Film Thickness Distribution for Annular Flow in Directional Wells: Horizontal to Vertical

Abstract

An experimental and theoretical investigation has been carried out on two-phase annular flow in inclined pipes. The study focused on the effect of the inclination angle on the liquid film thickness distribution. A conductance multi-probe instrument was utilized to measure the local liquid film thickness around half of the pipe periphery for inclination angles of 90, 75, 60, and 45 from the horizontal. A simple analytical model has been developed for the prediction of the liquid film thickness at the top and bottom of the pipe. The model is applicable for the entire range of inclination angles, from horizontal to vertical. Good agreement is observed between the prediction of the model and the experimental data collected in this study and from the literature. Introduction Annular flow is one of the most common flow patterns encountered in natural gas wellbores and pipelines. It occurs under conditions of high gas flow rates and low to medium liquid flow rates. The liquid flows as a film around the pipe wall, surrounding a high velocity core, which may contain entrained liquid droplets. The interface between the gas core and the liquid film is very wavy, and atomization and deposition of liquid droplets occur through this interface. Most of the experimental and theoretical studies on annular flow have been carried out either for vertical or for horizontal conditions. Changes in the physical phenomena occur as the inclination angle varies from vertical through off-vertical to horizontal flow conditions. Under vertical flow conditions, the liquid film distribution is uniform around the pipe periphery. As the pipe is inclined from the vertical to off-vertical, the film thickness distribution is no longer uniform. Due to gravity, the liquid phase tends to accumulate at the bottom part of the pipe. This results in a thicker film at the bottom and a thinner film at the top. P. 257^