The rheological behaviour of a water-soluble polymer (HEC) used in drilling fluids

Abstract

The rheological properties of drilling fluids have been always considered as critical aspects to the success of drilling operations; in this fact, the control of these properties was of paramount importance. In this paper, the rheological behaviour of a water-soluble polymer, namely hydroxyethyl cellulose (HEC) used in drilling fluids, was investigated. Steady-state shear rheology and frequency experiment were carried out on the sample at different concentrations ranging from 0.1 to 1.2 wt% and constant temperature of 25 ± 0.1 °C using a controlled-rate rheometer. The HEC solutions showed a shear thinning behaviour that was successfully fitted using the Cross model, where its parameters were found to increase with the HEC concentration. The steady-state shear rheological data allowed determining the intrinsic viscosity of the polymer (~ 15.05 dl/g) in distilled water; thereafter, an estimation of the molecular weight of HEC using the Mark–Houwink equation indicated that the studied sample was of high molecular weight (9.5 × 105 g/mol), which gave it good rheological properties for drilling fluid applications. The critical overlap concentration was found to be ~ 0.24 wt% using two methods, the intrinsic viscosity and the plot of the apparent viscosity versus the polymer concentration at specific shear rate. The frequency sweep measurements allowed confirming the viscoelastic behaviour of the polymer; HEC solutions behaved either as viscous or as elastic materials at low and high frequencies, respectively. This information is essential for mud engineers to develop and maintain the properties of drilling fluid to the required specifications.