London - The “most likely” flow rate of oil from BP’s damaged Deepwater Horizon subsea well in the Gulf of Mexico is now estimated at between 35,000 and 60,000 barrels per day.
The figures, which are based on updated information and scientific assessment, represent a major hike in previous estimates – the leak was generally reckoned to be around 18,000 b/d, less than a week ago.
The latest flow rate estimate from US authorities is based on a combination of analyses of high resolution videos taken by remote operating vehicles (ROVs), acoustic technologies, and measurements of oil collected by the oil production ship together with pressure measurements inside the top hat.
In particular, the “improved” estimates are informed by newly available, detailed pressure measurements from within the Deepwater Horizon’s failed blowout preventer (BOP) system taken over the past 24 hours – BP had previously signalled efforts to install pressure sensors in one of the lines being used to inject methanol to prevent the formation of hydrates in a lower marine riser package (LMRP) cap now in place on the BOP.
Scientists have also been able to draw on more than a week of data about the amount of oil being collected through the top hat, added a joint statement by US secretary of energy Steven Chu, secretary of the interior Ken Salazar, and chair of the National Incident Command’s Flow Rate Technical Group (FRTG) Dr. Marcia McNutt, director of the US Geological Survey.
“As we continue to collect additional data and refine these estimates, it is important to realise that the numbers can change,” said US energy secretary Steven Chu.”In particular, the upper number is less certain - which is exactly why we have been planning for the worst case scenario at every stage and why we are continuing to focus on responding to the upper end of the estimate, plus additional contingencies.”
The US government has demanded that BP’s containment capacity reaches 40,000-53,000 b/d by the end of June and 60,000-80,000 b/d by mid-July.
BP has installed two systems to collect oil and gas flowing from the MC252 well and transport them to vessels on the surface.
The LMRP containment cap located on top of the failed blow-out preventer (BOP). This system, which was installed on 3 June, takes oil and gas to the Discoverer Enterprise.
A second system, which started on 16 June, is connected directly to the BOP and carries oil and gas through a manifold and hoses to the Q4000 vessel on the surface. The Q4000 uses a specialised clean-burning system to flare both oil and gas captured by this second system.
The total volume of oil recovered from both the LMRP containment cap system and the Q4000 since they became operational is approximately 249,500 barrels. Officials have previously estimated that the LMRP cap could capture up to 18,000 b/d, and that the Q4000 could expand total leak containment capacity to 20,000-28,000 b/d.
Work on a first relief well, which started 2 May, continues and has currently reached a measured depth of 15,936 feet. A second relief well, which started 16 May, is at a measured depth of 10,000 feet. Both wells are still estimated to take approximately three months to complete from commencement of drilling.
BP, meanwhile, continues to caution that the LMRP containment cap – an engineered containment device with a sealing grommet – and the Q4000 have never been deployed at these depths (5000ft) and conditions before, and its efficiency and ability to contain the oil and gas could not be assured. Process animation – Click ’back button to return to this page
The success of the LMRP follows a failed bid stop the leak by pumping over 30,000 barrels of heavy mud at rates of up to 80 barrels a minute, and deploying a wide range of different bridging materials, the ’top kill’ operation on the failed BOP did not overcome the flow from the well.
Engineers had previously achieved partial success through the use of an RITT used at the well, which at one stage was drawing off 3000 b/d of oil. The RITT - a five foot long steel pipe with specially designed rubber baffles - was placed in the end of the leaking riser on 16 May, allowing oil and gas to flow up to the drillship Discoverer.
The recovery rate, however, subsequently dropped off due to issues relating to the flow parameters and physical characteristics within the riser in deep sea conditions.
US government investigators continue to interview witnesses regarding the incident. These have reportedly included: a worker on the Deepwater Horizon rig, who alleged that BP had taken risky shortcuts in its drilling procedures prior to the explosion; and another alleging that there were unusually pressure readings coming from the wellhead in the hours before the blast.
The investigation earlier uncovered “significant problems” with the BOP - the supposedly fail safe system installed to cut off the flow of oil and gas to the Deepwater Horizon drill rig.
The BOP has multiple rams that are supposed to slam shut to pinch off any flow around the drill pipe and stop the flow of oil from the well. There are also shear rams in the BOP that are supposed to cut and seal the pipe to
prevent oil and gas from flowing.
“We know that the blowout preventer, the BOP, did not properly engage,” US congressman Bart Stupak, chairman of the House Energy and Commerce Committee’s Subcommittee on Oversight and Investigations, told a hearing to
examine the causes of the incident.
BP was leasing the rig to drill an exploratory well in the Gulf of Mexico.The rig was owned and operated by Transocean, the world’s largest offshore drilling company, and was under contract from BP. Two days after the blast, the rig capsized and sank to the floor of the ocean. The accident resulted in 11 fatalities and oil leaks from three separate locations among the twisted wreckage.
According to Stupak, US investigators have found that the BOP appeared to have a significant leak in a key hydraulic system. This leak was found in the hydraulic system that provides emergency power to the shear rams, which are supposed to cut the drill pipe and seal the well.
A senior official at Cameron, which manufactured the BOP, told investigators that when the remote operating vehicles (ROVs) tried to operate the shear rams, they noticed a loss of pressure. They investigated this by injecting dye into the hydraulic fluid, which showed a large leak coming from a loose fitting, which was backed off several turns.
The leak did not seem to have been caused by the blowout because every other fitting in the system was tight, according to the Cameron official, who believed this was one of several possible failure modes: the leak depriving the shear rams of sufficient power, so that they could not cut through the drill pipe and seal the well.
Secondly, the investigation learnt that the BOP had been modified in potentially significant ways. The device has an underwater control panel. BP spent a day trying to use this control panel to activate a variable bore ram on the BOP, which should seal tight around any pipe in the well.
When BP investigated why their attempts to activate the bore ram failed, they learnt that the device had been modified. A useless test ram - rather then the variable bore ram - had been connected to the socket that was supposed to activate the variable bore ram.
Thirdly, the US team learnt that the BOP was not powerful enough to cut through joints in the drill pipe. They cited a Transocean document that stated: most blind shear rams (BSRs) are “designed to shear effectively only on the body of the drillpipe. Procedures for the use of BSRs must therefore ensure that there is no tool joint opposite the ram prior to shearing.”
“This seemed astounding to us because the threaded joints between the sections of drillpipe make up about 10% of the length of the pipe. If the shear rams cannot cut through the joints, that would mean that this so-called failsafe device would succeed in cutting the drillpipe only 90% of the time,” Stupak told the hearing.
“We asked the Cameron official about the cutting capacity of the blowout preventer on the Deepwater Horizon. He confirmed that it is not powerful enough to cut through the joints in the drillpipe. And he told us this was another possible explanation for the failure of the blowout preventer to seal the well, the congressman added.
A fourth finding was that the emergency controls on the BOP may have failed. The BOP has two emergency controls. One is called the emergency disconnect system (EDS). BP officials told investigators that that the EDS was activated on the drill rig before the rig was evacuated.
“But the Cameron official said they doubted the signals ever reached the blowout preventer on the seabed,” said Stupak. “Cameron officials believed the explosion on the rig destroyed the communications link to the blowout preventer before the emergency sequence could be completed. In other words, the emergency controls may have failed because the explosion that caused the emergency also disabled communications to the blowout preventer.”
Meanwhile, the BOP also has a “deadman switch” which is supposed to activate the shutoff system when all else fails. But, according to Cameron, there were multiple scenarios that could have caused the deadman switch not to activate. One was human oversight: the deadman switch may not have been enabled on the control panel prior to the BOP being installed on the ocean floor. Another is lack of maintenance: the deadman switch won’t work if the batteries are dead.
The deadman switch is connected to two separate control pods on the BOP. Both rely on battery power to operate. When one of the control pods was removed and inspected after the spill began, the battery was found to be dead. The battery in the other pod has not been inspected yet.
Another issue concerns the design. The deadman switch activates only when three separate lines that connect the rig to the BOP are all severed: the communication, power, and hydraulic lines. Cameron believes the power and communication lines were severed in the explosion, but it is possible the hydraulic lines remained intact, which would have stopped the deadman switch from activating.
“These are not the only failure scenarios that could impair the function of the BOP,” said Stupak. “The Cameron official we met with described many other potential problems that could have prevented the blowout preventer from functioning properly. Steel casing or casing hanger could have been ejected from the well and blocked the operation of the rams.
“The drill pipe could have been severed successfully, but then dropped from the rig, breaking the seal. Or operators on the rig could have tried to activate the shear rams by pushing the shear ram control button. This would have initiated an attempt to close the rams, but it would not have been successful. The shear rams do not have enough power to cut drill pipe unless they are activated through the emergency switch or the deadman switch.”
Stupak also revealed an “astonishing document” that Transocean prepared in 2001, when it bought the BOP from Cameron. It said there were 260 separate “failure modes” that “could require pulling of the BOP.” According to this report, “the predominant failures” included “ram locking mechanisms.”
“How can a device that has 260 failure modes be considered failsafe?” the congressman asked.
Problems with the BOP were also found to extend to the procedures for testing the device. The CEO of Transocean, Steven Newman, said in a testimony: “we have no reason to believe that they were not operational - they were jointly tested by BP and Transocean personnel as specified on April 10 and 17 and found to be functional.”
But this assertion seemed to be contradicted by a document prepared by BP on 27 April, one week after the explosion. According to this document, “BOP stack emergency systems are not typically tested once the BOP stack is on the seabed.”
“What this means that while some functions on the BOP may have been tested in the weeks before the explosion, the emergency systems, including the deadman system and the leaking emergency hydraulic system, were unlikely to have been tested,” Stupak concluded.