Optimizing drilling fluid rheology: The role of particle size distribution and advanced rheological modelling

This study presents the first integrated evaluation of how particle size distribution (PSD) of weighting materials affects both the rheological behaviour of water-based drilling fluids and the predictive accuracy of advanced rheological models. The originality lies in using complete mud formulations with multiple weighting materials, baryte, haematite, ilmenite, and Micromax, in both raw and milled forms, which enables a broader assessment than previously reported. Practically, the findings offer a pathway to optimize drilling fluid design for better viscosity control, improved wellbore stability, and reduced formation damage. Experimentally, reducing the D50 of baryte from 17.78 to 3.13 μm and haematite from 12.49 to 3.60 μm led to an approximate 50% increase in plastic viscosity and over 70% increase in yield point at a density of 16 ppg. Rheological models including Newtonian, Bingham Plastic, Power Law, Herschel–Bulkley, and Cross were applied, with Herschel–Bulkley and Cross models yielding R² values near 1.0 and RMSE as low as 0.23. Notably, finer particle sizes were better captured by advanced models, with Herschel–Bulkley and Cross outperforming simpler models, particularly at higher mud densities. These results demonstrate the critical role of PSD not only in fluid behaviour but also in selecting accurate rheological models for better prediction and formulation strategies. These results demonstrate the critical role of PSD not only in fluid behaviour but also in the selection of accurate rheological models for better prediction and formulation strategies.