Acid-modified potato starch as a high-temperature additive in water-based drilling mud

The growing demand for high-temperature (HT), sustainable, cost-effective, and high-performance drilling mud additives has driven research into bio-based natural polymer modifications for water-based drilling mud (WBDM) applications. Starch, an abundant and biodegradable polysaccharide, offers considerable potential as a fluid-loss additive and viscosity modifier in WBDMs. However, native starch degrades above 121 °C and exhibits sensitivity to saline contamination, restricting its use in high-temperature, high-pressure, and high-salinity drilling environments. Acid modification of potato starch via hydrolysis with hydrochloric acid was characterized using FTIR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. This study systematically examines the synthesis and characterization of acid-modified potato starch (AMPS) and assesses its rheological and filtration performance as an additive in bentonite-based WBDMs at 180 °C. Drilling mud formulations with varying AMPS concentrations (0.5–3.0 wt%) maintained plastic viscosity with a 15% reduction relative to base mud, yield points above 20 lb/100 ft², and a 30% reduction in high-temperature, high-pressure fluid loss compared to native starch muds, as well as a 10% reduction in gel strength, API fluid loss, and HPHT filtration at 180 °C and 200 psi. The results indicate that AMPS at an optimized concentration of 2.0 wt% significantly reduces API fluid loss and imparts enhanced shear-thinning (pseudoplastic) behavior compared to native starch. The Herschel–Bulkley model most accurately describes the mud flow behavior across all tested formulations. The mechanistic basis of AMPS performance is analyzed in terms of pore-bridging, filter cake formation, and clay surface interaction. Comparison with commercial starch products and relevant literature benchmarks demonstrates the competitiveness of AMPS as a green and sustainable WBDM additive.