their performance is significantly affected by the polymer type, shear rate, and salt content. Correlations between ionic strength and drag reduction ratio for both polymers are proposed. The correlations exhibit a reasonable agreement with the gathered experimental data. They can be used to quantify the adverse effects of different salt types and concentrations on drag reduction characteristics of polymers in straight tubing