Estimation of Drag Reduction by Polymer Additives at High Reynolds Numbers Using Rheological Measurements

Abstract

In industrial applications such as hydraulic water fracking, polymers are added at dilute concentrations to the flow causing significant drag reduction (DR) and leading to a massive reduction to pump energy cost. In recent years, an alternative approach that is based on rotational flow has shown capabilities of measuring DR based purely on rheological testing. Nonetheless, there are some limiting assumptions in this approach that can lead to inaccurate interpretation of the data, especially for non-Newtonian polymer solutions, where the Reynolds number (Re) is evaluated at the infinite-shear or solvent viscosities. However, it is well known that the apparent viscosity of the polymer solutions is higher than that of a solvent at a stable region and lower than infinite shear viscosity at an unstable one. In this study, we propose a theoretical form of the DR expression that is based on the Re, which is estimated at the apparent local viscosity measure. The work establishes a promising approach for screening DR agents using rheological measurements. Moreover, the study presents new theoretical findings and analyses for estimating DR and extrapolating the results to high Re. Two polymer solutions of xanthan gum (XG) and partially hydrolyzed polyacrylamide (HPAM) in distilled water are tested at concentrations between 5 and 150 ppm using a concentric double-gap cylinder. The proposed approach is found to be more consistent with the theory of linear flow (i.e., flow loop), where the DR in the stable region is found to be identically zero. The transition from stable to unstable regions is also consistent with the existing linear flow theory. This enhances the role of rheological testing for DR measurements and DR agent screening, which provides a platform for the application of simple and cost-effective rheometry in the DR industry.

Effect of Salinity on Drag Reduction of Additives and Mixtures under Turbulent Flow

“…It suggests that the decrease in DR with the addition of salt is a direct consequence of reduction in viscosity. Although a reduction in viscosity can indicate a decrease in DR, other rheological parameters, such as shear stress, should be considered for an accurate quantification of DR …”

“…Once the concentration exceeds c *, the increase in concentration results in retarded DR onset . It should be noted that in cases where the concentration was relatively high, the relation in eq becomes inaccurate as the viscosity of the polymer became an important factor. , For instance, Hashlamoun et al showed that DR has quadratic dependence on the viscosity ratio between the solvent and polymer solutions. This dependence may not be relevant in the flow loop case, where Re is very high, and consequently, the viscosity of the polymer solution can be as low as that of the solvent.…”

“…The dimension L = 55 mm represents the immersed height. Reprinted with permission from Hashlamoun et al Copyright 2023 American Chemical Society.…”

“…Moreover, the impact of varying the concentrations in a mixture was investigated using experimental design analysis to find the level of significance of the polymer in a given mixture. To fundamentally analyze the flow loop findings, two rheological studies have been performed using a rotational rheometer: (1) a study on viscosity under different salinity conditions as their values have a significant role in the effectiveness of the additives in water displacement in industrial applications , and (2) a study on shear stress behavior; as shear stress is directly correlated with the degree of DR, its measurements can give an insight into the DR mechanism and the salinity effect at mild shear strain conditions. – …”

Drag Reduction by Polymer Additives: State-of-the-Art Advancements in Experimental and Numerical Approaches

“…From these measurements, the averaged shear stresses (τ) and the shear strain rates (γ̇) are calculated in the stable and unstable regions based on rheometer-related geometrical constants [i.e., stress constant (α) and strain constant (β)]. In our recently published work, a double-gap concentric cylinder [HR-20 rheometer (TA Instruments–Waters LLC, DE, USA)] was used for such measurements. The setup consists of a Peltier jacket and an air-cooled Peltier circulator used to control the temperature.…”