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Structure

TransAT-Spill is a plume model designed for use in environmental risk assessment and oil spill contingency planning in conjunction with petroleum exploration or production in deep water seas. It tracks oil and gas from a subsea oil & gas spill in a coupled way, combining an Integral Plume approach near spill, with a far field oil droplet, gas bubble spill Lagrangian tracking. The Lagrangian Integral Plume model is coupled to TransAT Multiphase described earlier above the neutrally buoyant layer to track gas bubbles and/or oil droplet trajectories in 3D, the sea-current data. Dispersion of the droplets by small-scale turbulence is sub-modelled using a de-convolution approach.

sillmap1spillmap2

 

Physics and Workflow

Lagrangian Integral Plume Model

Lagrangian Integral Plume Model is a multiphase integral plume model based on the Lagrangian concept. The following phases are included:

  • Water (sea water)
  • Oil (dispersed droplets)
  • Natural gas (Free gas (bubbles))

The plume model is used in to adequately model the spill in the near field region where a mixture model is most appropriate. At some depth the plume gets trapped due to ambient ocean stratification. At this point the assumptions of a mixture model are no more valid.

Far field oil droplet, gas bubble spill Lagrangian tracking

The plume at depth of trapping is the initial condition for the far field model, where individual oil droplets are tracked using a Lagrangian Particle tracking approach. The model takes into account turbulent dispersion of the oil. In this stage transport of the oil is mainly determined by the ambient currents. If the oil reaches the surface, the slick is tracked. A wind component is added to the surface velocity of the water to model the effect the wind.

In short, the combined Plume/TransAT model accounts for the following physics:

  • Mass balance of oil, gas, hydrates, water
  • Momentum balance of oil/water mixture and gas
  • Energy balance of mixture (temperature)
  • Salinity transport
  • Gas dissolution
  • Hydrate formation, dissolution
  • Gas separation from oil/water plume
  • Ambient sea characterization

How Does it work

TransATSpill requires the following input data:

  • Outlet depth
  • Oil flow rate
  • Outlet diameter
  • Gas to oil ratio at standard conditions (GOR)
  • Outlet temperature

  • Vertical sea temperature profile
  • Vertical Salinity profiles
  • Wind data (unsteady, spatial)
  • Ocean current data (unsteady, spatial

TransATSpill produces the following outputs:

  • Plume Trajectory
  • Depth of trapping
  • Rise time to depth of trapping
  • Mixture properties along the plume trajectory

  • 3D transient output in the ocean
  • 2D transient output at the ocean surface
  • TransAT-SPILL is heavilly used for consultancy projects by ASCOMP, including BP, Shell, OMV Norge AS.

Contact TransAT Suite Team