Investigation of two-phase flow pattern, liquid holdup and pressure drop in viscous oil–gas flow

•Experimental investigation of two-phase pipe flow of dense gas and viscous oil.•Measurement of liquid holdup using narrow-beam and broad-beam gamma densitometers.•Detailed visual observations with the aid of high-speed video captures.•Comparisons of measured data to a model for stratified and slug flow. An experimental investigation was carried out on viscous oil–gas flow characteristics in a 69mm internal diameter pipe. Two-phase flow patterns were determined from holdup time-traces and videos of the flow field in a transparent section of the pipe, in which synthetic commercial oils (32 and 100cP) and sulfur hexafluoride gas (SF6) were fed at oil superficial velocities from 0.04 to 3m/s and gas superficial velocities from 0.0075 to 3m/s.