Synergistic effect of AMPS-based copolymer retarder and HEDP used for set-regulation of ultra-high temperature (≥200 ℃) cementing slurry: Performance and mechanism

This work proposed an ultra-high temperature set-regulation method to provide a reference scheme for the optimal retarder design of ultra-deep formation oil well cementing slurry. It was found that there was a synergistic retarding effect between 2-acrylamido-2-methylpropanesulfonic acid-based copolymer retarder and 1-hydroxyethylidene-1,1-diphosphonic acid, and the latter could serve as an intensifier for the former to significantly prolong the ultra-high temperature (≥200 ℃) thickening time of cement slurry. The thickening progress mechanism of cement slurry was studied from the perspective of hydration kinetics and mineral content evolution. Results indicated that the content of cement hydration products during the thickening process did not increase gradually and linearly, but increased rapidly within several minutes near thickening time due to the acceleration of hydration. The introduction of intensifier 1-hydroxyethylidene-1,1-diphosphonic acid extended the thickening time by highly delaying the hydration of silicate minerals (C 3 S/C 2 S), while less affected the hydration of aluminate minerals (C 4 AF/C 3 A). Furthermore, the synergistic principle between copolymer retarder and 1-hydroxyethylidene-1,1-diphosphonic acid was proposed from microchemical perspective. Analysis showed that the PO 3 2- was a stronger anchoring group than -COO - and could compensate for the decline of Ca 2+ chelating ability of copolymer retarder caused by decarboxylation and thermal oxidative degradation in ultra-high temperature and alkaline environment, thus further delaying the hydration.