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Subsea gas release seminar

Subsea gas release seminar. Petroleumstilsynet, Stavanger. Asmund Huser, Det Norske Veritas 15. November 2006. Content. Background/Objectives Approach Subsea Surface Air Results Effects Wind speed Leak rate Depth Conclusions and Recommendations. Subsea gas releases - Highlites.

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Subsea gas release seminar

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  1. Subsea gas release seminar Petroleumstilsynet, Stavanger Asmund Huser, Det Norske Veritas 15. November 2006

  2. Content • Background/Objectives • Approach • Subsea • Surface • Air • Results • Effects • Wind speed • Leak rate • Depth • Conclusions and Recommendations Version

  3. Subsea gas releases - Highlites • Increasing risk contributor • Surface model is imortant • DNVS method: • PLUSS SIDE • New surface term model • CFD model of dispersion • MINUS SIDE • Not validated for large releases + - Version

  4. Approach CFX -> approx formulas PHAST Underestimates Improved surface model Not validated PLUMERISE Dilution, large scale, deep water Olga, Profes Version

  5. Improved surface model • Outward radial flow gives larger bubble zone • Slip velocity = 0.3 m/s • Normal distribution of vertical gas velocity The surface model has proven to be one of the most critical parameters for the subsequent gas dispersion analysis Version

  6. Surface gas velocity profile Water depth = 300 m Version

  7. CFX model • Velocity profile • Turbulence profile • Temperature profile • Surface roughness • Stability • Surface heat flux • Humid air • Open seaturbulence missing Version

  8. Validiation of CFD model • Maplin Sands liquid propane release in sea. • Simulation of gas dispersion, heavy gas Version

  9. Database of CFD simulations • 50 Open sea simulations: • Leak rates from 10 to 450 kg/s • Water depths from 100 to 300 m • All cases are steady state • Wind speeds from 3 to 8 m/s • Mole weight from 17 to 26.5 • Makes approximation formulas • Show physical effects Version

  10. Approximation formulas Dimensionless groups L = f(Ug, Uw, Dg) 4 variables reduced to L/Dg = f(Ug/Uw) 2 variables Version

  11. Results test cases Release rte (kg/s) Time (s) Wind speed (m/s) Water depth (m) Scenario no. Version

  12. Effect of water depth, 100 kg/s, 6 m/s Version

  13. 100m depth, 100 kg/s, wind speed 6 m/s Version

  14. 200m depth, 100 kg/s, wind speed 6 m/s Version

  15. Effect of depth, 50 kg/s, 3 m/s Version

  16. 100m depth, 50 kg/s, wind speed 3 m/s Version

  17. 200m depth, 50 kg/s, wind speed 3 m/s Version

  18. 300m depth, 50 kg/s, wind speed 3 m/s Version

  19. Effect of leak rate, 300 m, 4 m/s Version

  20. 300m depth, 50 kg/s, wind speed 4 m/s Version

  21. 300m depth, 100 kg/s, wind speed 4 m/s Version

  22. 300m depth, 200 kg/s, wind speed 4 m/s Version

  23. 300m depth, 450 kg/s, wind speed 4 m/s Version

  24. Effect of leak rate, 70 m, 7 m/s Version

  25. Effect of wind speed, 300 m, 450 kg/s Version

  26. 300m depth, 450 kg/s, wind speed 4 m/s Version

  27. 300m depth, 450 kg/s, wind speed 6 m/s Version

  28. 300m depth, 450 kg/s, wind speed 8 m/s Version

  29. Effect of wind speed, 50 kg/s, 70 m. Version

  30. Conclusions and recommendations • Plume rise model in water need updates • Improved surface model suggested, • Needs validation • Needs to be generalized • Use two-phase CFD models to guide experiments • CFD model for air dispersion is flexible and show effects • Approximation formulas developed, • Gives quick estimates • Needs extensions • Effects in air are: • Increasing depth -> increase plume lengths • Increasing Wind speed -> increase plume lengths to a max • Increasing Leak rates -> increase touch down wind Version

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