Laminar and Turbulent Friction Factors for Annular Flow of Drag-Reducing Polymer Solutions in Coiled-Tubing Operations

Abstract

Summary The challenge of theoretical and numerical studies of annular fluid flow with varying eccentricity is mainly a result of the required coordinate systems. Computational-fluid-dynamics (CFD) modeling provides the state-of-the-art approach of investigating fluid flow in such complex geometries. In this study, results from a series of numerical simulations for the fully developed laminar flow of non-Newtonian power-law fluids in concentric and eccentric annular geometries are used to investigate the effect of eccentricity, flow-behavior index, and diameter ratio (ratio of the outer diameter of the inner tubing to the inner diameter of the outer tubing) on axial frictional pressure losses. The frictional pressure-loss gradients predicted by the CFD simulations were verified by comparing with the published studies and flow data from a field-scale experimental setup. At a constant flow rate, it is confirmed that frictional pressure losses decrease with increasing eccentricity. A good agreement was obtained with the Haciislamoglu and Langlinais (1990) correlation, and the results of this study, especially at low values of eccentricity. At very high eccentricities, data from the CFD model yield lower frictional pressure loss compared to Haciislamoglu and Langlinais (1990) correlation. This type of expression is obtained and the improved data of this study is incorporated. Next, this paper presents the results of an experimental study carried out to investigate frictional pressure-loss behavior of drag- reducing polymer solutions, flowing turbulently through an eccentric annulus. The experimental setup includes 30 ft of 3½×2⅜-in., 200 ft of 3½×1¾-in., 69 ft of 5½ × 4-in., and 79 ft of 5 ×3½-in. fully eccentric annuli. Data analysis enabled the development of a new correlation using fluid apparent viscosity at 511 sec–1, generalized Reynolds number, and diameter ratio, all of which can be easily determined in the field as independent variables. These new correlations for laminar and turbulent flow of drag-reducing polymer solutions present an improvement to existing correlations, and also permit undemanding hydraulic-program calculations for varying annular configurations.