Sinkhole elicits safety concerns
The state Office of Conservation has ordered all of the state’s 34 salt dome operators to show how close their caverns are to the outer edges of the subterranean salt domes containing them and, for caverns closest to the salt edge, also to prove they are structurally sound.
The directive, issued Jan. 30, is in response to the failure of a Texas Brine Co. LLC cavern in the Napoleonville Dome that is believed to be the cause of an 8.6-acre sinkhole in northern Assumption Parish, officials said.
Conservation Commissioner James Welsh has given operators until March 18 to submit the information.
Texas Brine has used its caverns in the Napoleonville Dome for the production of brine for the petrochemical industry, but a major use of the vast salt caverns is to store gas, oil and other hydrocarbons.
Patrick Courreges, state Department of Natural Resources spokesman, said in an email that the order affects 220 active salt caverns in Louisiana, up to 50 plugged and abandoned caverns and 11 pending permit applications for new solution-mined caverns.
He said the information may prove useful in further rule-making, but added that the Office of Conservation is also separately proposing a comprehensive set of rules on other aspects of brine mining.
Asked about the order’s timing, Courreges said the suspected failure of the Texas Brine cavern — a sidewall collapse at more than 5,000 feet deep — is unprecedented.
He said DNR and the Office of Conservation had no regulatory practices addressing the sides of caverns as a significant area of structural concern.
The sinkhole is also the subject of a joint hearing of the Senate and House Committees on Natural Resources at 10 a.m. Tuesday at the Capitol.
Scientists have speculated for months that Texas Brine’s solution-mined cavern, which had been plugged and abandoned by June 2011, got close to the northwestern edge of the salt dome between the Bayou Corne and Grand Bayou communities.
The cavern’s salt sidewall deep underground caved in under pressure from the outer rock, allowing millions of cubic yards of earth to mostly fill the cavern and to scramble the outer formations enough to cause a sinkhole to form and unleash oil and gas from strata nearby.
The dome is one of hundreds of these massive fingers of salt under the Gulf Coast that have been thrust up through overlying rock over millions of years.
The sinkhole and the discovery of methane under the area have resulted in an evacuation of 150 residences in the area for more than six months.
Courreges said the directive issued to companies that operate salt domes effectively breaks up caverns into three categories.
He said it imposes stiffer requirements to prove location and structural stability the closer a cavern is to the edge of a salt dome formation.
“For those that may be within 300 feet of a salt edge, operators have additional requirements to show their caverns are not only stable now but can be verified to be stable in the future,” he wrote in the email.
Solution-mining companies pump fresh water into a well drilled into a salt body, dissolving a cavity inside the salt and producing a highly saturated brine byproduct.
The brine byproduct is used primarily to produce chlorine, a basic building block in petrochemical products.
The Texas Railroad Commission, which regulates salt dome operators in that state, has never issued a similar statewide order, a commission spokeswoman said, but the agency amended its rules for hydrocarbon storage in salt caverns in the mid-1990s and forced operators to refile for their permits.
“In the context of that permit refiling process, Commission staff re-evaluated the proximity of caverns to the edge of salt domes or other caverns, and as a result, staff denied some permits or required special operating conditions on certain caverns based on proximity issues,” Ramona Nye, commission spokeswoman, said in an email.
The Louisiana Office of Conservation directive affects all operators of caverns created through solution mining, whether used for brine production or for the storage of gas, oil or other hydrocarbons, Courreges said.
Dow Chemical Company is the largest operator on the Napoleonville Dome, occupying more than 880 acres, DNR records show, and has more than 30 caverns in use for brine production or hydrocarbon storage,
Company officials said they are confident their caverns are not within the 300 to 500 foot area of concern but are updating maps and waiting on up-to-date information before they response to the directive.
“I would say at Dow we understand the directive, given the situation,” spokeswoman Stacey Chiasson said.
Texas Brine officials said 3-D and other seismic studies under way or nearly finished, which the Office of Conservation required in response to the sinkhole, would be used to comply with the statewide directive.