How much damage will the BP oil spill cause?
-Kees Willemse is professor of offshore engineering at Delft University. The opinions expressed are his own.-
Last monthâs explosion at the Deepwater Horizon rig continues to result in the leakage of an estimated 200,000 gallons (910,000 litres) of oil into the Gulf of Mexico each day.
According to U.S. President Barack Obama, âwe are dealing with a massive and potentially unprecedented environmental disasterâ.
While the leak is extremely serious, and Obamaâs words may ultimately ring true, the leak is (as yet) not one of the top 50 biggest oil spillages from either oil rigs or tankers in historical perspective:
â˘Â Â Â Some 7-10,000 tonnes of oil are so far estimated to have leaked into the Gulf of Mexico from Deepwater Horizon.
â˘Â Â Â The Exxon Valdez leaked some 36,000 tonnes of crude oil on the shores of Alaska.
â˘Â Â Â The largest ever off-shore leakage of oil occurred in 1979 in the Ixtoc-1 spillage when an estimated 476,000 tonnes of oil polluted the Gulf of Mexico (Bay of Campeche).
â˘Â Â Â The biggest ever on-shore spillage occurred in the aftermath of the 1991 Iraq War when an estimated 1.4 to 1.5 million tonnes was released in Kuwait by Iraqi military forces.
Most at risk from the Deepwater Horizon spill are the coastlines of Texas, Florida, Mississippi, Alabama, and Louisiana, including the wetlands near New Orleans where millions of migratory birds are currently nesting, and fish spawning.
The oil spill could also be catastrophic for the Gulf Coastâs substantial seafood industry, including oysters and shrimp.
To mitigate the environmental impact, measures will continue to be taken to prevent as much of the oil as possible reaching the shoreline, including setting fires to âburn-offâ the oil; soaking up the oil; and placing protective âbarriersâ around shorelines.
The precise scale of the unfolding disaster remains uncertain owing to the lack of clarity over how long the leak will last.Â In the worst-case scenario, as U.S. Interior Secretary Ken Salazar has suggested, the leak could continue for several more months.
Uncertainty is also increased by the fact that BP executives are reported to have admitted to members of the U.S. Congress that the amount of oil spilling could intensify — perhaps by several multiples of the current leakage per day — if they cannot cap the flow.
Hopes for a relatively early end to the leakage are resting largely upon the success of the operation to install a five-storey, 100 tonne containment dome.
The device was to be lowered by cranes around 1500 metres to the sea floor and, if possible, positioned over the two areas of leaking pipe.
If successful, the dome would serve as a giant funnel, collecting and piping it for collection on the sea surface. However, this operation has only been applied at a much smaller water depth and the first attempt to employ the device here has not been successful.
Even if successful, the dome will not stem all of the leakage (perhaps 80-90 percent of it) and there remains a risk of explosion when the oil reaches the surface because of the volatile mix of oil, gas and water.Â Thus, the operation can only be a âholdingâ one to buy time until the spillage can be shut off at the two remaining sources of the leak.
While shutting off the leakage at source will be an immensely difficult task, hopes will have been raised last week by the fact that BP successfully shut off the smallest of the three original leakages.Â This was done by placing a valve over the ruptured pipe and shutting it off using a remotely controlled submarine.
The best hope of shutting off the two remaining sources of leakage is getting the blow-out preventor working again.Â This is the system, which should act as an emergency cut-off to stop oil continually spilling out if a pipe is damaged, and which failed catastrophically last month.
However, the blow-out preventor is proving immensely hard to fix, in large part because of the exceptional depth of the water.Â Hopes rest largely upon robot submarines re-starting the system.
In the event that the blow-out preventor cannot be fixed, relief wells have begun to be drilled that could be used to siphon off the oil leaking from the holed pipeline.
This operation will take an estimated two to three months as the drilling is taking place at 1500 metres water depth and a further 5 kilometres into the hard rock.
The relief well can also be drilled such that the shaft of the new well enters into the shaft of the existing, problematic well. A cement prop can then be inserted to stop the flow in the first well. This requires extremely accurate drilling, but that technique has been proven before.
Inevitably, all of this environmental mitigation and emergency replacement activity is proving extremely expensive.Â The cost of operations to BP alone is an estimated 6 million dollars a day, and independent estimates have put the final bill at between 3 billion and 12 billion dollars.
However, the effects of this accident cannot be expressed in money terms alone, because of the growing scale of the environmental disaster if the oil spill cannot be contained soon.
Once the crisis is over, industry and government will need to make an urgent in-depth analysis of the cause of the accident to ensure that similar incidents can never happen again.