One of the most recent research areas in subsurface applications, including well drilling, is the use of eco-friendly and sustainably synthesized nanoparticles to improve drilling fluid efficiency. Typically, Shale formations present significant challenges to traditional drilling fluids, including fluid infiltration and shale swelling, which jeopardize wellbore stability. Although water-based drilling fluids (WBM) are environmentally preferred, their performance often requires enhancement through advanced additives. This study thus examines the synthesis of silica (SiO₂) and alumina (Al₂O₃) nanoparticles (NPs) using sustainable methods, employing Iraqi bentonite for silica and recycled aluminum scrap for alumina, to improve WBM efficiency. Mainly, a high-pressure, high-temperature (HPHT) apparatus was used to systematically investigate the influence of NPs as additives on the flow, filtration ability, and other rheological properties of WBM. Furthermore, the physicochemical properties of the synthesized NPs were characterized using various analytical techniques. Particle size distribution measurements indicated that SiO₂ NPs had an average particle size of 84 nm, while Al₂O₃ NPs produced at 1200 °C reached a size range of 80±60 nm. Most interestingly, rheological results showed that the addition of 1 g of SiO₂ NPs increased plastic viscosity from a base of 6 cP to 10 cP, whereas the addition of 1 g of Al₂O₃ NPs significantly boosted the yield point from 15 lb/100 ft² to 65 lb/100 ft². Moreover, filtration performance was notably enhanced; the addition of 0.5 g of Al₂O₃ NPs reduced the low-temperature, low-pressure (LTLP) filtrate volume from 10.25 ml to 5.24 ml and the high-pressure, high-temperature (HPHT) filtrate volume from 15.2 ml to 8.7 ml. Additionally, NPs, particularly alumina, caused greater shale stabilization. Specifically, adding 1 g of Al₂O₃ NPs reduces shale swelling from 24% in the base mud to just 6.9% after 24 h, and increases lubricity by lowering the coefficient of friction by around 27% (from 0.52% to 0.38%). The outcomes of this work indicate that the NPs effectively seal shale nanopores and enhance surface hydrophobicity, offering a cost-effective, high-performance solution for challenging drilling operations.
