Overcoming Salt Contamination of Bentonite Water-Based Drilling Fluids with Blended Dual-Functionalized Cellulose Nanocrystals

The depletion of onshore oil reserves along with a rapid increase in the global energy demand has driven the oil industry to explore and produce oil from deepwater fields. However, because of high salinity in the subsea formation, salt contamination is becoming one of the most critical challenges to bentonite water-based drilling fluids (BT-WDFs), causing undesirable changes in density, rheology, and filtration performance of the fluids. Herein, we reveal the mechanisms of the negative influence of salt cations on BT-WDFs and demonstrate the function of biomass-derived cellulose nanocrystals (CNCs) as anti-salt agents in the fluids through rational dual surface functionalization for the first time. Poly­(acrylamide) (PAM) and poly­(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) are coated on the CNC surface using an in situ free radical polymerization technique. The dual-functionalized CNCs (fCNCs) are attached to BT platelets on both their face and edge surfaces, effectively shielding the platelet’s ion-sensitive sites. Meanwhile, the highly negatively charged PAMPS on the surface of fCNCs immobilize ions via the ionic bond, preventing ions to be attached on the ion-sensitive sites of BT platelets. These dual functions lead to noticeable enhancement in the salt resistance of the BT-WDFs. Moreover, the salt resistance of the fluids can be further tuned by tailoring the coating ratio and concentration of fCNCs. This work demonstrates that CNCs can be used as sustainable and multifunctional agents in BT-WDFs through a rational surface functionalization design, paving the way for their application in deepwater reservoir excavation.