Modification of naturally occurring polymers for enhancing drilling fluid performance: A review

The performance and efficiency of drilling fluids in oil and gas operations are significantly influenced by the nature and modification of their polymeric additives. This review investigates the role of naturally occurring polymers (primarily cellulose and starch) and the impact of their chemical, enzymatic, genetic, and physical modifications on drilling fluid performance. Native forms of cellulose and starch have thermal stability, solubility, and rheological performance limitations, which restrict their application in demanding wellbore environments. However, through modifications such as carboxymethylation, acetylation, succinylation (OSA), cross-linking, and oxidation, these polymers exhibit improved physicochemical properties including enhanced viscosity, reduced filtration loss, and increased temperature and salt resistance. Experimental and literature-based analyses show that cross-linked and dual-modified starches are particularly effective in high-pressure, high-temperature (HPHT) drilling conditions. At the same time, acetylated and carboxymethylated forms offer utility in moderate environments. Despite promising physicochemical profiles, oxidized starch remains underexplored for drilling applications. This review underscores the importance of polymer selection and targeted modification in designing efficient, environmentally friendly drilling fluids for various operational scenarios.