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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
3
Blowout Preventer (BOP)
Event tree for gas release consequencemodelling
4
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
5
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)
8
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:
9
Explosion modelling
10
=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
12
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
13
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).
14
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
16
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
17
Outflow simulation results
18
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
19
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
20
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
21
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
22
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
23
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
24
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
25
Thank you