Vent wells burning gas from sinkhole area

11 19, 2012 by The Advocate

Assumption Parish and Texas Brine Co. LLC officials are reporting progress by specially built wells put to work collecting and burning methane trapped in a water aquifer under the Bayou Corne area.

Three vent wells already are burning off gas, and Texas Brine officials have plans to link flaring equipment on Monday to a fourth existing well that is being converted to the gas-removal process, company and parish officials said.

Workers initially found the wells’ perforations — small holes in the well casing that allow gas to flow inside the well bore — were clogged with clay. But since early November, drillers have been able to remove water inside the wells to get the gas to come up, or they reworked the clogged wells and added more perforations, officials said.

Texas Brine got the first well to start burning gas Nov. 2 south of La. 70 S.

Shaw Environmental and Infrastructure, the Louisiana Office of Conservation’s agent in the sinkhole response, has gotten two wells to burn gas since then, including one on Thursday north of La 70, parish officials said in a blog post.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said the more wells in place, the more gas that can be removed from under ground.

“And, hopefully, the sooner they can get it stabilized,” he said.

The Office of Conservation has ordered Texas Brine to take over the vent well operations and add more wells. Boudreaux said two new vent well sites have also been proposed, though routes to the sites are still being developed.

The gas was released into the Mississippi River Alluvial Aquifer after a Texas Brine salt cavern failed in August, and since then, the gas has permeated even-shallower sediments.

The cavern inside but near the western edge of the Napoleonville Dome underwent a “wall breach” several thousand feet underground, scientists believe. That failure set off a chain of events suspected of causing the sinkhole to emerge and releasing to the surface gas and crude oil naturally occurring in pockets along the edge of the dome.

Officials said that the gas freed by the cavern collapse now poses an uncertain risk to Bayou Corne residents who have been evacuated from their residences for more than three months. Meanwhile, officials have called for in-home air monitoring and specialized detectors and ventilation systems for slab-foundation homes.

Sonny Cranch, spokesman for Houston-based Texas Brine, said virtually all residents who picked up housing assistance checks Thursday from the company and own slab homes in the evacuation zone filled out forms allowing the new equipment to be installed on their property.

The evacuation order, affecting about 150 homes in the Grand Bayou and Bayou Corne communities, was issued within hours of the discovery of the sinkhole, though the presence of the gas now provides another reason to keep the order in place, parish officials have said

The sinkhole, which now has an 8-acre surface area, is located in swamps between the communities south of La. 70 on property leased by Texas Brine from Occidental Chemical Corp.

Boudreaux provided estimates showing the three vent wells had released 558,000 cubic feet of gas through Friday morning.

An investigatory well that the Office of Conservation ordered Texas Brine to drill months ago to peer inside its failed cavern has burned another 598,000 cubic feet of gas through early Friday.

Combined with the three vent wells, the four wells have removed nearly 1.2 million cubic feet of gas, the figures show.

By comparison, a gas release in late 2003 into the subsurface near the Grand Bayou community from a storage cavern inside the salt dome prompted the eventual installation of 36 vent wells. They removed 375 million cubic feet of gas before they were shut down in 2004, Office of Conservation officials have said.

Office of Conservation officials have said the 2003 incident is not comparable to the current incident because the 2003 gas was at much higher pressures than the pressures produced in the recently drilled Bayou Corne vent wells.

The well that Texas Brine is trying to convert to gas removal, however, has hit gas at 155 pounds per square inch, higher than the gas pressure in other vent wells, Cranch said.

But the higher-pressure well, which reaches down 430 feet, extends 300 feet deeper than the much shallower vent wells recently brought on line.

Cranch said company officials do not know yet if the higher pressure is related to a sizeable amount of gas or the greater depth of the well. Pressures increase at depth.

But he said Texas Brine is waiting on flaring equipment that can handle the higher pressure.

The well originally was bored to the caprock over the salt dome and under Texas Brine’s site as a means of installing seismic equipment, but that plan was halted when drillers hit gas.

Cranch said company officials do not know if that gas comes from a natural pocket or from the latest incident.

“Whatever it is, it’s going to be vented,” Cranch said.