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.