Numerical Study of Bottom Water Draw-Off of Stratified Oil-Water Pipe Flow

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Numerical Study of Bottom Water Draw-Off of
Stratified Oil-Water Pipe Flow
Yousef Zurigat Bssam Jubran Lyes Khezzar Salam
Al-Far

• Department of Mechanical and Industrial
  Engineering
• College of Engineering
• Sultan Qaboos University, Oman

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Plan

• Introduction Objectives
• Oil-water Transport dehydration issues
• Simulation Model
• Results
• Conclusions

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Water issues in Oil-Production

• Well life extension results in increased water
  Production (98)
• Need to separate water from oil (dehydration
  facilities cost money)
• Pre-separation may take place in transport
  pipelines
• Can we take advantage of it?

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Concept of Bottom Water Draw Off

• Depending upon prevailing conditions a water
  layer may form at the bottom of the pipe.
• It can then be selectively removed.

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Design Challenge of BWDO Concept

• What is the maximum water flow rate that can be
  drawn off (With Acceptable quality)?
• How can disturbance of the water/oil-in-water-disp
  ersion interface be avoided?
• If several draw-off points are used, how will the
  interface and flow regimes in between draw points
  be affected?

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Objectives

• For a single draw-off pipe, investigate the
  variation of oil concentration in the draw-off
  pipe as a function of draw-off flow rate and
  interface position.(Interface location not known
  a priori!!)
• Investigate the maximum possible water flow
  rates with acceptable quality (oil concentration)
  for two consecutive draw-off pipes.

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Flow Regimes of Oil-Water Mixtures

• Depending upon the oil superficial velocity
  several regimes are possible for horizontal water
  dominated flows

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Geometry and Flow Parameters

• Main pipe Diameter 0.68 m
• Draw-Off Pipe Diameter 0.240 m
• Oil-flow rate 8049 m3/day
• Water flow rate 43614 m3/day
• Interface Location 25 cm from bottom of main
  pipe.
• Simulation conducted with one and two draw-off
  pipes

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Modelling challenges

• Flow is complex and two-phase (dispersions
  present)
• Two Approaches
• 1. Single-Phase Flow Modeling If negligible
• slip between the phases and hold-up take
• place--?In the present regime!! (water-
• cut85, water superficial velocity1.3
  
• m/s)!
• 2. Two-Fluid Flow Modeling Actual Flow

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Mathematical Model

• SINGLE-PHASE FLOW MODEL
• Steady, Single-phase, incompressible and
  turbulent flow.
• Pressure drop approaches that of single phase
  flow
• Flow dynamics very similar to single phase flow
• Full three-D simulation

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Quantitative analysis of draw-off water
quality-Single Phase Flow Model

• Initial oil concentrations in the pipe regions
  above and below the interface are based on
  experimental data. The concentration of oil in
  free water assumed equal to 600 ppm in accordance
  with field data.
• The amounts of oil in the areas above- and
  below-the-interface streams which make up the
  draw-off flow are calculated based on the flow
  rates and the concentrations calculated in the
  first step above.

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Cut-off flow rates with water quality lt2000 ppm
from two tappings
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Two-Fluid Modeling

• In the PHOENICS, the concept of thermo- dynamic
  phase is used, i.e., the water and oil are
  treated as two different phases in the mixture.
  These two phases are in motion relative to each
  other due to the buoyancy effect, which leads to
  inter-phase momentum transfer.
• The Inter-Phase Slip Algorithm (IPSA) is adopted
  to predict the phenomenon in this work.

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Phase equations

• Each phase is regarded as having its own distinct
  velocity components.
• Phase velocities are linked by interphase
  momentum transfer - droplet drag, film surface
  friction etc.
• Each phase may have its own temperature,
  enthalpy, and mass fraction of chemical species.
• Phase concentrations are linked by interphase
  mass transfer.

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Phase equations (Cont.)
t time Ri volume fraction of phase i ri density
of phase i fi any conserved property of phase i
velocity vector of phase i Gf,i exchange
coefficient of the entity f in phase
i Sf,i source rate of fi
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Results
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Results (Cont.)
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Results (Cont.)
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Results (Cont.)

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Results (Cont.)

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Results (Cont.)
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Results (Cont.)

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Results (Cont.)

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AcknowledgementsPDOs FUNDING OF THIS WORK IS
GRATEFULLY ACKNOWLEDGED