Sinkhole seismic event studied

Photo provided by Louisiana State Police -- Assumption Parish officials said Saturday that increased seismic activity in the vicinity of  the Napoleonville Domehas led to growth in its adjacent sinkhole, as well as cracking of the soil in a drilling well pad, shown in the bottom right corner of this Dec. 19 photograph. Show caption
Photo provided by Louisiana State Police -- Assumption Parish officials said Saturday that increased seismic activity in the vicinity of the Napoleonville Domehas led to growth in its adjacent sinkhole, as well as cracking of the soil in a drilling well pad, shown in the bottom right corner of this Dec. 19 photograph.

Scientists believe the restless, 8.5-acre sinkhole in Assumption Parish swampland is undergoing a “growth event” after they noticed an upswing in seismic activity in the past few days within a brine-mining cavern carved into the massive Napoleonville Dome, parish officials said Saturday.

Officials first began noticing an increase in seismic activity about two weeks ago, said John Boudreaux, director of the Assumption Parish Office of Homeland Security and Emergency Preparedness.

Scientists reported that more than 80 seismic events were monitored two days ago, Boudreaux said.

“There was a tremendous amount of activity over the past couple of days,” Boudreaux said.

The sinkhole then “burped” up crude oil, debris and hydrocarbon to its surface around 10 a.m. Saturday, Boudreaux said. After the burp, the seismic activity decreased dramatically.

The latest “burp” is at least the third such event reported.

Officials believe the sinkhole formed near the Grand Bayou and Bayou Corne communities sometime between the night of Aug. 2 and the morning of Aug. 3.

Scientists believe the sinkhole is linked to the failure of a nearby Texas Brine Co. LLC salt cavern in the Napoleonville Dome.

The dome, a large underground salt formation, was pushed up vertically from ancient sea beds and, for decades, industry has used the dome for brine production. The perimeter has also been the focus of intensive oil and gas exploration.

Hollowed from the solid salt formation, caverns left by brine production are often used later for storage of natural gas, butane and other hydrocarbons. Brine is used for several industrial processes.

Louisiana Department of Natural Resources scientists have said they suspected that the Texas Brine cavern failed, allowing its saline fluid to gush out and open up the sinkhole.

Residents of 150 homes in the two communities were ordered on Aug. 3 to evacuate their homes and camps. The order remains in place.

Officials believe the recent “growth event” is centered on the east side of the sinkhole and possibly is related to shifting of salt and material within the cavern collapse zone, Saturday’s blog post from the Assumption Parish Police Jury says.

Boudreaux said the seismic activity has been pinpointed to shifting salt deposits just east of the failed cavern, about 900 feet into the ground.

Boudreaux said the seismic activity is a concern to parish officials because it indicates that something might be failing in the salt structure.

“We would assume that in order to create seismic activity, it’s something shifting ... in the salt,” Boudreaux said. “Not knowing what that may cause is concerning.”

The seismic activity also appears to have cracked the surface of a drilling well pad located directly above Texas Brine’s failed cavern and on the eastern side of the sinkhole.

The cracks, which are 1 inch wide and 14 inches deep, extend from the north side of the pad around to the southwest side of the pad, Boudreaux said.

The Office of Conservation has recommended that personnel and equipment should be removed from the well pad as a safety precaution as the growth event is analyzed, the Assumption Parish Police Jury blog post says.

In response, Texas Brine removed all of its equipment from the pad, Boudreaux said.

Boudreaux also said a few trees toppled on the south side of the sinkhole, but scientists have not determined yet if that means that the edges have sloughed off even further.

Boudreaux said officials still believe the sinkhole won’t outgrow scientists’ predictions that it would one day measure about 1,400 feet in diameter.

Wilma Subra, an environmental chemist who provides technical assistance to the Louisiana Environmental Action Network, or LEAN, said that while officials have noticed growth in the sinkhole after seismic activity in the past, this round of activity is concerning because of its severity, as evidenced by Texas Brine’s cracked well pad.

“The issue is that it may even go further and have an impact on the integrity of the well bore,” Subra said.

Texas Brine spokesman Sonny Cranch has said the company is aware of the buyout issue but is devoting all of its resources to respond to safety directives issued by the state Office of Conservation.

Cranch confirmed Saturday that Texas Brine officials removed cleanup equipment from the edge of the sinkhole and will continue to monitor the situation as it evolves.

“We’re going to take all precautionary measures,” Cranch said. “It’s not unexpected. It has happened before and will very likely happen again because of the nature of this particular situation.”

Cranch said Texas Brine will evaluate the cracked well pad before determining what to do with it.