1. n. [Well Workover and Intervention]
A chemical or fluid that alters the performance of an engineered slurry or treatment fluid. Some remedial cementing treatments require unpredictable volumes of cement slurry to achieve the desired results. When excess slurry is left in the wellbore, it may not be possible to remove the excess slurry by conventional means, such as reverse circulation, before the slurry thickens and becomes immovable. Mixing the contaminant with the slurry in the correct proportions increases the thickening time of the slurry, allowing it to be safely removed from the wellbore.