Alkanolamine-enhanced hydrothermal stability of xanthan gum in calcium chloride brine: Rheological behavior and...

Calcium chloride water-based drilling fluids are widely used because of their excellent inhibition performance, but rheological control remains a key constraint on their development. Xanthan gum (XG) is the rheological modifier of choice, yet its structural evolution and molecular mechanisms under high‑calcium alkaline hydrothermal conditions remain unexplored. Using inorganic bases as controls, this study investigated the effects of three alkanolamines on the rheological behavior and structural evolution of XG after hydrothermal aging in high-calcium brine. The results showed that the inorganic-base systems almost completely lost their rheological properties after aging, whereas the alkanolamine systems exhibited superior hydrothermal stability. Diethanolamine (DEA) performed the best, showing the highest low-shear viscosity, yield stress, and shear-thinning characteristics. Structural characterization revealed that the DEA system exhibited better preservation of β-glycosidic linkages, oxygen-containing environments, high-molecular-weight chains, and microscopic networks. Molecular dynamics simulations demonstrated that DEA formed a multipoint noncovalent interaction network with XG chain segments and maintained the local hydration environment, mitigating chain dehydration and local structural disturbance induced by high-temperature and high‑calcium conditions. This study elucidates the molecular mechanism by which alkanolamines, particularly DEA, enhance the hydrothermal stability of XG, providing a basis for the stabilization design of polysaccharide-based fluids under high-calcium alkaline hydrothermal conditions.