August 17, 2010
Methods That Have Been Tried to Stop the Leaking Oil
Efforts to Suppress the Flow of Oil
Since a fire engulfed the Deepwater horizon rig in the Gulf of Mexico on April 20, engineers have attempted a number of techniques to slow or stop the torrent of oil leaking from the wellhead 5,000 feet below the surface.
Sep. 21The Bottom Kill
The federal government has finally declared the Macondo well dead after nearly five months of failed attempts and semi-successes by BP engineers to permanently plug the leaking well in the Gulf of Mexico.
Aug. 14Making progress on the relief well
BP engineers continue developing a more specific plan on how to complete the bottom kill with minimal risk. When engineers pumped cement into the Macondo well's metal casing pipe during the static kill last month, it is possible that cement also entered the annulus, the space between the pipe and the bore hole.
Aug. 3The Static Kill
Engineers successfully pump mud through a valve on the blowout preventer and into the existing well’s metal casing pipe in a procedure similar to the failed top kill. They are able to pump mud slower and at lower pressure because a new cap atop the well has stemmed the flow of oil. Mud forces the oil and gas back down into the reservoir. Cement is also pumped in to seal the well.
July 15Testing to See if the Well Is Intact
A new capping assembly stops the flow of oil for the first time. Engineers begin monitoring pressure in the well to determine its integrity.
July 12Adding More Capacity
After days of delays due to weather, the Helix Producer, a production vessel on the surface, begins collecting oil. BP officials say that they eventually expect to have a total of four vessels on site to collect and process oil and gas. The Q4000 will be replaced by another vessel, Toisa Pisces, which will be connected to one of two floating risers that can be disconnected in the event of a hurricane.
July 10A Better Cap
BP replaces the cap put in place on June 3 with a tighter one that could potentially stop the flow of oil from the well. The new cap has some of the same types of components as the blowout preventer.
June 16Capturing More Oil
A second containment system begins siphoning oil and gas from the leaking well. BP estimates the system will carry 5,000 to 10,000 barrels a day to the surface, supplementing the roughly 15,000 barrels collected daily by a containment cap on top of the blowout preventer.
Using equipment originally put in place to inject heavy drilling mud during the failed top kill procedure last month, the new system extracts oil and gas directly from the blowout preventer, passes it through a manifold on the seafloor and pipes it up to the Q4000 surface vessel.
The Q4000 has no storage capacity and burns the oil and gas.
June 3Beginning to Capture Some Oil
A cap is placed over the top of the blowout preventer to funnel oil and gas to a surface ship. Methanol is pumped into the cap to prevent the formation of icy hydrates that could block the mile-long pipe rising from the cap. Oil continues to billow from under the lip and through four open vents on top of the device. Engineers are unable to close all the vents as originally planned.
May 31Another Attempt to Cap the Well
Engineers position submarine robots to shear the collapsed riser pipe so that a domeline cap could be placed over the blowout preventer to funnel some of the leaking oil to a tanker on the surface.
The new riser pipe has a 6.625-inch internal pipe to capture leaking oil and gas. Methanol and warm seawater is pumped down the riser to insulate the smaller pipe and prevent the formation of ice crystals, which caused the earlier containment dome to fail.
May 26The Top Kill and Junk Shot
In a procedure called the top kill, engineers pump heavy drilling mud into the well with hopes that the weight of the fluid overcomes the pressure of the rising oil. In another technique called the junk shot, objects including golf balls and pieces of rubber are injected into the blowout preventer. Both techniques fail to plug the leak.
May 16ATTACHING A TUBE
After two false starts, BP engineers successfully insert a mile-long tube into the broken riser pipe to divert some of the oil to a drill ship on the surface. Over nine days, the tube siphons off about 22,000 barrels of oil, which is just a fraction of the total spill.
May 7LOWERING A CONTAINMENT DOME
Workers lower a four-story steel box over the larger leak. But when crews discover that the dome’s opening is becoming clogged with an icy mix of gas and water, it is set aside on the seabed.
May 2DRILLING RELIEF WELLS
BP begins drilling the first of two relief wells that may later be used to inject mud and cement into the existing well.
April 30CHEMICAL DISPERSANTS
Crews inject chemical dispersant into the oil as it flows from the main leak underwater. The dispersant, conventionally used on the water surface, is intended to break the oil into small droplets, reducing its buoyancy. The full impact of chemical dispersants on the underwater ecology is unknown. The E.P.A. later orders BP to change to a less toxic chemical than originally used.
April 25REPAIRING THE BLOWOUT PREVENTER
Officials use remotely operated submersibles to try to activate the blowout preventer, a stack of valves at the wellhead meant to seal the well in the event of a sudden pressure increase. A crucial valve had never fully deployed, and efforts to activate the device after the explosion are unsuccessful.
How the Leak Started
Gerald Herbert/Associated Press
On April 20, the Deepwater Horizon, a drilling rig 50 miles off the coast of Louisiana in the Gulf of Mexico, exploded into flames. Two days later the rig sank, causing the 5,000 foot pipe that connected the wellhead to the drilling platform to bend. On April 24, robotic devices discovered two leaks in the bent pipe, nearly a mile below the ocean surface.
The wellhead was equipped with a blowout preventer, a 40-foot stack of devices designed to rapidly seal the well. But the preventer failed.