Vinylsulfonate fluid loss additives, based on the 2-acrylamido-2-methylpropane sulfonic acid (AMPS™) monomer, are in common use in field cementing operations. The eopolymerization of AMPS™ with conjugate monomers yields a fluid loss agent whose properties include: (1) minimal retardation; (2) salt tolerance; (3) high efficiency; (4) thermal stability; and (5) excellent solids support.
The performance characteristics of AMPS™ based fluid loss additives (ABFLA) are primarily dependent on two factors: the temperature state of the system and the physical parameters affecting polymer hydration. At temperatures below 200°F (93°C) ABFLA exhibit a "threshold" response between fluid loss control and polymer concentration. This distinct transition in fluid loss efficiency takes place at a specific ABFLA loading known as the critical polymer concentration (CPC). Below 200°F (93°C) ABFLA also possess an interrelationship between rheological character and fluid loss control. When the CPC for a particular slurry is reached, the yield value as measured by the 6 and 3 RPM Fann readings will fall dramatically from "neat" values, and good fluid loss control will ensue. As the temperature condition rises above 200°F (93°C), the response of fluid loss control to polymer concentration becomes more linear in nature. Additionally, fluid loss efficiency becomes increasingly influenced by factors such as polymer hydration time and the pressure and salinity environment under which hydration takes place.
ABFLA are powerful implements for the cement technologist. Knowledge of the unique performance characteristics of ABFLA is necessary for proper slurry design, test data interpretation, and recommended job procedures, all significant factors in the success of a field cementing operation.