BAYOU CORNE — Eleven new bubble sites have been found in inundated swampland west of an 8.5-acre sinkhole in northern Assumption Parish, including a frothing spot dubbed the “mother of all bubble sites,” officials said Tuesday.
The sites are roughly in a row west of an unnamed oilfield access road extending south from La. 70 South through the wooded swamp, a parish map shows.
The sites bring to 34 the number of known bubble sites in the Bayou Corne and Grand Bayou areas in the vicinity of the sinkhole on Texas Brine Co. LLC’s leased property.
Scientists think the Houston-based company’s salt cavern in the Napoleonville Dome failed deep underground, causing the sinkhole and unleashing oil and natural gas from formations along the salt dome face. That free gas is thought to be surfacing through many bubble sites and the sinkhole.
Parish officials added Tuesday that the discovery has led to speculation that the row of bubbles marks the edge of a suspected subsidence zone around the outer rim of the sinkhole and also prompted officials to shift the location of a 1,000-foot-deep well that Texas Brine had been directed to drill at the end of the access road.
The well will be moved to the front of the road, officials said.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said Shaw Environmental and Infrastructure Inc. recommended the change to avoid the possibility that the well, which will be used to collect seismic data, would be compromised in the future.
“They don’t want to make that critical mistake,” he said.
Shaw is the agent for the Louisiana Office of Conservation, which regulates salt caverns and is leading the response to the sinkhole and its side effects. Conservation Commissioner Jim Welsh ordered the well to be drilled as part of an agreement with Texas Brine earlier this month that ended the company’s lawsuit over response plans.
Boudreaux said Tuesday a representative of the landowner found the bubble sites late last week while checking the property from an airboat. He said the representative gave the frothing site the “mother of all bubble sites” moniker.
Boudreaux said the site was given the name, not for its size, but the intensity of its bubbling.
What is coming out of the new sites has not been determined yet, but Boudreaux said it can be assumed venting natural gas is causing the bubbles to emerge.
Boudreaux said Shaw and a contractor for Texas Brine collected samples from the frothing site Tuesday morning. Parish officials collected samples from another sizeable site on Sunday, Boudreaux said.
He said the other nine new bubbling sites are smaller and less intense than the other two.
The samples will undergo isotopic tests to identify the sites’ source and other tests that will show what kinds of gas are being released, such as methane or butane.
Boudreaux said the frothing site, which is about 1,100 feet west of the sinkhole, is in an area regularly covered with water, although the water depth has increased recently to about 5 feet.
He said officials said that the most-active of the bubbling sites is suspected to be arising from an old, submerged well that is serving as a conduit for the suspected gas venting. Boudreaux said soundings taken Tuesday in the bubble site hit cement.
Some bubble sites in the area preceded the formation of the sinkhole by several months but more have been discovered over time.
The first bubble sites were found in bayous in the area, under which, geologists have said, are sands that allowed for the quick transport of the “free” gas believed let loose under the Bayou Corne area.
A few bubbling sites have been found on land, sometimes when floodwaters cover previously dry ground.
Sites closest to the sinkhole have been determined to originate from this underground “formation” gas.
Sites farthest from the sinkhole have been determined to be releasing so-called “swamp gas,” which results from the decay of organic matter. Still other sites have been shown to be producing a blend of both kinds of gas.