BP Gulf Science Data Reveals Ineffectual Subsea Dispersant Injection for the Macondo Blowout

Abstract

After the Deepwater Horizon oil platform explosion, an estimated 172.2 million gallons of gas-saturated oil was discharged uncontrollably into the Gulf of Mexico, causing the largest deep-sea blowout in history. In an attempt to keep the oil submerged, massive quantities of the chemical dispersant Corexit R 9500 were deployed 1522 m deep at the gushing riser pipe of the Macondo prospect's wellhead. Understanding the effectiveness of this unprecedented subsea dispersant injection (SSDI) is critical because deepwater drilling is increasing worldwide. Here we use the comprehensive BP Gulf Science Data (GSD) to quantify petroleum dynamics throughout the 87-day long blowout. The spatio-temporal distribution of petroleum hydrocarbons revealed consistent higher concentrations at the sea surface and in a deep intrusion below 1000 m. The relative importance of these two layers depended on the hydrocarbon mass fractions as expected from their partitioning along temperature and pressure changes. Further, analyses of water column polycyclic aromatic hydrocarbons (PAH) of GSD extensively sampled within a 10-km radius of the blowout source demonstrated that substantial amounts of oil continued to surface near the response site, with no significant effect of SSDI volume on PAH vertical distribution and concentration. The turbulent energy associated with the spewing of gas-saturated oil at the deep-sea blowout may have minimized the effectiveness of the SSDI response approach. Given the potential for toxic chemical dispersants to cause environmental damage by increasing oil bioavailability and toxicity while suppressing its biodegradation, unrestricted SSDI application in response to deep-sea blowout is highly questionable. More efforts are required to inform response plans in future oil spills.

The choice of droplet size probability distribution function for oil spill modeling is not trivial

“…Studies had previously focused on the volume median size of oil droplets (d50) to understand its effect on emulsion stability (Tambe and Sharma 1994) and, immediately after the DWH, on the timing and amount of oil surfacing (Ryerson et al 2012). Ten years later, there is still an ongoing debate on the correct d50 of the DWH oil droplets, since the d50 estimated at the time of the spill was a decisive factor for the unprecedented use of sub-sea dispersant injection as a response strategy (Paris et al 2018). Droplet size distribution (DSD) estimates have thus been the focus of numerous analytical models, such as dynamical models (Zhao et al 2014, Gros et al, 2017 or equilibrium models with modified Weber number (Johansen et al, 2013) and of laboratory work under normal atmospheric conditions and temperature using the Ohmsett tank (Zhao et al 2016) and under high-pressure and coldtemperature using sapphire cell and jets experiments with gas-saturated petroleum (Aman et al, 2015.…”

Transport, Fate and Impacts of the Deep Plume of Petroleum Hydrocarbons Formed During the Macondo Blowout

“…Indeed, as gas suddenly expands with the pressure drop, the turbulent kinetic energy generated is high enough to atomize the oil in micro-droplets. When the oil is naturally dispersed by these thermodynamic processes, subsea dispersant injection (SSDI) which typically decreases the mean droplet size diameter, becomes largely ineffective since droplets are already small and entrained in a later plume (Paris et al, 2018). The outcome of such refinement needs then to be incorporated into models.…”

“…More than 7000 tons of chemical dispersants, namely Corexit 9500A and Corexit EC9527A, were applied at the ocean surface (∼ 5000 tons) and injected at depth at the broken wellhead (∼ 2000-3000 tons) in the attempt to break the oil into small droplets and ease its dispersal and degradation (Lubchenco et al, 2012). Such subsea dispersant injection (SSDI) was unprecedented and was tested by deploying increasing volumes of dispersant beginning on day 10 of the spill until the Macondo well was capped (Gros et al, 2017;Paris et al, 2018).…”

Oil spill modeling: Mapping the knowledge domain

“…In related work, a recent series of papers focused on response optimization for dispatching response vessels (Grubesic et al, 2017), prescribing the optimal configurations of exclusion booms to minimize spill impacts (Grubesic et al, 2018), and identifying optimal staging locations for response equipment in relation to sensitive coastal areas (Grubesic et al, 2019). Since the DWH, scholars have investigated the use and impacts of subsea chemical dispersant applications (Kleindienst et al, 2015) with recent work questioning the effectiveness of subsea applications to blowouts (Paris et al, 2018).…”