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Well design may be hampering spill efforts

Chron.com

Deepwater Horizon

Reduction in thickness of casing raises concern about well’s integrity

By TOM FOWLER and ERIC NALDER
HOUSTON CHRONICLE

June 21, 2010, 10:59PM

Kari Gooodnough Bloomberg: Seaweed covered in oil from the Macondo well sits on a public beach in Gulf Shores, Ala., earlier this month.

Money-saving measures BP took while designing the Macondo well in the Gulf of Mexico appear to have dogged efforts to bring the massive oil spill under control.

Documents released by congressional investigators show that modifications to the well design BP made last year included a reduction in the thickness of a section of the casing — steel piping in the wellbore

The modification included a slight reduction in the specified thickness for the wall of a 16-inch-diameter section of pipe toward the bottom of the well, according to a May 14, 2009, document.

Retired Coast Guard Adm. Thad Allen, commander of the response to the blowout and oil spill, has confirmed reports that concern about the strength of the casing led officials to stop efforts last month to plug the well from the top by injecting drilling mud and cement in a procedure called a top kill.

Another proposed spill control method, placing a blowout preventer on top of the one that failed in the original April 20 blowout, also was abandoned over concerns about well integrity. A blowout preventer is a system of shears and valves installed as a last line of defense against loss of well control.

The condition of the well also limits how much oil and gas can flow into containment systems now being used successfully to capture some of the flow. Even if a vessel could capture all the hydrocarbons gushing from the well, some would have to be released to keep well pressure under control.

Marvin Odum, president of Houston-based Shell Oil, the U.S. arm of Royal Dutch Shell, told the Houston Chronicle last week that the integrity of the well casing is a major concern. Odum and others from the industry regularly sit in on high-level meetings with BP and government officials about the spill.

If the well casing burst it could send oil and gas streaming through the strata to appear elsewhere on the sea floor, or create a crater underneath the wellhead – a device placed at the top of the well where the casing meets the seafloor – that would destabilize it and the blowout preventer.

The steel casing used in oil wells is strong, said Gene Beck, petroleum engineering professor at Texas A&M, but pressures deep in a well are powerful enough to split strong steel pipe or “crush it like a beer can.”

The strength and thickness of casing walls are key decisions in well design, he said. If the BP well’s casing wasn’t strong enough, it may already be split or could split during a containment effort.

BP spokesman Toby Odone said the decision to reduce the pipe thickness was made after careful review. The company said it doesn’t know the condition of the well casing and has no way of inspecting it.

BP is drilling two relief wells to intercept the Macondo well near the reservoir and plug it with cement. A rupture in the Macondo well casing probably wouldn’t affect that effort, said Donald Van Nieuwenhuise, director of geoscience programs at the University of Houston.

“When they start the bottom kill the cement will try to follow oil wherever it’s escaping, so it would actually hide a lot of sins in the well bore,” Van Nieuwenhuise said.

So far there are no signs that the section of the pipe below the sea floor is leaking.

The blowout preventer has been listing slightly since the accident, but officials believe that may have happened when the Deepwater Horizon sank while still attached to the well via a pipe called a riser.

A report from the National Oceanic and Atmospheric Administration on Monday noted research vessels found natural gas seeping from the sea floor several miles away from the well. Those appear to be pre-existing seeps that occur naturally, a NOAA spokeswoman said, and unrelated to the spill.

But the longer the well flows uncontrolled the more likely it is that the well casing could be damaged or the blowout preventer damaged further. Sand and other debris that flows through the pipes at high velocity can wear through metal over time, said Van Nieuwenhuise.

The chances of the well eroding from underneath and the blowout preventer tipping may seem unlikely.

“But everything about this well has been unlikely,” said David Pursell, an analyst with Tudor Pickering Holt & Co.

Reporter Monica Hatcher contributed to this report.

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