The Louisiana Department of Environmental Quality has asked the operator of a salt cavern near a sinkhole in northern Assumption Parish to describe what would happen if all butane that could be held in the underground storage facility were released to the surface, state officials said Tuesday.
DEQ Secretary Peggy Hatch asked for the updated worst-case scenario from Crosstex Energy LP of Dallas by close of business Wednesday after reviewing the company’s current risk management plan for the cavern, state officials said in a news release.
The Crosstex salt cavern, which holds 940,000 barrels of liquid butane under pressure, is 1,600 feet from the sinkhole on the adjacent Texas Brine Co. LLC property south of La. 70 south.
Crosstex submitted an updated plan in January to DEQ, agency officials said, a plan audited in June by the U.S. Environmental Protection Agency and found to be in compliance, state officials said.
But Hatch asked for the update out of “an abundance of caution,” state officials said.
DEQ officials said Tuesday there are “a lot of dynamic things” happening around the butane cavern, including expected well drilling, and community concerns have arisen.
“We want to put all that to rest with sound science,” said Rodney Mallett, DEQ spokesman.
Crosstex has two underground storage caverns for butane and propane in the vicinity of the sinkhole with a combined capacity of more than 3.1 million barrels, according to financial filings with the U.S. Securities and Exchange Commission.
But Hatch asked for the butane cavern’s plan because it is the closest to the sinkhole, Mallett said.
The updated plan for the butane cavern is due the same day about two dozen tractor-trailer trucks loaded with a disassembled drilling rig are expected to arrive at the Texas Brine site nearby, a Texas Brine spokesman said.
The rig, which will be 140 feet high, will be assembled on a well pad Texas Brine has been building on its site, Cranch said.
“They are ready to receive the rig for all practical purposes,” said Sonny Cranch, Texas Brine spokesman.
The Louisiana Department of Natural Resources has ordered Texas Brine to drill a relief well to see whether one of its salt caverns may have failed and caused the 2.5-acre sinkhole. DNR also wants to find out if the cavern is the source of natural gas releases in the area, as agency personnel suspect.
DNR scientists suspect the Texas Brine cavern may have been carved too close to the edge of the Napoleonville Dome and failed, releasing its brine contents and causing the sinkhole.
The sinkhole swallowed up forested swamps on Texas Brine property and released a foul diesel smell. The hole was found the morning of Aug. 3 and has grown slightly since then.
The Crosstex, Texas Brine and other caverns have been carved out of the 1-by-3-mile Napoleonville Dome.
The 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.
The Crosstex butane cavern drawing DEQ’s interest is outside a worst-case scenario zone for the estimated maximum expansion of the sinkhole, which stands at 375 feet across, parish and state officials said.
Madhurendu B. Kumar, director of the DNR Office of Conservation, Geological Oil and Gas Division, presented the worst-case scenario zone for the sinkhole to parish residents in an Aug. 7 meeting in Pierre Part.
Calculating based on the assumption that the 20-million-barrel Texas Brine cavern is the cause of the sinkhole, Kumar said in an interview after the meeting, the worst-case scenario would give the sinkhole a radius of 700 feet.
That is less than the sinkhole’s distance to the Crosstex cavern, parish officials confirmed.
When asked Tuesday, Chris Piehler, DEQ Enforcement Division administrator, said reports that release of the butane from the Crosstex cavern could be equivalent to an H-bomb explosion are “a little bit over the top.”
“I think that is alarmist,” Mallett added.
DEQ officials said Crosstex’s updated plan submitted in January considers risks for butane, natural gas and other gases and suggests a full release might lead to windows being broken at two-thirds of mile. Piehler said two-thirds of a mile is close to the Bayou Corne community, which has about 150 residences, but does not actually include it.
John Boudreaux, director of the Assumption Parish Office of Homeland Security and Emergency Preparedness, said officials are not concerned that the sinkhole would expand and swallow up the Crosstex cavern, but that the sinkhole could expand and shift the cap of sediment and rock that sits atop Napoleonville Dome.
Such a shift, though it would have to occur across 1,600 feet of caprock, could damage the casing of the well bore leading to the underground cavern, possibly releasing the butane, Boudreaux explained.
“It’s not impossible. No one can say that it can’t happen. The scientists are aware of that, but it’s very unlikely that it would happen,” Boudreaux said.
Jill McMillan, spokeswoman for Crosstex, did not directly address DEQ’s request in an email statement.
But she said Crosstex monitors its facilities hourly and is continuing to move natural gas liquid product in and out of its caverns for customers.
Since the sinkhole emerged, the company has hired a subsurface consultant to assist in evaluation of the caverns’ integrity and is surveying its facilities every seven to 10 days for subsidence or other shifts, she said.
“Based on these findings to date, we believe our facilities have not been impacted by the slurry-filled sinkhole, and there has been no indication their integrity has been compromised,” she said in the email.
A Chevron Pipe Line Co. cavern holding natural gas is in the vicinity of the Crosstex facilities, but is 2,300 feet from the sinkhole. Gareth Johnstone, Chevron Pipe Line spokesman, said Chevron does not believe its cavern is threatened by the sinkhole but has elected to draw down gas in the facility as a precaution.