Yesterday evening the first containment dome, or cofferdam, departed Port Fourchon on Chouest’s M/V Joe Griffin en route to the Macondo wellsite. The system is designed to help capture the oil at the seabed and collect it securely for processing. The 40x24x14 feet steel vessel, which weighs almost 125 tons, is expected to be lowered to the seabed today in a process that should take approximately 48 hrs.
According to Rigzone:
Following the approximately 12-hour trip aboard the M/V Joe Griffin to the Deepwater Horizon site, the 125-ton cofferdam structure will be lowered approximately one mile to the sea floor where it will be placed atop the largest leak source. It will serve as a containment chamber, collecting crude oil and funneling it to the Discoverer Enterprise drillship on the surface via approximately 5,000 feet of 6 5/8-inch drill pipe riser.
Low water temperatures approximately 42 degrees Fahrenheit and high (2,300 psi) pressures at the great depth in question will make the operation particularly challenging. In order to prevent pipe-clogging gas hydrates from forming under these extreme conditions, BP will work to ensure that the crude oil stays at an acceptably warm temperature throughout the riser. It will do so by pumping seawater from the surface into the annular space of a second, 21-inch riser that will encase the primary riser and by pumping methanol into the top of the containment dome. Crude will be processed aboard the drillship and separated into oil, gas, and water. The oil will be stored on the ship and ultimately offloaded at a terminal facility on land.
Here’s a good infographic provide by Rian.ru:
Above onstruction of the containment domes takes place Wild Well Control at Port Fourchon, LA. (Images © BP p.l.c.)
PORT FOURCHON, La. – Crewmen aboard the motor vessel Joe Griffith guide a pollution containment chamber onto the deck as the ship is prepared to depart Wild Well Control May 5, 2010. The chamber was designed to cap the oil discharge that was a result of the Deepwater Horizon incident. U.S. Coast Guard photo by Petty Officer 3rd Class Patrick Kelley.
Cofferdam departs Wild Well in Port Fourchon 5 May 2010 on the Chouest 280 workship named Joe Griffin. (Image © BP p.l.c.).