Experimental investigation of high viscous multiphase flow in horizontal pipelines

Abstract

Diminishing reserves of “conventional” light crude oil, increased production costs amidst increased world energy demand over the last decade has spurred industrial interest in the production of the significantly and more abundant “unconventional” heavy crude oil. Recent findings have shown that unconventional oil being a veritable energy source accounts for over two-thirds of the world total oil reserve. The exploration of this vast resource for easy production and transportation requires a good understanding of multiphase system for which the knowledge of the effect of fluid viscosity is of great importance. Heavy oils are known for their high liquid viscosities which make them even more difficult and expensive to produce and transport in pipelines at ambient temperatures. In the light of this, it has become imperative to investigate the rheology of high viscosity oils and ways of enhancing its production and transportation since a critical understanding of multiphase flow characteristics are vital to aid engineering design. It is clear from experimental investigation reported so far in literatures and in Cranfield University that the behaviour of high viscosity oil-gas flows differs significantly from that of low viscosity oils. This means that most of the existing prediction models in the literature which were developed from observations of low viscosity liquid-gas flow will not perform accurately when compared to oil-gas flow data for high viscosity oil. Therefore, this research work seek to extend databank and provide a clearer understanding of the physics of high viscous multiphase flows. Experimental investigation have been conducted using 3-inch and 1-inch ID horizontal test facilities for oil-gas and oil-water respectively using different oil viscosities. The effects of liquid viscosities on oil-gas two phase flow parameters (i.e. pressure gradient, mean liquid holdup, slug frequency, slug translational velocity and slug body length) have been discussed. Assessment of existing prediction models and correlations in the literature are also carried out and their performance highlighted. New/improved prediction correlations for high viscosity oil-gas flow slug frequency, slug translational velocity and slug body have been proposed with their performance evaluated against the results obtained for this study and in literature. As for high viscosity oil-water flows, a new flow pattern maps have been established for high viscous oil-water two-phase flow in horizontal pipe with ID = 0.0254 m for which four flow patterns were observed namely; rivulet, core annular, plug and dispersed flows were observed. Generally, it was observed that increase in oil viscosity favoured the Core Annular Flow pattern, similar behaviour was also observed for increased oil holdup. Comparatively analysis of results obtained here with low viscous kerosene and water flow study obtained under similar flow geometry and conditions shows significant difference in flow patterns under similar flow conditions.