Louisiana’s modern-day economy was built on the back of a single industry — oil and gas production.

The existence of the vast deposits of the valuable chemicals were first exploited in the 1930s, when wells began to pop up all along the coast line.

It was a time when no one gave a thought about causing damage to the immense, seemingly endless marshes.

The game was about making money, and land that previously had been viewed as worthless suddenly was discovered to be hiding wealth beyond bounds.

However, it also was a time when laws were in place that limited the amount of production, so for the next two decades, oil and gas were extracted from the depths without major impact.

It was only when the prohibitive laws, in the words of U.S. Geological Survey’s Bob Morton, “went away” and production spiked that people started noticing something.

Land around the oil facilities began to disappear more rapidly than did other marsh.

It was long thought that the reason for this had no direct link to the pumping of vast amounts of oil and gas, along with the millions of barrels in saltwater brine (also known as formation water), from the caverns beneath the organic marsh.

“We allowed the discharge of oil-field saltwater brine into Louisiana waters,” said Kerry St. Pe of the Barataria-Terrebonne National Estuary Program. “In 1992, there were 84 million gallons of brine being discharged into Louisiana surface waters every day.”

Photo by ANDY CRAWFORD

Canal dredging for oil and gas exploration has given salt water easy access to the marshes, but scientists are discovering other impacts dredging and subsequent drilling have had on Louisiana wetlands.

That practice was finally outlawed in 2000, but the damage around many facilities was done.

The logical conclusion was that the concentrated saltwater, which also contained high levels of radium 226 and organic compounds such as benzene, were killing the marsh grasses that held the surrounding marshes together.

“There were hundreds and hundreds of oil-field brine pits, and the brine leaked straight through them,” St. Pe said. “There was invariably a ring of open water where all the plants had died.”

But St. Pe and others had suspicions that the cause of the disappearing marshes so close to these production facilities was not all linked to the plant-killing brine.

A committee of researchers formed to look at the potential problems caused by extracting large amounts of fluid (oil, gas and brine) from the deposits lying thousands of feet below the surface.

“We concluded that, yeah, we are removing a lot of fluid, but it’s at such great depths that it couldn’t possibly impact the surface,” St. Pe explained.

It turns out that the committee should have gone with their hunch.

“Historically, when researchers looked at subsidence, they talked about such things as water-logging and the buildup of sulfides,” Morton said. “It’s sort of like going to the doctor and getting treated for the symptoms and not the disease.”

One of the diseases besetting the Louisiana marsh is, in fact, the vacuum left when oil, gas and brine are pumped from the ground, according to a study in which Morton was instrumental.

The USGS geologist partnered with Noreen A. Buster and M. Dennis Krohn to complete the study last year.

“When the fluids are produced, then the pressure goes down in the reservoirs,” Morton explained. “That causes the overburden sediments to settle.”

Here’s how it works.

Oil, gas and brine have for millennia filled vast formations that are, simply put, caves buried deep within the earth.

Photo by ANDY CRAWFORD

Oil-field structures are common sights to Louisiana fishermen. Though they hold fish at certain times of the year, these structures have accelerated the subsidence of Louisiana’s coast.

The roofs of these caverns remain put because of the pressure from the fluids within the cavities.

However, when those fluids are removed and the openings are left empty, the “overburden sediments” — the earth above the now-empty deposits — begin to smash the roof of the cavity.

This process is exacerbated in fields surrounding faults running through the Louisiana marsh. Fields such as Lirette and Lapeyrouse south of Chauvin are prime examples of the combined impacts of fluid extraction and fault movement.

“There isn’t a catastrophic movement of the faults like with the San Andreas,” Morton said. “It’s more like a creeping process.”

In some areas of the country, where the overlying sediments are made of rock or hard earth, the result can be large sinkholes when the caverns abruptly give way.

In Louisiana’s marshes, the result is a gradual sinking of the surface land, as the organic goo of which the coastal zone is composed begins to push into the holes far below it.

“They’re trying to fill that space that was once occupied by the oil, gas and formation water,” Morton said.

Morton and his associates made this conclusion by comparing the known historical rates of natural subsidence to that of the past 70 or so years.

“What we discovered is that natural subsidence is very low,” he said. “The subsidence around oil facilities was on the order of 10 times faster than natural subsidence.

“We saw patterns that were very similar from (oil) field to field.”

The correlation between oil and gas production and wetlands loss is clearly illustrated by a look at the rate of land loss since the 1940s.

The USGS estimates that the Louisiana coastline was receding by a little more than 10 square miles annually in the mid 1940s, but as oil-field production spiked, so did the loss.

The land loss by 1970 was almost 30 square miles per year.

Morton said the argument for a link is strengthened by the noticeable decrease in land loss since the 1970s peak of production.

“All the fields went into an acceleration in production in the 1960s and 1970s, and subsidence peaked in the 1970s,” he said. “There’s a really strong, compelling argument that the oil and gas and formation water is part of the underlying cause for why the rates of subsidence increased in historical times.”

Graphic courtesy of U.S. GEOLOGICAL SURVEY

Oil and gas deposits lie in underground cavities along with formation water, so when the deposits are sucked out through wells, the land sinks to fill the now-empty hole. This is especially noticeable where there are nearby faults.

But why would the rate of subsidence slow down simply because oil production declines?

Morton said there’s a fairly simple explanation.

“Once you remove that disruption to the subsurface (which is caused by pumping out the fluids from the deposit cavities), nature has a good way to equalize things,” he said.

It seems that the exploited fluids are, to a degree, replaced by other fluids squeezed from the sinking marsh.

And as the sinking marsh and those resulting fluids fill the void left by oil and gas production, subsidence slows.

“It will go back to a natural rate instead of this artificial rate that was going on when those fluids were being extracted,” Morton said.

But fluid extraction isn’t the only way the petrochemical industry has harmed the Louisiana coast.

Anyone who has spent time in the marshes knows that oil-field canals crisscross the coast.

These canals, St. Pe said, have worked hand in hand with fluid extraction.

What might be surprising is that the main culprit when addressing the issue of canals is not saltwater intrusion, which many associate with the killing of marsh grasses.

“Somewhere along the line, the public has gotten the idea that saltwater intrusion kills all marsh. We’ve gotten into the practice of blaming saltwater intrusion for all our problems,” St. Pe said. “Actually, it’s more of a problem when saltwater intrudes into areas that are fresh water.

“The saltwater marshes survive quite well. They evolved to live in those conditions.”

The real problem with the canals is that they change the hydrology of the marsh.

“They dig the canals and put the material on the sides, creating levees or spoil banks,” St. Pe said.

These high banks stop the natural flow and ebb of water over the marshes, choking them.

“It impounds water that would normally flow in a sheet over it. You actually cause chemical changes in the marsh that kill those plants,” he explained.

The main culprit is a buildup of hydrogen sulfide, St. Pe said.

And without the dense vegetation, the marsh simply falls apart, sinking until open water replaces the once high, albeit soggy, ground.

A second problem caused by the digging of canals is that natural bayous are connected artificially.

“Now those areas are subject to tidal flow,” St. Pe said.

Both St. Pe and Morton cautioned, however, that the petrochemical industry should not be isolated as the single source for all evil.

“Looking at the whole system, there’s just a whole bunch of processes that are the cause of subsidence,” St. Pe said.

Even without the extraction of oil and gas, along with the canal systems that accompany these facilities, Louisiana’s marsh would still be sinking.

What the petrochemical industry has done is simply accelerate the natural processes.

“We’ve always had subsidence. What we don’t have is the process to offset the subsidence, which is the Mississippi River,” St. Pe said. “We’ve removed part of the equation to the solution. We’ve removed the positive part of the equation (by leveeing the Mississippi).”