In deep wells the higher temperatures will reduce the cement slurry’s thickening time. Retarders are used to prolong the thickening time and avoid the risk of the cement setting in the casing prematurely. The bottom hole temperature is the critical factor which influences slurry setting times and therefore for determining the need for retarders. Above a static temperature of 260 – 275 degrees F the effect of retarders should be measured in pilot tests.
The most common types of retarders are:
• Calcium lignosulphanate (sometimes with organic acids) 0.1 – 1.5%
• Saturated Salt Solutions