Fluid-dynamic behavior of flow in partially obstructed concentric and eccentric annuli with orbital motion

Abstract

In directional drilling, the annulus is often eccentric and the eccentricity may vary along the well, due to the column weight and drilling conditions oscillations. Furthermore, by the gravitational effect, there will be a strong tendency for accumulation of solids at the lower part of the annulus, forming a settled cuttings bed that partially obstructs the flow, which may hinder or even stop the drilling process. It is important to study the flow patterns for these conditions, which have not been greatly discussed in the literature. The aim of this work is to evaluate experimentally and through numerical simulations, the laminar and isothermal helical flow of non-Newtonian fluids into horizontal annular sections with partial obstruction, and to analyze the effect of the orbital motion of the inner tube for the eccentric annulus. A pilot unit at the laboratory scale was used for the acquisition of data regarding hydrodynamic losses at atmospheric conditions (pressure and temperature) considering the system geometry (eccentricity), mass flow rate, fluid rheology (Xanthan Gum concentration) and rotation of the inner cylinder. Techniques of computational fluid dynamics (CFD) were also applied to obtain detailed information about the flow field, simulated in fully developed flow conditions.