The first containment dome—a 40'x24'x14' steel structure weighing almost 100 tons—was lowered to the seabed last night as the first onsite element of a subsea recovery system that responders hope may capture up to 85% of the oil flowing from the riser from the sunken Deepwater Horizon rig. (Earlier post.)
|The mobile offshore drilling unit Q4000 lowers a pollution containment chamber 6 May 2010. The chamber was designed to cap the oil discharge that was a result of the Deepwater Horizon incident. US Coast Guard photo by Petty Officer 3rd Class Patrick Kelley. Click to enlarge.||Oil washes onto the sides of the pollution containment chamber as it is lowered into the water at the Deepwater Horizon site. U.S. Coast Guard photo by Petty Officer 3rd Class Patrick Kelley. Click to enlarge.|
Once lowered to the sea bed, the next steps will be to connect the cofferdam to a ship on the surface for recovery of the leaking hydrocarbons. Once this operation is complete it will be possible to assess the effectiveness of the solution, BP says.
|“Basically, there are two ways of regaining control of a well that has blown out. One method is to attempt a surface kill by pumping or circulating fluid into the well that is blowing out. A second method is to drill relief wells directionally to attempt a kill from within the formation.”|
|—Ely et al., 1987|
On Wednesday, BP CEO Tony Hayward told the Houston Chronicle that it was considering trying the top-kill method to plug the flow. Top-kill is commonly used to control wells on land, but has never been used at the depth (5,000 feet, 1,524 meters)—and accompanying high pressures—of the Macondo well.
In this approach, the ROVs would remove a control mechanism from the blowout preventer (BOP) and reconfigure it. Then, hoses will be inserted into existing choke and kill lines on the device. Barges on the surface would first pump pieces of matting and rubber into the well, followed by heavy drilling muds and cement that should provide adequate pressure on the reservoir to close it.
Work on the first relief well, which began on Sunday 2 May, continues. It is expected to take some three months to complete.
Ely, J.W. et al. (1987) Conventional and Unconventional Kill Techniques for Wild Wells (SPE Annual Technical Conference and Exhibition 1987) doi: 10.2118/16674-MS
Schubert, Jerome (1995) Well Control Procedures for the Proper Identification and Handling of Kicks for the Prevention of Blowouts (Texas A&M)