Modelling HazardousConsequences of a Shale GasWell Blowout

Sergey Martynov & Haroun Mahgerefteh (UCL)

ShaleX Dissemination Event

Texas A&M, Doha, Qatar

18 March 20181

Presentation Scope

Motivation and objectives

Well blowout modelling methodology

Outflow model

Jet fires

Explosions

Results of the case study

Conclusions

2

Eagle Ford shale in Texas

http://the-earth-story.com/post/114862966776/drilling-shale-and-blowouts-this-is-a-classic

3

Background and Motivation

Failure of shale gas well facilities can have catastrophicconsequences for people and environment

Statistics shows that majority of blowouts happen duringdrilling when pressure kicks propagate into the well andBOP fails to divert the gas to a flare stack

Safe design of Major Hazards installations requiresquantitative risk assessment (QRA) based on modelspredicting the hazards

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Blowout Preventer (BOP)

Event tree for gas release consequencemodelling

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Hazardous Consequence

Jet Fire

Flash Fire

Explosion

Dispersion

Objectives

Development of model for simulating the transientoutflow of shale gas in the event of a wellheadblowout

Application of the wellhead blowout model to aspecific EU well to assess the hazards associatedwith transient fire and explosion over-pressure

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Modelling challenges

Model of the well discharge:

Transient compressible multi-phase flow;

Heat transfer through casing and viscous friction;

Complex multicomponent hydrocarbon mixtures;

Complex geometry of the well;

Modelling jet fires and explosion:

3D radiation profiles

Coupling with the outflow model

The well discharge flow model equations

+

= 0

+

+

where , , and are respectively the fluid density, velocity,

total specific energy and pressure, the spatial coordinate,

is the time, is the internal diameter, is the gravity

force, is the heat flux, and is the Fanning friction factor

Jet fire modelling

Release

direction

Release

point

Vertical

axis

Wind

direction

Object

is the lift-off distance (m);

and are the diameters of the frustum (m);

is the visible flame length (m);

is the flame length (m);

is the angle between the release direction andthe vertical axis;

is the tilt angle of the jet flame;

Schematics of the frustum representing ajet (after Chamberlain, 1987)

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Jet fire thermal radiation model

=

is the view factor; is the atmospheric transmissivity;

=

is the average surface emissive power (kW m-2);

= is the power radiated into atmosphere (kW);

is the heat of combustion (kJ kg-1) ;

is the mass flow rate (kg s-1);

= 0.21. + 0.11 is the fraction of heat emitted.

The radiated flux at the receiver object:

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Explosion modelling

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=3

is the energy of the blast wave (J/m3)

is the heat of combustion of a stoichiometric hydrocarbonair mixture (3.5 MJ/m3)

is the volume of the cloud in specific region of interest (m3)

is the radius of the released vapour cloud (m)

is the blast strength (-)

is the ambient pressure (Pa)

is the peak overpressure (Pa)

is the volume of the released stoichiometric cloud (m3)

is volume of unobstructed part of the cloud (m3)

is volume of obstructed part of the cloud (m3)

=

is the amount of vapour released (kg) is the cloud density (kg/m3) is the air-fuel stoichiometric concentration (vol%)

= +

Ignitionsource

is dimensionless radial distanceto the explosion source (-)

)

Explosion overpressure

Physical properties of the fluid

Fluid phase properties are simulated using an accurate equation ofstate for a typical natural gas composition

CH4 - 90 mol%

C2H6 - 4.5mol%

C3H8 - 3.5mol%

C4H10 - 2mol%

0

2

4

6

8

10

12

14

16

18

20

100 150 200 250 300 350

Pre

ssure

(bar)

Temperature (K)11

Motivation and objectives

Well blowout modelling methodology

Outflow model

Jet fires

Explosions

Case study

Results and Conclusions

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Case study - Methodology

Cuadrilla Roseacre Wood shale gasexploration project

Well geometry

Location and weather conditions

Formation pressure and temperature

Consequence modelling for possibledeviations from the nominal reservoirconditions, i.e. estimated magnitudes ofpressure kicks

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Map of Europe showing shale rock sedimentarybasins in Europe (SXT Deliverable 2.2)

Well site layout and weather conditions

Schematic of the drilling site layout and the shale gas explorationwells (Cuadrilla Elswick Ltd).

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Wind rose ofmeteorological

data at Blackpoolmeteorological

station, 2012

Welllocations

Offices

Reservoir conditions

Reservoir pressure hydrostatic gradient ~ 100 bar/km,

Reservoir temperature gradient ~ 23C/km.

15Formation temperature and pressure(UK Shale Gas Exploration, Cuadrilla Resources Ltd)

Case study parameters

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Parameters ValueWell parametersOverall lengthMaterial of constructionWall surface roughnessHeat transfer coefficientExternal diameterInternal diameterWall thicknessOrientation relative to horizontal

4000 mMild steel0.05 mm0 W/m2K (Adiabatic)127 mm114.4 mm6.2 mm90 o (vertical)

Reservoir parametersTemperaturePressure

343 K200 600 bar

Ambient conditions

TemperaturePressureWind SpeedRelative Humidity of air

293.15 K1.01 bara0 -10 m/s50%

Motivation and objectives

Well blowout modelling methodology

Outflow model

Jet fires

Explosions

Case study

Results and Conclusions

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Outflow simulation results

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0

50

100

150

200

250

0 1000 2000 3000 4000

Pre

ssu

re(b

ar)

Distance (m)

t = 0 s

t = 10 s

t = 20 s

0

50

100

150

200

250

300

350

0 0.2 0.4 0.6 0.8 1 1.2

Mass

rele

ase

rate

(kg/s

)

Time (s)The results of transient simulationsof the outflow (pressure, flowrate,phase composition, etc) are used asinputs for consequence modelling

The flow establishes very quickly in time

Thermalradiationcontours

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Incident heat flux contoursat the ground level aroundvertical flame formed atthe wellhead (0;0),predicted at various timesfollowing the blowout.

Instantaneous ignition.Wind speed = 0 m/s.

Thermal radiation safe distances

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The incident radiation heat flux as a function of thereceiver distance, predicted for the vertical well blowout

6.3 kW/m2

Safe distancecan bedetermined fora given radiationthreshold

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Thermal radiation safe distances

Safe distances to avertical jet flame forpersonnel and steelstructures.

Wind speed 10 m/s.Flat terrain, no firewalls.

Safe radiation thresholds:

Explosion overpressure hazards

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Potential damage to health caused by peak overpressurefor various types of locations

Type of location Peak overpressure (mbar) Potential damage

People in the open

300 Eardrum rupture

1000 Picked up and thrown; likelyfatality

People in normalbuildings

70 - 250 Significant likelihood offatality due to masonrycollapse and projectiles,particularly glass

Blast resistantbuildings

> 200Some likely fatality

Blast proof buildings > 1000 Some likely fatality

Explosions safe distances

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1

10

100

1000

10000

0 50 100 150 200

Peak

overp

ress

ure

(mbar)

Distance from explosion centre (m)

Simulated explosion overpressures as a function of distance from theexplosion source at the wellhead for various levels of confinement

Potentially fataloverpressurethreshold for

people in buildings

Level ofconfinement:

consistent withthe well layout

Conclusions

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A methodology has been developed to predict hazards associatedwith shale gas wellhead blowout

The methodology enables prediction of

o the transient flow rate,

o the thermal radiation from jet fires, and

o the explosion overpressure levels

The methodology was applied to evaluate safety hazards for ahypothetical blowout scenario for a realistic shale gas well

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Thank you