Dangerous hydrogen sulfide gas was detected Friday in fumes coming from crude oil drawn from an investigatory well tapped into a Texas Brine Co. LLC salt cavern in northern Assumption Parish, company and parish officials said.
The discovery of hydrogen sulfide Thursday from a methane stream flowing out of the well forced a shutdown and subsequent testing Friday of the well between the Bayou Corne and Grand Bayou communities, officials said.
Officials were trying to determine the source of the hydrogen sulfide gas, also known as H2S. They want to continue using the well to remove oil and gas from the failed salt cavern and perform other testing.
The Louisiana Office of Conservation ordered Texas Brine to abate one of the suspected consequences of the failed underground cavern.
Company officials said Friday Texas Brine is looking at equipment to scrub the possibly sulfur-laden oil and put it in sealed transport containers to prevent any H2S releases.
“They are looking into ways to address the hydrogen sulfide issue and the sulfur in the oil,” said Sonny Cranch, spokesman for the Houston-based company.
He said the well would remain shut down until the equipment is installed.
That the oil has sulfur content is not unheard of, although Louisiana is more often known for its “sweet” crude, which has a low sulfur content. “Sour” crude has higher sulfur content.
Also, on Friday, Louisiana Office of Conservation Commissioner James Welsh ordered Texas Brine to drill two 6,000-foot-deep wells and take other steps on geotechnical work around the cavern and a related nearby sinkhole.
Welsh gave Texas Brine until Dec. 28 to submit plans and until Jan. 15 to have rigs ready to drill, threatening fines if the deadlines were not met, Conservation officials said.
“The deadlines set in these directives are aggressive, but absolutely necessary and achievable to get to the bottom of this situation,” Welsh said in a news release.
Located inside the Napoleonville Dome, the salt cavern is believed to have been broached deep underground when a side wall caved in, causing the 8-acre sinkhole, tremors and releases of oil and gas from natural formations next to the dome.
The sinkhole, found Aug. 3, prompted the evacuation of about 150 residences in the Bayou Corne and Grand Bayou communities. The evacuation remains in place.
Welsh’s latest order is a response to Texas Brine’s plan for previously ordered geophysical modeling and expansion of seismic monitoring in the vicinity of the sinkhole, he said.
Conservation staff found Texas Brine’s plans were inadequate despite follow-up meetings to provide “further clarification” about what the office needed to find out.
Conservation officials said the two new deep wells would allow use of the best available technology to get a clearer understanding of what happened.
“These wells will provide additional information about the sinkhole and will help us continue to preserve the safety of the area and get the lives of these residents back to normal,” he said.
The cavern failure, scientists think, allowed 3.3 million cubic yards of earth from outside the dome to enter the cavern previously hollowed out from the salt, leaving a collapse zone of disturbed earth alongside the dome and beneath the 8-acre sinkhole.
A shallower overhanging section of salt on the edge of the salt dome also may have collapsed along with the salt cavern wall deeper underground.
Patrick Courreges, spokesman for the Louisiana Department of Natural Resources, of which Conservation is a part, said Friday officials want to be able to conduct seismic tests that can be shot from the base of the cavern.
The cavern’s original base is 5,650 feet deep, though the cavern has since filled with sediments and its bottom is less than 4,000 feet below ground level now, Cranch has said.
One well is to be drilled into the salt dome but to the side of the cavern, Courreges said. The other well will be drilled next to the salt dome in sediments near the collapse zone. The wells will be used in tandem to carry out seismic testing, Courreges said.
At 6,000 feet, the two wells will be nearly twice as deep at the 3,400-foot investigatory well that Welsh ordered Texas Brine to drill into the cavern in August and took the company about a month to bore.
“We will review the order and respond appropriately,” Cranch said.
The investigatory well has been used to remove about 4,000 barrels of oil and 600,000 cubic feet of methane from the cavern but the first time hydrogen sulfide was detected in that well was Thursday, Cranch said.
A previous hydrogen sulfide discovery last month in methane gas in a separate vent well forced a shutdown and planned closure of that well.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, acknowledged that discovery of hydrogen sulfide from the oil fumes may point to the source of the gas being different in the investigatory well than the vent well. The oil was sampled for direct testing, he said.
Boudreaux said the oil vapors from the investigatory well were measured at 28 parts per million as they diffused briefly into the atmosphere from an opened valve in equipment tied to the well.
The crude was moving past the valve at the time in a flow tube.
Another test of a sample of the oil in a sealed container found concentrations at 80 ppm without any diffusion into the atmosphere, Boudreaux said.
A test of methane, which comes up from the well before the oil, showed concentrations of only 1.75 ppm.
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