Gulf Oil Spill: Anatomy of a Disaster

Something was wrong. BP was preparing to plug its well 50 miles off the Louisiana coast, and longtime technical adviser Jesse Gagliano was running computer models to finalize details.

"We have a potential problem here," the Halliburton employee told three colleagues he met in the hallway in BP PLC's Houston headquarters. He said his computer model was predicting a "serious gas flow problem" with BP's well abandonment plan.

His idea for addressing the issue would never be carried out. BP decided it wasn't necessary. Five days later, on April 20, the well blew out, causing the worst offshore oil spill in U.S. history.

Special Section: Disaster in the Gulf
BP's Deepwater Accident Investigation Summary

In an internal report released Wednesday, BP stood by its decision, saying Gagliano's plan would not have stopped the explosion.

The disagreement was just one of several that emerged in the days and hours before the blast, according to BP's report and e-mails, documents and testimony gathered by federal investigators. Confusion surrounded crucial tasks and frustration rose among people involved.

The cause of the explosion, which killed 11 workers, remains under investigation by federal authorities. But as more information trickles out, the image of a high-stakes, high seas venture collapsing in disarray is sharpening.

The mile-deep exploratory well was being capped with cement so it could be abandoned until a production phase later.

BP operated the well, Transocean owned the rig and Halliburton carried out the cement job. They had to work together.

Yet key plans kept changing. Critical tests meant to ensure the well would be safely cemented were not going smoothly.

BP accepts some of the blame for decisions that led to the blowout, but its report also assigns fault to Transocean and Halliburton workers. Those companies, in turn, point the finger at BP's well design.

The head of the Deepwater Horizon rig, who was most familiar with its crew and operations, had left for training and was replaced by Bob Kaluza, who was less familiar with earlier problems surrounding the well. The operation was running 45 days late and millions of dollars over budget.

Gagliano's computer model exposed yet another possible problem. The longtime technical adviser concluded that the cementing operation needed more centralizers, devices designed to ensure that the casing — or drilling pipe — runs down the center of the wellbore to increase the chance for a perfect seal and prevent leaks. BP had planned to run six centralizers and had them onboard.

After a corridor chat with BP's senior drilling engineer, Gagliano worked up more models. By the evening of April 15, Gagliano had a model with 21 centralizers that resolved the gas flow problem. The 15 additional centralizers were acquired and scheduled for delivery the next morning, in time for the Halliburton cementers to do the job.

Still, the debate didn't end.

BP drilling engineer Brett Cocales learned the next afternoon, April 16, that his company's engineers had decided against using the additional centralizers because of questions about their mechanical integrity. Members of a BP investigation panel said Wednesday that those concerns were unfounded because engineers were mistaken about which centralizers had been shipped.

In an e-mail to fellow drilling engineer Brian Morel, Cocales explained the extra centralizers could help meet the goal of inserting the casing properly. Then he continued:

"But who cares? It's done. We'll probably get a good cement job," he wrote, frustrated it had taken so long to make a decision.

A few hours later, Halliburton cementer Nathaniel Chaisson, who was already on the rig, also learned the additional centralizers would not be used and notified Gagliano, who he said seemed concerned.

On April 19, Gagliano's models still showed that using only six centralizers raised the risk of a failed cement job. Still in Houston, he participated in the daily morning call with the rig. The centralizers weren't mentioned. He didn't raise the issue.

"BP made their decision," Gagliano recalled when testifying before a federal panel. He thought the worst-case scenario would be that they would have to go back to fix the cement job after it was completed.

Months later, BP is defending the decision. In Wednesday's report, the company said the decision not to use 21 centralizers likely didn't contribute to the cement's failure.

Meanwhile, the well lining job, known as casing, was completed. The casing, critical to ensuring no gas slips out of the wellbore uncontrolled, looked good, paving the way for that night's cementing.

The cement would essentially seal the gap between the well casing and the hole drilled in the seafloor. It would also shut in the well until the day BP was ready to extract oil and gas.

At 9 p.m. April 19, the Halliburton workers began the complicated cement job 5,000 feet below the surface.

Sometime during the night, Chaisson, the Halliburton cementer, noticed a BP drilling engineer calling Houston headquarters.

"We may have blown something out higher in the casing," the engineer said, triggering a flurry of phone calls between the rig and Houston.

Ultimately, they continued the job and Chaisson did not indicate there was ever discussion to halt the work.

Since then, however, BP has said it found weaknesses in the design and testing of the cement. It said the weaknesses may have allowed hydrocarbons to escape from the wellbore, causing the blowout. Halliburton insists the problem was not in the cement but in BP's design of the well.

By 1 a.m., on April 20, the cement job was completed.

"We have completed the job and it went well," Chaisson wrote to Gagliano in an e-mail at 5:44 a.m.

Confidence was up. Yet at the 11 a.m. meeting, rig leader Jimmy Harrell was unhappy.

BP's plan for shutting down operations didn't include a "negative pressure test" — a procedure that reduces the fluid pressure in the well to ensure there are no gas leaks. Harrell learned a long time ago this was risky. He demanded the test.

Meanwhile, in Houma, La., a group of VIPs — BP executives Pat O'Bryan and David Sims, and Transocean executives Daun Winslow and Buddy Trahan — boarded a helicopter headed for the Deepwater Horizon. They were going for a 24-hour "visibility" visit to one of their best-performing Gulf rigs.

They arrived on the rig floor as the negative test was going on. Winslow realized there was confusion over the pressures — indicating there might be a leak somewhere in the wellbore — and decided it was not a good environment for the group.

"Let's let these guys get back to work," he said, taking the VIPs to the pontoon area.

Harrell and a Transocean toolpusher, Randy Ezell, stayed to help with the test. Kaluza, the BP company man, was not satisfied. He got permission from Houston to run a second test.

After dinner, Chris Pleasant, a Transocean subsea supervisor, went to the drill shack to begin his shift. He was told that 60 barrels of mud appeared to have been lost during the pressure test.

Ideally, rig workers like to see little or no mud lost in the test. Losing too much mud can signal a leak in the casing — which could cause an oil spill, or in the worst-case scenario, allow gas and highly explosive methane to seep through the casing, leading to a blowout.

Wyman Wheeler, a Transocean toolpusher, said something wasn't right. He ended his shift and was relieved by Jason Anderson.

An argument erupted over how to do the second negative test. Anderson wanted it done as it had always been done on the Horizon, and finally persuaded the BP crew.

By 8 p.m., the test had ended.

"Go call the office," BP's well site leader Don Vidrine told his counterpart, Kaluza. "Tell them we're going to displace the well" — a critical task in which the mud that keeps the oil and gas under control is replaced with seawater before the well is closed and abandoned.

Vidrine's decision to proceed may have been a fateful one. BP now believes that Transocean and BP supervisors misinterpreted the results of the negative-pressure tests.While workers removed mud from the well, the VIPs ended a meeting with the rig leadership and headed for the bridge. Capt. Curt Kuchta showed them the controls and the radar. David Sims of BP got in a video-game-like machine that simulates piloting the rig. Winslow went to have a cigarette.

The phone on the rig floor rang. It was Ezell, who had reluctantly gone to dinner and was asking about the test results.

"It went good," Anderson responded.

"What about your displacement? How's it going?"

"It's going fine," Anderson answered.

But the rig crew apparently missed warning signs that oil and gas had entered the well. BP investigators suspect the rig crew was distracted by other "end-of-well activities."

It was 9:30 when Ezell followed Anderson's instructions and went to his cabin. He chatted with his wife. Then he turned off the lights and laid down to watch TV.

Eight minutes later, unbeknownst to Anderson, hydrocarbons started to shoot toward the rig. Three minutes later, rig workers started trying to control the well, but by then, mud was already flowing unchecked onto the rig floor.

Pleasant, the Transocean subsea supervisor, was doing paperwork. He had the rig leader sign some documents.

Senior toolpusher Randy Harrell closed out some permits and went to take a shower.

On the bridge, Sims got out of the simulator. O'Bryan stepped in.

It was 9:50 p.m.

The phone rang in Ezell's bunk.

"We have a situation," an assistant driller said. "The well is blown out. We have mud going to the crown."

"Do y'all have it shut in?" Ezell asked, horrified.

"Jason is shutting it in now," Curtis responded. "Randy, we need your help."

Ezell jumped into his coveralls, shoved his feet into boots, grabbed his hardhat and ran.

In Pleasant's office, a rig worker looked over.

"Chris, what's that water?" he asked, apparently seeing the fluid rising from the well and onto the rig.

"They're probably coming out the hole," Pleasant answered, fixated on the computer screen.

A minute passed.

"I see mud," the worker said.

Pleasant looked up. He called the rig floor. All three numbers. No answer.

"We got to go," Pleasant said, and took off down the hall.

It was nearly 10 p.m.

O'Bryan was in the simulator. Sims was on the bridge. Harrell was in the shower. Ezell was running to the rig floor. Winslow was smoking. The captain opened the portside door and saw fluid pouring onto the rig.

A loud hiss filled the rig. The first of two explosions shook the vessel.