Water-based drilling fluids (WBDFs) are the industry-preferred medium for drilling reactive shale formations, yet they remain susceptible to shale swelling, fluid invasion, and cuttings dispersion—all of which compromise wellbore stability. Although oil-based fluids (OBFs) provide effective shale inhibition, their high cost and adverse environmental profile limit their use. Nanoparticles (NPs) derived from waste feedstocks offer a low-cost, environmentally responsible alternative for enhancing WBDF performance, but no prior study has simultaneously evaluated both waste-derived SiO2 and Al2O2 NPs within a single WBDF system. This study synthesised SiO2 NPs from Halfaya bentonite clay waste and Al2O2 NPs from recycled aluminium scrap, characterised both materials by XRD, FTIR, FE-SEM, and AFM, and evaluated their effect on WBDF performance at a standardised loading of 2 wt%. Three fluid systems were tested under API RP 13B-1 conditions: a base WBDF (Fluid A), a SiO2 NP-enhanced WBDF (Fluid B), and an Al2O2 NP-enhanced WBDF (Fluid C). Characterisation confirmed amorphous SiO2 (primary particle size ∼7 nm by AFM; aggregate 62 ± 45 nm by FE-SEM) and crystalline γ-Al2O2 (primary ∼3 nm; aggregate 80 ± 60 nm). Both Fluid B and Fluid C improved rheological stability relative to Fluid A: plastic viscosity (PV) was reduced (Fluid B: 16 cP; Fluid C: 17 cP vs. 20 cP baseline) while yield point (YP) increased, consistent with NP-mediated enhancement of the clay particle network. LTLP filtrate volume was reduced by 20.9% (Fluid B) and 12.8% (Fluid C); HTHP filtrate volume was reduced by 27.2% and 16.9%, respectively, attributable to dense NP-reinforced filter cake formation that blocked pore throats. Shale swelling was suppressed to 9% (Fluid B) and 11% (Fluid C) volume increase at 24 h, versus 25% for Fluid A, reflecting osmotic pressure reduction and hydrophobic surface modification by adsorbed NPs. Waste-derived SiO2 and Al2O2 NPs are technically competitive alternatives to commercial NP additives in WBDFs for reactive shale drilling, offering estimated cost savings of 60–80% relative to commercial NPs. Future work should address the limitations of the present study: a single NP concentration was evaluated, field-scale HPHT aging tests were not performed, and all evaluations were conducted at laboratory scale under static conditions.
