A proposal for a constitutive equation fitting methodology for the rheological behavior of drilling fluids at different temperatures and high-pressure conditions

Abstract

Drilling fluids are complex suspensions of particles with a wide diameter range. While extensive research has explored the rheological behavior of drilling fluids, several limitations still exist. High-pressure and high-temperature (HPHT) conditions encountered in drilling fluids have introduced unique challenges, and only a few studies have attempted to develop a comprehensive equation that addresses both aspects concurrently. This study aims to perform a rheological characterization of a water-based drilling fluid (WBDF) containing xanthan gum under HPHT conditions and propose a constitutive equation to fit rheological data in such conditions. The experiments were conducted using an Anton Paar MCR 702TD rotational rheometer, coupled with a pressure cell. Steady-state flow curves were obtained at three different temperatures (25, 55, and 100 °C) and pressures ranging from 100 to 800 bar. The experimental data were fitted to the power-law model, and the rheological parameters of the model were fitted with variations in temperature and pressure. The fluid exhibited shear-thinning behavior, with the influence of temperature being more predominant than the effect of pressure, however, both variables have a strong relationship. Furthermore, we proposed a methodology to establish an equation capable of predicting the shear stress of the drilling fluid under HPHT conditions. The equation was also compared with different drilling fluids tested on different rheometers. This equation demonstrated excellent predictive accuracy within the fitted range. The insights provided in this study hold substantial implications for the oil and gas industry, as predicting the rheological behavior of drilling fluids under varying temperatures and pressures within the annular region of the well is essential for efficient drilling planning, particularly in offshore fields.