Influence of salt and temperature on the rheological and filtration properties of cellulose Nanofiber/bentonite water-based drilling fluids

Water-based drilling fluids (WBDFs) are popular due to their lower cost and superior environmental friendliness. The high thermal stability, high aspect ratio, and fiber-like structure of cellulose nanofibers (CNFs) have made them viable candidates for rheology and filtration modification in bentonite WBDFs (BT-WBDFs), because they can produce high levels of hydration and entanglement when dispersed in water, even at very low concentrations under harsh drilling condition. However, the rheology and filtration performance of CNF/BT-WBDFs in high temperature and high saline conditions remains largely unexplored. Herein, the influence of high temperature and high salt content on the rheological and filtration properties of CNF/BT-WBDFs was investigated. Two types of CNFs, i.e., TEMPO-mediated oxidized CNFs (T-CNFs) and mechanically disintegrated CNFs (M-CNFs) were applied. It was observed that the M-CNFs exhibited more effectiveness in enhancing the rheological properties of BT-WBDFs, while T-CNFs demonstrated superior filtration-reducing properties of BT-WBDFs. M-CNFs often exhibit a highly branched and tangled network, resulting in superior rheological properties; whereas the presence of more negative charge on the surface of T-CNFs enhanced the electrostatic repulsion with bentonite particles, preventing bentonite from flocculating or aggregating, resulting in reduced fluid loss. Furthermore, the T-CNF/BT-WBDFs showed better resistance to salt contamination compared to hot rolling, whereas the M-CNF/BT-WBDFs demonstrated better defense against hot rolling than salt contamination. However, the addition of salt in combination with high-temperature hot rolling severely affected the rheological properties as well as the filtration-reducing capabilities of both T-CNF/BT- and M-CNF/BT-WBDFs. The study highlighted the importance of CNF types on the rheological and filtration properties of WBDFs under high temperature and saline conditions, providing valuable insights for the potential application of CNFs in temperature-resistant and salt-tolerant drilling fluids.