Hydrogels prepared from cellulose nanofibrils via ferric ion-mediated crosslinking reaction for protecting drilling fluid

Ionic-covalent cross-linked poly-2-acrylamido-2-methylpropane sulfonic acid (AMPS)-N,N-Dimethylacrylamide (DMA)-cellulose nanofibril (CNF)-Fe3+ (PADC-Fe3+) hydrogels were synthesized by immersing CNFs reinforced covalent poly-AMPS-DMA (PAD) composite hydrogels into ferric chloride aqueous solution. To produce PADC-Fe3+ polymer with different CNF contents, CNF loadings of 5–20% were explored. The UV-spectroscopy analysis demonstrated the occurrence of CNF coalescence and optimized that 10% CNF loading resulted in the production of PADC-0.1-Fe3+ with the highest absorbance. Compared to copolymers (PAD or PADC-0.1) prepared without CNF or Fe3+, the synthesized PADC-0.1-Fe3+ showed much better tolerance to salt, high temperature, and shear. After adding synthesized PADC-0.1-Fe3+ as a filtrate reducer into the drilling fluids prepared with fresh water and 4% sodium chloride (NaCl), the filtrate loss was significantly reduced even at an elevated temperature of 200 ℃. Additionally, the addition of PADC-0.1-Fe3+ also increased the portion of fine cement particles in the drilling fluid.