Nanocristais de celulose de resíduo de algodão e aplicação em pastas de cimento para poços de petróleo

Abstract

There are 3 (three) main characteristics for a good durability of the cement sheath coming from the primary cementation: low porosity, low permeability and high mechanical strength. Cellulose nanocrystals (CNC) have been widely applied as reinforcement material in cement matrices, as small amounts of this nanomaterial considerably improve these 3 properties. For this reason, the objective of this research was to obtain nanocrystals from a cotton waste and to evaluate the influence of their addition, in different concentrations, on the compressive strength, porosity and permeability of Portland Casse G cement pastes. Cellulose nanocrystals were obtained from a cotton fiber residue from the sanding process, through acid hydrolysis (H2SO4 65% m/m). The stability of the resulting suspension was measured by the zeta potential, in addition the NC characterization was performed by transmission electron microscopy (TEM), TGA and DRX. Concentrations of 0 to 0.3% of NC were evaluated 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 175 nm 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 indicate that 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.