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MEK 4450 – Multiphase pipeline transport (IFE)
Lecture notes 2013-10-22, Morten Langsholt
• Multiphase technology – What, why, how • Pipe flow – single and multiphase flow • Importance of relevant experimental data • From lab to field scale • Multiphase test facilities • Lab-demo with measurements
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Multiphase pipe flow – a key technology for oil and gas production
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
What’s multiphase transportation? • Transport of gas, oil, water, chemicals and
possibly solid particles in the same pipe • Reduces need for new production platforms • Gather production from many wells and send
to existing platform or shore • Subsea separation and pumping/compression
may be required • More cost efficient • Often requires chemicals to prevent corrosion
and solids precipitation that can possibly restrict or stop the flow
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Multiphase transportation challenges
• Capacity problems due to viscous oils, emulsions etc.
• Solids precipitation can restrict or stop the flow
• Liquid accumulation during low flow rates in gas condensate pipelines • Large flow transients during production ramp-up
• Slugging and other instabilities can give problems in the receiving facilities
• Erosion/corrosion
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Application of multiphase flow models
• Tool for system design • Piping and equipment dimensioning • Heating and thermal insulation • Chemical choice and dosage
• Part of system simulator • Integrated system design • Subsea solutions • Operator training • Operation support – system overview • Surveillance: Compute non-monitorable parameters
- Liquid content, leak detection …
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Pipe Flow – Some considerations related to single
and multiphase flow
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Calculation of flow in pipes
in
out
• Conservation of • Energy • Mass • Momentum
• Thermodynamics
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Mass conservation • 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 = ρAU=constant along a pipeline
• Gas: Pressure reduced with 50% implies a doubling of U • Oil: Small density variations => U constant along pipeline
in
out
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Momentum balance – single-phase:
PL
PR
)(sin)( θgmAPP RL =−
L
Friction−
Friction
• Pressure gradient large enough for flow: Velocity depends on friction
Density Diameter T, external Viscosity Wall roughness Insulation (buried?) 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
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Oil samples - large differences in
fluid properties
Crude oils • Njord • Visund • Grane • Statfjord C
Condensates • Sleipner • Midgard
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Midgard
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
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
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.)
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Stratified/wavy- near horizontal pipeline
Large waves: More effective liquid transport
Stratified flow. Ugas normally >> Uoil
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Hydrodynamic slugging
• 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
Liquid slu
Taylor-bubble
Slug front in three-phase flow
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
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 eq. 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, multi-D, data from relevant and well-controlled flows
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Up-scaling from lab to field
• 13 parameters determine holdup(s) and pressure drop in three phase pipe flow
• To develop the closure relations, we need data • To cover the parameter space we need, say,
513 ~ 109 data points for 5 point resolution in each parameter
• We have ~ 200 field data points at present
• It is clearly impossible to cover the parameter space of three phase pipe flow with data
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Conclusion: we need models based on physics to
extrapolate beyond lab data
Lab Field
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Dimensionless numbers – dynamic similarity
• Reynolds number, ratio of the inertial forces to the viscous forces,
Re= =ρvL/µ
• 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:
Laminar vs turbulent flow Wave propagation, outlet effects, obstructions Formation of droplets and bubbles.
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
P = 100 bar 1 m/s
Corresponds to 10 m/s
Conditions in pipeline
1 m/s ρ = 1 kg/m3
Hydrodynamic forces proportional to rU2
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Wind = 3 m/s Light breeze
Gas – liquid interaction: governed by Dρ*DU2
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
Conditions in pipeline
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Conditions in pipeline – Drops and bubbles
Liquid layer can be significantly aerated (40% - 70%)
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
P = 100 bar
3 – 6 m/s
3 – 6 m/s σρ
σρ
2
2
tensionSurfacenalGravitatio
tensionSurfaceInertial
dgEo
dUWe
==
==
Drop/bubble sizes Capillary waves
60 mm/h
90 000 mm/h measured in lab
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Test facilities for study of multiphase flow behaviour
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
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, 2012
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
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
Some test facilities in Norway • IFE Well Flow Loop
• + All inclinations • + Indoor • + High gas density • + Transparent pipes • + Cost effective
• SINTEF – Large Sc. • + Long L/D • + Large diameter • + High pressure, N2
• Statoil - Herøya • + Real oil-gas system • + Formation water • + High pressure • + Long, high 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
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
MEK 4450 Multiphase Flow - IFE Oct. 22, 2012
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