Summary
Oil/water flow is a common occurrence during production and transportation
of petroleum fluids through pipes. Understanding of oil/water pipe flow
behaviors is crucial to many applications including design and operation of
flow lines and wells, separation, and interpretation of production logs. In
this study, the oil/water pipe flow was experimentally investigated for
different inclination angles (0°, ±1°, ±2° and –5°). A total of 324 tests were
conducted in a 0.0508-m (2-in.) ID 21.1-m (69.6-ft) long test section using tap
water and mineral oil with superficial velocities ranging from 0.025 to 1.75
m/s. The experimental results include observations of flow patterns and phase
distributions, and measurements of water holdups and pressure gradients. A
high-speed video system was used to observe the mixing status between oil and
water and to determine the flow patterns at various flow conditions. Quick
closing valves were used to measure the phase holdups and to demonstrate the
slippage between oil and water with the water cut to water holdup ratio. The
experimental results of flow pattern transitions, water holdups, and pressure
gradients are compared against predictions of the Zhang and Sarica (2006)
model. The model performance is analyzed based on the experimental observations
and the modeling considerations. Recommendations are presented for future model
improvement.
Introduction
Two-phase liquid/liquid pipe flow is defined as the simultaneous flow of two
immiscible liquids in pipes. Oil/water flow in pipes is a common occurrence in
petroleum production, especially for old oil field and for enhanced oil
recovery (EOR) with water injection (cold or hot). Moreover, two-phase
liquid/liquid flow is common in the process and petrochemical industries.
Although the accurate prediction of oil/water flow is essential, oil/water flow
in pipes has not been explored as much as gas/liquid flow. Models developed for
gas/liquid systems cannot be readily used in liquid/liquid ones due to
significant differences between them. The oil/water systems usually have large
difference in viscosities, similar densities, and more complex interfacial
chemistry compared to gas/liquid systems.
During the simultaneous flow of oil and water, a number of flow patterns can
appear ranging from fully separated (or stratified) to fully dispersed ones
(Lovick and Angeli 2004). Stratified flow has received more attention during
the past decades because of its low phase velocities and well defined
interface. On the other hand, fully dispersed flow can be modeled as a
single-phase flow provided that the dispersion effective viscosity is properly
estimated. There is limited information on the intermediate flow patterns,
which lie in between stratified and fully dispersed flows. In this study, the
gradual flow pattern transitions from stratified flow to dispersed flow are
observed and characterized. The water holdups and pressure gradients are
measured and analyzed.
A simple two-fluid oil/water pipe flow model was proposed by Zhang and
Sarica (2006) as part of a three-phase unified model. Flat interface was
assumed for the stratified oil/water flow. The transition from stratified flow
to dispersed flow is based on the balance between the turbulent energy of the
continuous phase and the surface free energy of the dispersed phase. The
inversion point and effective viscosity of the dispersion are estimated using
the Brinkman model (1952). The model predictions of the flow pattern
transition, water holdup and pressure gradient are compared with the present
experimental results. The model performance under different flow conditions is
analyzed and further improvements are recommended.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
23 June 2008
- Meeting paper published:
21 September 2008
- Revised manuscript received:
19 November 2008
- Manuscript approved:
6 December 2008
- Published online:
1 June 2009
- Version of record:
1 June 2009
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