By David J. Mitchell
River Parishes bureau
August 23, 2012
BAYOU CORNE — Texas Brine Co. LLC drillers tried Tuesday in northern Assumption Parish to make headway through about 325 feet of solid rock to reach the crest of a solid underground salt deposit, company officials said.
The 1-mile-by-3-mile salt dome, called the Napoleonville Dome, contains a hollowed-out salt cavern once operated by Texas Brine. state Department of Natural Resources scientists think it may be the cause of a large sinkhole that has formed between the Bayou Corne and Grand Bayou areas.
Texas Brine plans to drill an observational well from a company well pad about 1,000 feet from the sinkhole and then use sonar equipment to probe underground conditions. DNR ordered the well and diagnostic work to see what is happening inside the cavern.
Company officials said drilling is on schedule and moving as quickly as possible. Drilling is estimated to take 40 days to reach the cavern.
“It may take a little longer.... We may reach it in a shorter period. We just don’t know,” said Sonny Cranch, Texas Brine spokesman.
“But until we reach that point, we can do nothing but continue on this path,” he said.
Cranch spoke over the rumbling din of the rotating drill pipe powered by the 140-foot-tall rig’s machinery. Rigging holding up the spinning pipe slowly moved downward Tuesday morning as cap rock surrendered to the drill bit.
Drilling began in earnest late Monday and Tuesday as other developments arose:
- Crosstex Energy LP of Dallas began moving liquid butane on Monday, a day earlier than expected, from a storage cavern nearest the sinkhole to a second one farther from the sinkhole to allay community concerns about the flammable product.
The caverns are also carved from the Napoleonville Dome.
- Texas Brine contractor, Worley Catastrophe Response, will distribute another round of housing assistance checks to residents affected by a parish evacuation order. The checks will be given out from 9 a.m. to 6 p.m. Thursday at St. Joseph the Worker Roman Catholic Church Parish Hall, 3304 La. 70, Pierre Part.
- On Friday, a public meeting on the sinkhole and drilling operations is also planned at the church’s parish hall starting at 6:30 p.m.
Officials to issue a standing evacuation order applying to about 150 homes in the area when the sinkhole was found on Aug. 3. The sinkhole emerged from forested swamps about 200 feet from the cavern and has continued to grow periodically around the edges.
DNR scientists have said they think the cavern could also be the source of natural gas releases in bayous and wells that preceded the sinkhole’s emergence this month and have continued since then.
After some final preparations, workers with Riceland Drilling Co. of Lafayette began drilling about 10 p.m. Monday into the cap rock, the top of which is 377 feet underground, company officials said. The cap rock sits atop the salt dome.
Cranch said in an email later Tuesday that drillers, who are working 24 hours per day, had reached 539 feet underground by about 6 p.m., which is about 162 feet into the cap rock.
Cranch said drillers planned to stop at 600 feet underground to install casing, which is hollow metal pipe, and cement it into place before a final push through the cap rock into the top of the salt dome at 700 feet underground.
John Boudreaux, director of the Assumption Parish Office of Homeland Security and Emergency Preparedness, said it is likely that the setting, cementing and curing of that casing and cement will take through the weekend.
Once in the salt, Texas Brine’s drilling plan calls for the company to drill another 300 feet straight down and then start to turn the shaft toward the possibly failed salt cavern.
Cranch said the drillers will stop at a point 400 feet above the roof of the cavern, which is shaped like a narrow, upside-down vase.
Drilling could move a little more quickly once in the salt, Cranch said.
Along the way, as the observational well goes deeper toward its target, drillers will be stopping to install and cement in place progressively narrower casing pipe.
The cavern roof is at 3,400 feet underground, and the cavern extends down to 5,650 feet. The roof is 150 feet across. Its base is 310 feet across.
DNR scientists think the cavern may have gotten too close to the edge of the salt dome and failed, releasing brine into the outer sediments.
When asked Tuesday, Cranch said that if Texas Brine finds a cavern filled with brine, something else is occurring under the earth that may be causing the sinkhole and further investigation is needed.
While finding the brine would be the best-case scenario for the company, Cranch said, the company also wants to find what caused the sinkhole.
“In reality, all we want to know is what has happened,” Cranch said. “What caused that sinkhole and is this cavern, this particular cavern that this, this observation well is targeting, ... is it in any way connected to that sinkhole?”
Jill McMillan, spokeswoman for Crosstex, said Tuesday the transfer of butane from one Crosstex cavern to another is expected to take two months.
She said the company is working on pumping changes that could speed up the process.
The cavern contains 940,000 barrels of liquid butane that company told state regulators would not be released instantaneously at the surface as a gas even if infrastructure tied to the cavern and its access well is damaged.
McMillan said company officials believe the closer cavern, which is about 1,500 feet from the sinkhole, has not been affected by the sinkhole and poses no risk. The cavern receiving the liquid butane is 2,500 feet from the sinkhole.
“So we are just doing it in an abundance of caution to further alleviate concern,” she said.