Study of a novel cross linked graft copolymer starch in water-based drilling fluid

In the drilling industry, the demand for environmentally friendly additives with high thermal stability is increasing due to the dual factors of increasing environmental pressure and high-temperature oil layers. However, commonly used non-toxic and biodegradable additives, such as etherified modified starch, cannot withstand temperatures higher than 150 degrees C. Additionally, natural polymers with better thermal stability obtained through graft modification with sulfonated monomers face challenges in meeting the standards of toxicity and biodegradability. To address these technical problems, a novel graft and crosslink copolymer, St-AA/AM/NVP/MBA (SAANM), was synthesized from corn starch by combining graft modification with a non-sulfonated monomer and cross-linking modification. Laboratory evaluation results confirm that the thermal stability of SAANM in a nitrogen atmosphere was close to 300 degrees C, and it exhibits excellent temperature resistance up to 170 degrees C in bentonite-based mud, while also retaining the non-toxic and biodegradable characteristics of starch. The water-based drilling fluid (WBDF), added with SAANM, demonstrated outstanding rheological properties, fluid loss control performance, and environmental friendliness after aging at 170 degrees C and being polluted by high concentrations of NaCl or CaCl2. The successful application of SAANM in a high-temperature directional well in an offshore oil field confirms its potential for borehole cleaning and wellbore stability.