Numerical Study of Bottom Water Draw-Off of Stratified Oil-Water Pipe Flow Department of Mechanical and Industrial Engineering College of Engineering Sultan.

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

Flow

Department of Mechanical and Industrial Engineering

College of EngineeringSultan Qaboos University, Oman

Yousef ZurigatBssam JubranLyes KhezzarSalam Al-Far

Plan

Introduction & Objectives Oil-water Transport & dehydration

issuesSimulation ModelResultsConclusions

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?

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.

Draw-off pipeBottom-Water

Oil in WaterEmulsion

Interface

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-dispersion interface be avoided?

If several draw-off points are used, how will the interface and flow regimes in between draw points be affected?

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.

Flow Regimes of Oil-Water Mixtures

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

Stratified Flow

Stratified Flow with Mixing at the interface

Dispersion of oil in water and waterlayer

Oil in water Emulsion

Geometry and Flow Parameters

Main pipe Diameter = 0.68 mDraw-Off Pipe Diameter = 0.240 mOil-flow rate = 8049 m3/dayWater flow rate = 43614 m3/dayInterface Location 25 cm from bottom

of main pipe.Simulation conducted with one and

two draw-off pipes

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- cut=85%, water superficial velocity=1.3 m/s)! 2. Two-Fluid Flow Modeling: Actual Flow

Mathematical Model

SINGLE-PHASE FLOW MODELSteady, Single-phase, incompressible

and turbulent flow.Pressure drop approaches that of single

phase flowFlow dynamics very similar to single

phase flowFull three-D simulation

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.

Cut-off flow rates with water quality <2000 ppm from two tappings

3000

5000

7000

9000

11000

7000 9000 11000

First Tapping Draw-Off (m3/d)

Se

co

nd

Ta

pp

ing

Dra

w-O

ff (

m3

/d)

o/w 20000ppm

o/w 40000ppm

o/w uniform

Two-Fluid ModelingIn 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.

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.

iiiiiiiiiiii SRRVR

dt

Rd,,

)(

Phase equations (Cont.)

t timeRi volume fraction of phase i

i density of phase i

i any conserved property of phase i

iV

velocity vector of phase ii exchange coefficient of the entity in phase i

Si source rate of i

Results

Results (Cont.)

Results (Cont.)

Pipe 1 Pipe 2

Results (Cont.)

0.00E+00

1.00E-01

2.00E-01

3.00E-01

4.00E-01

5.00E-01

6.00E-01

7.00E-01

8.00E-01

9.00E-01

1.00E+00

0 0.2 0.4 0.6 0.8 1

h/D

R2

x=1.9, KEP

x=1.9, Level Model

x=1.9, Model KL

x=1.9, KECHEN

Results (Cont.)

0.00E+00

1.00E-03

2.00E-03

3.00E-03

4.00E-03

5.00E-03

6.00E-03

7.00E-03

8.00E-03

9.00E-03

0 2000 4000 6000 8000 10000 12000

Flow Rate From The First Draw-off pipe (m^3/day)

R2

Q2

Results (Cont.)

R2 distributions along the main pipe, KEP, BD1=7000, BD2=3000

0.000E+00

1.000E-01

2.000E-01

3.000E-01

4.000E-01

5.000E-01

6.000E-01

7.000E-01

8.000E-01

9.000E-01

1.000E+00

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

h/D

R2

x=1.9

x=4.5

x=6.9

x=9

15% oil

Results (Cont.)

R2 at x=8.74 for 2nd BWDO pipe with 1st pipe colsed

0.00E+00

1.00E-01

2.00E-01

3.00E-01

4.00E-01

5.00E-01

6.00E-01

7.00E-01

0.00E+00 1.00E-01 2.00E-01 3.00E-01 4.00E-01 5.00E-01 6.00E-01 7.00E-01 8.00E-01 9.00E-01 1.00E+00

h/D

R2

R2 @ 3000 m 3̂/dayR2 @4000R2 @5000R2 @6000R2 @7000R2 @8000R2 @9000R2 @10000

Results (Cont.)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

2000 3000 4000 5000 6000 7000 8000 9000 10000 11000

BWDO

h/D

h/D at 1200ppm for 95% water cut

h/D at 1200ppm for 85% water cut

Acknowledgements

PDO’s FUNDING OF THIS WORK IS GRATEFULLY ACKNOWLEDGED