Development of Innovative Polymers as Cement Retarders: Lab Study and Application

Cement must be designed in a way to ensure acceptable properties such as mixability, stability, rheology, fluid loss, and adequate thickening time. Different chemicals are used when designing cement slurries. Retarders are cement additives whose function is to retard, or delay the setting of cement slurries. For a well whose temperature is about 125 °F or less, we do not need to add any retarders. However, as temperature increases, the hydration process of Tricalcium silicate (C3S) increases and, hence, the thickening time decreases. In addition to retarder additives which are added to cements, retarded cements are available. These contain lignin, gums, starches, etc. which provide the retarding action. However, these may not be compatible with cement additives and the setting times may be difficult to control consistently. To explain the mechanism of retardation in Portland cement, the following four theories were proposed: adsorption, precipitation, nucleation and complexation. According to the adsorption theory, the retarder is absorbed on the surface of the hydration products inhibiting contact with water. This theory suggests that retardation is due in part to the adsorption onto the surface of the C-S-H gel hydration product formed around the grains rendering it hydrophobic. The precipitation theory suggests that the retarder reacts with calcium and/or hydroxyl ions and forms an impermeable sheet covering cement grains. In the nucleation theory, it is suggested that the retarder slows down the growth rate of hydration products by adsorbing on their nuclei. Finally, the complexation theory states that calcium ions are chelated by the retarder preventing the formation of the nuclei. It is possible that all of the above effects are involved to some extent in the retardation process. The predominant factor depends on the type of retarder used and the cement phases upon which the retarder acts. This study will detail mechanisms, interactions and lab and deployment performance of different polymers functions as retarders. The study will include thickening time tests, rheology tests, compressive strength development and compatibility tests with other conventional additives. Polymers with hydrocarboxylic acid derivatives and polymers with sodium lignosulfonate and/or hydrolyzed carbohydrates were fully investigated and characterized using proton NMR and FTIR techniques. These polymers were also used in effective formulations to cement different casings successfully.