Regulation and Stabilization of Rheological Parameters in Bentonite-Based Drilling Fluids with Ground Mandarin Peel Waste

This study evaluates ground mandarin peel (MP) as a low-cost modifier for sodium-bentonite water-based drilling fluids. Formulations with 2% (w/w) MP and 1–4% bentonite were prepared to locate the composition break point using segmented regression with the Davies test; the threshold was 2.5% bentonite (B/MP ≈ 1.25). Below this level, yield stress drops sharply, and American Petroleum Institute (API) fluid loss increases nonlinearly. Two 3% bentonite muds were then compared: a polymer-stabilized reference (0.3% xanthan gum (XCD), 1% low-viscosity carboxymethyl cellulose (CMC LV), 1% modified starch) and the same package plus 2% MP. Twelve-speed rheometry and API tests showed that adding MP left plastic viscosity essentially unchanged, increased yield stress to ~3.4 Pa, reduced API fluid loss from 9 to 5.5 mL per 30 min, and thinned the filter cake from 0.30 to 0.10 mm. Because MP is a zero-price waste stream, material cost remained essentially unchanged while performance improved. These results support a practical dosing window for MP and a polymer adjustment pathway; high temperature and high-salinity stability require further verification.