Multiple holdup equilibria and hydraulic gradients in stratified gas–liquid flows

Experimental ramp-up tests for a two-phase flow with very low liquid loading have been conducted for 2°, 3° and 2° + 3° straight pipe configurations. The liquid draining process resulting from the ramp-up operation is explained by multiple holdup equilibria. For the conditions of the experiments, the multiple holdup equilibria region extends down to a gas oil volume flow rate ratio of about 1000. The flow of a pipe segment operating in the multiple holdup equilibria region will obtain the low holdup equilibrium if the holdup at the end of the pipe is sufficiently low. Otherwise, the flow of the pipe segment will obtain the high holdup equilibrium. Liquid accumulation can be minimized by avoiding steep inclination angles at the culmination of uphill sections in low liquid loading gas condensate systems. Ensuring low holdup equilibria throughout the pipeline, where multiple equilibria exist, minimizes liquid accumulation and reduces minimum flow rate limits during operating conditions.