Abstract:

The latest version of the oil application of the Connectivity Modeling System (CMS) or oil-CMS is used to run a series of far-field simulations of the Deepwater Horizon (DWH) blowout (2010-04-20) in the Gulf of Mexico. These simulations adopt a two-phase approach with methane gas and liquid oil in the same oil droplet, following the concept of “live oil” that features gas-saturated oil formed under deep-pressure low-temperature conditions, as during deep-sea blowouts. When the oil droplets rise in the water column, they experience an internal degassing process (Pesch et al., 2018), which affects their size, density, and surfacing speed. The model adopts a log-normal droplet size distribution at the initial release time (iDSD). The dataset contains the diagnostics and post-processing analysis from three experiments: 1) Two-phase experiment, no degassing parameterized; all gas formed in a rising oil droplet due to pressure-dependent solubility is released into ambient water. 2) Full degassing experiment, where all the gas formed due to solubility decrease remains inside the droplet; internal degassing takes place. 3) An experiment with size-dependent partial degassing, in which i) the droplets < 0.2mm lack an initial gas phase, ii) rising oil droplets from 0.2mm to 0.8mm experience a linear increase of internal degassing process and the corresponding linear decrease of the gas dissolution into the ambient water; iii) droplets > 0.8mm have predominantly internal degassing, so that /all gas remains inside the droplet and affects droplet density, size, and rising speed accordingly. The dataset includes daily averaged oil concentration in the top meter of the ocean, in the 800-1200 m layer just above the depth of the blowout, and the full 4-D domain; it also includes horizontally-cumulative oil concentration throughout the water column, the position and time information for oil which exited the system or landed, as well as trajectory information over a variety of time periods.

Suggested Citation:

Paris-Limouzy, Claire B., Natalie Perlin, and Ana C. Vaz. 2021. Distribution of oil concentration and oil mass in the Gulf of Mexico following the Deepwater Horizon oil spill simulated by the Connectivity Modeling System (CMS) using two-phase droplet and internal degassing parameterizations. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/RTHEA0HX

Purpose:

This dataset provides a post-processed analysis of the Deepwater Horizon oil spill numerical simulations, including spatio-temporal 4D gridded daily oil concentrations and horizontally-cumulative oil mass in the entire water column. It is a product of the state-of-the-art far-field modeling of the deep-sea oil spill, including the internal degassing parameterization. The dataset could be used for comparative analysis with the observations and other validation techniques, as well as with other modeling efforts in sensitivity studies. It could also be used as spatio-temporal input data for ecosystem modeling applications.

Data Parameters and Units:

The numerical modeling output of the oil-CMS (Connectivity Modeling System) representing the trajectory, history, and attributes of individual oil droplets is post-processed to compute the spatio-temporal evolution of mass-conserved oil concentrations, horizontally-average oil mass distribution in the water column, oil mass of the droplets landed on the bottom or beach (shallow areas), and several others droplet statistics. Daily average oil concentrations are in units of ppb, and daily oil mass values are in kg. The dataset contains 45 individual files in NetCDF (.nc), Matlab (.mat), and text (*.txt) format and a dataset description in *.pdf format. The included descriptive document specifies all the included files and their parameters and units. Naming convention: Files labeled iDSD_2ph: no degassing; files labeled degas_full: full degassing; and files labeled degas_var: droplet size-dependent degassing behavior. The daily average oil concentrations have the parameters: time (days after the initial blowout, [days]), lat [degrees N], lon [degrees E], zbound (vertical level bounds, [m]), zlevs (mid-depth of vertical levels, [m]), depth (bathymetry, [m]), oil_conc [ppb] or time (days after the initial blowout, [days]), lat [degrees N], lon [degrees E], zlevs_bnd (vertical level bounds, [m]), depth (bathymetry, [m]), and oil_conc [ppb]. The droplet statistics contain the variables Ddepth [m], Ddiam [m], Dmass, Dtimes [seconds], dir0 [path name, string], and nums [constant]. The landed/exited oil text files have the format time (elapsed time since the beginning of the model run/onset of the blowout, [s]), depth of landing/exiting [m], latitude of landing site [degrees N], longitude of landing site [degrees E], and oil mass [kg].

Methods:

All the model simulations are 100 days long, in which the oil spill stops after 87 days. Oil particles are released at 28.736°N, 88.365°W, depth 1222 m or 300 m above the oil well, which is taken as a trap height. The model time step is 120 s; 3000 particles are released every two hours, equivalent to a total of 3,132,000 oil particles released over 87 days of the oil spill. At initial release time, the droplets have the log-normal droplet size distribution (DSD) with standard parameters mu=117 micron, and sigma = 0.62, based on best-known estimates from the observational and experimental data. These parameters assume the oil is not treated with chemical dispersants. Initially, the particles contain a volumetric fraction of liquid oil (methane gas) of 0.9311 (0.0689), and a density of 821.94 (113.78) kg/m^3. The surface evaporation half-life is 250 hours; horizontal diffusivity is set to 10 m^2/s in the present case. Ocean hydrodynamic forcing for the oil-CMS model uses the HYbrid Coordinate Ocean Model (HYCOM) for the Gulf of Mexico region on a 0.04-deg. horizontal grid and forty vertical levels from the surface to 5500 m. It provides daily average 3-D momentum, temperature, and salinity forcing fields for the CMS model. The surface wind drift parameterization employs surface winds and wind stresses from the 0.5-degree Navy Operational Global Atmospheric Prediction System (NOGAPS) with a wind factor of 0.03 of surface winds added to the upper-layer ocean currents. The transport and evolution of the oil particles are tracked by the oil-CMS model during the 100 days of the simulation, recording each droplet’s horizontal position, depth, diameter, density, oil mass, and fractions of gas/oil into the model trajectory output files every 2 hours. The parameters and units section contains more information on different types of post-processed data and the variables provided in the dataset. To obtain representative oil concentrations or oil mass on a regular horizontal and/or vertical grid, modeled oil droplets must be scaled to account for the total amount of oil spilled into the ocean during the actual blowout, as estimated from the reports (730,000 tons). The scaling is done differentially for the droplets, depending on their initial size and oil content. The data for the oil concentrations are daily average values in ppb units; the oil mass units are kg of crude oil. Horizontal 0.02-degree post-processing grid covers the entire Gulf of Mexico domain and beyond (18.1N-31.0N, 98.0W-77.0W), and the vertical grid as indicated in the file metadata. Post-processed NetCDF files were created using Matlab software package, v. R2017a, and many are compressed using Matlab capability to reduce NetCDF files size; maximum compression or ‘DeflateLevel’ = 9 is used. Non-gridded files labeled oilmass_landed.txt contain sedimented oil mass that reached the ocean floor/beach and is no longer is transported by the oil-CMS model. The files labeled *oilmass_exited.txt contain data for the droplets that exited the model domain. The data represents the scaled oil mass (in kg) for a given droplet. Note that the data are non-gridded, minimally post-processed, and presented in a particle-tracking framework; see the notes on the format in the Data Parameters and Units section. Additional droplet statistics are provided in Matlab (.mat) and *.txt format. Numerical simulations and post-processing were performed using a Pegasus supercomputer at the Center of Computational Science, University of Miami, in 2019-2020. Model code notes: CMS has a Lagrangian, particle-tracking framework, computing particle evolution and transport in the ocean interior. The website for the main CMS code may be found at https://github.com/beatrixparis/connectivity-modeling-system. The oil-CMS module is still under development.

Provenance and Historical References:

Simeon Pesch, Philip Jaeger, Aprami Jaggi, Karen Malone, Marko Hoffmann, Dieter Krause, Thomas B.P. Oldenburg, and Michael Schlüter. (2018). Rise Velocity of Live-Oil Droplets in Deep-Sea Oil Spills. Environmental Engineering Science, 35(4), 289–299. doi:10.1089/ees.2017.0319

Individual Files: