CNF have been successfully used to reinforce cement due to their exceptional mechanical performance.However, Sun and Wu [325] used CNF as a modifier of rheological, curing, and also mechanical performance of oil well cement (OWC). Rheological data were best fitted by the VomBerg model. CNF addition increased the yield stress of OWC and the degree of hydration of the final composites. Only with the addition of 0.04 wt.% CNF flexural strength was increased by 20.7%. However, excessive addition of CNF triggers a detrimental effect on mechanical properties, caused by the aggregation of CNF.