Preparation of high-performance AMPS-based retarders for ultra-high temperature oil well cement: An investigation into structural design and mechanism

Focusing on the development of ultra-high-temperature (>200 °C) retarders for cement slurries used in deep-well cementing operations, this study proposes a novel modification strategy for 2-acrylamido-2-methylpropanesulfonic acid (AMPS)-based copolymers. While incorporating rigid groups has been widely applied to enhance the thermal stability of polymers, charged functional groups play a significant role in improving their adsorption properties. The results from this study reveal that the integration of the cationic functional monomer methacryloyloxyethyl trimethyl ammonium chloride (MAPTAC) into a typical ternary copolymer with rigid side chains (PAIN) facilitates the synthesis of a new type of heterocyclic zwitterionic quaternary copolymer (PAINM). Macroscopically, compared with PAIN, PAINM demonstrates a maximum weight loss temperature that is 14 °C higher, an extended setting delay of approximately 100 min under ultra-high-temperature conditions, and a stable adsorption capacity that persists for up to 60 h without significant decline. On a microscale, a systematic analysis of the thermal degradation behavior suggests that polymer degradation involves the release of side-chain carboxylic acids, decomposition of amide groups, backbone chain breakage, and formation of unsaturated small molecules. Notably, the structural degradation of PAINM is significantly delayed compared to PAIN. This study verifies the effectiveness of AMPS-based polymer retarders in cement systems at 220 °C and clarifies their structural evolution and degradation mechanisms under high-temperature conditions.