UPDATE 11/8/2012 Louisiana Sinkhole? -Gulf Stream Shift Linked to Methane Gas Escaping from Seabeds

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Official Statement: Methane accumulating 20 feet underground near community by giant Louisiana sinkhole — “Immediate actions… to protect public safety” mentioned

Date: November 7, 2012
Emphasis Added

Conservation-ordered shallow well monitoring network detects natural gas pressure near community at 20-to-40-foot depth

Louisiana Commissioner of Conservation James Welsh today announced that the Office of Conservation will be coordinating with the state Department of Environmental Quality (DEQ) in seeking permission from property owners to do additional monitoring of Bayou Corne community homes to test for the accumulation of methane believed to be connected to the failure of Texas Brine’s cavern.

[...] Welsh said the action is being taken in response to analysis and review of data provided by the network of 18 shallow monitoring wells the Office of Conservation instructed its contracted agent, Shaw Environmental and Infrastructure, to install in and around the community. [...]

That monitoring-well network has detected underground natural gas at low pressure in an area shallower than the primary aquifer [...]

Welsh said that while the Office of Conservation will continue to take immediate actions as needed to protect public safety, the Office will also continue to hold Texas Brine LLC accountable [...]

[...] During hydrocarbon removal on Friday and Saturday, the casing pressure was reduced thus indicating brine was filling the casing. However, after this work, hydrocarbons continued to enter the casing from the cavern causing the casing surface pressure to return to 940-970 psig on Sunday.

[...] cavern floor had risen an additional 10 feet from the previous measurement on October 19. The cavern floor has come up approximately 52 feet since it was first measured on September 24. [...]

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Louisiana Sinkhole? -Gulf Stream Shift Linked to Methane Gas Escaping from Seabeds

“The new work could reinvigorate a debate on the risk of methane release from the oceans and whether destabilized hydrates make the continental slopes more unstable”

By Nature magazine and Virginia Gewin

Somewhere off the eastern coast of North Carolina, a frozen mixture of water and methane gas tucked in seabed sediments is starting to break down. Researchers blame a shifting Gulf Stream — the swift Atlantic Ocean current that flows north from the Gulf of Mexico — which is now delivering warmer waters to areas that had previously only experienced colder temperatures.

“We know methane hydrates exist here and, if warming continues, it can potentially lead to less stable sediments in this region,” says Matthew Hornbach, a marine geologist at the Southern Methodist University in Dallas, Texas, who led the study that is published online today in Nature. The results suggest that the warmer temperatures are destabilizing up to 2.5 gigatons of methane hydrate along the continental slope of the eastern United States. This region is prone to underwater landslides, which could release the methane, a powerful greenhouse gas.

Whether that methane would make it to the atmosphere and worsen global warmingis unclear, but scientists think that it is unlikely. “We don’t need to worry about any huge blow of methane into the atmosphere,” says Carolyn Ruppel, a geophysicist at the US Geological Survey in Woods Hole, Massachusetts. Rather, she says, Hornbach and his co-author Benjamin Phrampus, also of the Southern Methodist University, have uncovered a powerful new way to use data from the geological record to catch non-anthropogenic climate changes that are already happening.

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Gulf Stream Shift Linked to Methane Gas Escaping from Seabeds

The embarrassing reality is we don’t have any solid confirmation that these connections are causative rather than correlative,” says Charles Paull, a marine geologist at Monterey Bay Aquarium Research Institute in Moss Landing, California, who has studied this western Atlantic region in detail. He says that this latest work provides credible evidence that thermal changes in the oceans can destabilize hydrates.

But Mark Maslin, a paleoclimatologist at University College London, takes issue with the authors’ claim that destabilized hydrates make this area more vulnerable to slope failures — temperature changes alone won’t trigger underwater landslides. “Dramatic degassing events require a change in pressure,” he says.

There are other hydrate deposits around the world that deserve attention. The Arctic is undergoing rapid warming, dramatic loss of sea ice and changing oceanographic conditions. Essentially, says Ruppel, it is the place undergoing the maximum amount of change and therefore the best place to study these dynamics. She is now collaborating with Hornbach to collect more data there. “Ground zero for this research is in the Arctic,” says Hornbach.

This article is reproduced with permission from the magazine Nature. The article was first published on October 25, 2012.

Frozen zone
The authors’ approach combines models of subsurface temperature dynamics with seismic images to directly detect the depth at which the methane hydrate is no longer stable and shifts from a frozen solid to free gas. Because hydrate formation is dependent on temperature, the position of the bottom of this frozen zone can be used to estimate subsurface temperature dynamics.

Using seismic data collected in 1977 to model where they expected the frozen methane to become gaseous in the western North Atlantic margin, they found that the observed interface between the frozen solid and the free gas was much deeper than predicted. After systematically checking every detail, the team ruled out several factors that could have explained their observations — including sea-level changes, increased sedimentation rates or decreased heat flow through the sediments. They eventually realized that the only thing that could cause the discrepancy was that the water was cooler in the past. Phrampus ran the model again using data from much cooler waters 100 kilometers northwest of the Gulf Stream, and got an almost perfect fit.

Next, the authors modeled heat flow through the methane hydrate sediments in relation to time, and estimated that it would take around 5,000 years of warmer waters for all of the methane to sublimate and become gas. “We don’t know where we are in the 5,000-year time frame, but our best approximation suggests we are 800 to 1,000 years in,” says Phrampus.

Trouble ahead?
This work promises to reinvigorate an ongoing debate over the risk of methane release from the oceans and whether destabilized hydrates make the continental slopes more unstable.

http://www.scientificamerican.com/article.cfm?id=gulf-stream-shift-linked-to-methane-gas-escaping-from-seabeds

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Gas flowing from sinkhole

By David J. Mitchell

River Parishes bureau

November 04, 2012

BAYOU CORNE — Texas Brine Co. began burning off natural gas Friday that was trapped in a water aquifer near a sinkhole in northern Assumption Parish, officials said.

This was the first time state, parish or company officials have been able to get gas to flow from four “vent wells” driven into the ground around the sinkhole in order to draw the dangerous gas out of the aquifer.

Located in the swamps between Bayou Corne and Grand Bayou south of La. 70 South, the sinkhole is more than 5½ acres in size at the surface and has prompted authorities to issue a standing evacuation order on Aug. 3 applying to 150 homes.

Fears that the trapped gas, which is colorless, odorless and potentially explosive, could accumulate to dangerous levels at the surface has further justified the evacuation order, parish officials have said.

Authorities had counted on the vent wells to release the gas from the aquifer, but the effort was hampered at first because well casing openings designed to allow gas to flow upward to the surface had been clogged with silty clay. The fact that the gas is believed to be at low pressures possibly aggravated the clogging problem.

The well casing is a kind of piping that forms the outer wall of the well bore.

Sonny Cranch, Texas Brine spokesman, said that when company contractors removed water from the vent well casing late Thursday, natural gas began to flow to the surface.

He said water apparently had been impeding the flow of gas from the well, which is on Texas Brine’s leased site near the sinkhole.

Gas venting was stopped Thursday night and reached a “modest” pressure of 30 pounds per square inch at the wellhead, company officials said in a news release.

Contractors hooked up a temporary flaring system Friday morning and the gas will be allowed to flare, or burn off, this weekend during daytime hours, company officials said.

“Next week, additional water will be removed from the casing to allow greater natural gas flow,” officials said in the statement. “In addition, a more permanent flaring system will be installed to allow more continuous venting.”

Scientists believe the gas was released, along with crude oil, from underground pockets alongside the Napoleonville Dome when a Texas Brine salt cavern failed and caused the sinkhole.

The salt cavern located near the western edge of the salt dome developed a wall breach that allowed oil, gas and 3.3 million cubic yards of
sediment into the formerly brine-filled cavern inside the dome.

In other developments Friday, imaging of the sinkhole by Texas Brine shows that a deep, funnel-shaped void at the bottom center of the sinkhole has filled in, company and parish official said.

As a result, the depth of the sinkhole has been reduced from 449 feet to 170 feet, but the volume has increased from 550,000 cubic yards to 666,000 cubic yards, a cross-section says.

Cranch said the image was made before the eastern edge of the sinkhole sloughed in, or collapsed, later Tuesday. The sinkhole has undergone periodic edge collapses. Additional imagery is expected, he said.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said that since the Tuesday edge collapse, a large bubble site venting natural gas from the center of the sinkhole has stopped. Bubbling continues around the edges of the sinkhole and in area waterways.

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