Cellulose nanofibril-polymer hybrids for protecting drilling fluid at high salinity and high temperature.

A copolymer (PADH) was first synthesized from 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N,N-dimethylacrylamide (DMA), and 2-Hydroxyethyl acrylate (HEA) by UV-induced polymerization. Subsequently, cellulose nanofibrils (CNFs) were introduced into the copolymer through ironic cross-linking between ferric ions and carboxylate groups as well as sulfonic acid groups to produce a hybrid product (PADHC-Fe3+-3). The salt tolerance and thermal stability of the copolymers and the hybrid product were investigated. The results showed that the optimum HEA dosage was 5% (in relation to the total mass of AMPS and DMA). In addition, the fluid loss test showed that the hybrid product PADHC-Fe3+-3 had excellent salt tolerance (maximum tolerance: 26.5 wt% NaCl and 32 wt% combined salts) and thermal stability (maximum tolerance: 200 °C). The SEM images indicated that the filter cakes became denser after the addition of PADHC-Fe3+-3. The results demonstrated that the cross-linked hybrid product was very promising for industrial application in drilling engineering.