Anusha L. Dissanayake

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

Significance Environmental risks posed by deep-sea petroleum releases are difficult to predict and assess. We developed a physical model of the buoyant jet of petroleum liquid droplets and gas bubbles gushing into the deep sea, coupled with simulated liquid–gas equilibria and aqueous dissolution kinetics of petroleum compounds, for the 2010 Deepwater Horizon disaster. Simulation results are validated by comparisons with extensive observation data collected in the sea and atmosphere near the release site. Simulations predict that chemical dispersant, injected at the wellhead to mitigate environmental harm, increased the entrapment of volatile compounds in the deep sea and thereby improved air quality at the sea surface. Subsea dispersant injection thus lowered human health risks and accelerated response during the intervention. During the Deepwater Horizon 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.

Modelling of hydrothermal vent plumes to assess the mineral particle distribution

A new numerical model that integrates hydrodynamics, thermodynamics, and the chemistry of mineral formation in deepwater hydrothermal vents is developed. Transport and spread of plume fluid and the minerals formed are simulated in three stages: plume dynamics stage that is momentum and buoyancy driven; transition to far-field conditions as a gravity current; and far-field conditions where the mineral particles move according to advection–diffusion governed by ambient currents and settling velocities that eventually lead to bed deposition. Thermodynamics include the change in plume temperature and its related properties. Chemical reactions due to hot vent fluid mixing with cold entrained ambient water into the plume change its properties and the behaviour. The model considers the formation of several types of minerals. Model simulations and field measurements compare reasonably well for plumes in Atlantic and Pacific Oceans. Results for a simulation in East Pacific Rise 21°N are presented.

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

We present the development and validation of a numerical modeling suite for bubble and droplet dynamics of multiphase plumes in the environment. This modeling suite includes real-fluid equations of state, Lagrangian particle tracking, and two different integral plume models: an Eulerian model for a double-plume integral model in quiescent stratification and a Lagrangian integral model for multiphase plumes in stratified crossflows. Here, we report a particle tracking algorithm for dispersed-phase particles within the Lagrangian integral plume model and a comprehensive validation of the Lagrangian plume model for single- and multiphase buoyant jets. The model utilizes literature values for all entrainment and spreading coefficients and has one remaining calibration parameter

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

\kappa

Modeling the impact of CO2 releases in Kagoshima Bay, Japan

κ, which reduces the buoyant force of dispersed phase particles as they approach the edge of a Lagrangian plume element, eventually separating from the plume as it bends over in a crossflow. We report the calibrated form

Simulating the aqueous dissolution of petroleum emitted into the Gulf of Mexico during the 2010 Deepwater Horizon disaster

\kappa = [(b - r) / b]^4