1. Multiphase pipe flow – a key technology for oil and gas production

2. Pipe Flow: Some considerations related to single and multiphase flow

3. Calculation of flow in pipes
out in
Conservation of
Energy
Mass
Momentum
Thermodynamics

4. Mass conservation out in
Single-phase : Mass in - mass out = accumulated mass
Multiphase: Mass transfer comes in addition, e.g. for condensate:
Mass in - mass out + local condensation = accumulated mass
Steady state single-phase flow:
G = (density) * (pipe area) * (mean velocity)
= ρUA = constant along a pipeline

5. Momentum balance – single-phase:PR PL
Friction
Pressure gradient large enough for flow: Velocity depends on friction
Stasjonær tilstand
Friction = Friction force per area * wall area
Veggskjærspenning

6. Multiphase Pipe Flow Depends on:
Fluid properties Pipe geometry Environment
Density Diameter T, external
Viscosity Wall roughness Insulation
Phase fractions Pipeline profile/ T at inlet
Conductivity topography P at inlet
Heat capacity P at outlet
Surface tension
Etc...
Varies with P and T !
P=pressure, T=temperature

7. Oil samples - large differences in fluid properties
Crude oils
Njord
Visund
Grane
Statfjord C
Condensates
Sleipner
Midgard
Midgard

8. Multiphase flow Three-phase flow (here):
Simultaneous flow of oil-gas-water in the same pipeline
Flow regimes:
Describes (intuitively) how the phases are
distributed in the pipe cross section and along the pipeline
Superficial velocity:
The velocity a phase will have if it were the only fluid present

9. Flow regimes steeply inclined pipes
Bubbly flow:
Little gas, large Uoil
(All inclinations)
”Churn”-flow:
More gas, large Uoil
(steep inclinations)
Annular flow:
High Ugas, low Uoil
(wide range of incl.)

10. Stratified/wavy- near horizontal pipeline
Stratified flow. Ugas normally >> Uoil
Large waves: More effective liquid transport

11. Hydrodynamic slugging
Taylor-bubble
Liquid slug
Large waves that eventually block the pipe cross section  pressure build up
Intermittent flow – liquid slugs divided by gas pockets
Effective liquid transport
Void in slug: Volume fraction of entrained gas bubbles in the slug
Slug front in three-phase flow

12. Need for experimental data
MP-flows are complex due to the simultaneous presence of different phases and, usually, different compounds in the same stream.
The combination of empirical observations and numerical modelling has proved to enhance the understanding of multiphase flow
Models to represent flows in pipes were traditionally based on empirical correlations for holdup and pressure gradient. This implied problems with extrapolation outside the range of the data
Today, simulators are based on the multi-fluid models, where averaged and separate continuity and momentum equations are established for the individual phases
For these models, closure relations are required for
e.g. interface and pipe-wall friction, dispersion mechanisms, turbulence, slug propagation velocities and many more
These can only be established with access to detailed, multidimensional, data from relevant and well-controlled flows

13. Conclusion: we need models based on physics to extrapolate beyond lab data
Lab correlation
Lab
Field

14. Dimensionless numbers – dynamic similarity:4
             
Dimensionless numbers – dynamic similarity
Laminar vs turbulent flow
Wave propagation, outlet effects, obstructions
Formation of droplets and bubbles.
Reynolds number, ratio of the inertial forces to the viscous forces,
Re= =rvL/m
Froude number, ratio of a body's inertia to gravitational forces or ratio of a characteristic velocity to a gravitational wave velocity
Weber number, relative importance of the fluid's inertia compared to its surface tensions:

15. Conditions in pipeline
Hydrodynamic forces proportional to rU2
1 m/s
ρ = 1 kg/m3
P = 100 bar
1 m/s
Corresponds to 10 m/s

16. Conditions in pipeline
Gas – liquid interaction: governed by Dρ*DU2
Wind = 3 m/s
Light breeze
P = 100 bar
ρ = 600 kg/s
Ug = 3 m/s
Corresponds to more than 30 m/s, i.e. Full Storm
Typical gas-condensate pipe: Gas velocity of 6 – 7 m/s, corresponding to twice Hurricane force winds

17. Conditions in pipeline – Drops and bubbles
Hydrocarbon systems can have very low surface tension, in particular gas-condensate systems. Encourages generation of smaller drops and bubbles.
Typical values: Air – water: 0.07 N/m vs. Gas – condensate: < N/m
60 mm/h
3 – 6 m/s
Drop/bubble sizes
Capillary waves
P = 100 bar
3 – 6 m/s
mm/h
measured in lab
Liquid layer can be significantly aerated (40% - 70%)

18. Test facilities for study of multiphase flow behaviour

19. Open and closed loops
Open loops with air as the gas phase – atmospheric pressure
Simple to build, relatively low cost
Few safety barriers
Liquid phase e.g. water, vegetable oil
Common at universities
Closed, pressurised flow loops
More complex design, higher costs
More realistic gas-liquid density ratio
Crude oils possible (unstable, EX)
Safety barriers against pressure burst and explosion
MEK 4450 Multiphase Flow - IFE Oct. 22, 2013

20. Design considerations
Main goal for a test loop:
Establish well controlled and relevant multiphase flows
Common requirements:
Length/diameter ratio , L>300 D – flow develops along the pipe
Large diameter – diameter scaling difficult
Easily changeable pipe inclination
High gas density to give relevant gas-liquid density ratio
Large span in flow rates
Cost-benefit:
Pressure vs gas density; pressure drives costs
Flow velocities vs pipe diameter; Flow rates drives costs – pumps and separator
High L/D and pipe inclination drives cost of building

21. Some test facilities in Norway
IFE Well Flow Loop
+ All inclinations
+ Indoor
+ High gas density
+ Transparent pipes
+ Cost effective
SINTEF – Large Sc.
+ Large L/D
+ Large diameter
+ High pressure, N2
Statoil - Herøya
+ Real oil-gas system
+ Formation water
+ High pressure
+ Long, large L/D
- Short, low L/D
+/- Medium diam.
- Fixed inclination
- Expensive to run
- Outdoor
- Cumbersome to change inclination
- Small diameter
- Steel pipe
– Expensive to run

22. The Well Flow Loop – Principal Layout
Component list:
1: Oil-water separator
2: Gas-liquid separator
3: Gas compressor
4: Water pump
5: Oil pump
6: Heat exchanger, gas
7: Heat exchanger, water
8: Heat exchanger, oil
9: Main el. board
10: Flow rate meter, gas
11. Flow rate meter, water
12: Flow rate meter, oil
13: Inlet mixing section
14: Slug catcher, pre- separator
15: Return pipe, gas
16: Return pipe, liquid
17: Test section
18: Winch
MEK 4450 Multiphase Flow - IFE Oct. 22, 2013

23. Worldwide test loops

24. Worldwide test loops

25. Instrumentation Gamma densitometers PIV (Particle image velocimetry)
X-Ray tomography
LDA/PDA (Laser Doppler anemometry/Phase Doppler anemometry)
ECT (electrical capacitance tomography)
FBRM (Focused beam reflectance measurement)
PVM (Particle vision and measurement)
Shear stress probes

26. Pressure gradients
Differential pressure transducers; many measurement principles, accuracy, response times etc.
Connected to an upstream and downstream pressure tap (small holes in the wall)
The connecting pipe is called impulse pipe.
Pressure tap can be top/bottom/side mounted
Distance between pressure taps can vary widely (1 m – 100 m)
Measures wall friction and the hydrostatic pressure difference between the taps
dp/dz [Pa/m]= dp/dL, where dp is the differential pressure measured with the transducer and dL is the distance between the tappings

27. Holdup=Cross-sectional liquid fraction (H=1-a)
Gamma densitometer
Attenuation of photon flux due to absorption and scattering
Single media:
where N is the intensity, m is the attenuation coefficient (material property) and x is the distance travelled in the media
Two-phase gas-liquid
This can be developed to and explicit equation for the Holdup