Titanium dioxide-grafted polyacrylamide nanocomposites ameliorate the rheology and high-pressure high-temperature fluid loss of water-based drilling fluids

• Synthesized a novel TiO₂–polyacrylamide nanocomposite via inverse miniemulsion polymerization • Achieved thermal stability up to 300 °C with uniform nanoparticle dispersion and moderate colloidal stability • Enhanced drilling fluid rheology with a ∼3× increase in yield point and ∼4× increase in apparent viscosity • Reduced fluid loss by up to 27% under HPHT conditions and filter cake thickness by up to 66% • Demonstrated Herschel–Bulkley model as the best fit for predicting complex flow behavior of modified fluids The thermal and mechanical stability of water-based drilling fluids (WBDFs) is critical for efficient wellbore cleaning and pressure control, particularly under high-pressure high-temperature (HPHT) conditions, where conventional polymer additives often fail. The present work reports a novel acrylamide-functionalized titanium dioxide (TiO₂) nanocomposite synthesized via inverse miniemulsion polymerization and its effect on drilling fluid performance under HPHT conditions. Comprehensive characterization confirmed the successful grafting of polyacrylamide (PAM) onto TiO₂ nanoparticles (NPs) and demonstrated thermal stability up to 300 °C, uniform nanoscale dispersion, and moderate colloidal stability (ζ ≈ -10 millivolt (mV)). The TiO₂-PAM additive was incorporated into bentonite-based WBDF at concentrations ranging from 0.5 to 2.5 gram )g(per 350 milliliter (mL) of base drilling fluid. Under low-pressure low-temperature (LPLT) conditions, the modified fluids presented a 3-fold increase in yield point and a 30% reduction in fluid loss volume, whereas the filter-cake thickness decreased by two-thirds. Under HPHT testing at 120–160 °C and 500 pounds per square inch)psi(, the fluid loss volume was reduced by 20–27%, and the cake thickness was reduced by 30–42% compared with those of the unmodified drilling fluid. Rheological measurements revealed that the nanocomposite enhanced fluids retained pseudoplastic (shear-thinning) behavior, with plastic viscosity increasing from 9 to 30 centipoise (cP) and apparent viscosity from 29 to 119 cP at maximum additive loading. The gel strength profiles and slightly increases with increasing drilling fluid weight 8.3–8.7 pounds per gallon)ppg), underscoring the ability of the additive to improve the cuttings suspension without adversely affecting the drilling fluid density or pH. Rheological tests revealed that the Herschel–Bulkley model had the highest R² values (0.974–0.997) for all concentrations, outperforming the power law model (R² between 0.717 and 0.947) and the Bingham model (R² between 0.472 and 0.927). This model effectively captures yield stress and shear-thinning behavior, indicating that it describes fluid flow behavior more accurately. These findings demonstrate that the TiO₂-PAM nanocomposite offers a robust, readily implementable strategy to reinforce WBDFs against thermal degradation and fluid loss challenges.