BP (NYSE:BP) announced it has once again confirmed the integrity of the Macondo well and its associated relief wells following an extensive subsea survey this week to identify potential sources of a surface sheen near Mississippi Canyon block 252 in the Gulf of Mexico.
The latest survey marks the third time since the Macondo well was permanently sealed in September 2010 that it has been visually inspected at the sea floor and confirmed not to be leaking.
The nearly three-day-long inspection was also successful in identifying the cofferdam, a piece of containment equipment used during the Deepwater Horizon response, as the probable source of the surface sheen.
The survey was conducted jointly by BP and Transocean with Coast Guard oversight. It was also 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.
The cofferdam is a 86-ton, steel container that was lowered over a leaking drill pipe at the Macondo well site in May 2010 in an attempt to capture the oil and funnel it to the surface. A mixture of oil and slushy methane hydrates was trapped inside the cofferdam during the response.
On October 17, Remotely Operated Vehicle (ROV) video inspection observed small, intermittent drops of oil coming from an opening at the top and another on one side of the cofferdam. Samples of the droplets have been collected from the opening at the top, known as the stovepipe, and will be analyzed to confirm a match with the sheen. Droplets were also observed coming out of a small connection port on oneside of the cofferdam.
The Coast Guard has determined the sheen is not feasible to recover and does not pose a risk to the shoreline.
ROV inspection began October 15 on several potential sources of the sheen, including the drilling riser that once connected the drilling rig to the sea floor, the Macondo well head and the well head of its associated relief wells.
The survey confirmed that no oil is leaking from the Macondo well, nor from the relief well that ultimately intercepted and permanently sealed it. A backup relief well that never intercepted Macondo was also surveyed and confirmed to have integrity.
In addition, the entire length of the 4500-foot riser was visually inspected, with separate passes made for the top and two sides, and no oil was seen leaking.
The ROV inspection came after BP reported the sheen on September 16 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 ROV’s. That plan was approved by the Coast Guard and resulted in more than 70 hours of video inspection from October 15 through October 17.
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 once again confirmed the integrity of the Macondo well and the two associated relief wells with an ROV inspection that came after a separate surface sheen was reported near the well site.