Burnt coconut fibre as a sustainable additive for water-based drilling fluids: Rheological, filtration, and physicochemical evaluation

The development of sustainable drilling-fluid additives is essential for improving performance while reducing environmental impact. This study evaluates burnt coconut fibre (BCF) as a biodegradable bio-additive to enhance rheological properties, filtration control, and pH stability in water-based drilling fluids, in accordance with API standards. Five mud samples were formulated: a conventional NaOH-based control and four with BCF at concentrations of 29–114 g/L. Key properties, including density, plastic viscosity (PV), apparent viscosity (AV), yield point (YP), gel strength, pH, and fluid loss, were measured using standard API procedures. BCF physicochemical characteristics were analyzed via Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS). All measurements were performed in triplicate (n = 3), with statistical significance assessed using two-tailed Welch’s t-test (unequal variance; p < 0.01 for key improvements). Results showed statistically significant reductions in PV and AV across BCF-modified samples (p < 0.01), with PV decreasing from 31.5 cP (control) to 14.07–11.20 cP at 29–57 g/L BCF, accompanied by a strong YP of 22–24 lb/100 ft². Low-to-moderate concentrations (29–57 g/L) yielded the most favorable rheological profile, while higher loadings (86–114 g/L) caused excessive thinning. Gel strength developed progressively and remained stable, supporting effective solids suspension without excessive rigidity. Filtration tests revealed reduced early-stage filtrate invasion and thin, compact filter cakes at optimal concentrations. BCF moderated alkalinity, maintaining pH at favorable levels of ∼8.0. FTIR confirmed hydroxyl and carbonyl groups; SEM showed a porous, fibrous microstructure; and EDS indicated high carbon content (82.7 wt%) with trace alkali elements aiding pH modulation. These findings demonstrate that BCF is a cost-effective, bio-based additive that enhances drilling fluid performance at optimal concentrations.