Rheological and thermal characterization of the effects of high pressure and high temperature on the properties of water-based drilling fluids with xanthan gum

Abstract

The water-based drilling fluid with xanthan gum and limestone under high-pressure and hightemperature conditions is investigated in the following experimental study using an Anton Paar MCR 702TD rheometer with pressure cell. A wide range of mud suspensions is commonly used in the oil well drilling process. Water-based drilling fluid is used in some stages during the drilling process due to its low environmental impact and costs. HPHT conditions have several effects on the rheological behavior of water-based drilling fluids. For a better understanding of the process and knowledge of the implications of under HPHT conditions work, rheological and thermal analyzes were performed. Flow curves, flow startup, time, and shear stress oscillatory sweeps were obtained in order to study the rheological behavior in a temperature range of 4 to 125 °C and 10 to 800 bar pressures. Also, thermal stability was investigated through 16 hours’ dynamic thermal aging tests on Rover Oven Fann at temperatures of 55, 70, 90, 100, and 125 °C) in order to analyze the effects of thermal aging on its rheological properties. In addition to that microcalorimeter, tests were performed to determine the xanthan gum’s transition temperature, which was the first indication of a decrease in drilling fluid viscosity. The viscosity suffered a decrease due to temperature growth and increased with pressure increment. A methodology was proposed to obtain HPHT measurements for water-based drilling fluid with xanthan gum, considering a change in the xanthan gum’s conformation with increasing temperature. The static yield stresses obtained from the dynamic modules crossing were higher than the dynamic yield stress. Besides, temperature and pressure showed a decrease and a gain in the fluid structure, respectively. Next, an apparent viscosity fit was developed as a function of pressure, temperature and shear rate, based on experimental models. The experimental results showed that viscosity is sensitive to downhole conditions. Finally, the increase of the xanthan gum concentration in the drilling fluid was analyzed, presenting favorable characteristics in terms of transition temperature growth and fluid capacity considering operational scenarios.