Evolution of the Macondo Well Blowout: Simulating the Effects of the Circulation and Synthetic Dispersants on the Subsea Oil Transport

Abstract

During the Deepwater Horizon incident, crude oil flowed into the Gulf of Mexico from 1522 m underwater. In an effort to prevent the oil from rising to the surface, synthetic dispersants were applied at the wellhead. However, uncertainties in the formation of oil droplets and difficulties in measuring their size in the water column, complicated further assessment of the potential effect of the dispersant on the subsea-to-surface oil partition. We adapted a coupled hydrodynamic and stochastic buoyant particle-tracking model to the transport and fate of hydrocarbon fractions and simulated the far-field transport of the oil from the intrusion depth. The evaluated model represented a baseline for numerical experiments where we varied the distributions of particle sizes and thus oil mass. The experiments allowed to quantify the relative effects of chemical dispersion, vertical currents, and inertial buoyancy motion on oil rise velocities. We present a plausible model scenario, where some oil is trapped at depth through shear emulsification due to the particular conditions of the Macondo blowout. Assuming effective mixing of the synthetic dispersants at the wellhead, the model indicates that the submerged oil mass is shifted deeper, decreasing only marginally the amount of oil surfacing. In this scenario, the oil rises slowly to the surface or stays immersed. This suggests that other mechanisms may have contributed to the rapid surfacing of oil-gas mixture observed initially. The study also reveals local topographic and hydrodynamic processes that influence the oil transport in eddies and multiple layers. This numerical approach provides novel insights on oil transport mechanisms from deep blowouts and on gauging the subsea use of synthetic dispersant in mitigating coastal damage.

How Do Oil, Gas, and Water Interact Near a Subsea Blowout?

“…Finally, droplets with a diameter of 0.02-0.2 mm, typical of those expected at DWH for dispersant-treated oil experiencing significant latent breakup (Nagamine, 2014) could theoretically be transported 3-20 km before rising out of the intrusion layer. These transport distances are in general agreement with predictions for similar droplet sizes in farfield transport models (Paris et al, 2012;North et al, 2015).…”

“…simulate subsequent fate and transport of multi-fraction Lagrangian elements (Paris et al, 2012;North et al, 2015).…”

Evidence of lasting impact of the Deepwater Horizon oil spill on a deep Gulf of Mexico coral community

“…However, because the observed impact was patchy within many colonies (Figure 2), we consider it more likely that this variability reflected an uneven dispersion of the impacting agent in the water. If oil, dispersant, or a combination of the two were present as droplets (Adcroft et al, 2010;Paris et al, 2012) rather than dissolved when an underwater plume from the Macondo Well reached this aggregation of corals, the impact could have been patchy. Similarly, if the impact was in the form of toxic material adherent to particulate organic material or "marine snow" raining down from above (National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling 2011; Passow et al, 2012), then this form of delivery could also account for the patchy pattern of impact observed.…”

Influence of frontal cyclone evolution on the 2009 (Ekman) and 2010 (Franklin) Loop Current eddy detachment events

“…GoM-HYCOM was first employed to examine the evolving three-dimensional GoM response to Hurricane Ivan during 14-16 September 2004 (Prasad andHogan, 2007;Zamudio and Hogan, 2008). Since then, it has been used in several GoM simulation studies, either providing boundary and initial conditions to shelf models (Schiller et al, 2011;Kourafalou and Kang, 2012;Androulidakis and Kourafalou, 2013) or investigating physical or biological processes of the entire GoM region (Mariano et al 2011;Le Hénaff et al, 2012b;Paris et al, 2012;Valentine et al, 2012).…”