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"Sinkhole" du Bayou en Louisiane: du sulfite d'hydrogène a été mesuré hier en quantité importante

Publié par Brujitafr sur 7 Décembre 2012, 15:37pm

Catégories : #NATURE - ECOLOGIE

Hydrogen sulfide gas was detected Thursday morning in equipment that is part of an operation designed to burn off methane from a cavern beneath Texas Brine’s salt dome site in Assumption Parish, officials said.

But the potentially dangerous hydrogen sulfide gas does not appear to have escaped into the atmosphere from the salt cavern well between the Bayou Corne and Grand Bayou communities, parish and company officials said.

“The fact is, nothing vented into the atmosphere as best as anybody could ascertain,” said Sonny Cranch, spokesman for the Houston-based company.

Detection occurred between 8 a.m. and 9 a.m. and led to the shutdown of the well, said John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness.

The colorless gas, which has a rotten egg smell, is flammable and can be poisonous at high enough concentrations, but it also is a common problem that accompanies oil and gas drilling. The gas is heavier than air and can spread long distances aboveground.

Boudreaux said a subsequent test by parish officials later Thursday morning did not detect the gas on Texas Brine’s site and community-based air monitors also have not detected hydrogen sulfide.

The cavern well is one Texas Brine had been ordered to drill months ago by the state Office of Conservation to investigate the company’s failed salt cavern in the Napoleonville Dome south of La. 70 South.

As well as diagnostic testing of the cavern, the investigatory well is being used to remove crude oil and vent methane gas from the cavern.

Cranch said workers were removing oil and gas Thursday, detected a faint rotten egg smell and saw that the flare attached to the well appeared to burning off hydrogen sulfide.

A worker inserted an analysis device in a valve providing access inside a pipe that carries the methane to the flare stack, Cranch said. The piping is part of separating equipment that divides oil and gas rising up from the investigatory well.

The worker found a reading of 19 parts per million inside the flow pipe at a point before the gas reached the flare, Cranch said.

The U.S. Occupational Safety and Health Administration says workers should not be exposed to hydrogen sulfide already diffused in the atmosphere at 20 parts per million for more than 15 minutes in a work day.

The federal worker-safety agency says concentrations of 100 ppm are immediately dangerous to life and health, and death has been known to occur within 30 minutes at concentrations greater than 600 ppm.

The rotten egg odor can be faintly detected at 0.3 ppm and eye irritation can occur at 10 to 20 ppm, the U.S. Environmental Protection Agency says.

Scientists believe the Texas Brine cavern failure caused a sinkhole to form between the Bayou Corne and Grand Bayou areas just east of the dome and set in motion an underground chain of events that released oil and gas from natural pockets along the salt dome.

Boudreaux said officials plan to monitor the well Friday during oil and gas removal to see whether hydrogen sulfide can be detected again.

Texas Brine officials encountered hydrogen sulfide Nov. 19 in a separate vent well on the company site south of La. 70 South.

A small amount of the gas escaped into the atmosphere for about five seconds from a similar separator unit designed to divide water and gas from the vent well, officials have said.

The gas was found in the well bore and appeared to have come in contact with water in a separation tank. Company officials have said they shut in that vent well and plan to permanently plug it.

The well reached nearly 500 feet deep to the salt dome caprock, an area of salt domes known to contain sulphur in some cases.

Other vent wells still burning off trapped methane under the Bayou Corne area are much shallower.

Boudreaux said scrubbing equipment can be installed to keep the hydrogen sulfide from escaping from the investigatory well. That well reaches past the caprock and inside the salt dome to the top of the Texas Brine salt cavern at a depth of 3,400 feet.


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