Development and Performance Evaluation of a Foam Acid System for Effective Fracture Control in Carbonate Reservoirs

ABSTRACT To address challenges such as severe vertical etching, bottom water breakthrough, insufficient retardation, and high corrosivity associated with conventional acids in carbonate slit‐hole reservoirs under high‐temperature and high‐pressure conditions, novel foam acid systems are developed using acrylamide, 2‐acrylamido‐2‐methylpropanesulfonic acid, methacryloyloxyethyl trimethyl ammonium chloride, and octadecyl ethoxylated methacrylate. Hydrophobically bonded thickening agents (HAT‐1 and HAT‐2) are synthesized via free‐radical polymerization and combined with the surfactant O‐25(fatty alcohol polyoxyethylene ether) to form foam acids. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy are employed for acid characterization. The involved microstructures, surface tension, temperature resistance, pressure resistance, retardation, and corrosion inhibition characteristics are also tested. The considered HAT‐2‐based foam acid has a half‐life of 25 min at 140°C, maintains stability at 6–10 MPa, and exhibits a static‐retardation rate of 94.86% and an acid–rock reaction rate of 2.09 × 10 −6 mol/(cm 2 ·s), demonstrating strong retardation performance. Its corrosion rate on N80‐E steel is 6.462 g/m 2 ·h. Notably, the stability and drainage resistance of this foam acid are ensured by a synergy between HAT‐2–O‐25 hydrophobic interactions and hydrogen bonding with water molecules. Overall, this system serves as a new and efficient foam acid for acidifying carbonate rock formations.