New lessons from the worst oil spill disasterever30 June 2020, by Nancy Bazilchuk

Oil from the Deepwater Horizon poured into the Gulf ofMexico for 87 days, making it the largest ever accidentaloil spill on the planet. Eleven men died in the accident.Credit: Breck P. Kent/Shutterstock/NTB scanpix

Ten years ago, the Deepwater Horizon accident inthe Gulf of Mexico killed eleven men and resultedin the largest accidental oil spill in history. Years ofinvestigations concluded that the drilling crewmissed critical warning signals that would havestopped the problem. A new analysis suggests thatwasn't the case.

The magnitude of the Deepwater Horizon accidentis almost impossible to fathom. On April 20, 2010,eleven men died when the drilling rig exploded. Anestimated 507 million litres of oil spilled into theGulf of Mexico over 87 days, coating nearly 1000km of coastline with sticky black goo. Birds andmarine life took a beating, and shrimpers whorelied on the Gulf of Mexico were deeply affectedwhen fishing grounds were closed.

Years of investigations and legal proceedingsfound many reasons for the accident, including thatthe crew itself had missed critical informationwhich, had they noticed in time, would haveallowed them to address the problem before itexploded.

But a new analysis of data from the drilling platformpaints a very different picture of what haspreviously been found, said Dag Vavik, aNorwegian engineer with 30 years in the industry.Vavik recently defended his Ph.D. on the accidentat the Norwegian University of Science andTechnology.

"In previous investigation reports… we have beentold how the drilling crew failed to observe that thewell was flowing during the last 20 minutes beforethe explosion," Vavik said. "However, real time dataand witnesses from the Deepwater Horizon tell adifferent story."

Questioned industry standard

Vavik has nearly 25 years' experience designingoffshore floating drilling units, like the DeepwaterHorizon, and was well aware of the problems theserigs could face.

His experience made him question an industrypractice recommended in 2001 for separatingnatural gas from drilling mud. Vavik felt therecommendation could result in an uncontrolledrelease of mud and gas onto the rig.

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The oil spill from the Deepwater Horizon accident affectedmarine life and hundreds of birds, like this pelican. Credit:Breck P. Kent / Shutterstock / NTB scanpix

The Deepwater Horizon's mud gas separatorsystem was based on this recommendation. Theproblem was that the system was designed to allowgas and mud to return from the well by being routeddirectly to the mud gas separator without anyrestrictions, Vavik said.

His concerns about the industry practice led him towarn clients and alert his colleagues to theproblem. Ultimately, he ended up designing a newsystem for handling the mix of mud and gas fordeep water drilling ships commissioned byPetrobras in Brazil. He ultimately patented thedesign.

Vavik became deeply interested in the DeepwaterHorizon accident after reading BP's own report onthe disaster. The company found that one of themain problems contributing to the explosion wasthe design of the mud-gas separator system—theexact issue that Vavik himself had flagged yearsbefore, when the industry instituted its 2001practice.

"When I read this in the investigation report, Iblamed myself for not having done more than I did…to get the industry to change the industry practicewith having a mud gas separator directly connectedto the diverter system," he said. "At the time Ipromised myself to do whatever I could to preventsuch a disaster ever happening again."

Years later, however, Vavik found out that thedrilling crew probably didn't use the mud gasseparator system during the accident, and likelytried to divert this fluid directly overboard, which iswhat the written instructions said they weresupposed to do.

"In one way this was a relief," he said. "On theother hand, this meant that something else musthave caused this accident."

And that is what Vavik really wanted to find out.

Cleaning up some of the oil from the Deepwater Horizonaccident. Oil from the spill coated nearly 1000 km ofcoastline. Credit: Breck P. Kent / Shutterstock / NTBscanpix

Previously overlooked data

What launched Vavik on his Ph.D., however, wasthe discovery in 2014 that some information fromthe Deepwater Horizon had simply been dismissedas improbable.

To understand what Vavik found—and why itmatters—you need to first understand what thedrilling crew would have been looking for—and whatthey found.

The Deepwater Horizon drill ship was anexploration ship, looking for oil and gas. It was notdesigned to produce oil and gas, just to find it.Once the find at this particular drill site had beenconfirmed, the crew sealed off the well so it couldbe later developed for production. If all had goneaccording to plan, the drill ship would have movedon.

But things didn't go to plan. The well wasn't actuallysealed off properly, and instead, there was a hugebuild-up of gas in the well's piping system in thedays before drilling stopped and as the crew tried toseal off the well. This gas exploded on April 20 andcaught fire.

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Gas influx is a known problem, Vavik said, and theDeepwater Horizon had two independent sensorsthat should have detected it. In fact, the twosensors actually showed that there was no flow inthe system until right before the explosion.

But somehow investigators decided that the crewhadn't detected the problem. In their accidentassessment report, BP wrote that the "rig crew didnot recognize the influx and did not act to controlthe well until hydrocarbons had passed through theBOP (blow out preventor) and into the riser." Vaviksays that's not quite right.

Platform supply vessels battle the blazing remnants ofthe off shore oil rig Deepwater Horizon. A US CoastGuard MH-65C dolphin rescue helicopter and crewdocumented the fire on the mobile offshore drilling unitDeepwater Horizon, while searching for survivors.Multiple Coast Guard helicopters, planes and cuttersresponded to rescue the Deepwater Horizon’s 126person crew. Credit: US Coast Guard, public domain

Data suggests well was plugged

Using data from the sensors and a series ofsimulations in the lab, Vavik says that part of theproblem was that the system was plugged with gashydrates, which can form when natural gasencounters cold water and freezes into a kind ofnatural gas ice.

The plug of natural gas hydrates means that therewas no way for the crew to know exactly what wasgoing on until right before it happened.

Vavik said BP's investigations and simulationspredicted that thousands of gallons of fluid werecoming up from the well every minute during thelast 30 minutes before the explosion. However, hesaid, the two flow sensors showed that there wasno return flow from the well until right before theaccident.

"Several witness statements support what therecovered flow meter data was telling us. Thesituation developed extremely fast," he said. "Flowfrom the riser started to come back only a couple ofminutes before the first explosion."

Furthermore, Vavik said, some of the actionsknown to have been taken by the crew just beforethe explosion suggested that they knew there wasa plug in the system.

The crew was troubleshooting and investigatingwhat may have caused the anomalies they haddetected when the hydrate plug suddenly loosened,Vavik said.

"This caused rapid gas expansion and pressurebuilt up underneath the gas hydrate plug, allowingthe plug to move like a "bullet" in a gun barrel," hesaid. "Then it was too late to avoid the accident."

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The Deepwater Horizon drill ship before the accident.Credit: Wikipedia

A forensic study

Among Vavik's dissertation opponents was JeromeSchubert , an associate professor in petroleumengineering at Texas A&M University.

"Your dissertation was like a forensic study, step-by-step," he said during the defence. "You usedsimulations to back up your ideas. I liked your work,and it was great work."

Schubert said it was important for the industry tohave a better understanding of what can go wrongin deep water drilling situations, and that Vavik'sfindings did just that.

"That is the value of your work," Schubert toldVavik. "There were a lot of questions there (in theaccident) that no one had the answer to. You offerpotential reasons as to why things didn't looknormal."

Among the recommendations Vavik offered basedon his research was that the industry needs abetter way to detect influx of gas and gas hydratesearlier than was done on the Deepwater Horizon.The explosion couldn't have happened without tonsof natural gas entering the drilling systemundetected until it was too late, he said.

"The people who can tell the real story of whathappened are not here anymore," he said. "I hopethat the research work I have done will contribute togive the families and colleagues of the eleven mena better understanding of what really happened inthe last 45 minutes before the explosion."

Provided by Norwegian University of Science andTechnologyAPA citation: New lessons from the worst oil spill disaster ever (2020, June 30) retrieved 17 April 2022from https://phys.org/news/2020-06-lessons-worst-oil-disaster.html

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