Formation dynamics of subsurface hydrocarbon intrusions following the Deepwater Horizon blowout

Abstract

[1] Hydrocarbons released following the Deepwater Horizon (DH) blowout were found in deep, subsurface horizontal intrusions, yet there has been little discussion about how these intrusions formed. We have combined measured (or estimated) observations from the DH release with empirical relationships developed from previous lab experiments to identify the mechanisms responsible for intrusion formation and to characterize the DH plume. Results indicate that the intrusions originate from a stratification-dominated multiphase plume characterized by multiple subsurface intrusions containing dissolved gas and oil along with small droplets of liquid oil. Unlike earlier lab measurements, where the potential density in ambient water decreased linearly with elevation, at the DH site it varied quadratically. We have modified our method for estimating intrusion elevation under these conditions and the resulting estimates agree with observations that the majority of the hydrocarbons were found between 800 and 1200 m. Citation: Socolofsky, S. A., E. E.Adams, and C. R. Sherwood (2011), Formation dynamics of subsurface hydrocarbon intrusions following the Deepwater Horizon blowout, Geophys. Res. Lett., 38, L09602,

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

“…16, the trap depth of the first intrusion is close to the seafloor, and most of the dispersed phase transport will either be in the formation of subsequent intrusion layers (SPM) or Lagrangian particle transport in the water column (BPM passing particles to LPM). The observations during the Deepwater Horizon accident suggest that at most two subsurface intrusion layers resulted from the buoyant plume of oil and gas released at the seafloor [12,73]. Also, during Deepwater Horizon, the oil did not all surface directly above the wellhead, but rather surfaced with an offset in the down-current direction [74,75].…”

“…Using the correlation equations in Socolofsky and Adams [11,51], the separation point for this plume is predicted to be 0.28 m depth, and the peel point in quiescent stratification would be above the free surface. Although Socolofsky and Adams [11] suggested h S \h T as the criterion for a plume to be crossflow dominated, our recent experiments and the paper by Socolofsky et al [12] prefer the criteria h S \h P , and we follow this definition here. Hence, the plume in Fig.…”

“…While there are limited data for multiphase plumes with the combined effect of stratification and crossflow, Socolofsky and Adams [11] define plumes as crossflow-dominated when h S \h T and stratification dominated when h S [ h T . Empirical equations predicting these characteristic heights under idealized conditions (i.e., mono-dispersed, non-reacting dispersed phases in linear stratification or pure crossflow) have been fit to the experimental data and were applied by Socolofsky et al [12] to predict the intrusion height for the Deepwater Horizon accident. However, to include dispersed phase dynamics (compressibility, dissolution, and heat transfer), the combined effects of stratification and crossflow, and to predict the concentrations of dissolved components in the plume and intrusion layers, numerical plume models are required.…”

Diverse, rare microbial taxa responded to the Deepwater Horizon deep-sea hydrocarbon plume

“…Early during the DWH incident, before the damaged riser pipe was cut, hydrocarbon injection into the water column occurred as a pronounced jet that emerged from the broken riser pipe, altering deepwater chemistry in the vicinity of the Macondo wellhead. The jet of oil and gas ascending into the water column entrained cold seawater (Johansen et al, 2001;Socolofsky et al, 2011) and generated a prolific hydrocarbon-rich deepwater plume that was detected to the southwest of the well by its fluorescence signature (Camilli et al, 2010;Diercks et al, 2010;Hazen et al, 2010), and light scattering profile (Diercks et al, 2010), as well as by elevated concentrations of specific hydrocarbons (Camilli et al, 2010;Diercks et al, 2010;Valentine et al, 2010;Joye et al, 2011;Kessler et al, 2011b;Reddy et al, 2012) and of the dispersant Corexit (Kujawinski et al, 2011). The deepwater plume spanned depths between 1000 and 1300 m, in a region at least 35 km long by 2 km wide (Camilli et al, 2010).…”

Natural gas and temperature structured a microbial community response to the Deepwater Horizon oil spill

“…The organisms that consume ethane and propane, the other major components of natural gas, remain largely unknown in marine environments, but may include organisms related to methanotrophs or oil-degraders (6). Second, because of the depth of the spill, nearly all of the gas (2,7,8) and some components of the oil (9) remained in the deep ocean, forming plumes of dissolved or dispersed hydrocarbons between 1,000 and 1,200 m (10)(11)(12). The temperature at these depths was just 4°C to 6°C, much colder than surface water.…”