The latest release of natural gas discovered in an underground aquifer near Bayou Corne may be the third time in the past 13 years that gas has been loosed in shallow formations over or near the subterranean Napoleonville salt dome, according to a review of regulatory filings.
A consulting hydrogeologist working in spring 2004 to finish removing natural gas that was then trapped 150 feet under the Grand Bayou area found gas had been released into the same subsurface aquifer at least five years earlier, regulatory filings with the Louisiana Department of Environmental Quality say.
Twenty-eight residents living in Grand Bayou had to be evacuated on Christmas Day in 2003 when gas was discovered in an underground aquifer above the Napoleonville Dome. Casing was found to have failed in a well tied to a storage cavern carved from the salt dome and leaked gas.
A consultant working for Gulf South Pipeline Co., which was leasing the cavern from Dow Chemical Co. at the time, told DEQ in a May 2004 letter that molecular analysis showed some gas escaping from one of 36 vent wells intended to remove the Gulf South gas was actually releasing gas from a problem that was “wholly apart from the incident” in 2003-04.
The consultant, George H. Cramer II, raised the question of older gas in the aquifer as he was proposing a plan to end the venting of gas from the Grand Bayou area.
The Gulf South Pipeline incident resulted in litigation and in buyouts by the company of most residents in Grand Bayou.
The newest gas releases occurred in the vicinity of a 4-acre sinkhole that emerged Aug. 3 between Grand Bayou and Bayou Corne south of La. 70 South. The slurry hole, which is just past the edge of the dome, has prompted a standing evacuation of 150 homes in the area since Aug. 3.
Louisiana Department of Natural Resources scientists have said they suspect a damaged Texas Brine Co. of Houston salt cavern inside but near the side of the dome caused the sinkhole.
The vent well referenced in the 2004 letter to DEQ, called “UCAR-1,” was located on former Union Carbide property over the dome. Union Carbide is a subsidiary of Dow Chemical Co., which has major brine operations on the dome a couple miles east of the sinkhole.
“Historic observations at the Dow Chemical UCAR facility indicate that gas from other source(s) has been present in the aquifer under the facility for at least 5 years,” Cramer wrote to then DEQ Enforcement Division Administrator R. Bruce Hammatt on May 5, 2004.
In a recent interview, Cramer said there was no a specific event that led to the earlier gas release. He said the most likely source was leaking wells tied to oil and gas exploration in and around the dome.
Stacey Chiasson, Dow spokeswoman, declined to comment directly on the DEQ correspondence but said a vent well was drilled on the Union Carbide site in response to the 2003 Gulf South incident. She said the well was “depleted of gas” and agencies authorized it to be plugged.
Louisiana Department of Natural Resources and Assumption Parish officials are working with Shaw Environmental and a subcontractor to install new vent wells to find and release gas from the current incident.
Since late May, the area between Grand Bayou and Bayou Corne has had a growing number of widely distributed sites where gas has been found bubbling up from area waterways. Gas also has been hit in the aquifer, and earth tremors have been felt in the area.
Parish officials said the gas in the aquifer has led to fears that gas could gather enough pressure to get through the confining clay layer above the formation, reach the surface and accumulate to explosive levels. Numerous tests for months have not shown gas at bubble sites, in homes and elsewhere has come close to such levels.
Over the weekend, one vent well was finished and casing was driven for another, parish officials said in blog posts. Casing for the wells reached depths of 180 to 200 feet. The aquifer is 110 feet underground.
Venting or flaring of gas could start as early as Thursday, parish officials reported in the blog posts.
Officials plan a community meeting 6 p.m. Tuesday at the command post on La. 70 South in Bayou Corne.
Patrick Courreges, of the Department of Natural Resources, said the agency has not ruled out any of the natural gas storage operations on the Napoleonville Dome, including gas from the 2003-04 Gulf South incident.
“Further sampling and analysis of potential sources is continuing to attempt a clear determination whether the source of the natural gas bubbling is a deep natural formation or whether it can be narrowed to a processed source, such as a specific storage operation,” Courreges said in an email response to questions.
The dome is an underground salt deposit pushed toward the surface by geologic forces from a deep salt bed laid down by ancient seas. Such domes often have oil and gas trapped in pockets along their sides.
For decades, the 1-by-3-mile Napoleonville Dome has been the focus of oil and gas exploration, brine mining and hydrocarbon storage in the vast leftover brine caverns.
Fifty caverns are active in the dome, nineteen of which are used to store liquefied petroleum gas or natural gas, DNR figures show.
Cramer said the Gulf South cavern well failure released an estimated 600 million cubic feet of gas underground. The 36 vent wells removed about 375 million cubic feet from the aquifer or captured and reused it, he said.
He said it is not clear how much gas was left underground because much of it escaped to the atmosphere before venting began and some trapped under the dome caprock wasn’t measurable.
Chiasson and a spokesman for Gulf South Pipeline Co., which no longer leases storage caverns in the dome, said recent testing shows gas released from the 2003-04 Grand Bayou incident is not involved in the latest releases.
“To our knowledge, based on meetings with local and state agencies, a preliminary laboratory comparison between a Gulf South natural gas release sample and a current gas release sample indicates that these two events are not related,” Chiasson said in an email.
Courreges said DNR officials in the Office of Conservation and the group of scientists working with agency are not aware of such testing and have not been provided the data.