141
non-hydrostatic buoyant forcing. Models to predict the initial conditions to near- field
models must also capture changes occurring before the petroleum was released in
the seawater, such as phase changes occurring during ascent from the petroleum
reservoir to the seafloor (Zick 2013; Gros et al. 2016), the complex multiphase flows
within crippled oil well pipelines (Boufadel et al. 2018), and the breakup of gas and
liquid petroleum into bubbles and droplets in the initial jet at the spill orifice. Nearfield models may also account for the live oil chemical composition and the wide
range of thermodynamic and chemical processes it undergoes. At high pressure and
temperature, the petroleum fluids are non-ideal, and as pressure and temperature
change throughout their transport, the phase equilibrium between gas and liquid
petroleum is constantly evolving (Gros et al. 2016, 2017; Lehr and Socolofsky
2020). For a deepwater release, the liquid-phase petroleum may contain a large
amount of dissolved gases, giving a lighter, quite soluble live oil. The gas phase also
has significant fractions of heavier petroleum molecules dispersed within it, so that
after dissolution of the volatile constituents, gas-phase bubbles may condense to
liquid drops (Gros et al. 2017). Gradually, the buoyant near-field plume is arrested
by the density stratification in the ocean and is bent over in the downstream direction of the currents, eventually forming a lateral intrusion layer of dissolved petroleum and fine oil droplets mixed with seawater (Socolofsky et al. 2011; Gros et al.
2017; Dissanayake et al. 2018).
Once the oil reaches the far field, the remaining petroleum fluids rise out of the
intrusion layer. Depending on the spill, these may include gas bubble, condensed
gas droplets, live oil droplets, and weathered oil droplets, each advected by its own
buoyant rise velocity and the ambient currents and dispersed by turbulent diffusion
of the ocean. These droplets and bubbles can then be represented by individual elements in Lagrangian models and are subjected to transport and dispersion by local
hydrodynamic processes. Physical processes, varying on spatial scales from centimeters to tens of kilometers, and the continuing, complex biogeochemical processes
influence the final distribution and fate of the oil. In far-field numerical models of
oil dispersal, these physical processes are represented by the advection, driven by
the deterministic velocity from hydrodynamic models, by the parametrization of
sub-grid-scale turbulence, using a random displacement (Paris et al. 2013), and by
the droplet terminal velocity, given by the droplet sizes and buoyancy (Zheng et al.
2003). During their transport, the characteristics (diameter, density, composition) of
each droplet evolve continually due to biogeochemical processes, such as dissolution, biodegradation, particle flocculation and aggregation, sedimentation, and
evaporation (see Boehm et al. 2020; Bubenheim et al. 2020; Jaggi et al. 2020;
Le Hénaff et al. 2012; North et al. 2015; Paris et al. 2012; Yapa et al. 2010). Ambient
conditions will influence the rate at which these processes take place, and these
interactions need to be accounted for in the model.
Furthermore, the response actions selected for containment or mitigation of a
deepwater oil spill may also alter the chemical and thermodynamics characteristics
of the oil itself, both in the near- and far-field domains. Burning of surface oil, a common measure for containment of superficial oil, can result in the creation of heavy,
pyrogenic hydrocarbons in cases of incomplete combustion. Surface application of
9 Dynamic Coupling of Near-Field and Far-Field Models
non-hydrostatic buoyant forcing. Models to predict the initial conditions to near- field
models must also capture changes occurring before the petroleum was released in
the seawater, such as phase changes occurring during ascent from the petroleum
reservoir to the seafloor (Zick 2013; Gros et al. 2016), the complex multiphase flows
within crippled oil well pipelines (Boufadel et al. 2018), and the breakup of gas and
liquid petroleum into bubbles and droplets in the initial jet at the spill orifice. Nearfield models may also account for the live oil chemical composition and the wide
range of thermodynamic and chemical processes it undergoes. At high pressure and
temperature, the petroleum fluids are non-ideal, and as pressure and temperature
change throughout their transport, the phase equilibrium between gas and liquid
petroleum is constantly evolving (Gros et al. 2016, 2017; Lehr and Socolofsky
2020). For a deepwater release, the liquid-phase petroleum may contain a large
amount of dissolved gases, giving a lighter, quite soluble live oil. The gas phase also
has significant fractions of heavier petroleum molecules dispersed within it, so that
after dissolution of the volatile constituents, gas-phase bubbles may condense to
liquid drops (Gros et al. 2017). Gradually, the buoyant near-field plume is arrested
by the density stratification in the ocean and is bent over in the downstream direction of the currents, eventually forming a lateral intrusion layer of dissolved petroleum and fine oil droplets mixed with seawater (Socolofsky et al. 2011; Gros et al.
2017; Dissanayake et al. 2018).
Once the oil reaches the far field, the remaining petroleum fluids rise out of the
intrusion layer. Depending on the spill, these may include gas bubble, condensed
gas droplets, live oil droplets, and weathered oil droplets, each advected by its own
buoyant rise velocity and the ambient currents and dispersed by turbulent diffusion
of the ocean. These droplets and bubbles can then be represented by individual elements in Lagrangian models and are subjected to transport and dispersion by local
hydrodynamic processes. Physical processes, varying on spatial scales from centimeters to tens of kilometers, and the continuing, complex biogeochemical processes
influence the final distribution and fate of the oil. In far-field numerical models of
oil dispersal, these physical processes are represented by the advection, driven by
the deterministic velocity from hydrodynamic models, by the parametrization of
sub-grid-scale turbulence, using a random displacement (Paris et al. 2013), and by
the droplet terminal velocity, given by the droplet sizes and buoyancy (Zheng et al.
2003). During their transport, the characteristics (diameter, density, composition) of
each droplet evolve continually due to biogeochemical processes, such as dissolution, biodegradation, particle flocculation and aggregation, sedimentation, and
evaporation (see Boehm et al. 2020; Bubenheim et al. 2020; Jaggi et al. 2020;
Le Hénaff et al. 2012; North et al. 2015; Paris et al. 2012; Yapa et al. 2010). Ambient
conditions will influence the rate at which these processes take place, and these
interactions need to be accounted for in the model.
Furthermore, the response actions selected for containment or mitigation of a
deepwater oil spill may also alter the chemical and thermodynamics characteristics
of the oil itself, both in the near- and far-field domains. Burning of surface oil, a common measure for containment of superficial oil, can result in the creation of heavy,
pyrogenic hydrocarbons in cases of incomplete combustion. Surface application of
9 Dynamic Coupling of Near-Field and Far-Field Models