Nonlinear dynamical analysis of large diameter vertical upward oil–gas–water three-phase flow pattern characteristics

Based on two kinds of signals measured from mini-conductance probe array and vertical multi-electrode array (VMEA) conductance sensor, we study oil–gas–water three-phase flow in a vertical upward 125 mm ID pipe. Using the ratio of oil flowrate to total liquid flowrate (fo) and the superficial gas velocity (Usg), we draw the six different flow pattern maps under four total mixture liquid flowrates. In addition, we indicate that: (a) the increase of fo makes oil in water type slug flow occur at lower Usg; (b) for large diameter pipe and low flow velocity, the phase inversion of liquids occurs at about fo=0.9 and the increase of Usg makes the phase inversion of liquids move to low fo. Furthermore, we investigate the nonlinear dynamical characteristics of five water continuous phase flow patterns in terms of chaotic attractor morphological description and complexity measures (Lempel–Ziv complexity and approximate entropy), and find that: (a) the chaotic attractor morphological characteristics can identify three-phase flow patterns; (b) the combination of Lempel–Ziv complexity and approximate entropy can serve as a unique classification criterion of three-phase flow patterns. In this regard, the nonlinear analysis of conductance fluctuating signals can give an effective indicator to understand and identify the oil–gas–water three-phase flow pattern characteristics.