Modified natural polymers as additives in high-temperature drilling fluids: A review.

Drilling fluids are often referred to as the "blood" of the drilling process, as they play a crucial role in determining both the efficiency and safety of drilling operations. Natural polymers, derived from renewable sources, such as cellulose, lignin, chitosan, xanthan gum, and starch, offer inherent advantages such as sustainability, biodegradability, and environmentally-friendliness when used as additives in drilling fluids. However, the inherent properties of natural polymers are adversely affected by thermal degradation due to their low heat resistance under harsh drilling conditions, where temperatures can exceed 150 °C. To address these challenges, various modification techniques, including free radical polymerization, esterification, etherification, silanization, hydroxymethylation, and ionic crosslinking, have been employed. This paper provides an overview of recent advances in the application of modified natural polymers as additives in water-based drilling fluids (WBDFs) under high-temperature drilling conditions. It begins by discussing the degradation mechanisms of natural polymers at high temperatures, followed by a review of the techniques used for their modification. Subsequently, the application of modified natural polymers as rheological and fluid loss additives in high-temperature WBDFs is briefly presented. Finally, the challenges, environmental impacts, and future considerations for the use of modified polymers are outlined to guide future development of environmentally friendly, high-performance WBDFs.