ANSYS oil&gas seminar 2013

Technology for a better society ANSYS NordicOilGas Seminar Oct. 15 & 16 Oslo & Stavanger

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Stein Tore Johansen

SINTEF

The flow assurance challenges and possibilities for CFD to contribute.

Technology for a better society ANSYS NordicOilGas Seminar Oct. 15 & 16

• Exploration in colder and deeper waters:

• Drilling, construction, maintenance and operation is more expensive.

• Transportation of oil, condensate and gas in long pipelines may be very cost-effective if multiphase transportation is reliable.

• Main challenges for long-distance pipeline transportation:

• Handling of precipitation of solid materials as flow cools down (wax, hydrates, asphalthenes)

• Effects of pressure reduction (scale precipitation and resulting deposition)

• Cost effective sizing of the pipeline (reliable and stable operation – control with liquid surges and slugs)

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The Challenges

Technology for a better society ANSYS NordicOilGas Seminar Oct. 15 & 16 3

Shut down and restart

Shut down:

• Many solids form as the well flow cools down. The solids may deposit on the pipe wall or become dispersed particles in the liquid.

• Mature fields produce more and more water

• After shut-down the pipe may clog if the water in the pipeline is converted into solid hydrates.

Restart:

• Alternatively the pipeline may be open as operation restarts but becomes plugged during start-up.

• Cold Flow Challenge: Can we restart a shut down and cold pipeline without adding chemicals and without costly hydrate prevention measures ?


Example of compact hydrate plug: Ref. Kværner report on cold spots in Kristin X-mas tree and choke module


Example of wax ’slug’ in pig trap at Statfjord B Ref: H.P. Rønningsen, Statoil


Ref: H.P. Rønningsen, Statoil


Low liquid loading: The Snow White field pipelines

Flow with small liquid contents may still result in significant liquid accumulation !! In very long lines: Extreme challenges Uncontrollable flow instabilities

160 km long !


Aker Solutions Subsea Field Layout for Aasgard

Emerging technologies: Separation moves closer to the wells Seabed processing Downhole separation


More challenges: Icing on structures Wave impact on structures


Even more challenges: Blow outs - Scenario evaluation - Capping stacks - Explosion risk assessments Oil spills – prevention and clean up - Better oil boom technology - Dispersion and breakdown in the environment


• Oil exploration in the Arctic and near Arctic regions has many significant technology challenges.

• Operations in these areas need technologies which can give fast and accurate enough answers

• The complexity of the physics and chemistry involved is extreme !

• Length scales varies from sub-millimeter to hundreds of kilometers

• Time scales varied from seconds to years !

• Good flow assurance models needed which can predict system performance. Speed requirements are at least to simulate 10 times faster than real time!

• These models will be the workhorses for driving process simulators, operator training, optimization and troubleshooting

• CFD does not fit directly into this picture (detailed, too slow, too complex, tuning not possible if data is scarce )

• At the end, multi-billion USD decisions will in a foreseeable future be based on this type of models, and not on CFD

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The CFD Challenge


• Still, CFD has the capability to explain the complex interactions of physics and chemistry, together with experiments, in order to build simplified models with acceptable confidence.

• In addition, CFD has the capability to improve and design unit operations (separators, well inflow devices, oil-booms) in order to improve their performance.

• Computational Fluid Dynamics is a tool which relies heavily on the physical models and modeling concepts solving flow assurance problems related to precipitation of solids, or emulsion rich flows, cannot be done before appropriate chemistry and flow models are developed.

• A need for better models !

• The well completion systems become more and more complex 3D devices, which can only be analysed by 3D CFD.

• CFD is crucial in providing sub-models for more simplified and operational models

• CFD will have a large number of niche applications where there is no alternative to CFD !

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The CFD Challenge – Really a need for CFD ?


LedaFlow Q3D: Beyond the limits of full 3D – but restricted applicability to system assessment ( domain of 1D models)

However, we have still many successful application of 3D ANSYS Fluent !!


Capping stacks are deployed to stop oil/gas-release

They are lowered onto leaking BOP

The hydrodynamic pressure from the release can prevent successful landing of capping stacks

Hydrodynamics loads on capping stacks


Pressure distribution

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Feasibility of landing can be assessed by CFD, using ANSYS Fluent.

Weight of capping stack needs to exceed hydrodynamic forces

Potential hydrodynamic force varies between wells

We have analysed situations were hydrodynamic force exceeded gravity

Hydrodynamics loads on capping stacks


Subsea bubble plumes & oil spill barriers

Bubble source

Sea current Sea current

Bubble source

Oil slick accumulation

VOF applied to oil spill barriers

PhD: Qingqing Pan

oil.avi


Bubble plumes Lagrangian modeling of the plume New models for: • Bubble induced

turbulence • Free surface effects • Buoyancy modified

turbulence

0 0.1 0.2 0.3 0.4 0.5 0.6-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

r [m]

Ur

[m/s

]

Ur-standard

Ur-enhanced

Ur-exp.

0 0.1 0.2 0.3 0.4 0.5 0.6-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

r [m]

Uz [

m/s

]

Uz-standard

Uz-enhanced

Uz-exp.

-0.4 -0.2 0 0.2 0.4 0.60

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

r [m]

alp

ha

alpha-no-wake

alpha-with-wake

alpha-exp.

Radial flow, close to surface

Axial flow, close to surface

Radial gas distribution. Half way up.

PhD: Qingqing Pan


Position- (and time-) dependent Gas-flux density through sea surface ↓ Mass Source at Wall

Radial sea-surface velocity ↓ Moving Wall BC

Inhouse Subsea Plume Model, DeepBlow (Ø. Johansen), provides input to ANSYS Fluent model

Atmospheric Gas Dispersion Following Sub-Sea Oil/Gas-Release


Vertical Symmetry-Plane (Time-dependent Contours of Gas content)

Transient CFD simulations (LES) of gas-cloud development in ANSYS Fluent. Focus on explosion/fire hazard. Sensitivity-studies on e.g.: • Release-rates, depths and directions • Wind conditions

Videos: Symmetry plane gas-content contours 3D gas-content isosurface

3Disosurf.gif

symmetryplane.gif

symmetryplane.gif

symmetryplane.gif

3Disosurf.gif

3Disosurf.gif

3Disosurf.gif

3Disosurf.gif


Introduction/Motivation

Connectors

Gate Valves

Ball Valve

Actuator

Insert Choke

and actuator

Xmas tree

Manifold including

pig loop

Well jumperFlow loopHub

Connectors

Gate Valves

Ball Valve

Actuator

Insert Choke

and actuator

Connectors

Gate Valves

Ball Valve

Actuator

Insert Choke

and actuator

Xmas tree

Manifold including

pig loop

Well jumperFlow loopHub

Typical subsea production system

Assessing thermal problems due to cold spots (hydrate risk assessment)


x

y

Outflow, cooling water

x

y

Outflow, cooling water

Experimental setup

Partially insulated pipe with cold spot

Pipe dimensions: L = 2000 mm ID = 70 mm

Sections: = 3/8 L and 5/8L

Near horizontal inclination: θ = 2°

PhD: Uduak Mme


-500 0 500 1000 1500 200020

25

30

35

40

45

50

55

Time (s)

Tem

pera

ture

(C

)

2degExP

2degke-fine grid

88degExp

88degke-fine grid

-500 0 500 1000 1500 200020

25

30

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40

45

50

55

Time (s)

Tem

pera

ture

(C

)

2degExP

2degke-fine grid

88degExp

88degke-fine grid

Far field temperatures: k-epsilon model

Close field temperatures: k-epsilon model

PhD: Uduak Mme


-500 0 500 1000 1500 200020

25

30

35

40

45

50

55

Time (s)

Tem

pera

ture

(C

)

2degExP

2degLES-fine grid

88degExp

88degLES-fine grid

-500 0 500 1000 1500 200020

25

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55

Time (s)

Tem

pera

ture

(C

)

2degExP

2degLES-fine grid

88degExp

88degLES-fine grid

Far field temperatures: Large Eddy model

Close field temperatures: Large Eddy model

PhD: Uduak Mme

CFD framework for separation

Overall goal is to develop

simulation framework for

separation processes.

Phenomena of relevance:

Relative motion of phases.

Droplet behaviour in free settling

zone.

Droplet behaviour in dense packed

layer.

Droplet-droplet interactions.

Influence of surfactants on the

above.

Framework has been realized in

ANSYS FLUENT.

Model now ported to Star CCM+ , who is FACE Partner.

CFD framework for separation

Basis for model is the n-phase Eulerian model.

Dispersed phases (e.g. water droplets) are treated by means of

population balance modelling.

Additional functionality, such as adsorption/desorption kinetics is

implemented as user defined functions and scalar fields.

Phase distribution

(oil and water) Surfactant distribution

(soluble only in organic phase)


Singing Risers: Motivation

Corrugated pipes have experienced high levels of vibration (singing/

whistling)

Potential fatigue failure

Explosion risk

The movie is from the courtesy of Statoil, Norway

The picture is from the courtesy of Statoil, Norway


Singing related to vortex shedding on corrugations Vortices, in the axial plane of the pipe

Flow domain with 128 corrugations:

The predicted vortices along the pipe corrugations indicate the source of the sound


Singing Risers: Profile of the static pressure in the pipe

• The profile of the static pressure in the pipe indicates and "approximately standing wave"

Axial Pressure Contour pressure


• Large classes of flow assurance issues must be handled by 1D models to be industrially interesting

• Better models of the physics and chemistry is crucial in order to expand the application of CFD models in flow assurance

• However, many successful CFD applications can be demonstrated:

• Capping stack installation

• Bubble plumes and oil slick accumulation

• Explosion risk – atmospheric gas dispersion

• Thermal dynamics due to cold spots and risk reduction

• Chemistry controlled droplet coalescence and separation

• Aero-acoustical simulations of the singing riser phenomena

• The possibility of developing new models using UDFs has been a major success factor for ANSYS Fluent

• If good models are provided, CFD will become a very important element in the toolbox needed for modern flow assurance work

Summary

ANSYS oil&gas seminar 2013

Engineering

Transcript of ANSYS oil&gas seminar 2013