Gas well emissions worry EPA

In the daylight, the storage tank looks innocuous. It's the same sort of tank that can be found next to any oil or gas well in the West, and there are hundreds like it in Fort Worth.

But in infrared light, a plume of vapor can be seen escaping from the tank's vent.

The video, taken by the Environmental Protection Agency at a site in Colorado, is a vivid illustration of a problem that's beginning to draw attention: the amount of air pollution produced by natural gas extraction in the Barnett Shale field.

Researchers are only beginning to wrap their hands around the issue, but the early findings indicate that natural gas production is a significant part of North Texas’ air pollution problem. And it could be growing. At the least, it's worth studying to determine the scope of the problem, the researchers said.

There has been extensive research on emissions from cars and trucks, which account for much of the air pollution in North Texas. There's also been research into pollution from electric and cement plants.

"All those other sources have seen a lot of regulation," said Al Armendariz, an engineering professor at Southern Methodist University who has studied air quality issues for several years. "The oil and gas sector kind of snuck by."

Industry officials question whether some of the research is valid. But they also said there are cost-effective ways to reduce emissions from gas well sites.

Ground-level ozone

A study by the Texas Commission on Environmental Quality in 2006 estimated that storage tanks alone account for about 38 tons of volatile organic compounds a day, or 7 to 8 percent of the volatile organic compounds in the air in North Texas. Those chemicals are a key ingredient in ground-level ozone, the area's major pollution problem.

The storage tanks are a permanent part of most Barnett Shale gas wells. The wells produce not only gas but also water and a light form of crude oil commonly known as condensate. The tanks continue to fill up as long as the well is producing, and the water and condensate have to be trucked away.

The condensate, high in volatile organic compounds, evaporates easily. The environmental quality commission requires operators to get a permit for each tank, but the tanks can still release vapor through pressure valves.

To calculate the amount of chemicals released, researchers commissioned by the Houston Advanced Research Center hooked up a gauge to several storage tanks and calculated the average amount of chemicals released for each barrel of condensate. Then they multiplied the average by the number of barrels of condensate produced in the region.

David Templet, manager of environmental health and safety for Devon Energy, the largest producer in the Barnett Shale, said the measurement may not be accurate. The researchers took their samples in July, when the heat would have created more vapor.

"You really need to sample for 12 months" to figure a true average, he said.

Also, the amount of condensate that a well produces varies widely from place to place. Many of Devon’s wells produce almost no condensate, said Steve O’Connell, a Devon manager in North Texas.

However, Barnett Shale wells produce a lot of condensate in Wise, Denton and Parker counties, Armendariz said, citing Texas Railroad Commission data.

There are several ways to control emissions from wells that do produce condensate. One is to pipe the full stream of gas, including the condensate, to a processing plant. Another is to capture the vapor at the storage tank and pipe it to a processing plant.

There’s an upside for the producer — the less vapor that escapes, the more condensate there is to sell.

'Running 24-7’

Another source of pollution is the compressors used to move natural gas through pipelines. The compressors are usually powered by large engines — often running on natural gas from the same pipeline — and some of them have no emission controls.

Armendariz said he’s still finalizing the study, but he estimates that the compressors in the Barnett Shale field have a combined 2 million horsepower. That’s the equivalent of about 10,000 full-size pickup engines — in a region with 4.5 million people.

But unlike cars and trucks, "these engines are out there running 24-7," Armendariz said. "The newer ones are pretty clean, but they’re still not as clean as the newest automobiles."

The environmental quality commission began phasing in pollution control rules for compressor engines last year. Commission officials said in a statement that those controls "will have benefit toward reducing" the ozone problem by 2009.

But Armendariz said the commission is focusing only on some of the counties and on some of the engines that are producing oil and gas. And, he said, the state may have underestimated the number of compressors in the Barnett Shale. He is preparing a study that calculates the amount of pollution from compressors and other sources.

Templet, with Devon, said the company is sharing information with Armendariz and the environmental quality commission to ensure that the study is accurate.

Methane emissions

Methane, the primary ingredient in natural gas, is also one of the gases linked to global warming. Scientists theorize that methane, carbon dioxide and other gases have formed a layer around the Earth’s atmosphere that traps heat and has contributed to the rise in world temperatures.

The EPA lists natural gas systems — from production to distribution — as the second-leading cause of methane emissions and has started a voluntary program to encourage producers to reduce what they release.

It's common, for instance, for producers to simply release the gas into the atmosphere when they’re completing a well. That's the phase right after a well is fractured and water is being pumped out of it.

Devon and other producers are trying to capture the gas during completion. Timing is a factor, Templet said, since the well has to be hooked up to a pipeline for a "green completion." But Devon has recovered an estimated 80 tons of methane using the method.

"It costs us a significant amount of money to put that equipment in place, but we also get some money from the sale of the gas," Templet said.

The EPA is also pushing "low-bleed pneumatics." Gas producers often use pressure from their own pipelines to power gauges, valves and other equipment. On older sites, the gas is often vented into the atmosphere.

Low-bleed systems channel most of that gas back into a pipeline. Retrofitting a storage tank can cost a few hundred to a few thousand dollars, but the EPA estimates that the changes pay for themselves within a year.

'Many, many sources’

Judging the cumulative effect of the entire industry is difficult.

"From an air pollution standpoint, the problem has been that the oil and gas industry consists of many, many small sources that are individually small yet collectively add up to large sources of air pollution," said Jeremy Nichols, climate and energy program director for Denver-based WildEarth Guardians.

But a study by University of Colorado public-health doctors concluded that more research is needed on how the industry affects the health of people in energy-producing regions. The study was funded by the Natural Resources Defense Council, an environmental group.

The researchers concentrated on Garfield County, Colo., a largely rural area that had 4,521 oil and gas wells at the end of 2007. The report found ozone spikes that exceeded the EPA’s health standard, although they didn’t last long enough for the government to take action.

The study also found unsafe levels of benzene and other chemicals linked to cancer. However, there’s not enough information to show whether cancer or other illnesses have increased. And it’s not clear how prevalent the chemical levels are.

"There is no way of knowing whether the samples were minimum, maximum or somewhere in between," the report said.

It’s also not clear whether the chemicals are coming from the wells themselves, from truck traffic or from other sources, said Roxana Witter, a doctor and the study’s lead author.

"All the causes should be investigated," she said.

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