Crosstex Energy LP of Dallas has removed 940,000 barrels of liquid butane in a gas storage cavern inside the Napoleonville Dome in northern Assumption Parish, while removal continues in the only other cavern holding natural gas in the salt dome, a parish official said Friday.
The gas removal has been under way since shortly after the sinkhole, now 8.6 acres in size, was discovered in a swampland area just off the northwest side of the salt dome between the Bayou Corne and Grand Bayou communities on Aug. 3.
John Boudreaux, parish director of Homeland Security and Emergency Preparedness, said Crosstex removed all the liquefied butane early this month except for a small protective pad.
But he said Chevron Pipe Line Co. is continuing to remove natural gas from its nearby Bridgeline NS1 cavern, which is about 1,900 feet east of the sinkhole.
Gareth Johnstone, a Chevron spokesman, declined Friday to provide a timeline for complete removal, which began shortly after the sinkhole was found and involves a careful balancing of cavern pressures. Crosstex officials did not return messages for comment.
Crosstex had originally planned last fall to move the butane from a cavern closest to the sinkhole to an empty one 1,000 feet farther away in the dome. Boudreaux said the company ended up removing the butane altogether.
The location of the storage cavern near the sinkhole prompted early concerns about an explosive release after a major failure. But Crosstex provided an analysis to state regulators that natural downward pressures on the liquefied product a half-mile underground would not result in a catastrophic release.
Since then, the sinkhole has grown and scientists have raised questions about the long-term integrity of other caverns on the west side of the dome.
Scientists believe the failure of a Texas Brine Co. LLC salt cavern deep underground in the dome unleashed crude oil and gas in natural formations along the dome’s salt face.
Concerns about the gas and the sinkhole have kept an evacuation order for about 150 residences in Bayou Corne and Grand Bayou in place since it was issued in August.
Texas Brine and parish officials also announced progress on other fronts as well:
- Nine vent wells flared off methane gas trapped under the Bayou Corne area Friday and more such wells could be burning more gas soon.
- Texas Brine and contractor Boone Exploration Inc. plan a meeting and demonstration from 11 a.m. to 1 p.m. Saturday at Sportsman’s Landing, 1491 La. 70 South in Bayou Corne on a 3-D seismic survey planned for the area.
- Texas Brine is finished installing a permanent seismic array, under orders from the Office of Conservation, to monitor tremors in the area and to replace the array that had been in place through the U.S. Geological Survey.
- The access well Texas Brine drilled last year to reach its failed Oxy Geismar No. 3 cavern is blocked with salt, and a portion of it must be redrilled to remove the blockage.
The vent well progress represents a step forward after Texas Brine faced criticism for the comparatively slow pace of vent well installation.
Five new vent wells have come online recently in addition to four already in place but gradually were declining in the rate of gas flow.
“By tomorrow afternoon, there should be an additional six wells flaring as well,” Boudreaux said.
He estimated that one of the five new vent wells is burning off gas at a rate far exceeding any of the other wells.
While the flare attached to the well is not metered yet, Boudreaux estimated the vent well is removing between 175,000 and 215,000 cubic feet of gas per day. Older vent wells had reached the tens of thousands of cubic feet per day at their peak operational capacities.
Called Observation Relief Well 15, the new well is located north of La. 70 South between Bayou Corne and Grand Bayou, where CB&I engineers and other contractors working for the Louisiana Office of Conservation had installed two of the earliest vent wells.
Installing and operating the vent wells is one of a number of tasks imposed on Texas Brine by the Office of Conservation to abate the sinkhole and other side effects.
The vent wells are designed to remove between 50 million and 100 million cubic feet of gas estimated to permeate the shallow soils and an aquifer in the vicinity of the sinkhole and nearby Bayou Corne community. The gas, scientists say, poses a possible explosive threat to some residences in the area.
Company officials had announced plans to have as many as 26 vent wells removing gas, but Boudreaux said Friday the company is now looking at five more.