Rational design and adsorption mechanism of a multi-site retarder for oil well cement under 240 °C conditions

A multi-site adsorption ultra-high-temperature retarder (PAINDP) bearing sulfonic, carboxylic, and phosphonic acid groups was successfully synthesized. • PAINDP exhibits excellent overall performance and effectively prolongs cement slurry thickening time at 240 °C. • At ultra-high temperatures, PAINDP remains stably adsorbed on the C3S surface via –PO₃²⁻ and partial –COO⁻ groups. • PAINDP achieves stable multipoint adsorption on the cement surface, effectively coating the cement particles. To address the high-temperature degradation of conventional AMPS-based retarders and the narrow dosage window of small-molecule phosphonates in ultra-deep well cementing, a novel phosphonate-containing polymer retarder (PAINDP) with a multi-site adsorption architecture was designed and synthesized. FTIR and ^1H NMR analyses confirmed the successful synthesis of PAINDP. TGA and in situ FTIR results further demonstrated that the carboxylate and phosphonate adsorption groups remained stable below 260 °C, indicating good thermal stability. Cement-slurry thickening tests showed that, at 240 °C, the addition of 6.9% PAINDP extended the thickening time to 408   min, while maintaining low temperature sensitivity and dosage sensitivity. Mechanistic investigations revealed that the phosphonate groups and part of the carboxylate groups in PAINDP formed stable interactions with Ca sites on the C 3 S surface, thereby maintaining effective interfacial adsorption under high-temperature conditions and providing the cement slurry with sustained and stable retardation performance. This work provides a molecular design strategy and theoretical basis for developing high-temperature polymer retarders suitable for ultra-deep well cementing. Download: Download high-res image (418KB) Download: Download full-size image