cfd simulation of methanol flushing in subsea jumpers

CFD Simulation of Methanol Flushing in Subsea Jumpers

© 2011 ANSYS, Inc. September 16,

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Lubeena R

Mohammed Elyyan

Mohan Srinivasa

Introduction

• Hydrate formation is a concern in the deepwater production lines. This is normally

favored by the low temperature and the high pressure. Under the right conditions

hydrates can form anytime and anywhere hydrocarbons and water are present.

• The hydrate plugs act as a hindrance to hydrocarbon flow.

• On shut -in, the line temperature cools very rapidly to that of the ocean floor so that


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• On shut -in, the line temperature cools very rapidly to that of the ocean floor so that

the system is almost always in the hydrate region if the line is not depressurized.

• One common method for protecting subsea jumpers from the hydrate formation is to

flush the jumpers with methanol to displace and inhibit any water accumulation in

the lines.

Objective

• Use ANSYS CFD to predict the distribution of methanol and water in the jumper

after methanol flushing.

• Compare the numerical results with experimental results

– Amount of water and methanol remaining in the jumper after methanol flushing


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Problem Description

Methanol mass flow inletPressure outlet

(atmospheric pressure)

Oil, Water and Air


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Reference: Hydrate inhibition of subsea jumpers during Shut-in, T.Cagney and S.Hare,Total E&P Angola, and S.J.Svedeman, Southwest Research Inst.Copyright 2006, Society of Petroleum Engineers

Find the distribution of methanol and water in the jumper after

methanol is injected into the jumper

Oil, Water and Air

6.3m

Grid Details

Cell Count: 2.75M

Mesh: Hexahedral cells


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Initial Condition

Air

Oil


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Jumper volume- 0.22m3

Initial volume of air, oil and water in the jumper in % jumper volume:

Air- 33%

Oil-37%

Water-30%

Oil

Water

Model Details

• Transient solver

• Multiphase: VOF model with Species Transport model

• Turbulence: SST K-omega with turbulence damping at the interface

• Pressure-Velocity Coupling:

– SIMPLE

• Spatial Discretization Schemes:

– Green Gauss Cell Based for Gradient


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– Green Gauss Cell Based for Gradient

– PRESTO for Pressure

– Compressive for Volume fraction

• Time step size:

– 5e-3s for 10 and 16.5 m3/hr cases

– 1e-2s for 5m3/hr case

• Computational time taken:

– 1 day to run 16s in 12 CPUs (16.5m3/hr case with time step size 5e-3)

Methanol flushing: Animation


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Methanol flushing: Animation


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Comparison of Results with Experimental Data

Results comparison after one jumper volume of methanol flushing


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Water volume as % of jumper volume Methanol volume as % of water+methanol in jumper

- Time step size of 0.005s is used for the cases 10 m3/hr and 16.5 m3/hr.

- A larger time step size (0.01) is used for the case 5m3/hr, this might be one reason that 5m3/hr case results

are slightly far from the experimental results. A run with time step size 0.005s is going on to check this.

Summary

• ANSYS FLUENT is used to model methanol flushing in a subsea jumper and predict

the water and methanol distribution after the methanol flushing

• The simulation results are compared with the experimental results

– The amount of water and methanol left in the jumper at the end of methanol

flush

• Numerical simulation predicted the experimental behavior very well


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• Numerical simulation predicted the experimental behavior very well

– Higher methanol flow rates removed more water from the jumper

– Almost all the oil is swept from the jumper

– At the end of methanol flush, the two phase flow pattern in the lower portion of

the jumper was stratified with limited mixing at the interface between methanol

and water

• The numerical results are in good agreement with the experimental results

APPENDIX

• To see the animations in this presentation you will need to install the

swiff point player and enable ActiveX Controls in the Trust Center

Settings of Power Point Options.


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cfd simulation of methanol flushing in subsea jumpers

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