An overview of CFD applications in flow assurance

From well head to the platform

Simon Lo

Contents – From well head to the platform

•  Heat transfer in Christmas tree •  Multiphase flow in long pipe •  Severe slugging in riser •  Sand transport in pipes •  Temperature effects in transportation of viscous oil •  Hydrate formation •  Slug flow around pipe elbow •  Riser V&V •  3 phase separator •  Wave impact on platform •  Launching of lifeboat

Flow in and around a Christmas tree

Flow inside a Christmas tree

Temperature distribution inside a Christmas tree

Oil and gas flow in 100m pipeline

4 inch riser

55 m pipeline

10.5 m

Riser top

Riser base

Riser DP = Pbase - Ptop

Severe slugging in riser, Uni of Cranfield, UK

50 100 150 200 250 300 3500

0.2

0.4

0.6

0.8

1

Flow time t, s

Rise

r DP,

bar

ExperimentStar-CD-1Star-CD-2

DEM – particle transport in pipe

DEM - Pneumatic conveying of particles in pipe

Horizontal slurry pipeline flow

Liquid velocity

Inlet Outlet Middle

Particle volume fraction

Slurry flow in horizontal pipe

Uniform solid volume fraction (vf) and slurry velocity (V) g

L=10m

V

1m

D

Measurement plane

Slurry flow in pipe

d=90 µm, vf=0.19, D=103mm, V=3 m/s

d=165 µm, vf=0.189, D=51.5mm, V=4.17 m/s

Uniform solid volume fraction (vf) and slurry velocity (V) g

L=10m

V

1m

D

Measurement plane

d=270 µm, vf=0.2, D=51.5mm V=5.4 m/s

d=165 µm, vf=0.0918 D=51.5mm V=3.78 m/s

d=480 µm, vf=0.203, D=51.5mm V=3.41 m/s

d=165 µm, vf=0.273, D=495mm V=3.46 m/s

Effects of cooling in transportation of viscous oil

•  Temperature, density and viscosity after 200m.

Temperature Density

Viscosity 120 cP 20 cP

Sec. 01

Sec. 02

Sec. 03

Sec. 04

Sec. 05

Sec. 06

Sec. 07

Sec. 08

Sec. 09

Sec. 10

A-1 0.0846

0.0756

0.0756

0.0756

0.0756

0.0756

0.0756

0.0756

0.0756

0.0756 A-2 0.145

5 0.174

0 0.203

0 0.226

9 0.247

3 0.264

9 0.280

2 0.293

6 0.305

2 0.315

4

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Shea

r Str

ess

[N]

•  Increase in wall shear stress and pressure drop as viscosity increases.

Wall shear stress and pressure drop along pipe

Isothermal

With cooling

A CFD hydrate formation model

•  Oil-dominated 3 phase flow

Oil Water Gas Hydrate + water Hydrate

•  Eulerian multiphase flow model: •  Phase 1: Oil – continuous fluid •  Phase 2: Gas – dispersed bubbles •  Phase 3: Water/hydrate – dispersed droplets (fH=0) turn into

hydrate particles (fH=1)

Hydrate formation process

1.  Methane (CH4) from gas bubbles is dissolved into the oil. 2.  Water droplets come into contact with dissolved CH4, turn into

hydrate particles when the temperature drops below the hydrate nucleation temperature.

3.  The dissolved gas is consumed in the hydrate formation process.

Oil Water Gas Hydrate + water Hydrate

Temperature, hydrate and dissolved gas

Temperature of oil (Note areas cooler than hydrate nucleation temperature of 15.6°C.)

Hydrate fraction in water (Hydrate starts to form when temperature drops below 15.6°C.)

Mass fraction of dissolved gas in oil (Dissolved gas is consumed in hydrate formation and recovered when hydrate formation is completed.)

Pigging – Overset mesh for moving pig

Stratified gas-liquid flow Dispersed solid-liquid flow

Dynamic forces on pipe elbow in slug flow

Mass flux, velocity and density of each phase

Pressure and temperature

Flow direction

Model the long pipe using OLGA with slug tracking

Model pipe elbow using STAR-CCM+

Pressure variation due to slug flow pass elbow

Gas volume fraction Pressure on the outer part

Note the passing of liquid slug in “blue”.

Note the increase in pressure as liquid slug passes.

Comparison

Coupling model Experiment

Slug frequency (Hz) 0.5 0.5

Slug velocity (m/s) slug front: 2.8 to 3.6

slug tail: 3.0 to 3.5 3.6

Peak force on bend (N) 44 to 54 40 to 60

Maximum force on bend (N) 54 60

In industrial design with safety factor ‘2’: maximum force 141 N

Flow-Merging T-junctions Application Proving Group

Planar

60º

90º

21

Jumpers Application Proving Group

22

JumperBend

JumperRec

Pig Launcher / Cross over Application Proving Group

23

Oil Platform Riser Vortex Induced Vibration

•  Riser pipe via FV Stress •  URANS (Unsteady-Reynolds Average NS) •  k-ω turbulence model y+<10 •  2nd order time fluid and solid

–  Time step 1/100 of Vortex Shedding Period •  Implicit Coupled – Morphed 1 per time step •  Good Agreement

–  Drag (Cd) Shedding (St), Natural frequency

24

Oil Platform Riser Vortex Induce Vibration

25

Mid-span cross-stream displacement

Mid-span stream-wise displacement

Separator

Upstream pipework

Baffle plate

Inlet Diffuser Vortex breaker

Oil outlet

Vane packs

Gas outlet

Downcomer

Inlet

•  Modeling strategy: –  Local model of diffuser and vane pack –  Global model of separator

Nottingham – Multiphase flow in bend pipes

Large bubbles

Medium bubbles

Small bubbles

Liquid

4-phase model

27

3-phase separator

28

Gas Oil

Water

Courtesy of Rhine Ruhr / LSIM Australia

Wave loading on platform

•  High fidelity with multi-physics:

•  Wind and wave loadings

•  Stress

High fidelity, large domain, time dependent

Launching of life boat

LIFEBOAT LAUNCHING • combined 6 DOF, overlapping mesh, VOF (compressible)

Conclusions

•  CFD is becoming more widely used in flow assurance to study: –  Flow details in 3D: pipelines, equipment, junctions, valves, … –  Thermal management, conjugate heat transfer, cold down,

temperature dependent density and viscosity, hydrate, wax, ... –  Fluid-structure interactions: VIV in risers, sloshing in tanks.

•  CFD technology is being developed to support the modelling of the complex flows:

–  Advanced grid generation methods. –  Advanced multiphase flow models. –  Fast parallel solver to handle large complex models. –  Powerful visualisation technique to explain the complex flow.