Use of existing current profiling assets in the Gulf of Mexico to support the Deepwater Horizon response

The explosion and collapse of the Deepwater Horizon drilling rig in Mississippi Canyon Block 252 (MC-252) in the Gulf of Mexico in mid-April 2010 began the largest release of oil into the environment in US history. From 23 April, when the first oil sheen was noted on the surface, until 15 July, when the well was capped, oil flowed at varying rates from 1500 meters below the surface. Because of the high rate of flow and the use of dispersants, a cloud of oil and gas droplets was trapped between 1000 and 1300 meters depth. As the cloud was moved away by ambient currents, new oil and gas was added to the cloud. Since 2005, oil and gas platforms in the Northern Gulf of Mexico have been collected current profile data as mandated by the former Minerals Management Service (now the Bureau of Ocean Energy Management, Regulation, and Enforcement) in a Notice to Lessees (NTL). The data are transmitted to the National Data Buoy Center, where it would be quality controlled, stored, and broadcast over the Global Telecommunications System. The Deepwater Horizon was equipped with a 38 kHz Teledyne RDI ADCP and transmitted data minutes before the explosion occurred on the platform. Other platforms in the area, including Ram-Powell, Mars, and Holstein were collecting ADCP data during this time. The drilling rig used to drill the relief well, Development Driller 3 was also equipped with a 38 kHz ADCP, as was the Discoverer Enterprise rig used to bring oil and gas to the surface from the riser and BOP. The Development Driller 3 was in place at MC-252 and collecting ADCP data beginning 1 May 2010. The Discoverer Enterprise was drilling 55 km to the south-southwest of the Deepwater Horizon rig at the time it exploded. It remained there for ten days before moving to MC-252, 9 May 2010 to begin offloading oil and gas from the spill and collecting ADCP data. These two ADCP deployments of 38 kHz ADCPs, which penetrate to almost 1200 meters water depth, under good conditions, provided import- nt information at the site of the spill during the time that oil was flowing. The ADCP captures a time history of the direction that the oil and gas cloud moved away from the well head site. Weekly resultant current speed and direction information indicate the transport of the cloud. Additional ADCPs on platforms to the southwest of the Deepwater Horizon site provide information about the transport of the oil and gas clouds as they moved in that direction. CTD cast-based fluorometer and dissolved oxygen signatures of the oil in the months following the spill indicate the extent of the oil cloud at 1000 to 1300 meter depths. Combined with the ADCP data, a time history of the movement of the oil and gas cloud is possible.