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WASHINGTON — BP, running weeks behind schedule and tens of millions of dollars over budget in trying to complete its troubled Macondo well in the Gulf of Mexico, took many shortcuts that contributed to the disastrous blowout and oil spill there last year, federal investigators concluded in a report released on Wednesday. The central cause of the explosion aboard the Deepwater Horizon drilling rig was a failure of the cement at the base of the 18,000-foot-deep well that was supposed to contain oil and gas within the well bore. That led to a cascade of human and mechanical errors that allowed natural gas under tremendous pressure to shoot onto the drilling platform, causing an explosion and fire that killed 11 of the 126 crew members and caused an oil spill that took 87 days to get under control. The two-part report, compiled by a joint task force of the Bureau of Ocean Energy Management, Regulation and Enforcement and the Coast Guard and covering more than 500 pages, is the most comprehensive to date on the April 2010 disaster. Its findings largely mirror those of other investigations, including the inquiry by a commission named by President Obama to determine the causes of the calamity. That panel issued its findings in January. “The loss of life at the Macondo site on April 20, 2010, and the subsequent pollution of the Gulf of Mexico through the summer of 2010 were the result of poor risk management, last-minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response and insufficient emergency bridge response training by companies and individuals responsible for drilling at the Macondo well and for the operation of the Deepwater Horizon,” the latest report said. The report concluded that BP, as the well’s owner, was ultimately responsible for the accident. But it also said that BP’s chief contractors, Transocean, which owned the mobile drilling rig, and Halliburton, which was responsible for the cementing operations, shared the blame for many of the fatal mistakes. The study goes further than previous reports, citing seven violations of federal regulations as factors. Among them were violations of laws that required BP and its contractors to operate in a safe manner, to take measures to contain oil and gas for the protection of health and the environment, to conduct reliable tests of well pressures and to notify federal regulators of changes in drilling plans. The Justice Department is conducting a criminal investigation that could bring indictments and heavy fines. David M. Uhlmann, a professor at the University of Michigan Law School and former chief of the Justice Department’s environmental crimes section, said the Justice Department almost certainly reviewed the findings of the study before it was released. “Today’s report increases the likelihood that BP, Transocean and Halliburton will face criminal charges for their roles in causing the gulf oil spill,” Mr. Uhlmann said in an e-mail. “The Justice Department may have outside experts for both its criminal and civil cases, and it could develop additional information about the causes of the spill in those investigations, but it will be hard for the Department to distance itself from the findings of the Coast Guard and Boemre.” The well blowout unleashed a spill of nearly five million barrels of oil, fouling the gulf and hundreds of miles of beaches, marshes and fish habitats and causing billions of dollars in damage. The three companies have pointed fingers at one another and are engaged in multibillion-dollar litigation to try to spread the enormous costs of the accident. Families of crew members are suing the companies in federal court, seeking compensation and damages. BP said in a statement that it had long acknowledged its role in the accident and had urged its drilling partners to accept their share of the blame. “BP agrees with the report’s core conclusion — consistent with every other official investigation — that the Deepwater Horizon accident was the result of multiple causes, involving multiple parties, including Transocean and Halliburton,” the company said. It added that it had taken steps to improve its safety practices and strengthen oversight of its contractors. Lou Colasuonno, a Transocean spokesman, said that the report identified the cement failure as the primary cause of the accident and defended the actions of Transocean crew members. “We take strong exception to criticisms of the Deepwater Horizon drill crew, nine of whom perished fighting to save their fellow crew members and the rig, for the actions they took in the face of such an unprecedented emergency,” he said in a statement. A Halliburton spokeswoman said that BP was to blame for poor well design and that at least some of the cement set by Halliburton did not fail. The company absolved itself of any blame. “Every contributing cause where Halliburton is named, the operational responsibility lies solely with BP,” the statement said.
On April 20, 2010, the crew of the Deepwater Horizon was preparing to temporarily abandon BP’s “Macondo” discovery well in Mississippi Canyon (MC) Block 252 (Figure 1). In a few hours, they would have been ready to move the drilling rig off location so that a completion rig could move on. At about 10:00 p.m., the rig unexpectedly began to shake and a loud surging noise was accompanied by natural gas, drilling mud and sea water that shot high above the floor of the drill ship. The gas exploded and the rig was engulfed in flames. A second explosion followed and the electricity went out. Eleven men died instantly and 115 others rushed to the lifeboats or jumped into the Gulf of Mexico. This all happened so fast that those who died probably had no time to understand what was happening. Two days later, the Deepwater Horizon sank to the bottom of the Gulf of Mexico, and oil has been spilling into the Gulf at rates of at least 5,000 barrels per day since then(there are 42 gallons in a barrel). The MC 252 well is located in 5,067 ft of water about 50 miles from the coast of Louisiana. The total depth of the well was 18,360 ft below sea level (13,293 ft below the sea floor). This is not an unusually deep well nor was it drilled in exceptionally deep water compared to many other wells in the Gulf of Mexico. The Gulf drilling depth record was set earlier this year at more than 30,000 ft below the sea floor (The Oil Drum, January 18, 2010: http://www.theoildrum.com/node/6135#more), and the current water-depth record of 10,011 ft was set in 2003 (http://www.deepwater.com/fw/main/Home-1.html). Much information has surfaced since the accident through congressional and Mineral Management Service (MMS) hearings, public statements from the companies involved and, on May 16, a feature report on CBS Television’s Sixty Minutes program. Most of this information comes from eye-witness accounts by people on or near the Deepwater Horizon at the time of the blowout. I consider most of the publicly available accounts so far to be potential hearsay although they probably contain some good observations and elements of truth. I discount the value of the testimonials chiefly because none of these people were on the rig floor at the time of the blowout. In addition, the only people who have a comprehensive and fact-based understanding of the events leading to the accident are either sequestered by the companies involved or are dead. Chronology of the Disaster 1. The well had reached a depth of 13,293 ft below the sea floor. The final string of production casing from the wellhead at the sea floor to total depth had been put in the hole, and cemented in place on April 19, 2010. 2. Only 51 barrels of cement were used according to the well plan. This was not sufficient to ensure a seal between the 7-inch production casing and the previously cemented 9 7/8-inch protection casing (Figure 2). 3. Mud had been lost to the reservoir while drilling the bottom portion of the well (this is called “lost circulation”). It usually indicates good reservoir quality, an interval of lower pressure or both, and can result in an enlarged wellbore or “washout”. The significance of this is that it might have been difficult to create a good cement seal between the casing and the formation. It also would have been impossible to ensure the effectiveness of the cement seal without running a cement-bond log, and this was not done. 4. The cement contained a nitrogen additive to make it lighter so that it would flow more easily and better fill the area between the casing and the lost circulation-washout zone. This also may have decreased its sealing effectiveness. Gas from the reservoir may have further diluted the viscosity of the cement. 5. While waiting approximately 20 hours for the cement to dry on April 20, the crew began displacing the drilling fluid (“mud”) in the wellbore and riser with sea water before setting a cement plug and moving off location. This mud was pumped into tanks at the surface, and then onto a platform supply vessel alongside the rig (whose captain gave testimony before an MMS hearing last week). 6. Sea water is much lighter than drilling mud so there was less downward force in the wellbore to balance the flow of gas from the reservoir. The drilling supervisors knew that there was gas in the drilling fluid because a gas flare can be seen in photos probably coming from a diverter line in the riser (Figure 3). 7. The chart of drilling parameters for the last two hours before the blowout suggests that the riser and upper 3,000 ft of the wellbore were fully displaced with seawater by 20:00 on April 20, and the crew was circulating the drilling fluid Beginning 10 minutes later, at 20:10, the mud pit volume began to increase probably because of gas influx (Figure 4). The volume increased so much, that the recorder re-zeroed four times. When the crew stopped pumping at 21:08, the mud pit volume decreased and this may have alleviated some concern about gas influx. 8. At 21:30, they stopped pumping again and circulated, but the pit volume continued to increase(Figure 5). Standpipe pressure increased and decreased twice between 21:30 and 21:42 (standpipe pressure generally reflects bottom hole pressure). This, along with a steady increase in mud pit volume, suggests that surges of gas were entering the drilling fluid from a gas column below the wellhead, and outside of the 7-inch production casing. Gas had probably channeled past the inadequate cement job near the bottom of the well and, by now, had reached the seals and pack-offs separating it from the riser at the sea floor. 9. At 21:47, the rate of standpipe pressure and mud pit volume went off scale, and water flow was measured at the surface. The blowout had begun. Between 21:47 and 21:49 the gas behind the 7-inch production casing apparently overcame the wellhead seals and pack-offs that separated the wellbore from the riser. Almost instantaneously, the gas shot the water out of the riser and above the crown of the derrick. Then, the gas ignited and exploded. Issues That Can and Cannot Be Addressed There are many disturbing issues raised by the MC 252 well blowout. The Sixty Minutes report leaves the impression that there were clear indications of things that went wrong in the weeks leading up to the blowout. It further implies that BP and the other companies involved with the drilling operation ignored these problems in the interest of saving time and money. I do not believe that there is sufficient and credible publicly available information to address those issues at this time. Based on the chronology presented above, it seems strange that so little was apparently done in the hour-and-forty minutes between the notable increase in mud pit volume and the blowout, except to stop pumping twice. At the same time, it is easy to see the warning signs now that we know the outcome, and we do not know what was done or discussed at the time--we only have recordings on a chart. What can be addressed now is the larger issue that a flawed, risky well plan for the MC 252 well was approved by the MMS, and BP, Anadarko and Mitsui management. Similar or identical plans were undoubtedly approved and used by many operators on other wells drilled in the Gulf of Mexico. A plan that does not include enough cement to overlap the final and previous casing strings, and that does not require running a cement-bond log to ensure the integrity of the seal is a defective plan. The fact that there have not been blowouts on previous wells does not justify the approval and use of an unsafe plan. Interior Secretary Salazar has announced a suspension of offshore drilling permits and an indefinite ban on new offshore drilling. This will have a profound economic impact on many thousands of rig and associated service jobs. The result will undoubtedly be new regulations. More regulation will accomplish little, however, if the underlying problem is a lack of critical thinking by the companies that drill oil and gas wells and the government agencies that oversee their activities. |
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