«

»

Teachable Moments from the Deepwater Horizon Catastrophe

The Deepwater Horizon site. (Photo/NOAA). (via oceanservice.noaa.gov)

By Tania Tauer

The Deepwater Horizon oil spill has the unfortunate honor of being the largest offshore spill in U.S. history. The unprecedented disaster left 11 dead and spewed nearly 5 million barrels of oil into the Gulf of Mexico, covering more than 650 miles of coastal habitat with crude.

Last Thursday evening, CU students and Boulder community members gathered in a packed lecture hall on the University of Colorado campus to hear a panel of experts, led by former secretary of the Navy Donald Winter, who spearheaded the National Academy of Engineering’s investigation into the accident, explain the unfortunate causes and heroic, yet difficult, management of the spill.

Instead of delivering a contemptuous lecture, the panel presented the story of the negligence that caused the disaster and the creative solutions that ultimately contained it as lessons for the future.

In 2010, BP leased the Deepwater Horizon rig from Transocean to drill an exploratory oil well through the ocean floor in the Macondo prospect, off the coast of Louisiana. The rig’s crew found a series of four separate oil reserves at a depth of 18,000 ft. Upon this discovery, BP planned to “temporarily abandon” the well, a common procedure that seals off the drilled hole. This would allow the company time to build a costly pipeline to transport oil back to shore without having to pay about $1 million a day to keep the drilling rig in operation, explained Winter.

To temporarily abandon a well, cement is poured into the shaft of the well around a central pipeline to seal off any flow. But the Deepwater Horizon crew ran into complications when planning for their abandonment because of an unusual pressure gradient within the drilled hole, said Winter. Typically, pressure increases as you travel to lower depths. In this particular well, this phenomenon held true until the oil reserves were reached, at which point the pressure began to decrease. Dealing with this unique pressure profile required a mixture of cements to ensure the pressure in the well did not exceed the pressure required to fracture the surrounding rock, Winter explained.

Initial tests showed that the cementing job adequately controlled the pressure within the well. However, subsequent tests showed a huge pressure build-up within the pipes. Instead of addressing this issue, workers continued their plans to temporarily abandon the well. This decision allowed the pressure to continue increasing until the temporary seal on the well broke, releasing a volatile mix of hydrocarbons and natural gas that sparked an explosion that engulfed the Deepwater Horizon rig.

If proper procedures had been followed, the Deepwater Horizon disaster could have been prevented, said Winter. He acknowledged that with constant innovation in drilling technology it is difficult to set regulations that will be applicable to future drilling operations. However, policy makers learned a great deal from this incident and have enacted policy changes that will hold operating companies more highly accountable for the human and environmental safety of their oil rigs, he said.

A heavy band of oil seen during an overflight on May 12, 2011. (Photo/NOAA). (via oceanservice.noaa.gov)

The disastrous spill would have been less devastating if a piece of equipment, called the blow-out preventer, had not malfunctioned, explained Paul Hsieh, a US Geological Survey scientist who was named 2011 Federal Employee of the Year for his involvement in the federal management of the spill.

When the well pressure reached its limits, the blow-out preventer should have activated and sealed the well to prevent the outward flow of fluid. But the explosion jarred the drill pipe with such force that it was no longer able to properly secure the well, he explained.

Once the blow-out preventer failed, BP tried to use a containment dome to cover the leaking pipes and collect the renegade oil, a technique that has been used successfully to manage shallow water oil spills. However, engineers did not account for the cold temperatures and high pressure a mile below sea level that caused the released methane gas to crystallize and clog the dome, said Hsieh.

When the dome failed, President Obama decided the government would step in and oversee subsequent containment operations. Hsieh and a group of other federal scientists set up headquarters on an entire floor of the BP center in Houston, TX, and worked around the clock for the next three months to control the flow of oil out of the damaged well.

The government team failed at their first attempt to quell the flow of oil because of a drastic underestimation by BP as to the amount of oil gushing from the fractured well, Hsieh explained. The committee then developed a plan for engineers to cut off the top of the existing well and lower a specially designed capping stack over it. The capping stack was sealed, but a valve was left open to allow oil to continue to flow. Hsieh explained that the team feared the interior of the well had been cracked in the initial explosion. If the cap was closed while the well was compromised, then the pressure could build up in the well and cause the surrounding ground to fissure. This could cause oil to flow out of cracks in the ground rather than the drilled well, a situation far worse than the one at hand.

Before making the crucial decision about whether to permanently seal off the entire well, engineers had to test the well’s stability. Disappointingly, the test proved inconclusive and, based on protocol, they had 24 hours to decide whether to reopen the well or keep it sealed.

At this point, Hsieh was asked to model the integrity of the well. Subsequent action hinged on his calculations. An expert at modeling fluid flows, but new to modeling oil flows, Hsieh was able to adapt fundamental equations from water flow models to predict the behavior of the well. According to his findings, the test’s data agreed reasonably well with his model predictions for a stable well.

Based on Hsieh’s calculations, Secretary of Energy Steven Chu decided to keep the well capped for extended increments of time while closely monitoring its behavior. After three months of intense observation, the well was deemed stable and cement was poured over the cap to permanently seal the well.

As Hsieh finished this tense, whirlwind story, the audience collectively let out a sigh of relief as we vividly recalled the end of this four-month long debacle. While his actions awarded him the Federal Employee of the Year award, Hsieh was quick to turn attention away from his achievements and point out the importance of practicing effective science in crisis situations. He highlighted the necessity of mastering basic skills, learning fundamentals, being accurate and acting transparently.

While Hsieh listed these as imperative for acting in a crisis situation, really they are important values that can be followed by both scientists and non-scientists in day-to-day activities to prevent such crises. Perhaps if the operators of the Deepwater Horizon well had enacted these principles from the start, Hsieh would not have had to help contain one of the worst environmental disasters this generation has seen.

 

Tania is a fourth year PhD student in Chemical Engineering at CU-Boulder with an interest in renewable energy. Her graduate research focuses on the modeling of proton conducting materials for the development of battery and fuel cell devices. Tania holds a B.S. in Engineering Science from the University of Virginia. Besides writing and researching, she enjoys skiing, triathlons, and cooking.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>