Experimental analysis of synthetic oil-based mud enhanced with zinc oxide nanoparticles: Comparing rheological models

Rheological modeling is crucial for predicting the performance of drilling fluids under diverse operational conditions. While numerous studies have explored the influence of zinc oxide (ZnO) nanoparticles in water-based muds (WBMs), their effects on synthetic oil-based muds (SOBMs) remain largely unexplored. This study investigates the rheological behavior of ZnO-enhanced SOBM by comparing classical models Newtonian, Bingham Plastic (BP), Power Law (PL) with advanced models (Herschel–Bulkley (HB) and Extended Herschel–Bulkley (EHB). Experiments were performed at three volume fractions (vol %) of nanoparticle concentrations (0.072 vol %, 0.36 vol %, and 0.72 vol %) using both a standard rotational viscometer and the Advanced Taylor–Couette System Viscometer (ATCSV). Statistical evaluation with Coefficient of Determination (R 2 ) and Root Mean Square Error (RMSE) demonstrated that increasing ZnO loading significantly improves shear-thinning behavior, viscosity stability, and friction factor prediction, thereby enhancing SOBM performance under realistic drilling conditions. The EHB model achieved the highest predictive accuracy with R 2 values of 0.9998, 1.0000, and 0.9994 for 0.072 vol%, 0.36 vol%, and 0.72 vol% ZnO concentrations, respectively, with Root Mean Square Error (RMSE)values below 0.001. Apparent viscosity decreased by 9.2% (from 251 to 228 mPa·s) across the shear rate range of 19–382 s −1 , while friction factors reduced by 96% (from 27.76 to 1.15), demonstrating significant shear-thinning behavior enhanced by ZnO nanoparticles. Among all models, the EHB model consistently provided the most accurate predictions, capturing yield stress and non-linear shear-thinning effects across concentrations. To the best of our knowledge, this is the first systematic validation of ZnO-enhanced SOBM across multiple concentrations using ATCSV under wide range of shear rates, establishing a novel contribution beyond prior WBM-focused research. These findings deliver valuable insights for the development of high-performance, efficient, and environmentally responsible drilling fluids.