Hydrogen sulfide gas found in sinkhole-area vent well

Screen shot from State Police video -- The Assumption Parish sinkhole is shown in this Nov. 14 flyover video made by Louisiana State Police. Show caption
Screen shot from State Police video -- The Assumption Parish sinkhole is shown in this Nov. 14 flyover video made by Louisiana State Police.

Texas Brine Co. has shut down one of its two vent wells burning off methane trapped under the Bayou Corne community in Assumption Parish after a small amount of potentially deadly hydrogen sulfide gas was released to the atmosphere, company officials confirmed Tuesday.

Sonny Cranch, spokesman for Houston-based Texas Brine, said the well was sealed about 7 p.m. Monday immediately after detection and remained closed Tuesday as company officials worked on their next steps, adding the small gas release did not present a risk to the public.

“It was barely a minimum amount that went into the air,” Cranch said.

Hydrogen sulfide is a colorless gas that is flammable and poisonous at sufficiently high concentrations. The naturally occurring gas has a foul rotten-egg odor, can occur in natural gas deposits and is a known risk with oil and gas exploration.

Parish officials said in a separate blog post Tuesday that no community air monitors detected hydrogen sulfide, but warned residents about the discovery, saying high concentrations of the gas were found inside the vent well.

“Please be advised that H2S (hydrogen sulfide) is an extremely dangerous gas. Unlike methane, it is heavier than air and collects at low-to-the-ground levels,” the blog post says.

The vent well is located on Texas Brine’s property lease in swamps between the Bayou Corne and Grand Bayou communities south of La. 70 South.

Louisiana Office of Conservation officials said in a blog post Tuesday that the company set up a safety perimeter around the well, with barricades and gas monitors, under the office’s supervision.

The vent well is among six in the Bayou Corne area that have been bored by Texas Brine or contractors working for the Office of Conservation to remove methane lurking in an underground aquifer in the area and in even shallower sands above that aquifer.

About 150 homes in the Bayou Corne and Grand Bayou areas have remained evacuated since Aug. 3 when a large sinkhole was found in the swamps between the two communities.

Scientists believe a Texas Brine salt cavern inside the Napoleonville Dome failed and initiated a chain of events that created the sinkhole and released methane and crude oil naturally trapped in pockets along the side of the salt dome.

Louisiana Department of Natural Resources officials, private industry scientists and contractors have been setting up the vent wells to burn off the methane in an effort to get evacuees back in their homes and camps.

Cranch said workers had completed hooking up flaring equipment to the vent well in question earlier Monday and had only recently begun burning off methane when the hydrogen sulfide was found.

He said the gas was released from equipment that separates impurities from methane coming out of the well before it reaches the flare.

The separator releases what it collects every two minutes, Cranch said.

“When they smelled that from the separator, they shut it down,” Cranch said.

Patrick Courreges, spokesman for the Louisiana Department of Natural Resources, said officials believe any risk of hydrogen sulfide coming from the other five vent wells — three of which are flaring methane continuously — is very low because they are shallower compared to the other well.

But he said additional air monitoring was conducted around the five other vent wells and no hydrogen sulfide was detected.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said the flares would not burn off any hydrogen sulfide that might come up from the vent wells.

The purpose of the five wells is to remove gas inside the Mississippi River Alluvial Aquifer at 100 feet to 130 feet while the vent well that hit the hydrogen sulfide is the deepest of any of the vent wells at a depth of about 430 feet, parish and company officials have said.

That well also reaches the caprock of the Napoleonville Dome.

Office of Conservation officials noted Tuesday that salt dome caprock is an area known to contain hydrogen sulfide.

In fact, the caprock of some salt domes in Louisiana and Texas has been mined for sulphur through what is called the Frasch process dating back to the late 1800s. The last U.S. Frasch sulphur mine closed in 2000, according to the Sulphur Institute, an industry group.

Texas Brine’s site is over the salt dome and the band of caprock that sits on top of the 1- by 3-mile salt deposit.

But the site is near the western edge of the dome and so areas farther west, including the sinkhole and the Bayou Corne community itself, are not over the dome or the caprock, parish and Shaw maps show.

Louisiana Office of Conservation officials said they would be meeting with Texas Brine over the latest developments. Parish officials said Shaw Environmental and Infrastructure, the state office’s agent for the sinkhole incident, also would be investigating.

Courreges said officials will be assessing whether a way can be found to vent methane from the deep well safely or whether it is better to shut the well in and leave the hydrogen sulfide where it is.