Turbulent Drag Reduction by Polyacrylamide and Other Polymers
Authors: Sitaramaiah Gullapalli , Smith Charles L. 
Published: December 2007

Drag reduction in turbulent flow of several acrylamide base polymers has been investigated and compared with the drag reduction performance of polyethylene oxides. The carboxyl content of the acrylamide-acrylate copolymers studied varied between 0.2 and 40 percent. Rheological behavior of these polymers has been studied at low concentrations of 100 to 1000 ppm in distilled water, tap water and synthetic brine containing 8 1/2 percent NaCl and 2 1/2 percent CaCl2. The power law exponent, n, increased from values of 0.40 to 0.60 for polyacrylamides in distilled water and to unity in the brine solutions, suggesting Newtonian behavior at high concentrations of dissolved salts. The consistency index, K, increased about a hundred-fold in distilled water, which is characteristic of high polyelectrolytic expansion of the polymer chain. The shear dependence of viscosity decreased with the decrease of concentration and molecular weight and the increase of salt content of solutions. Solutions of a commercial polyethylene oxide have been found to be Newtonian at 100 to 1,000 ppm in all solvents. Drag reduction in pipe flow up to high shear rates of 30,000 sec-1 has been studied in tap water and in the synthetic brine. The velocity exponent has been observed to be 1.85 0.05 in these solvents and it decreased to values down to 1.4 with increased molecular weight of the additive. Good correlation of pipe flow data has been observed when treated in terms of Bowen's method. Drag reduction increased with molecular weight, concentration and flow rate for all polymers approaching values of 70 to 80 percent and, in the case polyacrylamides, better than 25 percent drag reductions have been observed in tap water than in API brine due to the polyelectrolytic expansion of the chains in tap water. It is recommended that low-salt content solvents be used for better efficiencies when polymers with ionic groups are used as fluid friction reducers.

Introduction

The drastic reduction of fluid friction by the addition of small quantities of long-chain high polymers to water has received much attention. polymers to water has received much attention. This phenomenon has interested the U. S. Navy for possible application in faster deep sea refueling and for augmenting the speeds of deep submergence vehicles. A number of Navy sponsored studies have appeared recently in the literature. The flow properties of these dilute polymer fluids have been discussed at length by Metzner and others. Merrill and others have investigated the relation between the chain length of the polymers in solution and their drag reduction performance. More recently Hoyt has suggested friction reduction as a method for the estimation of the molecular weight of the polymer. Fluid friction reduction additives have also been used in the field of petroleum technology where large quantities of fluids like acids, brines and fresh water are pumped into the oil wells, during fracturing operations. Increased flow achieved by the incorporation of polymer additives in these fluids results in large reduction of pumping costs. During the screening of a number of additives for this application, we have observed that polyethylene oxides and acrylamide polymers are by far superior to guar and other natural gums as well as to many cellulose derivatives. it also has been observed that the commercially available acrylamide polymers occur not only in different molecular weights, but also with different degrees of carboxyl content. Since these acid groups modify the solution properties of these polymers, the study of the properties of these polymers, the study of the influence of this polyelectrolytic property on drag reduction in turbulent flow has been considered significant.