New 3D map analysis shows source of gas in Bayou Corne

Photo provided by staff
Wednesday, September 18, 2013 - 10:24am

The sinkhole in Assumption Parish grows slowly, just like answers about it come slowly.

Tuesday night, scientists showed some new information that they learned by taking a second look at the ground beneath Bayou Corne.

Three-dimensional seismic mapping began in March, to give geologists a clearer understanding of what had taken place deep beneath the earth's surface since a sinkhole formed from a failed Texas Brine salt cavern in 2012.

Texas Brine announced in April that its mapping showed the ground around the cavern was stable and there were no large gas pockets below the sinkhole. Many Bayou Corne residents doubted the findings, in part due to their distrust of the company, so a group of internationally-renowned geologists reviewed their findings.

"And even though Texas Brine's data integrity and acquisition is good, I feel like we've got the best resolution," Don Marlin, the geophysicist contracted by Texas Brine to conduct the examination, said.

Marlin and his team pored over months' worth of data, but additional testing since April gave them a better data set.

"That's the evolution of data, so that's why this interpretation has gone through its modification and tweaks over time," he stated. "Primarily because we've been getting this data trickling in over time, and that's going to modify our interpretation, or at least modify mine."

Marlin's newest discovery was that the gas people have found in their homes comes from a pair of reservoirs right next to the edge of the Napoleonville salt dome. One is three acres in size and sits 1,000 feet below ground; the other covers 10 acres and is 1,500 feet down.

"This is the beauty of 3D," Marlin mentioned. "We can look at things from the outside, we can look at things from the inside, put things in perspective versus the cavern, and try to understand the subsurface better."

The new look at the 3D maps also shows what is happening in the cavern. All the earth that has fallen in is still muddy and loose, particularly at the top. The weight of the water above condenses and settles it, which creates more room for trees to be sucked in like in the videos that have drawn national attention.

"The uncertainty moving forward is how the settlement occurs, and how that material densifies," noted another geophysicist, Will Pettitt.

While the new analysis gives the scientists a better idea of what has happened and what will happen, they know their predictions are not perfect.

"Everybody knows it's grown, but this kind of gives you an idea of just how much it's grown," Gary Hecox said, pointing to a picture of the sinkhole's perimeter now compared to a year ago. Hecox is the geologist hired by the state to oversee the sinkhole response. "It's grown a lot more than even some of the best experts in the world thought it would."

Marlin's findings will go to the Blue Ribbon Commission, which will use them to determine how the sinkhole will continue to expand.

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