Optimization of Wellbore Annulus Cleaning Tool Based on CFD-DEM and Box-Behnken Design

During the oil and gas drilling process, inefficient cuttings transport may elevate cuttings concentration, leading to higher Equivalent Circulating Density (ECD) and easily triggering a series of wellbore stability issues. In this paper, a new type of annulus cleaning tool is developed, incorporating the H- B non-Newtonian fluid model and a coupled CFD-DEM to construct a numerical model for analyzing the cuttings transport behavior within the multi-layer wellbore annulus using the cleaning tool. The model, validated against experiments, reveals factors affecting Cuttings Transport Ratio (CTR). Through Box- Behnken Design (BBD), Response Surface Methodology (RSM), and Analysis of Variance (ANOVA), a correlation function for CTR is derived to optimize the cleaning tool parameters. Findings show an initial increase then decrease in CTR with nozzle quantity, diameter, and angle. Decreasing hydraulic diameter enhances CTR, whereas nozzle diameter variation has minimal impact at smaller diameters. After optimization, CTR reaches 95.76% with 4 nozzles of 10mm diameter, 32° angle, and 57mm hydraulic diameter. These results guide cleaning tool optimization design , improving cuttings transport efficiency, and ensuring safe oil and gas production.