Upward Gas-Liquid Flow in Concentric and Eccentric Annular Spaces

A limited amount of work exists on upward gas-liquid flow in annular spaces. This is a common scenario in drilling operations, especially in underbalanced drilling, and in high-production wells. To carry out this study, a 40-meter high laboratory facility with an annulus flow loop composed of a 5-1/2 in. outer-pipe and a 2-3/8 in. inner-pipe was used, with tap water as the liquid phase and compressed-air as the gas phase.

This work?s objective was to phenomenologically characterize gas-liquid flow in annular space, investigate possible causes of unexpected periodic formation of liquid slugs in the annulus, assess potential effects of eccentricity of the inner pipe, extract empirical relationships between two-phase flow parameters (e.g. pressure drop, holdup, and Reynolds, Weber and Froude numbers) for both concentric and eccentric configurations, investigate production hysteresis effects on test results, and test ramp-up sequences to try to mimic possible subsequent accumulation of liquid in the annulus.

The findings from this work revealed that total pressure drops in concentric and eccentric cases are similar at high gas superficial velocities; however, trends suggest that an eccentric inner pipe causes higher pressure drops at low gas superficial velocities. This is probably due to observed local liquid accumulations around the couplings of the inner pipe when in eccentric configuration. The presence of couplings affects the stability of the Taylor bubble in seemingly slug flows. No liquid accumulation was seen in any of the hysteresis or ramp-up scenarios tested. In ramp-up tests, pressure gradient spikes at the beginning of each test were found to be strongly dependent on the ramp slope.

This work contributes to the understanding of gas-liquid flow phenomena observed in the field, both in wells and in risers, when localized liquid flow reversal and/or accumulation may lead to gas production impairments. This work also sheds some light on how to best operate wells and facilities, and particularly on how to manage production ramp-ups.