Primary cementation consists in injection of cement into the annular space between the outer wall of the coating column and the rock formation. This process is extremely important in the oil and gas industry, aiming to fix the piping and prevent the migration of fluids between permeable zones. In its hardened state, it is extremely important to cement to be durable, providing a longer “life span” to the well. For this, 3 (three) characteristics are essential to the cement paste: porosity, permeability and compressive strength. Cellulose nanocrystals (CNC) has been widely applied as reinforcement material in cement and polymer matrices due to its unique properties such as: high crystallinity and contact surface, high Young modulus, high tensile strength and low thermal expansion coeficiente. For this reason, the aim of this research was to evaluate the influence of adding different concentrations of cellulose nanocrystals (0 to 0.3%) on mechanical strength of the cement (compressive strength), porosity and permeability. The nanocrystals were obtained from a cotton fiber residue arising from the sanding process, provided by the VICUNHA TÊXTIL® industry, Natal – RN. The obtention was carried out by acid hydrolysis (H2SO4  65% w/w), under constant agitation, for 60 minutes at 45ºC. The hydrolysis was stopped in an ice bath. The resulting suspension was subjected to 4 (four) centrifugation cycles of 15min at 11000rpm and 20ºC and then subjected to the dialysis process until reaching a pH close to 5-6. The stability of the resulting nanocrystal suspension was assessed by the zeta potential, in addition, the characterization of the CNC was made by transmission electron microscopy (MET), TGA, FTIR e XRD. The pastes were formulated based on the standards established by the API (American Petroleum Institute), with a volume of 600cm3  of paste and density of 15lb/gal. It was evaluated the concentrations of 0; 0.05; 0.1; 0.15; 0.2 and 0.3% of CNC in the compressive strength, porosity and permeability of the specimens. The results show that the resulting nanocrystal suspension was well dispersed, with needle-shaped nanocrystals (nanowhiskers) with a diameter and length of approximately 17 and 175nm respectively. The mechanical tests show a rapid gain in compressive strength (after 24 hours of curing), around 45% for the formulation containing 0.2% of CNC. Even after 28 days of curing, pastes reinforced with CNC still show better results when compared to the standard, with a gain greater than 30%, also for formulation 0,2%. The porosity and permeability tests show that even standard pastes (without the addition of CNC) have low permeability. Even so, the addition of nanocrystals reduced porosity by approximately 27% and paste permeability by 25% after adding any concentrations of CNC. The results indicatethat there is a great potential in the use of CNC to improve the mechanical strength of oil well cement, as well as reducing its porosity and permeability, thus enabling a more effective sealing of the annular space, preventing gas migration through the cement sheath and, consequently, improving well integrity.