Distribution law of Taylor bubble/liquid slug length in oil–gas–water slug flow and the measurement of gas/liquid flow rates based on thermal diffusion

Abstract

A novel online, non-separation, non-intrusive method based on thermal diffusion is proposed to measure the gas and liquid flow rates of oil–gas–water slug flow in this paper. Temperature fluctuations of a heated pipe wall induced by Taylor bubbles (TB) and liquid slugs (LS) are presented, and velocities and lengths of TB and LS are measured based on these temperature fluctuations. Meanwhile, the number of slug units required to calculate the average TB/LS length is analyzed, and the effect of gas/liquid superficial velocity, oil cut, and gas–liquid ratio on the TB/LS length distribution are respectively presented. The length ratio of TB and LS is found to be linearly and positively correlated with the gas–liquid ratio, which is independent of gas/liquid superficial velocities and oil cuts. Moreover, a simple and reliable model is built to directly associate the TB/LS velocity and length with the gas/liquid flow rates. Experimental results indicate that this proposed method is effective and accurate with root-mean-square errors of 0.025 and 0.052 m3/h for the calculated gas and liquid flow rates, respectively. The flow rate method based on thermal diffusion is simple, cheap, and radiation-free, and it provides a potential solution for the gas/liquid flow rate measurement of oil–gas–water three-phase flows.