The results are in from the latest battery of high-tech tests, but scientists still cannot rule out the possibility that a cavern formed by a brine well operation near a busy Carlsbad intersection might one day collapse.
What they do know is that the ground beneath the area is a messy conglomeration of cavities, fractured rock and brine-soaked earth. A report released recently by the New Mexico Oil Conservation Division spells out the findings from a series of electric resistivity tests that were done this spring.
“The data is confirming our original concerns,” said Jim Griswold, a hydrologist with the state agency.
While no one can say whether the site will ever collapse, state and local officials have been trying to find out exactly what they’re dealing with so they can determine how to protect a nearby roadway, a neighboring church, a feed store, a mobile home park and an irrigation canal that serves farmers throughout the lower Pecos River Valley.
The resistivity tests were designed to give officials a better idea of how big the void was under the old brine well facility. The tests, which use electrical current, showed a cavity below the well pad but it was not as clearly defined as geologists had expected.
Instead, differences in the current indicate there are fractured areas below the surface that are being kept buoyant by the brine, which is mined for use in oil and natural gas development.
“We thought that the brine cavity would really pop up on our charts as a big blue blob that was very distinctive. In hindsight, no. It’s popping up, but so are some other things,” said George Veni, executive director of the National Cave and Karst Research Institute based in Carlsbad. Veni and hydrologist Lewis Land of the New Mexico Bureau of Geology and Mineral Resources prepared the latest report.
The charts show a rainbow of colors, with blue representing the areas of low resistivity.
Despite the overwhelming swaths of blue, Veni stressed that people shouldn’t be alarmed.
“My main point is that if people look at our charts, they don’t get the wrong impression that the whole area is about to become a huge crater,” he said. “My gut feeling and from what I understand of the area tells me that most of those zones probably don’t have any significant risk of any significant subsidence. I can’t promise that of course, but based on what I’m seeing, it’s not likely.”
Still, Griswold said “it’s not good” and officials need to do more tests to determine the best option for stabilizing the area.
The brine well that was once operated by I&W Trucking first came to the attention of state regulators after two other brine wells collapsed in remote areas north of Carlsbad during a four-month span in 2008.
The collapses prompted the state Energy, Minerals and Natural Resources Department to issue a moratorium on new brine wells and initiate a review of all existing brine well operations.
The state determined the I&W well was a threat because it was similar to the two collapsed wells. They were all about the same age, drilled to similar depths and produced between 6 million and 8 million barrels of brine from salt layers deep underground.
The Oil Conservation Division spent more than a half-million dollars on an early warning system consisting of tilt meters and pressure sensors that monitor the site for any changes that would indicate the start of a collapse.
It has spent another $200,000 for the latest round of resistivity tests.
The city of Carlsbad also stepped in with about $1.7 million of its own money for monitoring and additional surveys to gauge the size of the void.
Until the next round of tests, officials said the monitoring equipment will continue recording data and the sign that warns approaching traffic of a possible sinkhole ahead will remain in place as will the no trespassing signs bordering the property.
“I think we’ve made some progress. We’re getting a better idea of the size and shape of it, but do we have an absolute answer? No. I wish we did,” Veni said.
Numerous suggestions for dealing with the site have been made over the last two years, including filling it with concrete or even excess salt from the federal government’s nuclear waste repository outside of Carlsbad.
“That’s simple to say but you don’t want to go randomly poking holes into this cavity and accidentally trigger a collapse,” Veni said. “You want to know what you’re doing and do it well and do it as safely as possible.”
The research being done at the site has been invaluable, since this marks the first time scientists have been able to study a potential sink hole before it collapses.
State officials are also monitoring more closely eight existing brine well operations in the state and are currently reviewing a permit application for a new operation near Carlsbad. They said demand for brine is expected to increase as oil and gas development picks up in southeastern New Mexico.
“What I’m hoping that people will do is look to New Mexico and say, ‘OK, what did these guys do.’ Hopefully, they’ll be able to say we got it right,” Veni said. “But even if we got something wrong, in hindsight the fact is that it’s still a learning experience for someone moving forward.”