Slurry Design For Shallow Well Cementing

Fluid-loss control additives for cement slurries have historically tended to undesirably retard compressive strength development at temperatures below approximately 13O'F. In order to counteract this retardation, calcium chloride set accelerator has often been added to the slurry. Unfortunately, calcium chloride adversely affects the performance of commonly used fluid-loss additives. Frequently, fluid-loss control can only be obtained by adding significantly higher concentrations of the additive. This often results in an unacceptably high slurry viscosity and cost. An ideal cement slurry for low-temperature applications should provide excellent fluid-loss control, adequate pumping time and rapid strength development. In addition, it is often desirable to use calcium chloride to economically accelerate the set of the cement, reducing the WOC (wait on cement) time. Recent studies of cementing applications at temperatures below 130_F have resulted in the development of cement slurries that provide excellent fluid-loss control, rapid strength development and are not adversely affected by the addition of calcium chloride. Excellent performance can be obtained using API Class A and C cements, as well as fly ash and bentonite containing lightweight slurries. Laboratory data comparing currently used fluid-loss additives with these newly developed slurries are presented. Case histories of wells cemented using these new slurries are also discussed.