American Block


At approximately 10 p.m. (CST) on Tuesday, April 20, an explosion rocked Transocean's Deepwater Horizon drilling rig in what has escalated into one of the nation's deadliest offshore drilling incidents of the past half-century.

After the initial blowout occurred, the leaking wellhead continued to feed the fire onboard the semisub until the rig ultimately collapsed beneath the deep waters of the U.S. Gulf of Mexico.

Situated on Mississippi Canyon Block 252, more than 50 miles southeast of Venice off Louisiana's coast, the Deepwater Horizon recently suspended drilling operations on the Macondo prospect. According to the Minerals Management Service, BP filed a permit to temporarily abandon the well on April 16.

The Deepwater Horizon semisub commenced drilling on the Macondo prospect in February 2010 and had recently terminated drilling at a depth of just over 18,000 ft.

Operating alongside the U.S. Coast Guard and the Minerals Management Service, BP has since launched a comprehensive, pre-approved oil spill response plan following the April 22 sinking of the Deepwater Horizon.

A collaborative investigation conducted by the Coast Guard and Minerals Management Service to determine the cause of the incident is in progress.

As the responsible party, BP is required to fund response and recovery costs. The Oil Spill Liability Trust Fund is also available to fund costs if required.

Below is a chronological overview comprising the events taking place from the moment the rig was submerged to the current well intervention measures taking place to subdue an oil spill identified at the well site.



On Thursday, April 22, the Deepwater Horizon experienced additional explosions in the aftermath of the first blowout, and subsequently sunk just below the surface roughly 130 miles southeast of New Orleans in almost 5,000 ft. of water.

There were approximately 700,000 gallons (2.6 million liters) of diesel fuel onboard the massive rig.

Following the Deepwater Horizon's initial explosion, the U.S. Coast Guard initiated a round-the-clock rescue mission, during which an estimated 126 crewmembers were able to evacuate from the rig. Seventeen workers were injured in the initial blast and were immediately transported to shore to receive medical care at facilities located in the Gulf coastal states of Alabama and Louisiana.

Eleven workers were reported missing Wednesday, April 21. After days of emergency response operations, the Coast Guard suspended the search for the 11 missing crewmembers at approximately 7 p.m. on Friday, April 23. The Coast Guard searched continuously for three days, the effort of which consisted of 28 air and surface sorties, covering more than 5,000 square miles.

On Thursday, April 22, operator BP initiated a plan of intervention to halt the oil flows beginning to surface around the submerged rig and well location using remotely operated vehicles. After the rig's collapse, a one-mile by five-mile slick had settled on the surface.

Specifically, BP mobilized 32 spill response vessels, including a large storage barge, as well as deployed resources comprising skimming capacity of more than 171,000 barrels per day, offshore storage capacity of 122,000 barrels with an additional 175,000 barrels on standby, supplies of more than 100,000 gallons of dispersants and four aircraft to carry out the dispersant operations.

With initial well intervention efforts under way, the Coast Guard announced on Friday, April 23, that oil no longer appeared to be flowing from the Macondo well head. Approximately 1,900 gallons of dispersant were applied Friday and 33,726 gallons of oily-water mix was recovered by surface skimmers.

However, during an overflight conducted by the Coast Guard over the weekend, a 20-mile by 20-mile rainbow sheen with areas of emulsified crude was spotted about 40 miles offshore.

On Sunday, April 25, the unified command continued intervention efforts in an attempt to contain the source of oil emanating from the wellhead. A plan was previously approved to utilize submersible ROVs in an effort to activate the blowout preventer on the sea floor and to stop the flow of oil, estimated to be leaking at a rate of up to 1,000 barrels/42,000 gallons a day.

At the start of the week ending April 29, rig personnel were evacuated from Diamond Offshore's Ocean Endeavor semisubmersible drilling rig, located on Mississippi Canyon Block 211.

Transocean's GSF Development Driller III was the first rig mobilized for the drilling of a relief well late Monday to secure the Macondo exploration well. According to BP's Chief Executive, Tony Hayward, the first relief well, expected to cost around $100 million, could potentially take up to three months to drill.

BP will also drill a second relief well using Transocean's Discoverer Enterprise drillship, currently en route to Mississippi Canyon Block 252. Both drilling rigs are under contract to BP.

During a flyover on Tuesday, April 27 at 5:00 p.m. (CST), the Coast Guard identified a rainbow sheen approximately 600 miles in circumference with areas of emulsified crude in the Gulf of Mexico. The edge of the sheen was approximately 23 miles off the coast of Louisiana. Five staging areas are now in place and ready to protect sensitive shorelines.

On Wednesday, April 28, the Coast Guard initiated an in situ burn on portions of an oil slick that continues to spread closer to the U.S. Gulf coastline, where ecological areas are at risk.

Furthermore, U.S. government officials revised estimates of the Macondo spill's volume to as much as 5,000 barrels of oil per day, or five times the original figure, on Thursday, April 29. The revised spill estimate was made public by the U.S. National Oceanic & Atmospheric Administration (NOAA).

BP has so far been unsuccessful in shutting off the well's oil flows using eight remote-controlled submarines to activate the blowout preventer and efforts have escalated under the Obama Administration's discretion. To date, more than 100,000 feet of boom (barrier) has been assigned to contain the spill. An additional 286,760 feet is available and 320,460 feet has been ordered.

As of Thursday, April 29, the oil spill response team has recovered 16,311 barrels (685,062 gallons) of an oil-water mix. Vessels are in place and continuing recovery operations.

White House Press Secretary Robert Gibbs has indicated that the future of President Obama's offshore drilling expansion plan opening up new areas in the eastern Gulf of Mexico could depend on the cause of the spill. The Interior Department has ordered a safety review of all offshore rigs.

The oil spill is now threatening coastal waters from Louisiana to Florida.