Science plays key role in determining amount of oil spilled during 2010 Gulf disaster

By Alisha Renfro, Coastal Scientist, National Wildlife Federation 

A “vessel of opportunity” skims oil spilled after the Deepwater Horizon/BP well blowout in the Gulf of Mexico in April 2010. Photo: NOAA.

The unprecedented scale of the 2010 BP oil spill and the further complexity introduced by its deep water location pushed scientists involved in the response effort to apply both old and new research methods to estimate the rate of oil flow from the well and the total volume of oil spilled. Currently in New Orleans, phase II of the BP oil spill trial – which will focus on that very question of how much oil gushed from the well into the Gulf during the 86 days between the initial blowout and when the well was finally capped – is underway. Ultimately, this total volume of oil spilled will play a key role in determining the amount of Clean Water Act penalties BP will pay. The decisions made during this phase of trial will come down on the hard work and innovation of the scientific community’s response to a spill that happened under difficult conditions that didn’t have easy solutions.

In an article in the December 2012 issue of Proceedings of the National Academy of Sciences, scientists involved in the response reviewed the different methods used to estimate the flow rate of crude oil from the well. The researchers concluded that the science supports flow rates that ranged from 50,000 to 70,000 barrels of oil per day, resulting in a total release of around 5 million barrels of oil from the well, with 4.2 million barrels making it into the Gulf of Mexico ecosystem due to recapturing efforts by BP.

In the days immediately following the April 20, 2010 well blowout, the flow rate of oil from the well was one of the most critical pieces of information needed to inform response efforts and prepare designs and procedures that could be used to try and cap the well. Measuring the rate of flow of oil was more complicated than it may seem as the material gushing from the well consisted of a combination of oil and natural gas. To meet this need, an official technical group was gathered which included experts from a variety of scientific disciplines that would work on estimating flow rate and the total volume of oil released.

Heavy band of oil seen during an overflight on May 12. Credit: NOAA.

Flow rate estimates were calculated from a variety of different methods, including oil collection at the sea surface, acoustic and video observations, sampling and analysis of the composition of the discharge material, infrared imaging from aircraft and from modeling the depletion of the reservoir after the well was capped. Some of these methods yielded what were considered more reliable estimates than others. However, quite remarkably, almost all of the methods reviewed in this article converged on flow rates that ranged from 50,000 to 70,000 barrels per day.

Based on the flow rate of oil and its variability with time, the science team involved estimated that approximately 5 million barrels of oil would have been discharged from the well over the 86 days it remained uncapped. Differences between flow rate measured at the well and flow rates calculated from what was observed at the ocean surface suggest that 2 million barrels of oil never made it to the ocean surface and remain in the deep sea. This suggests that the ongoing effects of the oil spill may not be known for years to come.

As phase II of trial continues this week, expert witnesses will testify on rate of oil flow from the Macondo well, using sound science to support their conclusions.