High-temperature alkaline stability of cement set retarders and their performance at 70–90°C

Hydroxycarboxylic acid salt (sodium gluconate), sodium lignosulfonate and a combination of carboxylic acid and sulfonate-type retarder (poly(4-styrenesulfonic acid-co-maleic acid) sodium salt) are typical set retarders for oil-well cement. The potential high-temperature alkali degradation of these retarders is assessed, and its role in altering the kinetics of cement hydration at temperatures between 70 and 90°C. The high-temperature alkaline stability of cement set retarders is poorly studied. However, it may represent one way to understand the delay in hydration induced by such additives, and the discontinuity of cement hydration, with the longer setting times at higher temperatures in that range. Degradation products are identified and their thermal stability is evaluated. Retarders containing carboxylic acid become partially fragmented at high pH and 90°C. The effect on cement setting kinetics is similar for hydrolysed retarders containing carboxylic acid groups: the setting times are longer at 80°C than at 70 and 90°C. The sulfonate groups of lignosulfonate-type retarder, treated at pH 13·4, 90°C, are partially converted to sulfate and the ether groups to alkoxides. The setting time changes linearly with temperature for the high-pH-treated lignosulfonate retarder in the studied temperature range.