It is a classic high-viscosity filtration reducer, thickener, and sealant in water-based drilling fluid systems. It belongs to anionic water-soluble cellulose ether polymers and is produced by alkalization and etherification modification of natural cellulose. Due to its high viscosity, strong wall-building properties, and excellent compatibility, it has become a basic treatment agent for freshwater/low-mineralization drilling fluid systems. Its core functions are to increase drilling fluid viscosity, control filtration loss, and stabilize the system flow pattern.