Summary
A unified model is proposed for the prediction of flow behavior during
production and transportation of gas, oil, and water through wellbores and
pipelines. In gas/oil/water three-phase-pipe flow, the phase distributions
and hydrodynamics are described on the basis of two criteria: gas/liquid flow
pattern and oil/water mixing status. The three-phase flow is treated as
gas/liquid two-phase flow if the two liquids are fully mixed or as a
three-layer stratified flow at low flow rates in horizontal or slightly
inclined pipes. Most three-phase flows fall between these two extremes:
partially mixed with slippage between the two liquid phases. Closure
relationships describing the distribution between the liquid phases, namely
mixing and inversion, are proposed. The model predictions are compared
with experimental data of gas/oil/water pipe flows. Significant improvements
are observed over the predictions by the two-phase unified model of Zhang et
al. (2003a), which assumes a fully mixed liquid phase.
Introduction
Three-phase gas/oil/water flow is a common occurrence in the petroleum
industry during the production and transportation of produced fluids.
Three-phase flow behavior, such as liquid holdups and pressure gradient, may be
very different from those of two-phase flow. These can have significant
impact on design and many flow-assurance issues including hydrate formation,
emulsion, wax deposition, and corrosion. Therefore, a reliable and general
model needs to be developed for prediction of gas/oil/water-pipe flow behaviors
under different flow conditions.
Experimental observations have shown that the flow structures of
three-phase-pipe flow are much more complicated than that of two-phase-pipe
flow. Açikgöz et al. (1992) classified flow patterns of horizontal
three-phase flow into 10 categories. Pan et al. (1995) identified seven
flow patterns for horizontal air/oil/water flow. For vertical
air/oil/water flow, Woods et al. (1998) identified eight flow
patterns. Multiphase-flow hydrodynamic modeling is based on flow-pattern
definitions. More flow patterns imply more discontinuities and greater
complexity in the hydrodynamic models. A successful model should unify
the predictions of both flow-pattern transitions and hydrodynamic behavior and
minimize these discontinuities at the same time.
A unified gas/liquid two-phase flow model has been developed by Zhang et al.
(2003a) for predictions of flow-pattern transitions, pressure gradient, liquid
holdup, and slug characteristics for all inclination angles from –90° to 90°
from horizontal. The model is based on the dynamics of slug flow, which
shares transition boundaries with all the other flow patterns. The
equations of slug flow are used, not only to calculate the slug
characteristics, but also to predict transitions from slug flow to other flow
patterns.
Similar methodology also can be used for gas/oil/water three-phase
flow. In three-phase pipe flow, the gas-vs.-liquid-phase distribution and
structures may be of primary importance compared with the distribution between
liquid phases because of the differences among the physical properties of the
three phases. Therefore, gas/liquid two-phase flow patterns may be adapted
to describe gas/oil/water three-phase flow, and additional closure
relationships could be used to describe the distribution between the liquid
phases, namely mixing and inversion.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
24 October 2005
- Revised manuscript received:
30 January 2006
- Manuscript approved:
3 February 2006
- Version of record:
20 June 2006
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