Investigating the Rheological and Filtration Behavior of Acetylated Yam and Plantain Peel Starches in Water-Based Mud Systems

Water-based drilling fluid systems are gaining popularity for their environmental friendliness and low cost. These fluids are highly sensitive to products used to modify fluid properties and control fluid loss. Traditional additives like carboxymethyl cellulose (CMC) work well but come with environmental issues and high costs and alternatives from agricultural sources are being sought. The potential of using acetylated yam peel starch (AYPS) and acetylated plantain peel starch (APPS) as substitutes for CMC in water-based drilling mud formulation under ambient and simulated downhole conditions of 27 °C and 150 °C, respectively, was investigated. The peels of yams and plantain, starchy foods, were chemically modified through acetylation and added to the drilling mud formulation at proportions of 0.2–1.0 g. FTIR confirmed the success of the modification by the presence of characteristic bands of carbonyl (C=O) absorption at 1730–1750 cm−1 and by the increase in C–O bands after the modification, which means that acetyl groups were successfully incorporated. The highest mud density recorded was 9.16 kg/m3 (ppg) with 1.0 g of additives, and the pH values ranged from 8.10 to 9.50, which is good for drilling operations. The plastic viscosity was found to be 4–7 cP at 27 °C and 3–6 cP at 150 °C for AYPS and APPS, respectively, which were lower than the CMC value but still retained viscosity at high temperature. The yield point values for the samples were 2–5 lb/100 ft2 at 27 °C and 1–6 lb/100 ft2 at 150 °C, which were slightly better for AYPS. Thermal aging did not significantly affect gel strength, which increased upon exposure to high-temperature conditions, especially at high additive concentrations, indicating that the rheological properties were preserved. Filtrate losses were 12–16.8 mL for AYPS and 12.5–17.2 mL for APPS under low-pressure, low-temperature conditions, which are similar to CMC (11–16 mL). APPS was the most effective filtrate-loss control of the modified starch systems under the HPHT conditions. Rheological modeling showed that shear-thinning behavior is predominant, and the Herschel–Bulkley and Casson models provided the best fits. In general, the acetylated yam and plantain peel starches have shown promising properties as alternatives for CMC for enhancing rheological properties and controlling fluid loss in water-based drilling fluids.