flow assurance with ansys cfd - esssesss.com.br/events/ansys2010/pdf/21_7_1750.pdf · flow...

© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Flow assurance with ANSYS CFDFlow assurance with ANSYS CFD

Lubeena, RMuralikrishnan, RMohan Srinivasa

Lubeena, RMuralikrishnan, RMohan Srinivasa

© 2010 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Agenda

• Introduction

• Flow assurance with ANSYS

– Risk avoidance

– Hydrates

– Sand transport

• Horizontal gas-liquid flows

• Gas liquid flow in vertical pipes


Risk avoidance

• Need to ensure

– Operating conditions within envelope of safe operation

• Modeling for risk avoidance

– Fluid flow and heat transfer

– Non-Newtonian rheology

– Temperature dependant properties

– Can perform these simulations with a high degree of confidence


Risk avoidance

Heat transfer in bundled pipelines

EXPERIMENTAL AND CFD STUDIES OF HEAT TRANSFER IN AN AIR-FILLED FOUR-PIPE TUBE BUNDLE L. Liu, G. F. Hewitt, S. M. Richardson


Wax and hydrate formation

• Wax formation ≠ clogging

– Flow can alter structure

• Most promising strategy

– Thixotropic visco-plastic

fluid

• Simulations used for

– Stability of wax layers

– Transient start-up

• Coupling with 1D codes


HydratesComputational modeling of methane hydrate dissociation in a sandstone coreKambiz Nazridoust, Goodarz Ahmadi, Chem Engng Sci 62 (2007) 6155 – 6177


Joule Thompson effect

PUBLISHED RESULTS SIMULATION

Pressure distribution along

shock-tube

Temperature distribution

along shock-tube


Ideal vs Real

IDEAL GAS REAL GAS

SUBSONIC

REGION

SHOCK

HEATING

J-T HEATING

SHOCK

NO J-T

HEATING

Mach Number Mach Number

Static Temperature Static Temperature


Sand/Particulate Transport

• Sand is often produced out of the reservoir in both onshore and offshore production systems, particularly in reservoirs that have a low formation strength

• Sand production may be continuous, or sudden - as when a gravel pack fails

• The sediment consists of finely divided solids that may be drilling mud or sand or scale picked up during the transport of the oil

• Sand deposition could lead to corrosion of the pipeline

• Problem of sand deposition and re-entrainment– Inclined pipelines, pigging sand plug

pipeline

• Particulate modeling in ANSYS Fluent 13.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0.5 1.0 1.5 2.0 2.5 3.0

Mean Slurry Velocity, m/s

Me

an

Slu

rry

Pre

ss

ure

Gra

die

nt,

Pa/m

Skudarnov et al, 2001

Newitt et al, 1955

FLUENT CFD - Schiller Drag

FLUENT CFD - Wen & Yu Drag

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3 0.4 0.5 0.6

Solids Volume Fraction

Y / D

Fluent CFD: dp = 120 um

Matousek, 2002 (dp = 120 um)

Fluent CFD: dp = 370 um

Matousek, 2002 (dp = 370 um)


Operating envelope: Gravel packs

• Design criteria for gravel packs

– Minimum pump rate to avoid rat holing

screen out

– Maximum pump rate to avoid

formation fracture

– Need to determine safe envelope of

operation

• Critical velocity/shear stress for settling

Horizontal open hole gravel pack placement requirements in selective completion projects, Anais do ENAHPE 2009

The relevant parameters calculations were only possible via a robust 3D Computational Fluid Dynamics Simulation

(CFD). The application of the critical shear stress methodology for open hole gravel packs design in multizone

completion projects indicates less conservative results which can make possible operations in critical operational

windows scenarios.


Terrain slugging

0

10000

20000

30000

40000

50000

60000

4 5 6 7 8 9

Pressure Drop

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

4 5 6 7 8 9

Mass Flow Rate


Hydrodynamic slugging

• Hydrodynamic Slugging– Waves grow on the liquid

surface to bridge the pipe

– Kelvin-Helmholtz instability the cause for wave formation and slugging

– Modeling of interfacial instabilities will be crucial

• Problems due to slugging– Fatigue

– High frictional pressure drop

– End of production when low flow rates

– Production slop due to high static pressure changes due to long slugs.


Problem Description

• The entrance to the pipeline is arranged to give a stratified flow, in which the

gas flows above the liquid in parallel streams, and slugs originate from

waves at the gas–liquid interface that grow to fill the pipe cross-section.

Gas Inlet

Liquid Inlet

Splitter plate

Diameter: 0.078m

Length: 37m

International Journal of Multiphase Flow 32 (2006) 527–552


Results:

Slug Origin and Growth

• Slugs are developed from long waves that grow to bridge the pipe– Kelvin–Helmholtz Instability

• Slugs and Large Waves

– Slug: Liquid layer ahead of it is relatively deep, while the liquid height drops sharply behind its tail.

– Large waves: More gradual decrease of liquid height in their tail profile

• Some slugs grow as they travel the pipeline and others are dampened and disappear before reaching the outlet of the pipeline.


Animation:

Slug Evolution

26.62m & 27.22m


Animation:

Slug Evolution

34.55m & 35.11m


Experiment

ANSYS FLUENT

Comparison of Simulation Results

with Experimental Results


Hannibal slug catcher simulationCourtesy Genesis Oil and Gas consultants

• Gas pipeline from off-shore field to land-based Hannibal terminal

• Slug catcher separates residual liquid from gas at end of pipeline

• Plan to increase pipeline capacity to supply new power station

• Does capacity of slug catcher

also have to be increased?

• Inlet conditions for liquid-gas from Olga 1D pipeline model

Inlet

from

pipeline

Gas

outlet

Liquid

outlets

Estimated cost of modifying slug catcher $25M


Slug Catcher High Flow Operation

• Can slug catcher cope with increase in capacity of pipeline? – Yes!

• Liquid carry-over only in form of fine aerosol

Liquid carry-overFlow rates

Peak

Level

© 2010 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary© 2010 ANSYS, Inc. All rights reserved. 20 ANSYS, Inc. Proprietary

Gas-liquid flow in vertical risersGas-liquid flow in vertical risers


Flow regime map in vertical flows


Gas lift

Dispersed bubbly flow regime

Bubble Size effect on the gas-lift technique PhD

thesis of S´ebastien Christophe Laurent GUET


Annular & Churn flow in a vertical pipeDa Riva and Del Col, CES (2009)


3D churn flow simulations


Modeling vertical flowsDesign challenges

• A priori identification of flow

regime/transition

– Flow maps available for simple

riser configurations

• Frequency and severity of

slugging

• Pressure surges, fatigue,

erosion etc.


Possible modeling options in CFD

1. Resolved bubbles simulation with VOF model

– Computationally expensive

2. Combination of models

– Eulerian model for dispersed flow regime (implicit)

– VOF model for slug flow regime (explicit)

– Switch models appropriately

– Multi-fluid VOF

3. Eulerian model with appropriate sub-models

– Account for bubble coalescence and breakup

– Use appropriate drag laws for various bubbles


Simulations conducted

• Euler-Euler model with population balance

• VOF model

• Multi-fluid VOF model in ANSYS 13


Experimental conditions

• Experimental conditions to demonstrate fidelity/robustness of models

– Bubbly regime

– A few flow conditions

where an initially bubbly

flow transitions to a slug

flow regime

• Two different fluid combinations

– Air-Water

– Air-Oil

s

lU

s

gU

5 m

6 m67 mm

Cross-sectional

data collected.

Well mixed inlet

Bubble diameter = 5 mm

= 0.25 m/s

Chemical Engineering Science 65 (2010) 3836–3848


Transition to a slug regime

Air-water Air-oil

0.067 m


Bubbly flow results

Usg = 0.05 m/s and Usl = 0.25 m/s


Predicted flow-map


Holdup predictions


VOF model

• Air-water system in churn turbulent regime

• Pipe length truncated to 3m to interest of computational time

• 7 inlets for air

– Initial air bubble of

size around 10 mm

• Bubbles coalesce to form big bubbles


Model for bubbly � slug transition

economically…


Conclusion

• Increasing use of detailed simulations for understanding issues in flow assurance

• Improvements in ANSYS CFD 13 suited for modeling flow assurance.

• High confidence in modeling gas-liquid flows in vertical and horizontal flows.

• Interesting time ahead!

flow assurance with ansys cfd - esssesss.com.br/events/ansys2010/pdf/21_7_1750.pdf · flow...

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