Friday, May 07, 2010

Methane Gas Bubble Triggered Explosion At Deepwater Horizon Rig In Gulf Of Mexico While BP Executives Were Celebrating the Rig's Safety Record

According to an Associated Press report published in both the Anchorage Daily News and the New Orleans Times-Picayune, among other sources, a methane gas bubble escaping from the drill site triggered the explosion which killed 11 and ultimately led to the sinking of the Deepwater Horizon rig in the Gulf of Mexico. Officials now estimate that more than 3 million gallons of crude have poured into the Gulf (Skytruth previously estimated 12.2 million gallons, but has provided no new estimate). This is also impacting Alaskan oil operations; the Interior Department has given Shell Oil until May 18th to provide more information about the company's exploratory drilling plans this summer in the Arctic Ocean. Shell will also fall under the temporary halt to all pending U.S. offshore drilling proposals, putting the company's summer Arctic drilling plans in limbo.

The Times-Picayune has a page of related stories HERE, which include reports about progress installing the containment box. View full-size graphic of the latest extent of the oil slick HERE.

The source of the information is from interviews provided by Robert Bea, a University of California Berkeley engineering professor who serves on a National Academy of Engineering panel on oil pipeline safety and worked for BP PLC as a risk assessment consultant during the 1990s. He received them from industry friends seeking his expert opinion. Ironically, seven BP executives were on board the Deepwater Horizon rig on April 20th celebrating the project's safety record. They were about to get one hell of a wakeup call, as far below, the rig was being converted from an exploration well to a production well.

As the workers removed pressure from the drilling column and introduced heat to set the cement seal around the wellhead, the chemical reaction created heat, destabilizing the seal and allowing a gas bubble to form inside the pipe. USA Today reports that Halliburton is under fire for possibly removing a mud safety barrier prematurely before a final cement plug was place in the well, which would have weakened emergency measures to control the powerful blowout caused by pressurized natural gas. As the gas bubble rose up the drill column from the high-pressure environs of the deep to the less pressurized shallows, it intensified and grew, breaking through various safety barriers. Up on the rig, the first thing workers noticed was the seawater in the drill column suddenly shooting back at them, rocketing 240 feet in the air. Then, gas surfaced, followed by oil. When the gas flooded into an adjoining mud room with exposed ignition sources, the first explosion occurred. Next to the mud room was the room where the BP executives were celebrating. The executives were injured, but survived. But out on the rig floor, nine rig crew and two engineers died.



This, of course, leads to questions as to whether the gas bubble would have been contained by the protective equipment had the well been drilled in shallower water. According to Answerbag.com, underwater pressure increases at a linear rate with increasing depth. For every 33 feet (10 meters) of water depth, the pressure increases by 1 atmosphere. This means that while the pressure would be equal to 10 atmospheres at 330 feet of water, the pressure would increase to 152 atmospheres in 5,000 feet of water. To provide more perspective, the published crush depth of combat submarines is around 3,000 feet.

A blowout preventer that would work fine in 330 feet of water would be useless in 5,000 feet of water unless specifically reinforced for the greater depth and pressure. Obviously, the blowout preventer installed in 5,000 feet water would be designed to withstand stronger pressure, but perhaps the engineers miscalculated the necessary strength. A blowout preventer can snuff a blowout by squeezing rubber seals tightly around the pipes with up to 1 million pounds of force. If the seals fail, the blowout preventer deploys a last line of defense: a set of rams that can slice right through the pipes and cap the blowout. Deepwater Horizon was also equipped with an automated backup system called a Deadman, which should have automatically activated the blowout preventer without human intervention.

Based on the interviews with rig workers, none of those safeguards worked.

The Mobile Press-Register published an interesting story on the discovery of the oil fields and the origin of the Deepwater Horizon rig. In September 2009, BP began exploring a promising oil field in the Gulf which they discovered through seismic imaging and data crunched on a supercomputer. The new oilfield was designated Tiber, and estimated to hold at least 3 billion barrels of crude, or six months' worth of U.S. consumption. The field was almost six miles (9.6 kilometers) beneath the Gulf of Mexico's floor, in a spot where the water is almost one mile deep. To access it, BP and its drilling contractor, Transocean Ltd., used the $365 million rig called the Deepwater Horizon, a floating thicket of machinery the size of two football fields, which held a crew of 130 and cost more than $500,000 a day to rent from Transocean.

But the Deepwater Horizon, as a drilling rig, didn't hang around to pump Tiber's crude. The self-propelled rig motored to the site of its next exploration at a place designated Macondo, located in water also a mile deep. There it began drilling into Mississippi Canyon Block 252, where the series of events triggering its demise began on April 20th.

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