BEIJING, July 16 (Xinhua) -- BP said Thursday its latest attempt to plug the Gulf of Mexico oil leak had survived its first test, with no oil escaping for the first time since the Deepwater Horizon rig exploded in April.
The British energy giant conducted a test in which it closed valves and vents on a tight-sealing containment cap installed atop its well off the Louisiana coast earlier this week.
"I am very excited to see no oil flowing into the Gulf of Mexico," BP Vice President Kent Wells said, but added it was only the beginning of a 48-hour testing process designed to analyze the condition of the underwater wellbore.
The success came 85 days after the April 20 explosion on the BP-leased rig that killed 11 workers and triggered the spill.
Now begins a waiting period to see if the cap can hold the oil without blowing a new leak in the well.
Data gathered during the test will be reviewed at six-hour intervals over a 48-hour period.
Higher pressure readings are positive because it means the well is containing the oil, while lower pressure means new leaks may have appeared after BP choked off the flow of oil from the top of the well, officials said.
During the past three months, BP has tried a series of measures but did not claim victory until Thursday.
Why did it take such a long time for BP to control the oil spill? First, we have to consider the location of the leak.
The oil leak occurred around 1,500 meters underwater. Trying to stop the leak at such a depth was extraordinarily difficult because of the high water pressure at that depth.
As the water pressure increases by one atmosphere for every 10 meters of depth, 1,500 meters underwater can reach pressures of around 150 atmospheres. It means an area of one square centimeter has to support pressures of around 155 kilograms.
Ordinary machinery could not support such high pressures, not to mention humans. Therefore, the spill could only be contained by special devices and the containment had to be conducted by remote control.
However, building temporary deepwater devices needs a great amount of time and the process of remote control is slow and complex.
Factors such as underwater currents and chemical and physical conditions also should be considered.
Given such unpredictability, the failure of BP's previous efforts are understandable.
For example, attempts to place a 125-tonne containment dome over the largest leak and piping the oil to a storage vessel on the surface failed in May, when gas leaking from the pipe combined with cold water formed methane hydrate crystals that blocked the opening at the top of the dome.
This time, however, BP's officials were "obviously encouraged" by Thursday's results.
But it remains only a temporary fix to the oil leak. BP's permanent fix, a relief well, is still days or even weeks from being completed, and a hurricane in the wrong place could set that timetable back.
U.S. President Barack Obama on Thursday welcomed the stoppage of oil flow into the Gulf of Mexico, saying it is a "positive sign" but still in the testing phase.
The disaster is the worst offshore leak in U.S. history.