OREANDA-NEWS. December 27, 2012. BP announced it has once again confirmed the integrity of the Macondo well and its associated relief wells following a recent subsea survey to identify potential sources of a surface sheen near the Deepwater Horizon accident site in the Gulf of Mexico.

The latest survey marks the fourth time since the Macondo well was permanently sealed in September 2010 that it has been visually inspected by remotely operated vehicles (ROV) at the sea floor and confirmed not to be leaking.

Under a plan approved by the Coast Guard, BP and Transocean deployed ROVs early last week to determine whether there is residual oil still trapped under wreckage on the sea floor that may be escaping and causing the sheen on the water’s surface. The Coast Guard has said the sheen is not recoverable and poses no risk to the shoreline.

The four-day survey was conducted jointly by BP and Transocean, owner of the Deepwater Horizon drilling rig, with Coast Guard oversight. It was performed in the presence of the Federal On-Scene Coordinator (FOSC) for the Deepwater Horizon oil spill, as well as representatives from the Interior Department’s Bureau of Safety and Environmental Enforcement (BSEE) and Bureau of Ocean Energy Management (BOEM) and State On-Scene Coordinators from Louisiana, Mississippi and Florida.

During the survey, the ROVs inspected the drilling rig, portions of the riser that once connected the rig to the sea floor and BP’s cofferdam, an 86-ton, steel container that was lowered over a leaking drill pipe during the Deepwater Horizon response in 2010 in an attempt to capture the oil and siphon it to the surface. The cofferdam, which was not part of the operation to seal the well itself, now sits abandoned on the sea floor, roughly 1500 feet from the Macondo well. While the survey was focused on finding still-trapped oil in the wreckage, it also looked at the Macondo well head and the well heads of its two associated relief wells to confirm integrity.

No conclusive evidence of hydrocarbons leaking was observed from any of the surveyed areas. However, a white, cloudy substance appeared to be emanating from several places on the overturned rig, and samples of the substance were collected. BP will review the results of the investigation with the Coast Guard.

The Macondo well was capped on July 15, 2010, and permanently sealed with cement on Sept. 19, 2010. The well was later plugged and abandoned with the approval and oversight of the U.S. government. Well integrity was confirmed during and after the abandonment process.

On Aug. 25, 2011, BP again confirmed the integrity of the Macondo well and the two associated relief wells with an ROV inspection that came after a surface sheen was reported near the well site.

A third ROV inspection followed when BP reported another surface sheen at Mississippi Canyon 252 on September 16, 2012, to the National Response Center. Following the discovery, BP took a number of voluntary actions to monitor the situation, including surveys by aircraft and vessel. The FOSC then issued a Notice of Federal Interest to BP and Transocean, which together developed a plan to survey the well area with ROVs. That plan was approved by the Coast Guard and resulted in continuous monitoring from October 15 through October 17. It also led to the discovery of oil droplets leaking from an abandoned piece of subsea equipment used in the response called a cofferdam. Days later, ROVs plugged openings in the 86-ton container, which sits roughly 1500 feet from the Macondo well head, to prevent additional residual oil from escaping.

The fourth and latest ROV inspection was conducted after BP on Nov. 2 reported a sheen in the vicinity of the accident site.

BP will continue to work with the Coast Guard and Transocean on any further steps, as needed, to address the results of the most recent ROV survey.