GONZALES — Louisiana Conservation Commissioner James Welsh on Friday ordered the seven companies operating on the Napoleonville Dome in Assumption Parish to determine if natural gas is contained in the groundwater and the salt dome caprock beneath their installations.
Welsh directed the companies to capture, vent or flare any gas that is found and analyze potential effects on groundwater in the Mississippi River Alluvial Aquifer, Louisiana Department of Natural Resources officials said in a news release.
The new work was called for after DNR had directed Texas Brine Co. of Houston to drill an investigatory well to see whether its abandoned salt cavern inside the salt dome is the cause of a large sinkhole that formed on company property located between the Bayou Corne and Grand Bayou communities.
The sinkhole’s discovery prompted an Aug. 3 evacuation order affecting about 350 people.
Welsh’s order, a “formal declaration of emergency and directive,” follows three instances since Sept. 8 when drilling or boring work — near the sinkhole and at two sites between that sinkhole and the Bayou Corne community — encountered gas pressure when drillers pierced the aquifer’s upper level, DNR officials said.
Gas also was found at one of three sites deeper underground in the salt dome caprock, a tough rock layer on top of the dome.
“This new data indicates the presence of natural gas in the aquifer and caprock near the existing salt dome operations, and the Office of Conservation is ordering immediate action to assess that risk and take actions where necessary,” Welsh said.
Welsh’s office has hired Shaw Group to oversee evaluation of natural gas in the groundwater and removal of any natural gas.
Patrick Courreges, DNR spokesman, said what the companies are asked to do depends on what the companies would find.
“At this point, we’re in a mode of let’s find out what we’re dealing with,” Courreges said. “We got an idea of how we’re going to approach it, but now we got to do the actual work to find out.”
The Napoleonville Dome is a 1- by 3-mile underground salt deposit that natural forces pushed up vertically from ancient sea beds. The dome has been used for brine production, oil and gas exploration and hydrocarbon storage for decades. The sinkhole has formed along the dome’s northwestern edge.
The Napoleonville Field contains about 60 brine wells or caverns used for hydrocarbon storage, according to DNR figures.
DNR scientists believe the Texas Brine cavern could be the cause of the sinkhole and of the natural gas releases that bubbled up through area bayous beginning two months before the sinkhole emerged and which have continued to proliferate since then.
But DNR officials have cautioned other possible causes are being considered and have followed another track to see if natural gas is inside the aquifer in the region.
Drilling and boring to test the aquifer and its overlying soils has focused on shallow pockets where the aquifer rises high into a confining clay layer overlying the aquifer, DNR officials have said.
Pro-Tech, a contractor hired by the state Office of Conservation, hit gas pockets Thursday at a depth of less than 50 feet, Courreges said.
Pro-Tech was drilling monitoring wells to sample for natural gas north of La. 70 between Bayou Corne and the sinkhole, DNR officials said.
Walker-Hill Environmental, which was hired to drill an observational water well, was working in the same area but south of La. 70 when it hit gas Friday at 90 feet, Courreges said.
He said that well has been plugged. DNR officials and the contractor pulled the drilling rig down in order to deploy safer equipment that can better deal with possible gas pockets and plan to drill another well in the aquifer in the same vicinity, Courreges said.
In both cases, the companies had bored into the top of the aquifer layer when they hit gas.
“If there is gas in the aquifer, that is exactly what you’d expect,” Courreges said. “It’s going to be at the top.”
He said that if water runs downhill, natural gas wants to go up, away from pressure, until it reaches a barrier where it is stopped, such as the confining clay layer on top of the aquifer.
An earlier instance of gas pockets involved work by Texas Brine, DNR officials said.
The company was using sonic rig equipment to bore into the ground in the vicinity of its investigatory well and the sinkhole to install seismic equipment for monitoring.
The boring hit gas at 120 feet, at the top of the aquifer, and again inside the salt dome caprock at 420 feet, DNR officials said.