Experimental study on nano-silica for improving rheological properties of water-based drilling fluids in deepwater deep wells

In deepwater oil and gas drilling operations, the thickening of drilling fluid at low seabed temperatures can easily result in lost circulation, while thinning at high formation temperatures can reduce the cleanup efficiency of wellbores. The present study explores the potential of utilizing nanoparticles to regulate the rheological properties of water-based drilling fluids (WBDFs) under cyclic temperatures of 4-90°C. Through various analyses such as bentonite slurry particle size distribution, zeta potential measurements, quantification of polymer adsorption, and solution viscoelasticity experiments, the study clarified the mechanisms through which nanoparticles enhanced the rheological properties over a broad temperature range. The results indicated that after 16 h of hot rolling at 180°C, the WBDFs exhibited more than 75% variation in rheological parameters within the temperature range of 4-90°C. The incorporation of nanoparticles diminished these variations, with nano-silica demonstrating the most pronounced effect. The incorporation of 1% nano-silica reduced the apparent viscosity variation from 77.8% to 40.6%. Post-hot rolling analysis showed a 57% decrease in the absolute zeta potential of the bentonite slurry, indicating weakened electrostatic repulsion and subsequent particle flocculation/coalescence. In contrast, the nano-silica-modified bentonite slurry maintained variations in zeta potential within 18% and exhibited significantly reduced changes in particle size, suggesting enhanced colloidal stability. Furthermore, nano-silica displayed dual functionality by inhibiting the desorption of polymer from bentonite surfaces and reinforcing the three-dimensional network structure of polymer solutions. These synergistic mechanisms contribute to the improved rheological performance of drilling fluids to support deep oil and gas drilling operations in deep water.