Degradation kinetics of synthetic acrylamide polymers as a viscosity and filtration control additives in the low-density water – Based drilling fluid systems

Abstract

The impact of synthetic polymers in water-based drilling fluids (WBDFs) along with other functional additives is a critical task to ensure wellbore stability. In this regard, three different synthetic acrylamide polymers with various degrees of sulfonation–DoS (0–30%) and molecular weight of ≈2.8–3 million DU were investigated. The sulfonic substitution was verified using NMR techniques. The thermal-stability of these polymers was quantitatively investigated using a reliable titration technique.The quantified time-temperature kinetics of polymer degradation was correlated with their respective performance in low-density WBDFs in terms of filtration and viscosity. The WBDFs were formulated using NaCl brine, synthetic polymers, bentonite and other additives. The WBDFs were hot rolled at 250 °F and 350 °F for 16 h and the viscosity and filtration control was determined.The WBDFs investigation showed that the three polymers maintained desired viscosity (AV: 35–65 cp) and reasonable filtration control (<15 ml) for the fresh and aged fluids up to 250 °F. However, at elevated temperatures, the filtration performance at 350 °F got deteriorated. The present work, for the first time, explains this impact of temperature on the WBDF performance on the basis of time-temperature kinetics of polymer degradation. It was also noted that at the elevated temperature of 350 °F, moderately sulfonated polymer (DoS = 15%) had shown significantly better filtration control and viscosity compared to the other polymers as evident from both viscosity and filtration tests. The optimum performance of the polymer with moderate sulfonation was explained using a novel approach as a competing effect of two distinct mechanisms: variation in activation energy parameter of polymer degradation rate and change in polymer length with increasing degrees of substitution. The insights gained on the time-temperature dynamics of the polymer stability in the present work could also be utilized for devising the polymer replenishment strategy for the drilling automation processes.