Threshold velocity of non-Newtonian fluids to initiate solids bed erosion in horizontal conduits

Abstract

Predicting the minimum velocity of non-Newtonian fluids required to erode a solids bed is an important task for guaranteeing efficient solids transport process. This paper describes a combined theoretical and experimental investigation of the threshold condition of non-Newtonian fluids, including water, water-based mud (WBM) and oil-based mud (OBM), to initiate erosion of a solids bed. Drilling fluids with different base fluids have different threshold velocities, depending on the adhesion effect generated by the presence of stagnant fluids in a solids bed. Therefore, a new semi-mechanistic model of erosion criterion is proposed. In the model, a resistive force is introduced to handle the adhesion effect produced from different fluids, and it is quantified through an empirical correlation developed from the results of drain tests. A torque balance for driving and opposing forces is then constructed and solve numerically at the contact point of a superimposed particle for the determination of the threshold velocity. Model's predictions agree with experimental data obtained from bed erosion experiments with the use of WBM and OBM having similar rheological properties.