Failed cavern still producing

Five miles as the crow flies from the Bayou Corne-area sinkhole near La. 1000, Petrodome Operating LLC is drilling for oil deep underground.

Petrodome is backed by an Australian company, Grand Gulf Energy Ltd., that has a trove of proprietary seismic data allowing the company and its partners to plumb strata a few miles off the Napoleonville Dome for oil and gas finds others have not tapped, company news releases and well records show.

Hydrocarbons have been known for decades to collect in pockets along the edges of massive upthrusts of salt like the Napoleonville Dome as the strata along their sides are deformed upward by the rising salt.

According to online state well records, Petrodome began drilling in late October after the Louisiana Office of Conservation issued the company a permit Aug. 17.

That’s two weeks after the sinkhole was found off the northwestern edge of the dome and an evacuation was ordered for 150 homes in the area.

Scientists with the Louisiana Department of Natural Resources and private industry believe a Texas Brine Co. salt cavern inside the salt dome had a wall breach that set off a chain of events leading to the formation of the sinkhole and an upwelling of oil and gas.

Natural gas is now trapped in the aquifer and has been found in far shallower sediments near the Bayou Corne community.

The drilling project illustrates the case-by-case approach the Office of Conservation and DNR have taken on continued industrial activity and oil and gas exploration over the salt dome and around its perimeter since the emergence of the sinkhole in early August and the tremors and natural gas releases preceding the sinkhole.

The seven companies with facilities on the dome, for instance, including Texas Brine, are being allowed to continue their normal operations and at least six existing oil and gas wells remain active in the Napoleonville Field, which covers a broad area that includes the dome, DNR records show.

But on Aug. 15, two days before the state office issued Petrodome the permit, Dow Chemical Co. agreed to the Office of Conservation’s request to halt its previously permitted work to plug and abandon another cavern inside the salt dome just east of the sinkhole, DNR correspondence shows.

The state office permitted the work May 1, which was before the first reports of natural gas bubbles in area bayous were made, and extended Dow’s permit in mid-July after bubbles and tremors were gaining attention.

The plugging project, which a Dow official said has been in planning since 2006 as part of its worldwide cavern plugging effort, is on hold while scientists investigate the cavern failure and sinkhole.

When a cavern is abandoned, a series of cement plugs are used to seal off the well that ties the underground cavern to the surface.

In the case of Dow well No. 5, five plugs were in place when the project was halted by the state, said Jeff Hertzing, a Dow cavern specialist. He said it will take four more plugs before the well is considered permanently sealed.

Patrick Courreges, spokesman for DNR, did not dispute the agency’s case by case handling of continued operations.

He explained the difference in handling the Dow salt cavern and Petrodome drilling project is tied to their proximity to the sinkhole.

The Petrodome rig is three miles from the northeastern edge of the salt dome and five miles from the sinkhole, which is on the opposite, or northwestern, side of the dome.

In addition, Petrodome’s drillers are planning to bore down 13,000 feet, more than a mile deeper than any cavern activity in the dome, Courreges said.

“Both the lateral surface distance and the difference in depth show that standard drilling and production operations would have no impact on the situation on the western side of the salt dome,” he said.

The Dow cavern is far closer and shallower.

Courreges said the state office halted the plugging of the Dow No. 5 for two reasons: out of an abundance of caution for public safety given the cavern’s proximity to the sinkhole and the uncertain nature, at the time, of the source of natural gas in the aquifer, and also to ease re-entry of the cavern if needed.

“Re-entering a wellbore that had not already been cemented to surface would be less problematic,” Courreges said.�

According to 1987 Dow correspondence with DNR, the cavern was used for hydrocarbon storage from 1961 until 1985 when it was switched to brine use. More current records show it has been inactive.

Hertzing said the cavern held ethylene dicholride in the late 1970s and early 1980s but has been inactive for many years and has become a long-term maintenance headache, putting it among about 100 out-of-service Dow caverns worldwide marked for closure.

“Dow 5 is on our list,” he said. “It’s no longer a useful asset for us any more.”

He said Dow did not object to DNR’s request. Also, the well is stable and is being monitored, Hertzing said, and it is plugged from the surface.

“And we’re ready to do whatever the DNR requires for us to finish it off when they are comfortable with allowing us to finish it off,” Hertzing said.

By Nov. 5, Petrodome drillers had reached nearly 4,800 feet underground, DNR records show.

The company is directionally drilling from an agricultural field south of La. 1000 under homes along each side of the highway to a point north of the highway, Courreges confirmed.

Gina Vedros, 49, whose home is in Grand Bayou, was evacuated after the sinkhole and lives in a rear apartment with her husband at her brother’s house off La. 1000. That house is across the highway from the Petrodome drill rig.

“I think things should be put on hold until this situation is resolved, until we’re back home,” Vedros said.

She was evacuated from Grand Bayou in 2003 and early 2004 after an earlier gas leak on the salt dome, and she has a pending suit against Dow Chemical over a property buyout.

Vedros pointed out another drilling rig north of La. 70 South near Paincourtville had a blowout in the summer of 2010.

That rig was operated by Mantle Oil and Gas LLC of Friendswood, Texas, but Grand Gulf was a major investor and the job was part of its effort to tap strata around the salt dome.

Vedros questioned what would happen if there were another blowout from the latest drilling.

“It’s just not something that should be going when we’re still in an emergency situation, (and) our parish is still involved in an emergency situation,” she said.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said the parish has not objected to the drilling project because of its distance from the sinkhole. He said multiple emergency incidents do not often happen but can be dealt with.

“You just deal with them,” he said. “If it takes more people, you call for the additional resources needed, and you get it done.”

He noted that another drilling project, deepening an existing well, is planned down La. 1000 from the Petrodome project.