Optimization design of bentonite mud mixing ratio for horizontal directional drilling in silt layers

Abstract Long-distance horizontal directional drilling through silt layers is prone to shrinkage and pipe-holding accidents, which are highly correlated with the bentonite slurry ratios used in the field. To address the aforementioned issues, this paper investigates the optimal mixing ratio for bentonite mud in silt layers through indoor single-factor optimization experiments and response surface experiments. Based on a horizontal directional drilling project for road cable installation in Zhongshan City, Guangdong Province, China, disintegration tests on silt layer soil sample and field application methods were conducted to validate the effectiveness of the optimal mixing ratio. Research indicates that adding 5% hematite powder, 3%–5% sodium carboxymethyl cellulose, 8%–10% graphite powder, and 16%–18% lignite resin can produce bentonite mud with high density, high lubricity, high suspension capacity, and low fluid loss, suitable for silt layers. The final optimized formulation for the bentonite slurry is determined as follows: 5% sodium bentonite, 5% hematite powder, and 0.25% soda ash as the base slurry + 4.5% CMC + 8.8% GP + 17.2% SPNH. Compared with two commercially available solutions, the optimal mixture ratio used in this trial prevented the disintegration of the silt layer soil samples and ensured the overall stability of the silt layer. Following on-site construction, the pipe pullback operation was successfully completed, providing a reference for horizontal directional drilling projects in similar silt layers along China’s southern coastal regions.