Numerical modeling of Offshore Oil Spill : Weathering

Numerical modeling of Offshore Oil Spill : Weathering processes

Authors Aditya Kumar Mishra G. Suresh Kumar Tushar Sharma

1/5/2015

Presented by: Aditya Kumar Mishra MS (Research Scholar) Department of Ocean Engineering

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Presentation outline 1. Introduction 2. Objective and scope 3. Methodology i. ii.

Mathematical model Solution strategy

4. Results and discussion i. ii.

validation Results from the model

5. Conclusions 6. References

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Introduction

Why Marine Oil Spill is hazard? • Difficult to recover • Toxicates the air • Destroys the marine life • Consist of carcinogens • Can causes acid rain

• Foul the near shore and offshore facilities • Income losses and property damages to sectors like tourism and fisheries

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Oil weathering/fate processes • Series of chemical and physical changes that cause spilled oil to decay

1. 2. 3. 4. 5. 6. 7. 8.

Spreading Evaporation Dissolution Emulsification Natural dispersion Photo-oxidation Bio-degradation Sedimentation

hours days

years

Time scale

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Oil weathering on sea surface (physical system)

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Objective: To model the weathering/fate of an oil spill for oil property prediction and oil spill assessment

Scope • To identify the primary factors affecting oil spill on sea surface • To investigate the effect of emulsification on rate of evaporation • To develop a numerical model for time evolution of crude oil properties on sea surface

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Mathematical model Assumptions: • Crude oil single component • Crude oil spilled is well-mixed • Effect of wind , wave and current on spreading is neglected • Oil slick temperature equal to sea surface temperature

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4. Basic Modelling Theory……. ICPST-2014 •

Spreading : (Sebastian and Soares, 1995)

dA  k 1 A1V (4/3) dt •

(1)

Evaporation : (Mackay et al., 1983)



 

 b T0  Tg Fe  dFe k2 A   exp a  dt V0 Toil  

 

k2  2.5 x103 w0.78 (Sebastian and Soares, 1995) •

Nomenclature

(2)

(3)

A = spill area (m2) K = spreading constant(~150 s-1) V = volume of oil spilled (m3) Fe = volume fraction of oil evaporated (vol%) K2 = mass transfer coeff. of evaporation (m/s) K4 = dissolution mass transfer coefficient (m/s) Y = volume fraction of oil evaporated(vol%) To = initial boiling point of crude oil (K) Tg = gradient of distillation curve (k) a = constant (6.3) b = constant (10.3) Fd = fraction of oil dissolved (vol %) S = solubility of oil (g/m3) S0 = initial solubility of oil (g/m3) ρoil = initial density of oil (kg/m3)

Dissolution : (Shen et al., 1993)

  dFd S  k4 As   dt 1000  oil  

(4)

Solubility of oil in sea water

S  S0 exp(0.1t ) (Mackay et al., 1983) (5) 1/5/2015

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4. Basic Modelling Theory……. ICPST-2014 Nomenclature

• Emulsification (water-in-oil ):

Y  dY 2  k3 Ws  1 1   dt  YF 

( Mackay et al., 1980a) (6)

effect of emulsification on evaporation

k2e  k2 1  Y  (Lehr et al., 1994)

•

(7)

Natural dispersion :

Ws = wind speed at 10 m from sea surface (m/s) K3 = mass transfer coefficient of emulsion (m/s) µ = viscosity of oil (kg/m-s) Y = water content of oil slick (vol %) YF = maximum water content of oil (vol %) K2e = effective mass transfer coefficient (m/s) Vdis = volume of oil dissolved (m3) Da = rate of entraintment (s-1) Db = rate of oil not returning to surface h = slick thickness (m) St = surface tension (dynes/cm)

(Sebastian and Soares, 1995) (8)

dVdis   Da DbV0 dt 1 Db  (1  50  hst )

0.11(Ws  1) 2 Da  3600

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(9)

(10)

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4. Basic Modelling Theory……. ICPST-2014 • Viscosity

 c1Y   0 exp   1  c2Y • Density

    c3 Fe   

(11)

(Berry et al., 2011)

e  Y sw  ref (1  c4 Fe ) •

Nomenclature

(Berry et al., 2011)

(12)

Volume balance : (Guo and Wang, 2009)

µ = viscosity of oil at time t (cP) µ0 = initial viscosity of oil (cP) Tref = temperature at which viscosity was measured before spill (K) Toil = temperature of the oil slick (K) Vnet = volume of oil after each time step (m3) Fm_emul=mass fraction of oil (wt%) ρf = density of oil after each time step(kg/m3) ρ0 = intial density of oil (kg/m3) Fdis = volume fraction of oil dispersed (vol%) C1 = constant (2.5) C2 = constant(0.654) C3 = constant( 2.5 ) C4 = constant( 0.18 )

 1   Fe  Fd  Fdisp   (13)  Vnet  V0    1 Y   • Volume fraction to mass fraction conversion:

(1  Fv f )  (1  Fmf )

0 f

(14)

(Stiver and Mackay, 1984)

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4. Basic Modelling Theory……. ICPST-2014

Numerical/Solution strategy Inputs Spill condition, initial oil properties, wave condition Estimate/specify initial constants/ Initial condition T=0

T=T+h

Runge –Kutta fourth order:

Runge –Kutta fourth order • • • • •

Rate of spreading Rate of evaporation Rate of water content Rate of dissolution Rate of dispersion

Update: A, Fe, Fd, Y, Fdis Calculate :

T>Tmax

Outputs v, µ, ρ

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Spill conditions/Oil properties values

Statfjord Crude oil

Density (Kg/m3)

832

Viscosity (at 40oC) (cP)

3.03

T0 (Initial boiling point) (K)

301

Oil type : Light oil Volume spilled : 1000 m3 SWT : 250C wind speed : 4.17 m/s

Tg (gradient temperature) (K)

500

Solubility (at 25oC) (g/m3)

31.7

Parameters

Oil -water interfacial tension (dyne/cm)

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Maximum water content*

90 %

Aghajanloo and Pirooz (2011)

Asphaltene content (wt %)*/**

2%

*Janeiro et al. (2008)

Wax content (wt %)*/**

8%

Resin content (wt %)*

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6%

** ADIOS oil property database (NOAA, version 2.0)

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4. Basic Modelling Theory……. ICPST-2014

Validation

• N. Hurford and I. Buchanan (1989), “Results of the 1987 forties crude oil trial in the North Sea”, In International Oil Spill Conference (Vol. 1989, No. 1, pp. 525-532), American Petroleum Institute.

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4. Basic Modelling Theory……. ICPST-2014

Results from the model

Effect on rate of evaporation

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Volume balance of oil slick due weathering processes

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Conclusions • Sea surface dynamics endures the slick life on the sea surface • Formation of surface emulsion causes significant reduction in evaporation rate • Emulsification enhances the oil volume for cleanup • Accurate prediction of the emulsion properties and eluding the emulsion formation can reduce the required cleanup effort and spill impact

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References W. Stiver and D. Mackay (1984), “Evaporation rate of spills of hydrocarbons and petroleum mixtures”, Environmental science & technology, 18(11), 834-840. W. Lehr, D. Calhoun, R. Jones, A. Lewandowski and R. Overstreet, (1994), “Model sensitivity analysis in environmental emergency management: a case study in oil spill modeling, “In Proceedings of the 26th conference on Winter simulation (pp. 1198-1205), Society for Computer Simulation International. W. Lehr, R. Jones, M. Evans, D. Simecek-Beatty and R. Overstreet (2002), “Revisions of the ADIOS oil spill model”, Environmental Modelling & Software, 17(2), 189-197. W. J. Guo and Y. X. Wang (2009), “A numerical oil spill model based on a hybrid method’, pollution bulletin, 58(5), 726-734.

Marine

N. Hurford and I. Buchanan (1989), “Results of the 1987 forties crude oil trial in the North Sea”, In International Oil Spill Conference (Vol. 1989, No. 1, pp. 525-532), American Petroleum Institute. K. Aghajanloo and M. D. Pirooz, (2011), “The Simulation of the Oil Weathering Processes in Marine Environment”, In Proceeding of the 4th International Conference on Environmental and Computer Science, ICECS. 1/5/2015

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Questions?

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