Petroleum dynamics in the sea and influence of subsea dispersant injection during Deepwater Horizon

Abstract

During the disaster, a substantial fraction of the 600,000-900,000 tons of released petroleum liquid and natural gas became entrapped below the sea surface, but the quantity entrapped and the sequestration mechanisms have remained unclear. We modeled the buoyant jet of petroleum liquid droplets, gas bubbles, and entrained seawater, using 279 simulated chemical components, for a representative day (June 8, 2010) of the period after the sunken platform's riser pipe was pared at the wellhead (June 4-July 15). The model predicts that 27% of the released mass of petroleum fluids dissolved into the sea during ascent from the pared wellhead (1,505 m depth) to the sea surface, thereby matching observed volatile organic compound(VOC) emissions to the atmosphere. Based on combined results from model simulation and water column measurements, 24% of released petroleum fluid mass became channeled into a stable deep-water intrusion at 900- to 1,300-m depth, as aqueously dissolved compounds (∼23%) and suspended petroleum liquid microdroplets (∼0.8%). Dispersant injection at the wellhead decreased the median initial diameters of simulated petroleum liquid droplets and gas bubbles by 3.2-fold and 3.4-fold, respectively, which increased dissolution of ascending petroleum fluids by 25%. Faster dissolution increased the simulated flows of water-soluble compounds into biologically sparse deep water by 55%, while decreasing the flows of several harmful compounds into biologically rich surface water. Dispersant injection also decreased the simulated emissions of VOCs to the atmosphere by 28%, including a 2,000-fold decrease in emissions of benzene, which lowered health risks for response workers.

Integral models for bubble, droplet, and multiphase plume dynamics in stratification and crossflow

“…Simulations are built by utilizing the various methods in each of the main Python modules of TAMOC; the ./ bin/ directory on the Github repository provides example scripts for typical types of model simulation. The model was first introduced in [33,34] and has been applied to simulate the thermodynamic behavior of Deepwater Horizon oil [29,35] and to hindcast a short period of the Deepwater Horizon oil spill [30]. This section presents the technical details of the modeling suite needed to appreciate the validation and application sections that follow.…”

“…This allows the model to predict the evolution from live oil (liquid oil with large amounts of dissolved gas) to dead oil (liquid oil with the volatile components removed) via ebullition of the gas out of the liquid phase as a fluid particle decompresses and cools. In general, TAMOC can consider two-phase particles, such as was reported in Gros et al [30]. Here, we simplify these dynamics and compute the phase equilibrium at the release and initialize only single-phase particles (gas or immiscible liquid) that are assumed to remain single-phase throughout their ascent through the water column (though they may transition from gas to liquid after the volatile components dissolve into seawater).…”

“…Models differ in their complexity, with oil-well blowout models generally requiring non-ideal equations-of-state and solubility models [28]. Here, we utilize a discrete particle model developed for the Deepwater Horizon reservoir fluids [29,30] and focus our discussion on the dynamics of multiphase plumes in the environment.…”

Modern Assessment of Natural Hydrocarbon Gas Flux at the Coal Oil Point Seep Field, Santa Barbara, California

“…The potential changes in bubble sizes are caused by a combination of gas transfer through the gas‐liquid interface and changes in hydrostatic pressure as gas bubbles rise through the water column (McGinnis et al, ; Rehder et al, ). In order to assess the relevance of these changes, the Texas A&M Oilspill Calculator (TAMOC) model (Gros et al, ; Gros et al, ) was used to predict the changes in bubble size as a function of depth. The TAMOC model was provided with bubble gas composition at a depth of 70 m (see supporting information Table S2), aqueous concentration of oxygen (Scripps Institution of Oceanography, University of California, ; see supporting information Table S1) and atmospheric equilibrium nitrogen concentration.…”

Numerical Modeling of the Interactions of Oil, Marine Snow, and Riverine Sediments in the Ocean

“…Predictions from deepwater oil and gas blowout plume models (Dissanayake et al, ; Johansen, ; Spaulding et al, ; Yapa & Li, ) can be used to calculate the oil in the water column, in intrusions, and on the surface. Spaulding et al () estimated that total insoluble hydrocarbon into the deep plume was 1.09 × 10 6 ± 1.422 × 10 5 during the DWH spill and Gros et al () estimates that about 73% petroleum mass remained in the water without dissolving in the days after the fallen riser was removed from the wellhead. Without further information we amended the list of marine snow components included in the SLAMS model to include the following: diatoms, picoplankton, fecal pellets, TEP, river sediments, and oil.…”