A critical review of mechanism research and application of chemical additives to improve salt resistance of water-based drilling fluid

Marine drilling fluid shows insufficient performance stability in high salt environments, and the research on the synergistic mechanism and compatibility effect of different chemical additives under compound salt conditions is insufficient. Thus, it isn’t easy to improve the salt resistance adaptability of the drilling fluid system. This review covers how acrylamide (AM)-propane sulfonic acid copolymers can form a compact filter cake to control filtration in salinity salinity-changing environment due to the strong adsorption of the amide group/pyrrole ring in the molecular chain and stable hydration ability of the sulfonic acid group. Because of their good cost performance and performance stability, they have become core additives for salt-resistant drilling fluids. Emulsifier and sulfonate surfactant were used together to construct a “polymer-emulsifier composite membrane” to enhance the compactness and impermeability of the filter cake. The salt resistance mechanism of the above formulations comes from three aspects: strong polar groups that inhibit clay hydration through hydrogen bonding and electrostatic interaction; sulfonic acid groups that form stable hydration films to reduce filtration; emulsifiers that construct salt-resistant composite films at the oil-water interface; and components that enhance filter cake compactness and interface stability through compounding. Therefore, the salt resistance and comprehensive performance of drilling fluid in high temperature and high salt environments can be effectively improved by group design, compound optimization, and interface control. Based on the review, it is proposed that the development of green additives and nanomaterials with controllable polymeric structure should be focused on, and the environmental protection and long-term adaptation stability of additives in a complex marine environment should be studied by combining molecular simulation with microscopic characterization.