High Temperature Aging Behavior and Failure Mechanism of Polyacrylamide‐Based Acid Thickeners

ABSTRACT Polyacrylamide is widely used in petroleum drilling due to its excellent thickening ability in hydrochloric acid systems, yet as petroleum development advances toward ~10,000‐m‐class ultra‐deep wells and downhole temperature rise substantially, the high‐temperature aging behavior and failure mechanisms remain insufficiently elucidated. Herein, we synthesized three polyacrylamide‐based thickeners, including an AM homopolymer, an AM/DAC copolymer, and an AM/DAC/NVP terpolymer, and systematically investigated their high‐temperature aging behavior and failure mechanisms. It was found that all three thickeners lost stability during high‐temperature acidic aging. Initially, the polyacrylamide‐based thickeners formed gel‐like flocculates, which further evolved into brownish‐black solids with increasing aging temperature and time. Mechanistic analysis indicates that, under high‐temperature acidic conditions, polyacrylamide‐based thickeners undergo acid‐catalyzed hydrolysis of AM amide groups and DAC ester linkages to form polyacrylic acid structures, while NVP suppresses this process by weakening neighboring‐group effects; then the resulting polyacrylic acid undergoes further dehydration/condensation to form intrachained anhydride (cyclization) and interchain anhydrides (crosslinking), increasing hydrophobicity and ultimately causing the failure of the thickeners. This work elucidates the aging behavior and failure mechanism of polyacrylamide‐based thickeners in high‐temperature acidic, guiding the design of high‐temperature acidic thickeners.