Subsea dispersant injection in response to a deep water oil and gas well blowout can improve the effectiveness of dispersant treatment; reduce the volume of oil that reaches the water surface; reduce human and wildlife exposure; disperse the oil over a large water volume at depth to reduce concentration; reduce the persistence of any oil that does surface; enhance oil biodegradation; and reduce shoreline exposure to floating and surface-water entrained/dissolved oil. Potential trade-offs of subsea dispersant use include increased water column and benthic resource exposures to oil at depth.
To better understand the implications of subsea dispersant use, RPS scientists modelled a hypothetical deep water well blowout in the northern Gulf of Mexico to predict oil fate and compare the environmental exposure of no intervention to four different response options: mechanical recovery, in-situ burning, surface dispersant application, and subsea dispersant injection.
Comparative Risk Assessment (CRA) of Response Options for an Uncontrolled Subsea Oil Well Blowout in a Deep Water Marine Environment
American Petroleum Institute (API)
We used probabilistic modelling to evaluate the influence of variable metocean conditions (i.e., wind, currents and temperature) on oil and gas fates and flow field characteristics. Using individual runs representative of specific metocean conditions, we simulated several different combinations of response options and compared oil fate, the amount and area of surfaced oil, and the area or volume of different surface and subsurface environmental compartments in which predicted exposure concentrations exceeded screening thresholds for potential effects.
RPS developed a CRA tool to systematically evaluate the potential environmental trade-offs associated with changes in oil distribution in the water column due to different response technologies. This compared the relative risk for environmental compartments using the oil spill exposure model results and information describing the relative distribution, density, and recovery potential of valued ecosystem components. Simulating a hypothetical deep water well blowout in the Gulf of Mexico with our CRA tool to examine consequences of different oil spill response technologies demonstrated that subsea dispersant injection was more effective for reducing oil exposures and relative risks to valued ecosystem components as a whole, and particularly those occupying sea surface and shoreline habitats.