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12 06, 2012 by The Advocate
Vent wells burning off gas trapped in an aquifer under homes and swamps in northern Assumption Parish have removed slightly more than 2.7 million cubic feet of gas since flaring began, parish officials said.
But what remains unclear at this point is what kind of progress that figure represented through Wednesday evening toward diminishing the gas threat for the Bayou Corne and Grand Bayou communities, officials said.
About 150 homes in the area have been under an evacuation order since Aug. 3.
Scientists believe the gas migrated upward from natural formations along the Napoleonville Dome after a Texas Brine Co. LLC cavern in the salt dome failed this summer and caused a large sinkhole to form in swamps south of La. 70 South.
Methane had been bubbling up in area waterways for more than two months before the sinkhole was found Aug. 3 and continued to bubble up Wednesday with no significant decrease, parish officials said.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said more information is needed about what has happened to the free methane believed in the aquifer under the area.
“It’s to be determined,” he said Wednesday.
Boudreaux and Texas Brine officials have noted that the rate of gas flow from vent wells has declined since flaring began.
Sonny Cranch, spokesman for Houston-based Texas Brine, said there is an indication the gas flow is diminishing but noted, as Boudreaux did, that water in the vent wells or other restrictions might be limiting the flow.
However, the reduced vent well flow may not necessarily reflect a reduction of gas volume in the aquifer, he cautioned.
“It could be a diminishing amount of natural gas, but it also could be the restricted flow issue,” Cranch said.
Several of the vent wells ran into this problem early on before gas could be brought to the surface.
The failure of the Texas Brine cavern also unleashed crude oil from pockets along the salt dome that found its way upward and into the sinkhole, which now has a surface area of more than 8 acres, as well as into the broken Texas Brine cavern, scientists believe.
Cranch provided figures showing that through Tuesday morning, the company had removed a combined 6,732 barrels of “liquid hydrocarbon” from the cavern and sinkhole.
But the rate of oil removal from the cavern has also receded and the amount of new oil appearing on the sinkhole surface has diminished substantially, Cranch said.
Scientists with the Louisiana Office of Conservation and its contracted agent, Shaw Environmental and Infrastructure, have suggested the cavern failure tapped an oil- and gas-bearing formation thousands of feet deep known as the “Big Hum.”
But officials are not able to say how much oil and gas is in the formation.
“Study is ongoing by Office of Conservation staff and Shaw E&I to determine the potential volume in place, but more work is needed to gather and analyze data to develop a useful estimate,” said Patrick Courreges, spokesman for the Louisiana Department of Natural Resources, of which the Office of Conservation is a part.
“Work is being conducted continually to get to the bottom of this situation,” Courreges said.
Officials have also not pinned down with certainty which formation or formations the gas and crude are coming from.
Courreges added the Office of Conservation and Shaw are analyzing the crude to determine the age of the formation or formations that are the source or sources of the oil and gas being stirred up by the sinkhole-forming events.
Texas Brine has been directed to conduct seismic studies of the area to see what is happening underground and whether the geology matches the theory put forward so far to explain the cause of the sinkhole’s emergence and related oil and gas releases.
Texas Brine submitted an initial plan on time but, Courreges said, the office directed the company to make changes “that will better protect public safety and will help gather better information on the sinkhole area.”
That revised plan is expected to be completed later this week, Courreges said.
While response efforts move along, methane fears affect daily life.
On Monday, Assumption Parish school officials redirected a bus route from an evacuated Bayou Corne neighborhood after a shallow well known as a Geoprobe hit gas at a depth of 30 feet below residential property on Crawfish Stew Street, school and parish officials said.
School Superintendent Earl “Tibby” Martinez said that when word of the gas find got out, the bus driver became concerned about driving through the neighborhood with 34 Assumption High School students on board.
The driver picks up six more students from the neighborhood, he said.
The neighborhood is under the mandatory evacuation order, but parish officials have not forced residents to leave.
Martinez said the school bus stop was moved to Jambalaya and Gumbo streets, which are close to La. 70 but off the highway.
As a safety precaution for now, the school bus won’t be heading deeper into the neighborhood, so students must meet the bus at the new pickup point closer to the highway.
“We’re just trying to comply and see what we can do and mind the safety of all the kids,” Martinez said.
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