Application of Hybrid Polymer Containing POSS as High-Temperature- and High-Salt-Resistant Fluid Loss Additive in Water-Based Drilling Fluids

Deep drilling often faces high-temperature and high-salt environments. Bentonite/water-based drilling fluids (BT/WBDFs) suffer serious fluid loss. Polyhedral oligomeric silsesquioxane (POSS) is introduced to synthesize a hybrid fluid loss additive (PAAD) through emulsion polymerization with acrylamide and 2-acrylamido-2-methylpropane sulfonic acid, and dimethyl diallyl ammonium chloride. The hybrid polymer exhibits improved filtration control performance in BT-WBDFs under conditions with a coexisting high Na+ concentration and high temperature. BT-WBDFs added with 2.0% PAAD exhibit satisfactory performance for reducing fluid loss under contamination of 20% NaCl, even at a high temperature of up to 220 °C. Microstructure analysis demonstrates that forming "polymer–clay" gel through intermolecular forces and promoting clay particle dispersion efficiently stabilizes BT-WBDFs. PAAD shields against the adverse effects of Na+ and promotes the hydration and dispersion of BT, finally forming a thin and compact filter cake. This study can provide a basis for applying POSS in the design of efficient additives for drilling fluids.