Polyanionic Cellulose (PAC) is a CMC derivative with a larger degree of substitution and, therefore, better water solubility. PAC-LV is much more effective than CMC in improving the rheology of drilling fluid in waters containing potassium, calcium, and magnesium ions, resulting in a three-fold increase in drilling fluid loss. Further, it reduces CMC-LV to a half. Compared to CMC, even less PAC is required to achieve the same drilling fluid rheology. Besides, PAC maintains its properties at high temperatures when the fluid ceases circulation in the well. Moreover, it promotes a convenient gelatinous form and offers better performance than CMC in combination with other polymer-based shale inhibitors.
Considering the final drilling fluid properties, using PAC is more cost-effective than CMC, since less than half as much additive is enough.