Aug. 10 (Bloomberg) -- BP Plc suspended drilling of a relief well that aims to permanently plug the source of the largest offshore oil spill in U.S. history as a storm approached the site in the Gulf of Mexico.
The precaution will delay interception of the damaged Macondo well by two to three days, to Aug. 15 or Aug. 16, National Incident Commander Thad Allen said in a conference call with reporters today. The drilling rig will remain as London-based BP prepares pressure tests it expects will aid the effort to kill the well, Allen said.
Workers on the floating drilling rig inserted a temporary plug this morning after the U.S. National Hurricane Center said showers and thunderstorms over the southeastern Gulf of Mexico may form a tropical cyclone. Tropical cyclones range in strength from depressions to hurricanes.
The National Hurricane Center upgraded the storm to tropical depression five with maximum sustained winds of 35 miles (56 kilometers) per hour at 7:30 p.m. local time, according to an advisory on the center’s website.
The center of the system was located about 260 miles south to southeast of Apalachicola, Florida and is expected to approach the north central Gulf by late Wednesday or early Thursday, according to the advisory.
The depression was forecast to become a tropical storm tomorrow. Winds of 39 miles (63 kilometers) per hour would make it a tropical storm.
A tropical storm warning was issued for the northern Gulf from Destin, Florida to Intracoastal City, Louisiana, including the city of New Orleans.
The system is not expected to become as strong or cause as long of a delay as Tropical Storm Bonnie, which forced the evacuation of the drilling rig last month, Allen said.
BP still intends to inject mud and cement through the relief well into the damaged well this month as a permanent plug, Allen said. BP stopped the leak July 15 after installing a new cap on the well, which began gushing after an April 20 explosion on the Deepwater Horizon rig, killing 11 workers.
Additional pressure tests to be conducted during the weather delay may determine whether cement injected from the top of the well last week completely sealed all of the gaps that would allow oil and natural gas to reach the surface, Allen said.
The relief well will still be needed to establish whether the well is sufficiently plugged and it may be needed to inject more mud and cement, he said.
The tests also may reveal how much pressure the relief well will encounter once it penetrates the well’s outer shell and enters an area known as the annulus, Kent Wells, senior vice president for exploration and production, said on a subsequent call with reporters.
Knowing that would help engineers prepare to pump mud and cement at sufficient pressure to kill the well, he said. It’s too early to say how long it will take to kill the well after the interception, he said.
The relief well has been drilled to a depth of 17,909 feet (5,549 meters) below the ocean surface, BP said in a statement on its website today. It was about 30 feet from the intercept point when drilling stopped, Allen said.
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