Water‐based drilling fluids formulated with mature fine tailings

Abstract Mature fine tailings (MFT) are persistent, highly stable colloidal suspensions generated as byproducts of bitumen extraction from oil sands. Given their environmental risks, identifying viable applications for MFT could reduce their accumulation while offsetting natural resource use. In this study, MFT was used to formulate water‐based drilling fluids, and the effects of xanthan gum (XG) and salinity were evaluated through filtration and rheological testing. The addition of 0.2 wt.% XG to 4 wt.% and 8 wt.% MFT‐based fluids reduced fluid loss by 82% and 70% under low‐temperature, low‐pressure conditions. In the presence of 4 wt.% NaCl, fluid loss increased slightly by 5% and 16%, while further addition of 1 wt.% CaCl 2 increased it to 26% and 23%. Under high‐temperature, high‐pressure conditions, 0.2 wt.% XG reduced fluid loss by 79% and 80%, respectively. XG increased apparent viscosity, yield point, and gel strength, indicating improved structural integrity and suspension capacity, whereas electrolytes, particularly CaCl 2 , reduced these properties. Compared to conventional bentonite‐based WBMs, MFT‐based systems showed comparable or improved filtration performance. Rheological analysis confirmed strong shear‐thinning behaviour, best described by the Herschel–Bulkley model.