Flow of power-law fluid in a partially blocked eccentric annulus

One of the most significant benefits of directional drilling is the increase in well productivity using multiple wells from a single vertical wellbore. During directional drilling, the drill pipe rests on the low-side of the annulus because of gravity. Moreover, cuttings beds form on the low-side of the annulus. Cuttings beds are undesirable because they increase hydraulic resistance of the annulus and consequently, the bottom hole pressure and Equivalent Circulating Density (ECD). Beside this, the annular flow becomes complicated. As a result, predicting relevant hydraulic characteristics of the annulus (friction pressure gradient and wall shear stresses acting on the bed and wellbore) becomes challenging due to lack of accurate hydraulic models that account for bed formation in eccentric annulus. In this study, a numerical simulation-based investigation has been performed in order to analyze the effect of cuttings bed formation on annular flow of power law fluid in a partially blocked eccentric (90%) annulus under laminar flow condition. The investigation is conducted using Computational Fluid Dynamics (CFD) software (ANSYS Fluent). The effects of fluid rheological properties (fluid behavior index and consistency index) and flow geometry (diameter ratio, and cuttings bed height) on velocity profile, frictional pressure loss and bed/wall shear stress are investigated. CFD simulation results are validated with available experimental measurements and they have shown reasonable agreement. Subsequently, the results are systematically analyzed using dimensionless hydraulic parameters (fRe and Pi(bed)) and geometric constants (a and b) to develop approximate models for frictional pressure loss and average bed shear stress. When compared with CFD simulation results, the new models have demonstrated better accuracy than the existing ones.