Study on Non‐Thickening Retarded Acid Passivation Agent and Its Mechanism

ABSTRACT In acidizing treatments for low‐permeability carbonate reservoirs, conventional acids often preferentially flow into high‐permeability zones, reducing overall efficiency. This study develops a non‐thickening retarded acid system using the fluorocarbon surfactant FS‐6 to achieve deep penetration. At an optimal concentration of 0.1%, FS‐6 demonstrated a high retardation rate of 74.4% at 50°C and 73.5% at 70°C, reducing the acid–rock reaction rate to 8.3 × 10 −6 mol/(cm 2 s). Mechanism analysis revealed that perfluorohexane‐1‐sulphonic acid (FS‐6) adsorbs onto the rock surface, forming a hydrophobic film that increases the HCl contact angle from ∼20° to >80° and lowers surface tension to ∼30 mN/m. Scanning electron microscope (SEM) confirmed smoother surfaces with reduced etching pits. This system effectively controls reaction kinetics and wettability, enabling more uniform acid distribution and deeper treatment, offering a promising solution for enhanced stimulation in high‐temperature carbonate formations.