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

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 • Thermodynamics • Conservation of • Energy • Mass • Momentum

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: L PR PL Friction • Pressure gradient large enough for flow: Velocity depends on friction • 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 Annular flow: High Ugas, low Uoil (wide range of incl.) Bubbly flow: Little gas, large Uoil (All inclinations) ”Churn”-flow: More gas, large Uoil (steep inclinations)

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 Field Lab

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

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

17. P = 100 bar 3 – 6 m/s 3 – 6 m/s 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: < 0.005 N/m 60 mm/h Drop/bubble sizes Capillary waves 90 000 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 • - Outdoor

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