Gas flowing from sinkhole

Texas Brine Co. began burning off natural gas Friday that was trapped in a water aquifer near a sinkhole in northern Assumption Parish, officials said.

This was the first time state, parish or company officials have been able to get gas to flow from four “vent wells” driven into the ground around the sinkhole in order to draw the dangerous gas out of the aquifer.

Located in the swamps between Bayou Corne and Grand Bayou south of La. 70 South, the sinkhole is more than 5½ acres in size at the surface and has prompted authorities to issue a standing evacuation order on Aug. 3 applying to 150 homes.

Fears that the trapped gas, which is colorless, odorless and potentially explosive, could accumulate to dangerous levels at the surface has further justified the evacuation order, parish officials have said.

Authorities had counted on the vent wells to release the gas from the aquifer, but the effort was hampered at first because well casing openings designed to allow gas to flow upward to the surface had been clogged with silty clay. The fact that the gas is believed to be at low pressures possibly aggravated the clogging problem.

The well casing is a kind of piping that forms the outer wall of the well bore.

Sonny Cranch, Texas Brine spokesman, said that when company contractors removed water from the vent well casing late Thursday, natural gas began to flow to the surface.

He said water apparently had been impeding the flow of gas from the well, which is on Texas Brine’s leased site near the sinkhole.

Gas venting was stopped Thursday night and reached a “modest” pressure of 30 pounds per square inch at the wellhead, company officials said in a news release.

Contractors hooked up a temporary flaring system Friday morning and the gas will be allowed to flare, or burn off, this weekend during daytime hours, company officials said.

“Next week, additional water will be removed from the casing to allow greater natural gas flow,” officials said in the statement. “In addition, a more permanent flaring system will be installed to allow more continuous venting.”

Scientists believe the gas was released, along with crude oil, from underground pockets alongside the Napoleonville Dome when a Texas Brine salt cavern failed and caused the sinkhole.

The salt cavern located near the western edge of the salt dome developed a wall breach that allowed oil, gas and 3.3 million cubic yards of
sediment into the formerly brine-filled cavern inside the dome.

In other developments Friday, imaging of the sinkhole by Texas Brine shows that a deep, funnel-shaped void at the bottom center of the sinkhole has filled in, company and parish official said.

As a result, the depth of the sinkhole has been reduced from 449 feet to 170 feet, but the volume has increased from 550,000 cubic yards to 666,000 cubic yards, a cross-section says.

Cranch said the image was made before the eastern edge of the sinkhole sloughed in, or collapsed, later Tuesday. The sinkhole has undergone periodic edge collapses. Additional imagery is expected, he said.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said that since the Tuesday edge collapse, a large bubble site venting natural gas from the center of the sinkhole has stopped. Bubbling continues around the edges of the sinkhole and in area waterways.