The Slug and Churn Turbulence Characteristics of Oil–Gas–Water Flows in a Vertical Small Pipe

The intention of the present study was to investigate the slug and churn turbulence characteristics of a vertical upward oil–gas–water three-phase flow. We firstly carried out a vertical upward oil–gas–water three-phase flow experiment in a 20-mm inner diameter (ID) pipe to measure the fluctuating signals of a rotating electric field conductance sensor under different flow patterns. Afterwards, typical flow patterns were identified with the aid of the texture structures in a cross recurrence plot. Recurrence quantitative analysis and multi-scale cross entropy (MSCE) algorithms were applied to investigate the turbulence characteristics of slug and churn flows with the varying flow parameters. The results suggest that with cross nonlinear analysis, the underlying dynamic characteristics in the evolution from slug to churn flow can be well understood. The present study provides a novel perspective for the analysis of the spatial–temporal evolution instability and complexity in oil–gas–water three-phase flow.